Classic/Antique Car Repair: compression test 1954 belair, combustion chambers, dirty environments

Question
HI PAUL, IVE JUST COMPLETED A COMPRESSION TEST ON MY 6 CYL 235 54 CHEVY. ALL CYLINDERS READ BETWEEN 105 AND 110 P.S.I. THIS WAS A DRY READING WITH ENGINE HOT. IS THIS READING ACCEPTABLE FOR THIS YEAR AND MAKE VEHICLE? HEAD WAS COMPLETELY REDONE, BLOWS BLACK AND BLUE SMOKE. THANKS

Answer
Vito:

If you do a cylinder leakdown test, you'll find that you've got blowby past the rings. Yes, you'll have to tear the block down and do the cylinders, too. Might as well do the bearings, oil pump, and timing chain, while you're at it.

Many engines wear (top end vs. bottom end) at an equal rate. The old 235 (and its predecessor, the 216) was one of these, and additionally, it was a fairly high-wear motor; often 40K was about all you got out of one, especially if they were lugged and run in dirty environments.

When you sealed up the top end by giving it a valve job, you didn't do the equivalent (rings) to the bottom end, and all of that nice, new compression is sucking cylinder wall oil right past those old, tired rings into the combustion chambers, on every piston downstroke. It's also running rich, as there's reduced volumetric efficiency and compromised ignition function with good valves and bad rings. Hence the colorful smoke!

Bad news, I know, but if you want to be right, break out the hoist and socket set!

--Paul