Compression test

[baileyem]

Don
I finally did a compression test on my early model A4. I did the test twice. The first time was with the engine cold after having an overnight resting period. The second test was also done on a cold engine, but Marvel Mystery Oil had been squirted into the cylinders.

Test results: #1 80, #2 62, #3 90 #4 105 (W/O MMO)

#1 87 #2 92 #3 98 #4 135 (W/MMO)

The engine runs well, but tends to foul #4 plug after several hours of running.

Is there anything good , bad, or otherwise that my test results indicate?

Mike

[Don Moyer]

Mike,

Your aft plug certainly isn't suffering from bad compression, but there seems to be a lot of carbon forming in that combustion chamber based on the anonymously high compression your reading in that cylinder. Is it possible that you have a late model cooling system on your early model engine? This kind of carbon buildup in the fourth cylinder is usually associated with the late model cooling system, which tends to give the aft cylinder a continual cold shower with the diverter cap directing all incoming cooling water aft.

I'd recheck the compression several more times in the above manner, but being sure to squirt the MMO away from the manifold side of the engine, toward the cylinder bores. Burn the MMO off after each application before the next compression test.

Don

[baileyem]

compression test

Don
Thanks for the quick answer. No, I don't believe that there are any late model parts in the cooling system. Everything conforms to what early model parts are supposed to look like.

I will follow your instructionsover the course of the season, and report back if any more anomallies show up.

Thanks, Mike