Packard Forum Index » Post-War (1946-54)

What should the compression check numbers be on a stock Straight Eight?

I removed all spark plugs and placed a compression gauge in each cylinder when the engine was hot and came up with numbers that were between 107 and 118. The numbers were generated after cranking the engine for 5 compression cycles using the starter.

Are these normal readings?

This was done after I adjusted the valves today with the engine hot (took about 45 minutes to complete the valve adjustment procedure) using the Peter Toat method.

Maximum compression values vary with a number of things including the compression ratio, the altitude at which the engine is located, condition of rings & valves, etc. A compression ratio of 7.0 to 1 (factory spec.) should give cylinder compression values of 119 psi at sea level, 113 at 1000 feet of altitude, 108 at 2000 feet, etc. Anything higher than 119 would indicate that the cylinder head has been cut, or carbon accumulation (which you wouldn't have on a fresh engine rebuild). I'd expect to see the values even out as the rings begin to seat. - check it again in 500 or 1000 miles.

Attach file:

---

  (122.33 KB)

Thanks for the info.

Yes the engine is very new (only about 2 hours cumulative running time).


We are at 238 feet so I would think 118 PSI should be fine.

After 1000 miles I will try it again.