Lister Engine Forum

Slow Speed Diesel Engines => Changfa Engines => Topic started by: bigbad on October 30, 2021, 03:22:54 AM

Title: Slow rpm Chang fa?
Post by: bigbad on October 30, 2021, 03:22:54 AM
I am looking at websites for the Chang fa and related and I only see conflicting info - mostly look at the mfg page.  One part they say 800ish rpm and on another part of the same page they say something like 2,500 rpm.  Is there a Chang fa that is really a slow speed engine?
Title: Re: Slow rpm Chang fa?
Post by: guest18 on October 30, 2021, 03:33:53 PM
I donít know of any Changfa, Chang-Chai (Chinese) diesels that are designed to operate continuous at speeds below or near 1000 rpm.

All the S195 and larger horizontal single cylinder (Changfa, Chang-Chai) Chinese diesels operate, I believe up to 2,200 rpmís. Most work fine direct driving an 1800 rpm 60hz or 1500 rpm 50hz generator head. They are tough engines that proven themselves to take quite a beating and still able to run for long hours. All engines are designed to run at certain speeds and itís best to stay within the parameters the manufacturer specíd the engine run.

Veggie is a member here and on the microcogen.info forum. He has modified S195 engines to operate at lower speeds successfully. He spent hours on his projects and acquired the knowledge to get these engines to run at lower speeds reliably. It does cost money for the average person to do these modifications. I believe Veggie had access, or known people in a machine shop to machine the parts for his engines. His work is beautiful I would recommend checking out some of his builds.

I my opinion, Veggie is an exception to the rule of staying within manufacturerís specíd engine operating parameters.



Title: Re: Slow rpm Chang fa?
Post by: 38ac on October 30, 2021, 03:35:59 PM
Member here Veggie modified one to run at maximum efficiency when running slow and his work is impeccable.
That being said they are all variable speed governed. You can run one anywhere from just off idle to full RPM and have good governor response without doing anything to it other than adjusting the throttle. If you intend to run one at a lowered RPM, AND and at full load AND continuous then it would be beneficial to back down the injection timing a few degree. Other than that don't worry about it. Remember that when you lower the operating speed that the availabile HP also drops. A 195 is probably a 6HP engine at 1000 RPM, just guessing from experience.
Title: Re: Slow rpm Chang fa?
Post by: mobile_bob on October 30, 2021, 03:53:17 PM
i did a lot of testing back around '07-'09 with a changfa s195
it had no problem running and carrying a load at 1000rpm

i didn't back off the timing, and used it to drive a 555 alternator at 2880watts at 28.8 volts

no problems at all, and i think i could have gone lower with as suggested reduced timing, but because the unit was setup to run dual speed 1800 and 1000 i didn't want to alter the timing.

tough as nails engine's that likely could be made to run at lower rpms, and do it well.
i always figured that 1000rpm was a good spot to run at, but i know veggie got one running slower.

bob g
Title: Re: Slow rpm Chang fa?
Post by: guest18 on October 30, 2021, 04:02:34 PM
Yes Veggie did get one to run slower than a 1000 rpm.

On one of Veggieís projects he machined the flywheel to accept  additional weight. The additional weight helps with rotational stability (inertia). +1 on retarding injection pump timing.

Here is a topic of his slow running S195.

http://www.microcogen.info/index.php?topic=477.0
Title: Re: Slow rpm Chang fa?
Post by: bigbad on October 31, 2021, 11:56:06 AM
Thank you all!  A Chang Fa fits my budget at this point  ::)  Are they as versatile about fuels as the Lister engines, i.e. biofuels, waste oil, etc.?
Title: Re: Slow rpm Chang fa?
Post by: mobile_bob on October 31, 2021, 06:10:14 PM
here is a list of fuels i tried in the s195

bearing in mind it was built with a closed cooling system, radiator, 7lb cap, running between 205-214deg F

1. pump diesel
2. home heating oil
3. hydraulic oil
4. 30 weight motor oil
5. 15/40 motor oil
6. 50 weight motor oil
7. 15/40 waste motor oil
8. kerosene
9. straight corn oil,(wesson cooking oil)
10. atf (automatic transmission fluid)
11. lamp oil (walmart stuff in the bottle)

at operating temperatures, the engine ran cleanly with very small amount of grey smoke at full load, that on all fuels, there was no difference in visible smoke.

i think the only limiting factor is make sure the engine is fully warmed up, and the fuels are clean, well filtered.

also of note, the engine would start from cold (70deg ambeint) with 50 weight motor oil, but it would smoke for about 30 seconds, then it cleaned right up and you really could not tell the difference between 50 weight and pump diesel.

there is one thing you should be aware of, that is the ash residue burning motor oils, and waste oils.  the ash residue likely will be somewhat abrasive and "may" shorten the lifespan of the cylinder kit.

if you do an analysis, i think you will conclude that the savings in fuel cost burning waste oil stocks out way the cost of repair parts.  so you probably want to put in a stock of replacement cylinder liners, pistons, rings, gaskets.

for my application, i figured to mix the waste fuel sources 50/50 with pump diesel, then filter to 1 micron.   and i would never use any waste oil sources that i did not know the origins of.

at the time i ran a mobile service, so i knew where the waste oils came from, and what they were.  what i did not want was unknown waste oils that might have brake fluid, brakleen, paint thinners, or any other unknown waste that might be a carcinogen.

what i would not run in any engine i cared about would be waste cooking oils, they might be at the very least acidic, likely high in salts and other corrosives. however i might use some from a source that regularly changes their oils, and would put the waste back in the 5 gallon jugs they get the new stuff in.  then i might use the stuff after well filtering, settling out the heavies first.  then maybe i would run some after the engine is warmed up, and then switch back over to pump diesel to clear the injection system (pumps, lines, injector). i would also keep a good eye on crankcase oil contamination, pull the head and check for carbon buildup and any signs of premature wear.

i might also mention my engine is an idi (indirect injection), so in my opinion it will likely burn just about anything flammable, some very well with good lifespan of parts, some well with reduced lifespan of parts.

my bet is the darn thing would run on bacon grease, if it was preheated enough to make it through the injection system.

having reported all this, all testing was done prior to the tier 4 ban on import of these engines.  read whatever you like into this report, however be aware that burning anything other than low sulfur diesel fuel is likely to put you afoul of the US EPA, and probably other controlling authorities in whatever country the reader might be contemplating such use.

just because the engine can burn these alternate fuels, does not mean you should burn these fuels,  so bear this in mind. 

best to use alternate fuels only in the case of emergencies.

and of course let your conscience be your guide.

bob g



 
Title: Re: Slow rpm Chang fa?
Post by: guest18 on October 31, 2021, 07:02:04 PM
Bob,
I agree with everything you written.

I would like to add that my Pre-Ban S195ís were DI (Direct Injected) engines. I did not go through to the extent you have to see what the engines would effectively burn, but the DI engines had no problems burning a 50/50 mix of #2 Off-Road Diesel & New 15-W40 Diesel Oil. A matter of fact while testing, it ran much quieter and showed no loss in power. And it Started up with no starting aid @ 40 degrees F. This testing was also done prior to the Tier 4 ban.

I wish I kept one of those engines.

For my current diesel genset I just run #2 Off-Road Diesel I donít go through enough to be concerned.
Title: Re: Slow rpm Chang fa?
Post by: guest18 on October 31, 2021, 07:37:54 PM
Here is some info I dug up and posted on microcogen back in October, 2009

https://www.microcogen.info/index.php?topic=171.0



For those that are not able to log in to view attachments on microcogen click on the attachments below:
Title: Re: Slow rpm Chang fa?
Post by: veggie on November 01, 2021, 05:11:17 PM
Here is the slow speed changfa.
It runs at 900 rpm and can pull up to 3kw electrical power.
https://www.youtube.com/watch?v=aOhg1Q1rd6E (https://www.youtube.com/watch?v=aOhg1Q1rd6E)

My neighbour loved it ... and bought it.  :)

So yes, with a few modifications, the Changfa engines make good slow speed diesels.
I have seen many videos of these engines running in China as slow speed power plants.
Many on grain grinders and tractors.

Come to think of it, my neighbour asked if I would like to buy it back. ::)
Hmmm ... how could I sneak a 600 lb  bright green generator into the garage without my wife noticing  ;D
Title: Re: Slow rpm Chang fa?
Post by: guest18 on November 02, 2021, 02:10:56 AM
If you can buy that thing back you should jump on it. :) Give her some money and tell her to go out and get herself something she likes. It works, Iíve had to do it many times.
Title: Re: Slow rpm Chang fa?
Post by: bigbad on November 07, 2021, 06:40:50 AM
Thank you!  Is the S195 not allowed into the US now?  Can anyone recommend an honest place to buy one - so that I know that I want I am ordering is what I will get?  Does that engine use a removable cylinder sleeve?  It is nice to know that it will run below 1000 rpms.  Initially, I will need an engine to put out more power - use a gen head, compressor and a few other tools.  Once I get my place built, I can revamp the engine to run a 3KW gen head. 
Title: Re: Slow rpm Chang fa?
Post by: Fred8 on November 07, 2021, 12:34:32 PM

despite the Misinformation and ignorance  people spread about running Diesels slow, you CAN run any engine at low speed if you do it right and without problem.  It's a standard practice in industry to over size and under drive/ rev engines.  Many industrial engines have charts to show what power they make at what RPM.
It's simply a matter of matching the engine speed to the power.

If an engine makes 100HP at 2500 RPM, it will make ( say) 20HP @ 1200 RPM.  if you are putting an 18 HP load on it and turning it at that speed, The engine IS in fact working and will work fine.  I have read a lot where people say engines need the ring revved out of them constantly or they will fail which is just poppycock.

For a generator, gear the head to give the desired RPM  at the RPM the engine delivers the required power and thats it.  Will still be working hard but will not be as stressed or wearing out that fast.

You could easily run an engine out a vehicle this way and get slow speed and long life with good economy. I'm negotiating now on a 90Hp 4 Cyl engine that I want to put on a 10KW head.  Will run nice and slow and quite in that setup with an electronic governor  and last a VERY long time.
Title: Re: Slow rpm Chang fa?
Post by: mobile_bob on November 07, 2021, 01:13:00 PM
the s195 is not allowed for import into the US currently, and has not been allowed since 2006.

it does have a removable liner, and is rebuildable, there are many parts suppliers on aliexpress and alibaba, among other places like ebay from time to time.

if you are trying to get a new one, in the US, it will either be a NOS that someone has set away, or a used engine, or possibly one that someone has managed to get slipped by customs.  of the three options, the first two are legal to sell and own, the third option is illegal to sell and if the seller is caught by the epa it likely would be tracked down by them and confiscated.

i don't know what the fair market value is for an s195 NOS in the crate, but because of the rarity it is likely going to be north of 750 bucks and maybe a lot more?

problem being finding one and getting to an agreeable price between seller and buyer.

used ones come up form time to time, and sometimes you can get a deal, but i would expect them to go for at least 500 bucks for a known good runner, or more.  maybe less for one that has no history or record of how many hours it has on it or what kind of maintenance it has had.  even those are going to fetch up to 500 and maybe more.

like anything else, it is a supply and demand thing.  if there are few engines and there are more buyers, the price goes up, and up.

i would be interesting to see one come up for auction on a forum.

bob g
Title: Re: Slow rpm Chang fa?
Post by: bigbad on November 09, 2021, 01:43:22 PM
Pardon my ignorance, but what is NOS?
Title: Re: Slow rpm Chang fa?
Post by: bigbad on November 09, 2021, 01:59:17 PM
Don't know if I should continue this thread or start a new one...is there an engine comparable to the Changfa that IS legal to sell in the US...that has similar reliability?  I am looking for water cooled, with an electric starter as an option...removable sleeves....
Title: Re: Slow rpm Chang fa?
Post by: guest18 on November 09, 2021, 03:44:14 PM
The only engine that is similar to a changfa is a Kubota EA330. The changfa is an  r175 much smaller than a s195.
The kubota is a great engine but be ready to shell out $3,200.00. Unless your lucky to find NOS (New Old Stock) The kubota EA330 likes being ran from 2400-3000 rpm. I would not recommend running a factory stock one at slow speeds. It was discussed earlier. Keep within the manufacturer's operating speed and it should run for a long time. Some people are hell bent on insisting that an engine has to run at extremely slow speeds for it to last. A matter of fact, engines that are not set up to run at Extreme slow speeds can be torn to pieces in a very short time.

Look up and study Critical Speed.

I think Kubota and some other manufacturers had done their homework. Why buck their R&D.

It's funny, some Kubota gensets have well over 20,000 hours before major overhaul.

 Did you look over and read about Veggie's work?
He did some nice work to an S195.
Yes, there are exceptions.
Title: Re: Slow rpm Chang fa?
Post by: mobile_bob on November 09, 2021, 07:10:03 PM
no problem

NOS= new old stock, or basically new still in the crate never used
Title: Re: Slow rpm Chang fa?
Post by: Fred8 on November 10, 2021, 12:09:19 AM
Lots here are hell bent on insisting that an engine has to run at extremely slow speeds for it to last. And that is far from the truth. A matter of fact. Extreme slow speeds engines can be torn to pieces in a very short time.

Whom is insisting an engine be run at EXTREMELY slow speeds? Can you provide a Link?  I have NEVER seen anyone mention let alone insist that anywhere so I'd be interested to see where you got that " a lot here" are doing that?

Running an engine at less that full speed  is NOT the same as extremely slow Speeds. Running any engine at around half speed is not either. To me extremely slow would be like Idle and I have NEVER seen anyone recommend that on any forum. The idea that an engine HAS to be loaded up and run at or near full  RPM is extremely ignorant and flies in the face of real world practical applications especially with heavier machinery where longevity due to the cost of having to virtually deconstruct the machine the engine is in to replace it is much more than the engine is worth itself.

Slowing and derating engine speed and output is extremely common in the marine, Mining, power generation agricultural and other application sectors  where oversize engines are slowed and reduced in power output for a number of reasons, Longevity, being a main one.

For the applications and engine sizes of relevance here, running an engine  extremely slow would be producing an output of 1-2 hp and I haven't seen anyone with use of that sort of low power here nor is it discussed anywhere I have seen in the home power generation groups which seems the main interest here as well.


I would think common or not so sense would tell a person that Lugging an engine would be bad for it and unless you were running something like a 3208 CAT at idle, anything in the scope of this Forum would produce useless power at very low speeds and be non viable anyway. That is a whole lot different to running something at reduced speed though.
You would most likley be well enlightened to look up how engine manufacturers rate their engines at Various RPM and see what the Military, power generation and pumping industries do as far as sizing and the speed they run different engines.

Never heard of anyone running an engine extremely slow but that's a big difference between running it under Max RPM and de rating it accordingly. 

Exaggeration of what people are saying to suit ones own proclivities however is a different matter.
Title: Re: Slow rpm Chang fa?
Post by: guest18 on November 10, 2021, 12:36:57 AM
Fred8, I modified my post some. Hopefully I cleared some things up. My understanding is extremely low speed for a stock (unmodified) engine would be an engine running well under a manufactures recommended operating speed. I guess what Iím trying to convey is with a stock engine, most of the time itís best to keep an engine within the manufactures operating Parameters. We both and others understand that when an engine operates at a lower speed the engines hp has to be de-rated.
 
Title: Re: Slow rpm Chang fa?
Post by: mobile_bob on November 10, 2021, 01:20:24 AM
there are at least 3 schools of thought

1. those that operate within the manufactures recommendations, probably best for longevity.

2. those that operate well under the manufactures recommendations, with added flywheel mass, changes in timing, etc.  nothing wrong with that, so long as you know something about what you are doing and accept some level of risk

3. those that operate at the bleeding edge, flat out max load, with arguable reduced lifespan, and ok if you accept the risks involved and know what you are doing.

me?  with a changfa in a co-gen plant?  i fit comfortably within #3 group!  short runs, full load, flat out.  i accept the risks, also i think i have a pretty good idea what i am doing, with tightly controlled coolant temperatures, monitoring systems, emergency shutdowns, and limited run times.

why?  because i have proven to my satisfaction that peak efficiency comes at full load operation, with an enclosed cooling system (pressurized) operating within 205-214F.  this is where max. efficiency of the engine is attained, max heat recovery from both exhaust and coolant,  and peak power.

results?  yes there will be a reduction is lifespan, in hours, but
the operation calls for a max run time of 2 one hour runs/day, so the engine while running fewer hours before overhaul will last several years.

i figure cost per kw/hr and btu/hr recovered

bottom line is this, every application has its own goals, concerns and risks involved.

i think to hwew' point
you should be aware of the engine's critical speed, that is a valid point.  no engine should be operated at critical speed that is if you want it to last and not have some form of premature failure, some of which can be quite catastrophic like broken crankshafts or engine cases, or mounts.

all you have to do is ride a ferry boat or be anywhere around a diesel locomotive
you can feel the boat vibrate like hell as the throttle opens and the rpm passes through critical speed... and you will note the man with the throttle in his hand does not allow the engine to operate at that speed any longer than is necessary. 

it can be felt in the ground around the train yards, as they throttle up.

small engine's may not demonstrate this effect so plainly, but the thing also has a critical speed that should be avoided.

bob g
Title: Re: Slow rpm Chang fa?
Post by: Fred8 on November 10, 2021, 01:24:00 AM

Fred8, I modified my post some. Hopefully I cleared some things up.

Well no, you haven't cleared anything up. The points I addressed are unchanged

Quote
Some here are hell bent on insisting that an engine has to run at extremely slow speeds for it to last.   

Please Clarify who these " some are"  with links to where they "insist" The engines be Run at extremely slow Speed and exactly what that is.  Best to  clear up any ambiguity and be accurate don't you think?  The only "Insistence" I can see here is your own in that engines have to be run full tilt.  That notion is completely undermined in industry as I mentioned.


[/quote]A matter of fact at Extreme slow speeds, engines can be torn to pieces in a very short time. Unless lots of modifications are done to an engine.
[/quote]

Again, can you specify and give an example of what an extremely slow speed is ( and a link to those insisting on them and what they are specifying as an example would be best)  and can you explain what those Modifications are?

I haven't read every thread here but I'd be real interested to see what those insisting on extremely slow speeds are saying over all and in context.

As for Critical speed,

"The critical speed of a shaft occurs when the shaft rotational speed is at or close to resonant conditions. In this condition the torsional vibration of the shaft increases greatly, and will impose very high shear stress on the crankshaft. These levels of stress could even cause crankshaft failure."

It is A speed, not every speed below maximum speed on an engine.  Most engines have a speed at which they vibrate at a greater degree, harmonics dictate that an engine cannot be balanced at  Every speed.
Furthermore, the load an engine is driving either direct or by belt will also have it's own harmonics and imbalances and transmit those to the engine and change the speed at which it's natural frequency occurs.

"Extremely slow speed" which again without specification can only be taken to mean at or slightly above idle is more likely to be a product of lugging the engine than anything to do with Critical speed.

If running an engine at lower than full speed was such an inherent danger, one would have to wonder why the Transmissions in modern Vehicles are not set up to run the engine high in the rev range as to lower down and use the torque the engine supplies. 
Many vehicles have gone to larger engines  that produce more torque and rev lower for Fuel economy for one thing.

If this Critical speed you speak of is such an issue. There is no way the engine in my vehicle would have a redline of 7000 RPM but cruise at highway speed at less than 1600 RPM and do it literally all day long nor would it be able to idle for hours in traffic Driving the AC and alternator.

I think it would be pretty clear to most interested in facts rather than pushing an agenda to be seen to be right that running an engine at lower than max speed is not going to tear it up and  running the thing near idle which would be extremely slow is stupid and nonsensical in the first place.  Running any engine at half speed is far from extremely slow not is it going to cause the thing to detonate as you infer.

Again, to clear up any misunderstanding, please specify what you believe is " extremely Slow Speed" and give links to examples where people are insisting this.

I always always relish the opportunity to lean something new as I am sure do others.    :)
Title: Re: Slow rpm Chang fa?
Post by: mobile_bob on November 10, 2021, 01:53:57 AM
Damn Glort, take a chill pill man!

;)

bob g
Title: Re: Slow rpm Chang fa?
Post by: guest18 on November 10, 2021, 02:09:48 AM
Deleted
Title: Re: Slow rpm Chang fa?
Post by: Fred8 on November 10, 2021, 02:11:50 AM

1. those that operate within the manufactures recommendations, probably best for longevity.

This brings up an interesting point......

I have NEVER seen a manufacturer recommend ANY engine speed.
What I do see is a power output figure at a specific RPM. Sorry to anyone that thinks otherwise but that is NOT a recommendation to operate at that speed, it's a RATED power figure at what that engine will do, normally a MAXIMUM  output figure, still below max RPM, NOT what you should run the engine at.


This is why industrial engines often come with power curve charts to show what they will do at specific  speeds. I am amazed people are not aware of those.
If the Max HP/ RPM figure was a recommendation, why isn't everyone, especially those so concerned with critical speed problems not driving their vehicles round at the Figure given for it's maximum power output which is what these Numbers are, NOT an engine operation speed recommendation. 

The numbers merely tell you what the engine will do at that speed.  That is all.

Perhaps I have missed something and if so I'd sure like to be educated if someone could show me where any manufacturer says something akin to "This is the recommended speed to operate this engine".
That is nothing like a MAX power figure at a certain RPM manufactures specify.

Further more, there is also a max Torque figure specified which is regarded as the sweet spot and where vehicle manufacturers, especially Trucks and things like locomotives try to gear their equipment to.  Cruising speed in a vehicle in top gear is always closer to the much slower max torque figure than it is the max power figure which is far higher up. And again, if Operating the engine slower was going to grenade it, how do city cars especially manage to put around for a couple of decades without snapping cranks or falling apart.

Here is a power output Chart of a Cummins engine.


Engine Model    Max. Power HP (kW)     Peak Torque lb-ft (Nm) @ RPM     Governed Speed (RPM)
X12 500            500 (373)                 1700 (2305) @ 1000                         2000
X12 455           455 (339)                        1700 (2305) @ 1000                        2000

We see here that the peak torque is at half the RPM of the peak power.
Would someone like to ring Cummins  ( or Cat, Kubota, JBC, Yanmar, Detroit, Volvo, Mercedes, Ford, Deutz, MTW, Perkins, Isuzu, Honda, GM or any other manufacturer) and ask if operating their engine at 1000 RPM ( or whatever is)  in the peak torque range, going to cause issues with critical speed failure or damage the engine operating at that speed?

I think we all know what the answer is going to be and that for mine shoots down any of this idea that an engine operated below max power rating will destroy it.  It's simply  maligned fantasy to suggest that as is the idea people would operate an engine at " extremely low speed".

I also looked at the Changfa site being a recognised small engine Builder and while they don't specify Torque Figures I could find,  They do only give RATED HP/ speed figures. No where could I find anything that even alluded to as much as " Engine recommended operating speed. " If anyone can, please link to it because i'd like to see where I missed it.

As such I can dismiss the position of " Manufacturers recommendation" for engine speed as a fallacy and contortion of the truth.
It's not even a Recommended RPM speed, that where specified, is usually listed separately and is higher again.

Calling a manufacturers power output rating as the recommended operating speed is simply wrong and ignorant of what is actually being specified by those whom don't understand what they are reading.   


Quote
you should be aware of the engine's critical speed, that is a valid point.  no engine should be operated at critical speed that is if you want it to last and not have some form of premature failure, some of which can be quite catastrophic like broken crankshafts or engine cases, or mounts.

I agree.
I wonder how many people know that or manufacturers that could even be found from?
Again, it is a Single speed or very narrow range, it's not any speed under the max power rating of an engine.

Quote
all you have to do is ride a ferry boat or be anywhere around a diesel locomotive
you can feel the boat vibrate like hell as the throttle opens and the rpm passes through critical speed... and you will note the man with the throttle in his hand does not allow the engine to operate at that speed any longer than is necessary. 

A great example.  I would say though that a lot of this is in the drive train however that is just as important to avoid.

Quote

small engine's may not demonstrate this effect so plainly, but the thing also has a critical speed that should be avoided.

I'd suggest with a little observation it is discernable and it is at very low speed where anyone with any mechanical sympathy or common sense would not operate an engine and on a small engine would be at a point where the power output would be near useless anyway.
It's also dependent on load.



Just for clarity, please note I am not trying to attack you Bob or what you said personally, your comment just sparked a thought  of a good point that seems to have been missed/ maligned till now and which I wanted to address and clarify.
Title: Re: Slow rpm Chang fa?
Post by: guest18 on November 10, 2021, 03:42:23 AM
Fred8,

Here is some stuff that might be of interest. It shows some of the info your requesting.

1A08 Military Standard Engine:
http://everyspec.com/MIL-STD/MIL-STD-1100-1299/download.php?spec=MIL-STD-1226A.013509.pdf
Page 8 shows speed range for continuous operation.
Page 29 shows operating speed range.
Page 23 Critical speeds for directly attached end item.
Page 24 Vibratory torque at critical speeds for directly attached end item.

Iím doing a build with one of the two I have. Should be done some time next year.


Kubota EB series engines:
https://www.sv-zanshin.com/r/manuals/kubotaebseriesbrochure.pdf

For my application 2600 rpmís works best with my EB300 genset.

I would like to add that the EA300 and EB300 are pretty much the same engine. I believe the differenceís are: injector pump timing, injector pump and injector calibration, fuel limiter calibration and Governor speed. The EA300 is set to run up to 3000 rpm, and, the EB300 is set to run up to 2600 rpm.


Honda GX390 Tech Manual:
https://www.trictools.com/wp-content/uploads/2015/07/HONDA-GX-390-TECH-MANUAL.pdf
Pages 3 and 4 shows recommended engine speeds.
Page 10 Resonance Check (critical speed)

Used a GX390 on a build about a year ago.
Engine had a vibration problem at just under 2600 up to over 3000 rpm. This was with the engine mounted on the pad. Engine running without drive pulley attached. I was surprised that a Honda could have such bad vibration at the speeds mentioned. Packed it up and returned it.
Title: Re: Slow rpm Chang fa?
Post by: 38ac on November 10, 2021, 03:51:16 AM
NOS = New Old Stock.
Title: Re: Slow rpm Chang fa?
Post by: guest18 on November 10, 2021, 07:33:57 AM
Don't know if I should continue this thread or start a new one...is there an engine comparable to the Changfa that IS legal to sell in the US...that has similar reliability?  I am looking for water cooled, with an electric starter as an option...removable sleeves....



bigdad,

There is possibility that you might be able to get a Changfa engine.
Here is the link: http://www.pelletmasters.com/products/index.html#dieselpower
If they still are available you would have to purchase a complete pellet mill in order to get one.
Title: Re: Slow rpm Chang fa?
Post by: mobile_bob on November 10, 2021, 11:53:38 AM
(i typed the following late last evening, but forgot to hit "post" so it is probably out of sequence)


i have been guilty in the past of getting into the weeds, and over time found it to be non productive for myself and for the members of the forum.

we can argue fine points, and believe me i can do that as well as anyone
but what is to be gained?

when i mention the oem recommendations on operating speed, i should have expanded on that a bit perhaps, and related it as  recommended "operating range", rather than speed.

i think most folks understand that.

most all stationary engine manufactures, or those that build for that purpose, and for purposes of heavy loading in particular do recommend an operating range.  by that it is meant  that this is the range of speeds that the oem recommends the use of their engine under load.  stationary engines are likely far more heavily loaded than the typical automotive engine which can get by quite nicely operating over anywhere from idle to redline (which btw is a recommended don't go over line)

lets take hwew' kubota single cylinder diesel, iirc it is rated for 2600-2800rpm at rated load, and the power curve stops at something just over 2200rpm or so, its not that the engine won't run under 2200, its just that it vibrates badly at around that speed.  likely one of the critical speeds that they don't recommend running at, especially under load.

(my  bet is hwew has talked to the kubota engineers about this issue.)

it is apparent to the user that this is not a good speed to operate at, because the thing shakes and vibrates so bad that it works parts loose, which generally is not a good thing, unless you want a asphalt packer or concrete screed vibrator ?

getting back to automobiles and critical speeds, these engines are generally very stiff, compact, well balanced, well engineered, with serious attention to things like harmonic balancers, and engineered mounting systems, along with the decoupling effect of the almost ubiquitous automatic transmission.

go back to the 40's and early 50's and the 6cyl stick shift transmission cars and trucks, one could certainly determine by feel what he might not understand as a critical speed but knows that "hey, i don't want to drive in this gear, this thing vibrates my teeth out"
its doubtful that the oem's had to make a recommendation on what engine speed to operate under, they left it to the user who figured it out within the first few blocks of leaving the dealership, or....

he was like some of those old farts that lugged the crap out of their car or truck and you could hear every part of the vehicle vibrating like mad, gears clatter, driveline ringing a horrible tune, and the old deaf guy oblivious to what was happening, or he was driving down the road in first gear at 55mph turning 6 grand! (that was my poor dad, he couldn't hear a thing)

as for your point on industrial engines and power curves, and folks not aware of such, i think you are sadly misinformed.  while there might be some newbie that doesn't know about such things, it is doubtful that you will find but a tiny percentage of the members on this and other forums that are unaware.

(skipping down a bit to your cummins reference)

if we go back to the 60's and early 70's cummins made a taper nose ntc335 engine
it had a critical speed problem in that if you loaded the engine at a certain speed you ended up with a broken crankshaft

ford tractors, 50's with the 4cyl diesel had a similar problem, recommendation was to not load the tractor at some specific rpm, i don't recall what it was either, but broken cranks were not uncommon.

the reason that cummins is now able to get max torque down to 1000rpm is they have built the engine massively stronger than it has ever been.  you can build any engine heavy enough to stand up to about any critical speed issue you like, but almost without exception, the bean counters don't want an oz. of extra iron or expense put into a design without very good reason.

car and pickup reference again

the engine in the typical 5k lb suv has what? 300hp or more these days?
what does it take to in hp to move a 5k lb suv at highway speeds, maybe 100hp?
what does it take to plug around town at 30mph? maybe 25 or 30 if the a/c is on?
the typical car engine is asked to deliver on average probably a quarter of its capacity
and likely half of that driving around town, with brief excursions.  so maybe you are lugging around at some critical speed in your car, putting around town, however because the engine is built to make upward of 300hp it is over built for the need required to putt around at that speed, it is decoupled and isolated so the driver has no feel that it is even happening, and yes it is not a problem.  don't feel it therefore it doesn't exist?  ya right.

every engineering book ever written on internal combustion engines, beit for cars, trucks, planes,  trains, boats, or anything else has a chapter on critical speeds and what is done to deal with them..  you either overbuild and isolate the engine, or if you can't you instruct the operator on where not to run the engine under load.

i mentioned the ferry boat
they are an interesting case study in critical speed

the engines are generally very rigidly mounted to the boat superstructure, and as such engine vibration is transmitted through the hull and around the boat.

when the captain leaves the dock and starts to throttle up he does so , increasing rpm slowly, sometimes remaining at a lower rpm while he clears the dock and/or other obstructions, but as he increases the rpm the engine will enter critical speed, at that precise moment you can feel the boat start to violently vibrate and you can also feel the surge as the captain shoves the throttle open so he can quickly pass through that rpm.

it is actually very interesting to witness having studied the phenomenon, to actually feel the process from before, during and after.  its not something most of us would think about, but that captain sure does.

after witnessing that i went looking for other examples, and came across a railroad yard, and found the same thing taking place, they start to slowly throttle up, then at some rpm the ground starts to vibrate and the engineer cracks up the throttle and he gets through that rpm quickly.  again very interesting.

if you would like i can refer you to a two volume set of engineering books from MIT on engine design, believe me critical speed is a very real thing that must be dealt with one way or another.


its been a very long day, i will part with you for now
and time willing,  pick up where we left off tomorrow.

fair enough?

bob g


Title: Re: Slow rpm Chang fa?
Post by: sirpedrosa on November 10, 2021, 03:04:13 PM
Hi Gentles,

Bob G, please, Glort is no longer here! maybe... maybe a clone of him, perhaps an ancient good person whom answers by name David.

Remember king David from scriptures?

I know, a horse is a horse... and a wolf will never be a sheep , but with some discreet rant, not wearing out keyboards, letting others make their point of view, etc, etc.....

Everyone can have a 2nd chance, but.... but the water will never run twice under same bridge.

If, and only if we have a reborned David... maybe he can stand along.

My very deep thoughts.

Cheers
VP
Title: Re: Slow rpm Chang fa?
Post by: mobile_bob on November 10, 2021, 04:11:10 PM
Sirpedrosa

i am not much for "an eye for an eye" and all that
and i am ok with turning the other cheek, however

slap me once, i will turn the other cheek
slap me again, and all bets are off!

:)

i don't believe anyone answered to the name "glort" in this thread, so maybe we have nothing to be concerned with.

i just don't see the need to be aggressive with ones response, and i also realize there are cultural differences around the world and with the members of forums, this one being no different.

having said that, one should check himself to make sure he is countering a point of view, not the one who presents that point of view.  when it starts to look personal, it is much like a former supreme court justice said when asked "what is pornography?" his response
"i don't know how to describe it but i know it when i see it"  and i think that philosophy applies hear.

if i have learned anything from life, it is simply this,  "if it don't feel right, it probably isn't right?"

which follows "if it walks like a duck, quacks like a duck" what do you suppose it is?

perhaps we should all take a step back and remember what we type may not be read in the spirit it was written in.

bob g
Title: Re: Slow rpm Chang fa?
Post by: 38ac on November 11, 2021, 01:44:20 AM
A Blackstone MP is a single cylinder 31HP diesel engine rated at 850 RPM. I used to own one.  It had a rivited plate next to the governor housing that boldly stated DO NOT OPERATE THIS ENGINE UNDER 750 RPM. It was also in the manual, it didn't go on about it with a long winded explanation, just said don't do it. Why? I don't know?
Just adding this since the one poster stated he had never seen or heard of it.
Title: Re: Slow rpm Chang fa?
Post by: BruceM on November 11, 2021, 05:43:37 PM
https://www.youtube.com/watch?v=xkBKXB--els

Awesome low speed, old iron engine, that Blackstone MP.  Thanks 38ac.











Title: Re: Slow rpm Chang fa?
Post by: mobile_bob on November 11, 2021, 06:27:54 PM
another example of critical speeds i witnessed first hand back in the late 80's while working in a truck shop, they had a "on truck" wheel balancer, that would allow for balancing the complete rotating assemble, hub, drum, wheel and tire.

now i understand that this is a balance issue, but it was very interesting that the critical speed was not a single speed but sometimes as many as 3-4.

lifting the front axle off the ground, just off center, so that one tire was still in contact, but most all the weight off of it, we would spin up the lifted tire with a 10hp 3phase 3450 rpm motor with a friction drive. 

it was interesting to see the doors while closed on the truck, literally hammer themselves in the door jambs to the point that it would chip paint! 

as the wheel began to slow down, the doors would stop pounding, and slow a bit more they would start back pounding again, then quit when it slowed a bit more, etc etc

these were examples of critical speeds that could be correctly rather easily with lead weights,

it was pretty easy to tell, that uncorrected one would not want to drive the truck at any of those speeds, because while the doors probably wouldn't start beating around, it is likely one would feel the vibration even though dampened and decoupled by tire to road contact.

btw, that blackstone is a monster!  and i love it!

bob g
Title: Re: Slow rpm Chang fa?
Post by: 38ac on November 11, 2021, 11:31:28 PM
 Bob, as has happened to several other of my diesel treasures a person came along who had a larger desire to own that Blackstone than I had desire to keep it.

As it pertains to engines, broad generalities can almost always be dismissed. As my MP Blackstone proves to say any engine can be operated under rated RPM is simply untrue. However is is true that most engines are happier when not run balls to the wall, maximum RPM and maximum load.  The bulk of the time an engine will let an attentive operator know when it isn't happy. My 1115 Changfa type has a balance shaft as most do and at varying RPMs the gear clatter in serious. Obviously, it will last longer if operated at an RPM where the gears are not being tortured. Single cylinder engines are much more susceptible to this behavior for reasons that should be obvious thus to compare multi cylinder gasoline engine and say what is operationally good for one of those must be OK for a single cylinder diesel just doesnt work. 
Title: Re: Slow rpm Chang fa?
Post by: Fred8 on November 13, 2021, 01:05:50 PM
Fred8,

Here is some stuff that might be of interest. It shows some of the info your requesting.

Thanks for proving exactly what I have been saying.

Quote
Kubota EB series engines:
https://www.sv-zanshin.com/r/manuals/kubotaebseriesbrochure.pdf

The documents show an engine speed RANGE of 1400 to 2800 RPM on one of these engines and a similar RANGE on the others.  It also shows what the power output is at those lower than max rated power speeds. I don't see anything that says don't operate below this speed or only operate above this speed. 

Quote
For my application 2600 rpmís works best with my EB300 genset.
And for another lower load application 1800 May have been perfectly fine and does not mean the engine is going to self destruct as you have implied previously.  YOUR application is not necessarily the same as everyone else's.

As the graphs show and as I was saying, the output is different at different RPM.  If your engine needs full or close to max RPM for the load on it so it does not Lug, then obviously it will be happier and that's the place to run it.  If the load on the engine is equivalent to what it will put out at a lower RPM, Then Running it at that speed is not going to destroy it because the power  output at that speed is sufficient.



Quote
Honda GX390 Tech Manual:
https://www.trictools.com/wp-content/uploads/2015/07/HONDA-GX-390-TECH-MANUAL.pdf
Pages 3 and 4 shows recommended engine speeds.

SPEEDS being the operative word.
Here we see an operating RANGE of 2000 to 3600 RPM.  That is neither " extremely slow"  nor is operating the thing at any speed above 2000 going to cause problems providing the output of the engine at that sped is sufficient for the load.

I also see a note: " Operate the engine at not more than 90% of the maximum horsepower available at a given rpm".  Again what I have been saying, the output changes with engine speed.  And again, it would seem obvious not to lug an engine which will occur then there is too much load for the power produced at a Given RPM. I would have thought people playing in this game would also realise there is no point to running an engine at a speed where it is say producing 10 Hp when the load is only going to generate a max of 5 HP.
Slowing the engine down in this case will save fuel, noise and wear and tear. But it does not seem to agree with the forum agreed position.


Quote
Page 10 Resonance Check (critical speed)

This is more to do with the equipment attached than the engine itself. It talks about with the equipment and the engine loaded.

On this modern engine and the Kubot,a There is no referral to Minimum engine speed or speeds to avoid.
I did not look at the first example, there was a warning on my browser about the file so I did not download it. Being a Military engine It would be more than conceivable it had certain and critical parameters.  Same with the old engine mentioned. Obviously if the engines have this specified one would be smart to observe it but how many MODERN engines that one can get now have this?
On the modern engines given as examples, there is proof they CAN be operated at lower than max recommended RPM and I see no suggestion let alone proof that running them outside of the max rated power speed will damage them.

Obviously if there is some specialised engine or something old that has a Min RPM for whatever reason that is different but I would say that does NOT apply to the majority most people are going to use here.

 
Quote
I was surprised that a Honda could have such bad vibration at the speeds mentioned.

Engine isn't going to be perfectly balanced at every speed and I note the range you mention is far from the  " extremely slow" You have repeatedly mentioned but also repeatedly failed and obviously avoided to specify what that is and who has said that most likely because you are the only one saying it. 

Clearly there is a forum position that is the accepted one on this and none other will be considered.
If people want to run their engines at full rated speed even if not needed, all good by me.  Shame there is not more emphasis on fact than going with the group mentality even when proven by the manufacturers documents shown it's not the hard and fast rule it's made out to be.

Carry on!   ::)
Title: Re: Slow rpm Chang fa?
Post by: guest18 on November 13, 2021, 02:07:54 PM
Deleted

Title: Re: Slow rpm Chang fa?
Post by: mobile_bob on November 13, 2021, 02:34:59 PM
seems to me we have two issues at hand

1.  perhaps glort has a "man crush" on hwew?  and...

2. just because one has never educated himself on things like critical speeds, has never witnessed them, doesn't understand the millions of dollars spent on research to either mask them, or move them outside the operating range of the engine and driven units, and doesn't believe in them "does not" mean they don't exist

i have heard there are those that are "flat earthers" maybe we have one here?

;)

bob g
Title: Re: Slow rpm Chang fa?
Post by: guest18 on November 13, 2021, 02:41:02 PM
Deleted
Title: Re: Slow rpm Chang fa?
Post by: mobile_bob on November 13, 2021, 05:16:45 PM
hwew

you should be deeply flattered my friend, it is generally only movie star hero's that have man crushes!

i can feel the warm glow all the way here!

bob g

you know its ok to be flattered, we are an all inclusive, non discriminatory group of folks here, we won't think anything less of you.
Title: Re: Slow rpm Chang fa?
Post by: guest18 on November 13, 2021, 05:18:43 PM
Deleted
Title: Re: Slow rpm Chang fa?
Post by: mikenash on November 13, 2021, 08:55:00 PM
seems to me we have two issues at hand

1.  perhaps glort has a "man crush" on hwew?  and...

2. just because one has never educated himself on things like critical speeds, has never witnessed them, doesn't understand the millions of dollars spent on research to either mask them, or move them outside the operating range of the engine and driven units, and doesn't believe in them "does not" mean they don't exist

i have heard there are those that are "flat earthers" maybe we have one here?

;)

bob g

Hey Bob the critical speeds are certainly a "thing" - especially when you have rotating masses at different speeds in different planes

In many of the sites i work on we have "lineshaft" pumps - a series of vertical shafts down a well driving a pump at the bottom in the water, and a 6-cyl John Deere engine (horizontal crankshaft) providing the drive, and, obviously, a right-angle drive in between.  All of these have had critical speed ranges that need to be avoided established by trial and error and both written on the pumpshed wall and programmed into the engine controller

So the combination of the lineshaft & the JD might be fine from idle to 1800 RPM then prone to shaking itself to bits from 1850 - 2200, then OK again from 2200 - 2450

It's certainly a well-recognised phenomenon
Title: Re: Slow rpm Chang fa?
Post by: 38ac on November 13, 2021, 09:37:18 PM
Would critical speeds be the correct term for the RPM ranges where the gear train on my Changfa type 1115 sounds like it is crushing rocks? It doesn't have lots of hours, maybe 400 total.  The gear noise hasn't gotten any worse but it isn't operated in the speed ranges where it was bad when new.
Title: Re: Slow rpm Chang fa?
Post by: mobile_bob on November 14, 2021, 12:24:44 AM
i think "any" speed where there is undue vibration is a critical speed
and should be avoided for longevity purposes.

doesn't mean you can run at that speed, but you accept some level of risk in doing so.

every rotating part has its own resonance, right down to the drive belts

no one designs a drive system to run where the belts are hard to keep from jumping all around, when either an increase or decrease in speed can easily control the whipping around, and if you can't change the speed because of frequency control (as in generator use) then you have to use other means to control the resonance/whip.

i noted speeds on my s195 where the balance shafts vibrated and raised hell, now in my case i could change the rpm and stay well away from that speed.  had i not been able to there are ways of at least dampening or basically covering up the problem, that doesn't mean it goes away, or doesn't still exist, just that it might be reduced to an acceptable level.

the gear cover of a changfa has enough overlap on an s195/1100 and maybe the 1115
to allow for drilling/threading and installing an oil return from a bypass filter to admit oil directly onto and into the gear train at the balance shafts.

the gear train normally only gets a misting of oil, enough to keep things lubricated and maybe cooled enough, but not enough to provide damping of those straight cut gears.

years ago i had an old worn atlas 12" lathe, and when running in back gears the gear train was horribly noisy,  a dribble of oil would quiet the gear train right down dramatically.  the same could be done with the changfa's.  we all know they have enough oil capacity to allow for some to be used for this purpose.

back on topic

a few nights ago, while watching youtube, i came across a clip of the american straight 8 engine's

buick among others made straight 8 engine's, the earlier versions only had 3 main brgs, which was ok so long as you didn't exceed some rpm where the resonance/critical speed would allow for enough crankshaft whip to allow the rod big end to contact the lower part of the crankcase, knocking out a hole and you know the rest.

the obvious fix was to add a couple more main brgs, this did not mean that there was no more resonance/critical speed, it was just that it was constrained.

so you either stiffen things up to raise the resonance to a place you are not going to be, or you mask it so it can't be felt, or if you can't do either you make note  in the engineering spec's not to run at that speed.

and no you won't read much about this issue in the common repair manuals, but this stuff is supplied by the oem's engineering dept to those that are incorporating this engine into a piece of equipment.  the equipment engineering dept are sure aware enough to inquire about critical speeds and you can bet they ask and get that information.

i mentioned a while back on this post about a two volume set of internal combustion engine engineering books published by MIT. they have examples of critical speeds and a section devoted to understanding and dealing with the issue.  if i had to advise anyone here about such things, i would certainly favor the published works of engineers with decades of experience over any faceless unpublished character on an internet forum.

bottom line, if you have issues with a project and you are wondering about this sort of thing,  don't take my word for it! and don't take the word of anyone else that claims such concerns are unfounded,  go to the library and do a little reading, it is quite fascinating.

Title: Re: Slow rpm Chang fa?
Post by: guest18 on November 14, 2021, 12:38:06 PM
Bob, I know you remember the Honda GX390 generator project that I pulled the plug on.

I remember us discussing how the engine was using a huge amount of gas in an hour running near 3000 rpm. The engine was blowing out black smoke and were scratching our heads for a while until we figured what was going on. We first thought it could be the drive pulley out of balance so the pulley was removed. The engine was ran again and it still had vibration problem from 2600-2800 rpm. But, when the speed was brought up to near 3000 rpm the shaking got so intense that it numbed my hand. Iíve never experienced such vibration on a Honda engine like the GX390. It turned out that the vibration caused the needle valve in the carb not to seat properly and in turn too much fuel was being fed to the carb. I would of never guessed that this phenomenon could happen. The real kicker was the engine seemed to run fine at 3600 rpm. The engine still had vibration but, not as intense.

I have no idea how the Honda engine was assembled in the factory. I could be wrong but I donít think every engine is balanced separately during assembly. This engine could of had a poor tolerance stack on parts.
Title: Re: Slow rpm Chang fa?
Post by: 38ac on November 14, 2021, 04:23:49 PM
Back to lowered output and RPM,  ALL, not some, engines are used under maximum available output,  not just the industrial applications noted by the one poster.  There is no such thing as an engine that is rated at, or operated at the maximum potential HP,  all engine that are USED for some purpose are derated to perform adequatly In the intended application. Not even a Top fuel dragster, NASCAR or Formula 1 engine is operated at maximum potential, why?  because it must finish the race to win the race. The engines uses in these and other racing venues are capible of trememdous HP and RPMs,,,if one doesnt care if they blow up in 2 seconds, thus they are derated to win races. A top fuel engine is derated so it will run for 5 seconds, a NASCAR engine is derated to run 500 miles, a formula 1 engine must run for so many hours and minutes otherwise it will power a loser. Th engines in our cars, trucks, industrial engines etc are all derated so as to meet a set of parameters set by engineering and sales which are operating life, build cost, weight, end use requirements and final product cost.  As all this applies to this topic nobody with sense is going to accept that a Changfa diesel is delivered at the maximum potential HP and that if operated at less than that it is going to blow up because we all know that quite the opposite is true, thus there is no need to keep going on about it when no body stated or implied it to begin with. Slowing an engine down to some extent automatically derates it even more than the advertised rating BUT there is a point where there nothing to gain by it which varies with the individual enginlie.    Are there critical speeds where most engines shouldn't be operated for maximum life?,  yes but that takes an engineering degree, or lots of experiance and a good set of ears to figure out. It isn't black and white, as sone suggest its always a balance of performance, operating cost and life expectancy
Title: Re: Slow rpm Chang fa?
Post by: veggie on November 14, 2021, 04:33:47 PM

Good points  38ac,

Slowing an engine can provide some benefits in the form of reduced noise, lower fuel consumption etc...
BUT, there is a point where inefficiencies become problematic.
If enough heat is not generated, incomplete burning and wet stacking can occur.
In the case of a changfa, low crankcase temperatures can prevent the evaporation of any light properties (fuel) that enter the oil past cold rings at startup.
An engine continuously running too slow may be over-cooled due to the cooling system being far to big for the HP being generated. If a thermostat is not added to the system to maintain good cylinder head temps, then inefficient combustion may present itself.
Title: Re: Slow rpm Chang fa?
Post by: mobile_bob on November 14, 2021, 06:15:37 PM
luckily we don't need an engineering degree to determine critical speeds
we can simply call the engineering dept of the manufacture in most cases, and in those that we can't (such as the changfa) it is so easy to determine if one is motivated to do so.

99% of folks with a changfa in this country, will run the engine at or near its rated rpm if belt drive, or at 1800rpm for 60hz direct drive, either speed is above at least one critical speed.

my trigen is built with resilient 3 point mounting, with the mounting axis inline with the crankshaft and st head centerline (being direct drive).  with the 3pt mount and resilient mounts, i can slow the engine and find a critical speed iirc at or around 1200-1300rpm
where there is not only much more noise from the countershaft gear clatter, but also a pronounced rocking motion and a heavier overall vibration. 

because it not only drives the st head but also twin 555 alternators, i don't want to run at that rpm, and found that by reducing to 1000rpm everything settles down again and that is where the low speed control was set.  the critical speed range not only was noisy and a lot of vibration, but because of the rocking moment of the assy and the outboard mounting of the twin alternators, i didn't want them shaking back and forth violently.

so at high speed it runs at 1800 for direct drive 60hz, at low speed 1000rpm for the twin alternators and lower db and fuel consumption.

in my opinion the changfa's are very tough compact engines, the crankshaft is very short and stiff with the flywheel mounted close to the outer main brg. it is doubtful that one could damage one of these engines running at any rpm below that which would start throwing parts all over the place... i have no idea what rpm it would take, nor do i want to know.

all we have to do is look to the guys that put them in trucks and haul all sorts of stuff, lugging along, stalling, lugging, and then reving like hell going down the hill.  tough little engines.

so i don't worry about the engines critical speed doing damage to itself, but i do know that it is hard on driven components.

now give me a 13hp chinese clone gas engine?  and yes i would be more concerned with critical speeds for the engine longevity. i would probably check with honda for one of their gx390's to see what they publish about operating ranges, and if i could i would talk to an engineer at honda about any critical speed concerns, that is "if" i found that once i built something the thing seemed to vibrate heavily at my chosen rpm.

i don't like things that vibrate, especially with thin aluminum crankcases containing the problem.

but that is me, and  i am a bit more particular i suppose.
and it would also depend on my intended use, if it were some intermittently used unit
maybe quick and dirty has its place, i can agree to that, but

if it is something that i anticipate running long hours, having to depend on its continued operation, then yes i will be doing everything i can to see that it is done right, and i will not be running at any speed that produces unusual vibration.

fwiw, which is worth about half what you paid for it.

bob g
Title: Re: Slow rpm Chang fa?
Post by: 38ac on November 14, 2021, 06:26:37 PM
Correct Veggie, and in the case of air cooled engines lowering RPMs also dramatically affects cooling. Some air cooled engines have much excess cooling capacity some do not. The Honda twins are well know to have valve sticking problem due to excessive heat when operated at high loadings at lower than max governed RPMs.
Title: Re: Slow rpm Chang fa?
Post by: guest18 on November 14, 2021, 11:25:53 PM
When I was in the lawn care business I had a zero-turn that had a 25 hp Kawasaki vertical V-twin. The engine had well over 2000 hours put on it and never burned oil. The only issue was starter bearings. It was mostly ran wide open except for mowing wet grass. Running the blades at lower speed helped prevent grass clogging the mower deck. That engine was a great engine most of the time. The only time I had concerns was when it was extremely cold. The cooling fan blew a huge volume of air over the entire engine and oil cooler that the engine and oil had a hard time reaching operating temperature. There were a couple days that the oil was not able to burn moisture out the oil. There were times when checking the oil that there was a milky substance on part of the dipstick and filler tube. The Briggs V-twin Vanguard engines had an oil cooler that could be removed for colder operation. A business partner that helped when I was busy had one of the Vanguardís on an older Walk behind and he never had problems reaching operating temperature. But in the summer, with the oil cooler functioning the engine always ran hot. The shrouds on the Vanguard had to be removed about 4 times a year to clean grass clippings from the engine cooling fins. The Kawasaki V-twin had the one piece shroud taken off for inspection once a year to check for clippings between the block and cooling fins. The way the Kawasaki engine was designed it seemed to pretty good for Commercial lawn mowers.
Honda did not have a strong network for the V-twin commercial engines in the south east. Most were Kawasaki and Kohler this was most likely due to lower cost, parts  and dealer network. Honda never could compete  with Kawasaki and Kohler. In my area.

Getting back to Air cooled engines. I agree that some engines have excess cooling capacity and some donít. Sometimes you can find out how good engines are before purchasing one by visiting sites like lawnsite.com


Title: Re: Slow rpm Chang fa?
Post by: mobile_bob on November 15, 2021, 01:17:57 AM
the city has a toro zero turn that has a water cooled kawasaki with over 4500 hrs on it
it had to have the head gaskets replaced because the operator didn't know it was water cooled and the water pump was leaking,, with a one gallon capacity it didn't take long to overheat.

new head gskts and reassembled, and has been running 4 year since then.

i wish i had a kawasaki water cooled v twin to play with.

bob g
Title: Re: Slow rpm Chang fa?
Post by: 38ac on November 15, 2021, 01:24:27 AM
Henry we had a large Husler dealer here and they were big on the V twin Hondas. There was a very large issue with them hanging the exhaust valve on one cylinder, it took a while but they figured out that part throttle operation was the culprit and a bulletin was issued on it.
Title: Re: Slow rpm Chang fa?
Post by: guest18 on November 15, 2021, 02:35:28 AM
the city has a toro zero turn that has a water cooled kawasaki with over 4500 hrs on it
it had to have the head gaskets replaced because the operator didn't know it was water cooled and the water pump was leaking,, with a one gallon capacity it didn't take long to overheat.

new head gskts and reassembled, and has been running 4 year since then.

i wish i had a kawasaki water cooled v twin to play with.

bob g

Be on the lookout for a used John Deere 425 that has a Kawasaki FD620D engine. My brother bought one for $300.00 some dollars over a year ago. It had a blown head gasket. He said something about a head bolt pulled out of the block. I think it just sitting around.  I would imagine a helicoil would fix it.
Title: Re: Slow rpm Chang fa?
Post by: guest18 on November 15, 2021, 02:43:16 AM
Henry we had a large Husler dealer here and they were big on the V twin Hondas. There was a very large issue with them hanging the exhaust valve on one cylinder, it took a while but they figured out that part throttle operation was the culprit and a bulletin was issued on it.

I remember around 2006 or 2007 our Hustler dealer had a few with Hondas and they were not popular. It could be that word got around as what you described.
Title: Re: Slow rpm Chang fa?
Post by: guest18 on November 22, 2021, 04:00:12 AM
Deleted