Slow rpm Chang fa?

[38ac]

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

[veggie]

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.

[mobile_bob]

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

[38ac]

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.

[guest18]

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 Vanguard’s 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 don’t. Sometimes you can find out how good engines are before purchasing one by visiting sites like lawnsite.com

[mobile_bob]

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

[38ac]

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.

[guest18]

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.

[guest18]

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.

[guest18]

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