engine was warm. any particular oil I Need to use for this? or will any old stuff work? I have part of a quart of 0w-30 for the honda sitting around, will that work?

 

Yes, that oil will work. I use a common oil squirt can, you know the type you use to oil different things. Fill up the can, insert nozzle into cylinder, squirt a couple of shots and retest. In theory, the oil will form a liquid seal on the rings and thus compression will read higher during test. Naturally having bad valves, broken rings,, holes in pistons will not result in higher readings.

Not remembering what cylinders you tested, just keep in mind, if the timing chain has jumped a link, all readings will be lower.

 

I thought it was better to test on cold engines because you get the real compression before thing's warm up and seal better?

This though, is coming from the 2 stroke world. If you get 115 psi of 120 psi warm, it's a false reading and you'll think you wont have problems. Do it cold and you find yourself at 95psi. Pull the top end apart and will find scored walls and/or worn rings.

 

first of all how are you doing this test...?

second of all if a cylinder is using oil it will be on the plugs... also you will have an abnormally high cranking compression pressure...


with the engine fully warm...

Unplug fuel inector main harness so NO fuel is Pulsed.
Unplug Coil plug at coil so Ignition does NOT spark
OPEN throttle body throttle plate to WOT (Wide Open Throttle) position...


I would unscrew all 4 spark plugs on once side on a V8 and all 6 plugs on the 300-6 and keep wires close to cylinder as to not mix up the order...

crank the engine so that it rolls over at least 3 if not 4 times but each cylinder getting the same amount of cranking time...



read the gauge and note the highest reading..

the gauge may not be fully accurate so dont worry about the low number... but the uniformity between cylinders....

you MUST make sure the throttle blade is OPEN or you wont get a good cranking compression pressure...

if you want to use anything to test the "wet" cranking pressure use a oil squirt can and use ATF and give each cylinder 1 good squirt...thats all you need

 

eh... not a real reading in real world.. you want warm as things seal together.. you dont run cold while driving you run warm so you want the test when warm...

cylinders and pistons and rings arent as "true" when cold..and tolerances are much looser...

 

my testing methodology:
warm engine to operating temp
disconnect ignition coil
remove spark plug from cylinder to be tested
screw adapter into spark plug hole, about as tight as I would screw in a spark plug
screw in hose to adapter (hand tight)
attach compression gauge to other end of hose
have assistant crank engine about 5 seconds with gas pedal to floor

I didn't know I should disconnect the fuel injectors, I had not been doing that. I'm also seeing motor oil and ATF for the wet test... what to use? I aim to do the complete test today (and wet test if results are unfavorable)

 

I would have had to refresh my memory on the proper procedure, but I did remember the motor had to be warm. I'd disconnect the computer relay since it gives power to the injectors.

 

My Chilton's manual says any readings less than 75% of the highest cylinder's reading are suspect. Does that apply to the whole engine, or to each bank separately?

 

looks like I'll have to post a screenshot... here we go



I did 3 runs of the test on each cylinder... anyone know if I should use the average of the runs, or the max?

 

Also need with and without oil added to the cylinder.