Running Engine Without Clutch... - Snowmobile World : Your #1 Snowmobile Forum

Dynamo^Joe · 06-25-2003, 09:09 PM

Seen a comment of this subject over on another forum....

Quote:

...the guys telling you not to run the engine without a clutch are correct, kinda.
The engine will run just fine without it and it should not cause the run-away problem that you mentioned.
The engine was designed to have that extra weight on the end of the crank for balance reasons.
Torsional vibrations are the reason that the Rotax engines have dampners on both the clutch and flywheel.

I've run the engine without a clutch on. I had such a hard time to get the engine to run over 7 grand. Was totally furious, removed the clutch, started the engine, pegged it and did not care if the engine sent the connecting rods thru the case via air mail to China.

...never did blow up.

kielbasa · 06-26-2003, 09:41 AM

hard time to get it to spin 7 grand without the clutch?? I personally don't think you could easily send a rod out the side unless you spin it at 20 grand (well, maybe not 20 grand), but as soon as you get past the pipe it'll just four stroke, kinda like a built in rev limiter....now if you lean it out big time and try it again you may have different results.....try it and let me know...

Dynamo^Joe · 06-26-2003, 10:17 AM

whuhh...now that I read what i wrote, i missed a few details. "tired last night"

It was one of our H2oX engines. When we would test on the beach the engine would barely muster up 7000+ rpm.
Why wont it go?
...did all the tests, compression, leaned the jets, checked ignition, changed ignition, changed stators, changed mag, changed beer brands, changed my gotch...
*sigh*
Put all of these engine parts including the crank into our "winning" engine....ran kick a$s..

Put all the parts back into the original engine....7000 rpm.

Took clutch off and the engine went off the tach. Ooh I was soooo mad im surprised that the engine didnt seize from overheating. Basically Rocketman pulled the tether when i wasnt looking.
...Oh well, didnt blow up like some guys will say if there is no primary on the engine.

Found the problem. Something about the bottom of one exh port being too low, shorting out the charge into the pipe or something like that. Changed the cylinders and the engine ran fine.

Anyhoo...my point is, I dont think that running the engine without the clutch will lead to disaster in the short time that people do run the engine like that.

kid rocker · 06-26-2003, 02:08 PM

Joe, I was told by a Ski-doo Rep not to run the engine without the primary clutch. I asked him the reason, and "he" told me that the primary clutch acts as a counter balance and could cause the crank bearings to go. It made sense to me because of the added vibration to the crank and connecting rods. But then again no problems with you running yours without the primary clutch. Hmmmm, makes one think a little bit.

dawg · 06-27-2003, 10:47 AM

i have also heard about this counter balance and thats why u should never run an engine with out the primary clutch on it.

clutchman · 06-27-2003, 09:57 PM

if you like to, or in racing situations, should, tear the motor apart and go through everything, you should never run it without the clutch on. if it is siting in the garage waiting for the snow to fly, and you go rideing to have fun on the weekend, or whatever, don't do it! harmonics and balance is the main thing, with no clutch and a heavy flywheel the balance is all screwed up, compression isn't exactly the same in all cylinders, the crank and bearings will be abused. the clutch isn't only balanced cintrifugally, but laterally as well with the entire bottom end ballenced as a unit.

but what do i know ??? ???

just an opinion.

kielbasa · 06-28-2003, 07:41 AM

man, these engines sound pretty tender if running w/o a clutch ruins them....I just can't see how a little bit of extra harmonics is gonna trash a roller bearing crank...I almost want to say any dampening afforded by the clutch is primarily for clutch longevity vs. the engine, just my guess....at work we run engines (four strokes) several hundreds of hours with SEVERELY out of balance pulleys and have yet to see any engine damage...just accesories breaking off is all.......

Allen Avram · 06-28-2003, 08:57 AM

I would strongly advise not to run a snowmobile engine without the clutch...the reason being that it acts as a harmonic balancer to smooth out the power stroke of each cylinder...otherwise your crankshaft will literally go to pieces...any of you that have built an auto engine for the street or the race track will understand this...the more horsepower an engine makes, the more critical it is to have a harmonic balancer that is made to handle the horsepower...Motorcycle engines also have a harmonic balancer, ie-the clutch, F1 motors...any piston motor has one...the only engine that I can think of that does not have one is a turbine engine...Hope this helps...Al.

99zx · 06-28-2003, 11:22 AM

I believe that since the clutch is not pinned or keyed for positive orentation that is does little to balance vibration. If it was balanced with the crank,rod weight and piston weight than it has one correct way of going on and it should be held with more than a taper lock because a taper lock can slip. Even a neutral balance harmonic balancer is keyed to go on one way (350 chevy). Harmonic balancers disipate tortional vibration how does a clutch dissipate this motion? Running without a clutch should not hurt the motor until you reach an rpm that the crank tortional vibration comes in step with cylinder firing frequency. In the oct/nov 1999 snow tech had a great artical on engine vibration.

Allen Avram · 06-28-2003, 01:07 PM

99zx: A snowmobile clutch ie, tra, is a balanced unit when both sheaves alignment marks are lined up...a tapered crankshaft on a snowmobile engine does not need a keyway...its a press fit...a harmonic balancer on a 350 chevy engine is keyed because the timing marks are on the harmonic balancer...the timing marks on a ski-doo are on the magneto, which is keyed to only go on one way...artic cat has available offset keys to change the timing...A harmonic balancer is alot smaller and weighs alot less than a snowmobile clutch...how the h/balancer works is there is two steel sheaves with a medium made of rubber or a fluid (Fluid Dampener for high performance) this medium acts as a shock absorber...a snowmobile clutch, just because of its sheer mass does the same thing...Hope this helps, Al.