VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1933-1936 1934 Engine Compression

I'm trying to determine the condition of the engine I picked up before I put it in my 1934 chevy. It runs and sounds great. The engine has had several owners since it was rebuilt so there is no way of determining how many miles are on it. I ran a compression check just after I got it fired up and the numbers ranged from 80 psi on the lowest cylinder to 98 on the highest cylinder. So the question is. What kind of numbers should I see.
Thanks for you imput.

Any time there is more than 10 pounds difference between cylinders there is something wrong. If it were mine I would remove the cylinder head first. That will give you a good opertunity to inspect the cylinder walls etc. Then I would do a valve job....and you don't need hardened seats.

If I was you I would do a re-test on the compression. Motor should be warmed up. Write down each cyl comp number on test #1, then go thru it a 2nd then a 3rd time to see if each cyl has a consistent reading.

That will give you a better idea of exactly what you have.

Check the plugs to see how they are reading, clean them up for the 2nd test. Use brake clean spray and a used toothbrush to work the plugs over and air dry them. Before re-installing check each plugs gap.

lets see how this works out before you get into tearing down.


mike

You could also put a small amount of engine oil down the spark plug holes and redo the compression check. This will give you an idea what condition the rings and valves are in. A massive pressure increase indicates rings leaking little or no increase valves are leaking. The next time the engine is started have very good ventilation as there will be lots and lots of blue smoke but will clear in a few seconds.
Tony

Thanks to everyone that contributed. These are all good ideas. I have the engine sitting beside my house with the radiator hooked up. I plan to retest the compression after I have run the engine for an hour or two. I'm hoping this will give the rings a chance to reseat then selves, also work out any rust that may have accumulated. I have given it a complete tune-up, points, condenser, cap, plugs, and wires. Does anyone know how much compression a new rebuilt engine should have?

For that low compression engine any where from 90 to 100 pounds - depending on the compression gauge and engine cranking speed.