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What is Normal Compression

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bobinyelm
Join Date: Jun 2017
Posts: 16 Olympia, WA
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2017-07-03          196806


Going through my new-to-me Gator CX 4X2 and noticed not a lot of resistance as the starter spins the Kawasaki engine over.

I askem JD dealer, and they had no idea what was normal compression-the tech just said "not a lot."

I did a compression check and the first compression stroke made 30psi, and after about 5 strokes was up to 75psi. Further cranking accomplished nothing additional. That's with a very strong battery spinning teh motor over pretty quickly.

I did a search and one post mentioned 57 psi minimum is acceptable, and another post said 170psi is min-normal for each cylinder on a 2 cyl Kawasaki (that sounded high to me).

BIG difference!

I set the valves (tight 0.007", loose 0.005"), but the intake was a tight 0.005" and the exhaust was a loose 0.007" so the additional adjustment I made probably didn't alter the compression.

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What is Normal Compression

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gatoraider
Join Date: Nov 2008
Posts: 540 Maryland
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2017-07-04          196807


The 57 psi is Deere's low limit for the FE290D. I believe 170-180 is the low for the FD620D. My experience with rebuilds, the 290 is around 150 and the 620 is around 200. The big thing with the twin is both cylinders being within 5% of each other. I certainly think a twin would run with lower compression if both cylinders were around the same. Also 57 is quite a drop from 150. ....

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What is Normal Compression

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Trainpilot
Join Date: Mar 2015
Posts: 67 Ukiah, CA
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2017-07-04          196813


Did you hold throttle open during test? That can make a big difference. If the air filter is severely restricted that could also reduce indicated compression and might make engine more prone to flooding. Some of our rigs seem like they have very little cranking resistance/compression, yet they have been running well like that for years. (620 v-twins). If the engine runs well warm and doesn't have excessive blowby I''d be inclined to run it and not go looking for trouble. In the Mules, purging air from the cooling system is critical, and head gasket problems are the common result of neglecting this step. If you really want to wrench on it, you could pull the heads and inspect the valves and cylinders. You could try, with ignition off and/or spark plug leads disconnected, turning the engine over by hand using the primary clutch. This might give you a sense of how the internals are holding up. Don't underestimate your natural senses. A bad valve, for example, may be heard leaking through the intake or exhaust during this procedure. Or leakage past the rings might be heard through the oil filler tube. Stinky oil--just sniffing the dipstick--can indicate bad rings or bad valve seals. If there is a big difference between one cylinder going past TDC and the other, that might also provide some insight. These engines are, in many respects, overbuilt for the amount of power they produce. A 620 cc motorcycle engine typically puts out 40-80 hp, whereas this engine puts out more like 17. Something to keep in mind. ....

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What is Normal Compression

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bobinyelm
Join Date: Jun 2017
Posts: 16 Olympia, WA
TractorPoint Premium Member -- 5 Tractors = Very Frequent Poster

2017-07-05          196814


You make some good points there.

When I do a car engine compression test I always make sure the throttle is held wide open. I completely neglected to do this in this situation and given how close d the butterfly is to get the idle speed down for smooth gear engagement, I'm sure the closed throttle restricted the intake air to produce good compression values.

I believe the horse power rating for the CX Kawasaki is like 8 or 9hp so It pretty much loafs along.

Given how little maintenance I believe my unit was given over at 640 hours, I guess I am looking for trouble. I am sure it never got a transmission fluid change, and I don't know when the order was changed.

I was willing to take a chance given the purchase price, and hopefully everything will be fine. It is a learning process.

Thanks, Bob ....

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