Problems with compression test.

[cdestuck]

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.

 

[ILENGINE]

Does the engine have compression release, which would account for the low compression

 

[cdestuck]

Does the engine have compression release, which would account for the low compression

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

 

[Mark H_NO]

I've never heard of motorcycles having a compression release. I've worked on a few, but haven't done compression tests on any.

 

[cdestuck]

I've never heard of motorcycles having a compression release. I've worked on a few, but haven't done compression tests on any.

Years back I did have a two cylinder 650 Yamaha had a compression release. It was a manual lever underneath the clutch lever that you would pull in to start the bike. Just more of a manual release.

 

[Tiger Small Engine]

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.

If the engine is starting and running, you have considerably more than 65 psi compression. A healthy 4-stroke will have 110 to 160 psi. There has to be a compression release on camshaft. Try to find detailed engine specs online for compression readings on your bike. Better yet, if there are concerns, do a leak down test to pinpoint problems.

 

[CraigH]

I've always been taught that you should have a fully charged battery, all plugs out of the engine and wide open throttle.
That method has never failed me.

 

[StarTech]

See this why you should always look up your equipment by the equipment model number. This way you know for sure if a compression release is involved or not. Just can't go at it unknowing what you have in front of you.

 

[Hammermechanicman]

 

[woodstover]

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

Yes, remove all spark plugs when doing compression as well as full throttle. The starter is fighting the compression of the other 3 cylinders. You want it spinning as freely as possible for checking compression.