Compression - Good enough, or Not

[High Hopes]

I am reassembling my engine after a valve job and many minor fixes. With the head back on, with the manifold still off, and cranking by hand I observed the following. There is little oil in the engine.

- Compression was about 30 psi with a dry head.

- Compression went to about 50 psi with some Marvel Mystery Oil (MMO) poured into the sparkplug holes.

- Compression across all cylinders was uniform.

- Two intake valves were spitting oil spray out their manifold port. This seemed to decrease with time either because the valves were seating better or because the MMO all drained out with previous cranking.

- I heard a squirting / squeezing oil noise. I fear this may have been oil blowing by the pistons. I'm not sure where else the oil could have been going. This was only heard when the compression gauge was in a cylinder. It might have been an oozing exhaust port?

Questions:

(1) Is hand cranking a suitable way to check compression? If not, how should it be measured?

(2) Should I continue to assemble the engine, fill it with oil, run it, and then measure compression again?

(3) Or, should I bite the bullet and drop the crank and go for the whole nine yards and do a complete overhaul? I really only need about five more years out of my A4 before I move to a bigger boat (I hope).

Steve

[Don Moyer]

Steve,

I'd put at least a quart or two of oil in the crankcase so that the level is
above the pick up screen. Then remove the plugs and turn the engine over on
the starter. Most engines will develop around 20 psi at starter RPM which
will be better for your rod and main bearings and will give you a more
consistent compression reading than hand cranking will.

Do you remember what the compression was before your valve work? As long as
it was 85 psi or above I would hope that once the valves seat (which usually
will not happen until you run the engine for at least a few minutes) you'll
have plenty of compression to see you through the next 5 years.

Don

[High Hopes]

Don,

Just to follow up. Compression was 105, 102, 96, & 105 measured a week ago. There might be a stuck oil ring on #3, but didn't see the benefit of tearing down the engine for this one item. Maybe some MMO will work it loose.

Steve