What should my compression be??

[29 Chandler]

On my 1929 chandler 65 I recently did a compression check of the cylinders. As the engine has not run in many years I was using the hand crank to spin the motor. I am sure if I had squirted oil in the clyinders I could have raised my figures. I am not so concerned with how high/low the figures are but that they are similar among the 6. I have not been able to find the compression ratio for my engine. Here are the figures from my test:

1 - 75 psi

2 - 70

3 - 80

4 - 80

5 - 70

6 - 70

Thanks in advance for your help.

[Guest DeSoto Frank]

Chris,

Those numbers sound pretty good for "an engine that has not run for many years".

My old (pre-war) MoToR's manuals suggest that actual compression pressure is not as important as eveness between cylinders and that all readings should be within 10 pounds of each other (which your Chandler seems to have).

My "desk copy" (that is, the one that sits under my desk @ work <img src="http://www.aaca.org/ubbthreads/images/graemlins/grin.gif" alt="" />) MoToR's only goes back to 1935, but the lowest Compression Ratio listed therein is for Willys for their L-head four-cylinder: 5.13:1....most other 1935 cars range from about 5.5:1 to 6.70 : 1 ("High Compression" - use "Ethyl"!); I'd guess that your Chandler falls in the 4:1 to 5:1 CR range.

Take a pump can and squirt some motor oil into each cylinder (about 4-5 pumps) and take your compression readings again (have the thottle and choke butterflys tied or held open) and note the new readings. If the readings stay consistent, but go up, this is because the oil has sealed the rings against any leakage temporarily.

If the "oil test" does not raise the reading on a given cylinder, that would suggest leakage either past the valves or the head gasket.

Someone else might provide specific pressure data, but 70#-80# doesn't sound too bad, especially if the cylinder walls are dry and you're hand-cranking.

Frank McMullen

[Guest]

I you divide the compression by atmospheric pressure (ie approx 14) you get 5 to 1, 5,35 to 1 and 5.7 to 1. I would think the engine is in pretty good shape. My pontiac that had 4.5 to 1 comp ratio before I machined the heads and put in pistons that poke up above the block a little bit now reads around 90 to 95 when hot.

Happy hobbying