bry593

After performing a dry/wet compression test resulting in pressures of 160 to 195, I put a scope in the bores to see what I might learn. I found quite a lot of carbon buildup, which might explain why my pressures came up about 5 psi when wet. What I didn't expect was dished pistons.

Are stock '68 400 4-barrel pistons flat tops? What is normal compression psi for this engine?

How thick should the head gasket be? This engine appears to have composition gaskets, maybe .03 thick or so.

Does this mean the engine has been rebuilt at some point?

Fun71

Composition head gaskets show the heads have been off at some point. The factory gaskets were steel shim at ~.018" thick.

joe_padavano

From the 1968 Chassis Service Manual

bry593

Thanks Joe. Apparently engine was rebuilt with LC pistons. I’m guessing my compression is high on a few cylinders due to carbon buildup. Probably sticky rings as well. I’ve been squirting a 50/50 kerosene/atf in the cylinders to loosen the crud. I might even remove the engine from the car since at this point it is pretty much disassembled.

You know, when I started this 442 “repair”, I was just going to replace some exhaust manifold gaskets and engine harness....

edzolz

Those MAWs will surface in any project.

Yellowstatue

I thought the 400 pistons were supposed to be dished from a distant memory...so after conducting a thorough search of my brain I came up empty. Then I realized that I had a Technical Bulletins Dept. in the library and low and behold discovered Volume 18, April, 1968, Number 7, Page 64, states (briefly) '68 Manual is NOT correct. All 400 cu. in. pistons are dished, the high compression 1/32" (dish) and the low compression 1/4" (dish). As per Fig17. pg. 64.