Low compression - next steps?

[tenders]

more info: sometimes oil pools around the top of #4 spark plug

does this indicate worn rings, or valve issues? both? neither?

This has happened to me. Cause: loose plug.

[ronstory]

This has happened to me. Cause: loose plug.

Agree, if the plug is tight... check the plug itself for crack. Otherwise, swap plugs and see if the problem follow the plug or stays with the cylinder #4.

[rkohl44]

This has happened to me. Cause: loose plug.

The Manual says (page 1-8): torque value on spark plugs is 30 Ft-lbs.

My junior high metal shop class told me to put in spark plugs hand tight and then a little bit more.

I've been waaaayyy loose on my plugs if 30 is what I'm aiming for. I don't even have a torque wrench. Could this be why I have oil around the top of #4?

[tenders]

Agree, 30 ft-lbs is too tight for our old heads. But if the plug is in fact sufficiently tight as you mention, where is the oil coming from?

[rkohl44]

You're right, tenders. It's coming from inside the cylinder. I'll tighten the plugs more than I have in the past and see how that changes things.

#3 sometimes has a little oil. #1 and #2 have no evidence of oil around the plugs and much better compression. All plugs have been tightened to the same degree.

I guess the underlying question is whether the low compression on #4 is related to the oil pooling around that plug. Worn rings AND loose plug combo?

[Dave Neptune]

Seats & metal seals

The sparkplugs the A-4 uses have a "metal crush gasket", that collapses and seals. First be sure the seat where the plug seals is clean and free of debris. Common practice with these seals is finger tight to get the seal in contact and then about a 1/4 turn. This is OK but about 20 lbs of torque should be sufficient.

Tapered type seats are much different to seal.

There should be no leaking of oil past the plug. Install a new set with proper gap and torque. You should feel the metal gasket collapse and then tighten firmly or use a torque wrench if you are unsure of your arm rating.

Also note that a loose plug won't seal very well and it won't conduct the firing of the spark to a good ground IE a weak spark. Spark needs to be blue and snappy crisp sounding.

Dave Neptune