Problems with compression test.

Hammermechanicman said:
"All single cylinder motorcycles over 250 have a compression release"

My kawasaki 350 Bighorn didn't have a compression release.
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That is because you Yanks are so tough . or perhaps just heavy .
To be honest the last new bike I bought was an SR 500 Yamaha ( Street version of the XT ) and it had a valve lifter on it as did the XT .
Smaller engines can be walked past TDC but big ones tend to kick back .
 
bertsmobile1 said:
All single cylinder motorcycles over 250 have a compression release
Most kick start twins had a compression release
IT changed when our friends at Nippon Denso managed to make a reduction gear starter that was small enough & cheap enough to fit to a motorcycle
Not sure about old HD's but there is no way any one under 300 lbs will kick my G 14 BSA over without a compression release
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This is a 4 cylinder 650 1980 Yamaha with electric start. I really don’t believe there is a acr on this bike.
 
bertsmobile1 said:
That is because you Yanks are so tough . or perhaps just heavy .
To be honest the last new bike I bought was an SR 500 Yamaha ( Street version of the XT ) and it had a valve lifter on it as did the XT .
Smaller engines can be walked past TDC but big ones tend to kick back .
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Anybody who had a big 2 stroke single knew how to "straight leg" start a bike. Work the engine around to the compression stroke. Shove yourself up high enough to extend the leg on the kick start out straight and drop your body weight down on the straight leg. Trying to start it sitting on the seat and just kicking it usually resulted in a painful kickback.
Screenshot_20240719_092902_Chrome.jpg

Pic off the internet. There is a reason the Kickstart lever on this bike was over a foot long.
 
Mark H_NO said:
I've never heard of motorcycles having a compression release. I've worked on a few, but haven't done compression tests on any.
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Hello Mark yes in fact many older single cylinder motors had a valve lifter to ease starting, but not on modern engines that I know of.
 
Never seen a mechanical ACR on a multi cylinder 4 stroke bike. Honda did have one on the XL500S. It was a 500cc 4 stroke thumper that pretty much killed off the 2 strokes used in flat track racing. Back in the heyday of big single racing 2 strokes it was common to have a compression release activated by a lever on the handlebars. Wasn't used for starting but rather modulation of power while holding WOT.
 
It's an interesting question, but it's mostly academic. Your best compression test is to run the motorcycle. If it runs smoothly and accelerates well, you have good compression, and that's all that matters.

It's often the test gague or your procedure. I've seen 80 psi on a chain saw, yet it performed perfectly. Always believe performance over a gague, unless you are a pilot flying on instruments in an aircraft, and in the clouds!
.
 
cdestuck said:
I hope I don’t get thrown off for this, but I’m having problems with the compression test, but this is on a four-cylinder motorcycle. I didn’t know where else to ask, but I thought you guys could be a big help.

I bought a compression test kit at Harbor Freight and hooked it up as I should in a while. Turning the engine over with the throttle open. It only reads about 65 pounds for each of the four cylinders. I thought the gauge was faulty and I exchange it Harbor Freight for a new one does exactly the same. How can I only be getting 65 pounds. The engine would never run at that level. The engine does run fine, but I’m just trying to take a test to determine how the cylinders are. Thanks for any help you can give me.
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Continental aircraft engines are good down to 40# per the mfg. 65 is not spectacular but is probably much higher when running. Should run.
 
cdestuck said:
Good thought. So I found a video of someone doing a compression test on the same engine as I have. He went through it and made no mention of a compression release. He came out with readings over 100 and the only difference he did is to remove all four spark plugs to do the test. I just took out one at a time when I did mine so tomorrow morning I will replicate his procedure and takeoff four out. I will report back my findings
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Stick the plugs back in the caps and ground them.....give the spark somewhere t go.....
 
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