1941 Packard 356 8 cylinder - Low Vacuum After Rebuild

Posted by hynesjm on 2021/9/12 19:49:57
Hi All,

I have a 1941 180 with a recently rebuilt 356 straight 8 cylinder that has hydraulic lifters (I believe, see attached picture) that I have never been able to get to idle smoothly or have acceptable vacuum. No matter what I have done with Carburetor or timing, I struggle to get 13 inches of vacuum at idle of ~570-600 RPM.

I have been trying to find a major intake manifold leak that would explain this, but
can't seem to find an obvious leak. I am now wondering if a valve train with a misaligned cam or without sufficient clearance (~.03 to .07") is to blame?

From the build sheet, the following camshaft information was listed (note that engine builder was not Packard specific, but was a very sharp guy):

Cam Lobe Separation: 110.38
Centerline set to: 107.25

I have done compression and leak down checks, and while they look a little low (101 psi avg with 97 on the lowest , 7% leak down avg on each cylinder, highest at 9%), I don't think that would explain the very low vacuum readings?

cyl-Comp-Leak Down

Is there a way to check valve lash on an assembled engine? Everything I have read is checking and grinding valves to achieve the desired .03" to .07" clearance, but I haven't seen much on checking an already assembled engine.

Attach file:

jpg  IMG_8889.JPG (2,658.04 KB)
160461_613e9cec0e5e7.jpg 3264X2448 px

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