Engine comprssion

[jeepers52]

What is the min compression in an old engine that has never been rebuilt. Trying to decide if I should do a rebiuld or try to fix the little things in the engine to make it run. Thank you

[wesk]

Have you read your TM 9-8012 page 74?

The actual number is not as important as the relative numbers between the 4 cylinders. The Book gives you a minimum of 100 PSI with 135 as the norm. It also suggests that there should not be a difference between cylinders of more than 20 PSI.

You should include the vacuum test on page 80 before making a final decision.

If you do not mind a lack of performance then you could tolerate compressions as low as 80 PSI as long as each cylinder is with 10 PSI of the others.

[jeepers52]

Thank you,

I did read the old book, and I was afraid of what you might say. I am running about 75 in each one. I guess I know what that means.

Thanks for all your help. More questions to come, I'm sure. I really want to do a good restoration on this one.

[wesk]

Do the vacuum test and a leak down test before you tear down the engine. This will give you valuable information to use as you inspect the disassembled engine and help you avoid overlooking any needed repairs.