Problems with compression test.

[digr]

Let the piston compress at least three times

 

[Hammermechanicman]

The cheap HF compression tester doesn't have the Schrader valves at the end of the hose. You can't use it for small engines or motorcycle engines

It it ain't like this it ain't gonna work

 

[cdestuck]

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.

Well today, I did take all the spark plugs out and check the compression while holding open the throttle. Still got the same 65 may be a pound or so more. Then I also had the engine running and checked the compression in one of the cylinders and it was still the same. I’m really baffled. Could certain engines actually run with 65 pounds? I’m lost.

 

[Hammermechanicman]

I give up.

 

[cdestuck]

The cheap HF compression tester doesn't have the Schrader valves at the end of the hose. You can't use it for small engines or motorcycle engines

It it ain't like this it ain't gonna work

I am not at the bike now until Sunday. I will check to see what the bottom of the connector looks like. It advertises that is good for motorcycles and small engines. Of course that’s their advertisement

 

[woodstover]

Well today, I did take all the spark plugs out and check the compression while holding open the throttle. Still got the same 65 may be a pound or so more. Then I also had the engine running and checked the compression in one of the cylinders and it was still the same. I’m really baffled. Could certain engines actually run with 65 pounds? I’m lost.

Did you remove all the plugs when you checked the compression after the engine was running??

 

[cdestuck]

Did you remove all the plugs when you checked the compression after the engine was running??

Yes I did. I’m lost over these findings.

 

[bertsmobile1]

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

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

 

[bertsmobile1]

Yes I did. I’m lost over these findings.

First of all what motorcycle are you talking about ?
Second what model compression tester are you using ?
Screw in or rubber bung ?
Next try spraying all around the plug hole and the tester tubing with soapy water I would expect you will be blowing bubbles every where
Does the tester have solid tube or flexible hose ?
I am tempted to say what did you expect from a $ 2 Chinese compression tester from the biggest cause of over consumption on the planet ?
HF = Junk ( 99 % of the time )
FWIW the compression tester I use cost $ 120 ( Aus ) back in the days when $ 200 was a weeks wages and it still works perfectly
When I started to do small engines it was fine for mowers but hit & miss on hand held gear so I bought another from Goodwoods because their stuff always works .

 

[Tiger Small Engine]

Yes I did. I’m lost over these findings.

Around 75 psi (give or take) is about the minimum for a 4-stroke small engine to start and run. Obviously, you have a compression release, or your gauge is inaccurate. Put a little oil into the cylinder and test it again. If the reading increases substantially, you have worn piston rings. Don’t get too focused on compression numbers if engine is starting and running strong. Perform a leak down test if it is bothering you that much.