Compression testing

[SilverSHO]

Okay, I stopped at Advance the other day and picked up a compression tester to see what's up with my #1 and #3 cylinders. I've never used one before, but it seems pretty straightforward. Just looking for some pointers before I go out and do this.

 

[sdpatt]

Be aware that any hose, tubing, extension or gauge that you add to the spark plug hole is going to decrease the indicated compression because it is effectively increasing the volume of the combustion chamber. I found consistent numbers from using the screw-in fitting with the O-ring seal. Unless you have another helper to turn the key, you will have to use the screw-in type. The catch was that the fitting had a longer hose which showed a 5 psi lower compression than the press-on adapter.

I have heard that the engine should be measured hot and cold. I'm not sure which way is the accepted standard. It made a +5 psi difference on my engine when measured hot.

 

[fredhurderjr]

Honestly though, the 5psi difference is in the normal range for a decent operating engine. It's when you find things like "30psi" that you have a major problem. The big thing is to look at the difference between the cylinders. Example: Cyl. 2 is at 210psi, cylinder 1 & 3 are at 200psi, there's no problem there. If 1 & 3 are at 150psi, that's a problem, as the difference is too great.

Good luck!

 

[naval-avi8or]

I don't know if your gauge or the info your using tells or not but I have watched a mechanic do this test and you need to take two different readings. One dry and one wet(use a squirt can and shoot a a shot of oil in the cylinder) just make sure you don't over do it if you do suck the oil out before you start the motor so you don't hydrolock it.

 

[olympic]

Do the tests with all 6 plugs removed. Also, hold the TB open while cranking to let air in.