Hi,
i have performed a compresion test. With, wires disconected, i have measured each cylinder. The readings were between 105 and 115 psi. The good news is that they are close. The bad news is that I do not know what 110 psi means. It is low, it is ok?
What should the compresion be?
Thanks

 

Probably should be in the 150-160 range.

If the engine runs well wouldn't worry about it. The engine may well soldier on for a long time in with low compression...although horsepower will be down a bit. I suspect your low-ish numbers are simply the result of normal wear; worn rings most likely. A leak-down test would confirm where your compression is going

Cheers
DD

 

Did you do it with all of the spark plugs out and the throttle 100% open?

With numbers that low I would rather expect it to be an oil burner. But like Doug said, it'll probably run many many more miles before engine failure (if thats what you're afraid of)

 

Simple test to see if there is excessive wear.

You state that all the readings are close, this is a good sign, they should be within 10% of high to low.

With all the spark plugs out and a good battery, place about one teaspoon of engine oil in each cylinder before doing a repeat compression test. Once again the increase in compression should not exceed 10%, if it does the rings are worn.

Totally agree with others in that you may indeed get quite a few more miles out of the engine before a major overhaul is necessary.

Be sure to keep an eye on the oil pressure as well. Low oil pressure would indicate bearing failure is immanent.

 

Thanks. I will do that

 

Oh, I should have mentioned that if there is no large (more than 10%) increase in compression readings, then I would suspect the gauge you are using is reading low. Nothing much to worry about, very unlikely all the valves are worn equally.

Cheers and good luck.

 

I have a 1975 4.2L and my readings cold, with all plugs out and carb pistons in fully up position is 118 - 125 and engine runs fine.