BUICK NAILHEAD 401 COMPRESSION

RFFILM

Newbie
I am rebuilding a 1927 Roadster with a Buick Nailhead 401.

We recently ran a compression test and all but 1 was putting out 150 PSI. 1 was outputting 120 PSI.

Any suggestions on what could be the issue?

Thanks, new to cars, so sorry if there isn't enough info here.
 
It is either a seal issue with the rings or valves, or a mechanical issue with the valve action (bent pushrod, loose/broken rocker, defective lifter, worn cam lobe(s).) Try a squirt of oil in the cylinder to rule out ring seal, and inspect the valve train components for that cylinder. See if the valves depress the same as the other cylinder’s valves. A leak down test is the next step to determine the source of a leak.


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As Steve mentioned,BUT ALSO the best things to do to check the health of ANY engine is cold & hot compression & cylinder leak down tests. As also mentioned put a ounce of oil in the affected cylinder & see IF compression improves quite a bit. Not 20-30 pds. But 50 or more. ALSO while doing a leak down test listen for where the air is escaping. Can hear it up top via the crankcase, rings. From the carburator or the exhast pipe, valves.
ONLY when this is done can you determine what may be wrong.
Unless it was a low compression 401 to begin with the compression readings should be more like 175+
Look for the engine code on the right side in front of the valley pan & we would be able to tell/identify not only the engine type but also by the VIN code on the left in front of the valley pan also will identify the car it originally came out of.

Tom T.
 
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