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91
Changfa Engines / Re: Slow rpm Chang fa?
« Last post by mobile_bob on November 10, 2021, 01:53:57 AM »
Damn Glort, take a chill pill man!

;)

bob g
92
Changfa Engines / Re: Slow rpm Chang fa?
« Last 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.    :)
93
Changfa Engines / Re: Slow rpm Chang fa?
« Last 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
94
Changfa Engines / Re: Slow rpm Chang fa?
« Last 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.
 
95
Changfa Engines / Re: Slow rpm Chang fa?
« Last 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.
96
Changfa Engines / Re: Chang-chai and ST head, deal? Or no deal?
« Last post by guest18 on November 09, 2021, 11:23:06 PM »
Yes you were lucky.
97
Changfa Engines / Re: Chang-chai and ST head, deal? Or no deal?
« Last post by veggie on November 09, 2021, 09:18:40 PM »

WOW !!  :o

Lucky that you stripped it down.
After a good cleanup and re-assembly it should be a good runner.
As mobileBob noted, parts are available easily for these engines.
AliExpress has lots of parts at good prices.


98
Changfa Engines / Re: Slow rpm Chang fa?
« Last 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
99
Changfa Engines / Re: Slow rpm Chang fa?
« Last 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.
100
Changfa Engines / Re: Slow rpm Chang fa?
« Last 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....
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