I'm working on a friends car and we checked the compression with it cold. We retrieved the following readings: #1 cyl 70 lbs, #2-80 lbs., #3-80 lbs., #4-100 lbs., Engine has been running for about 6 months. Based on these readings what do you suggest? Is it ok to go ahead and get the engine running and drive it like it is or are you taking a chance of doing further damage? Run some diesel or ATF through the carbs and see if that would loosen the valves up some, then recheck Compression after a few hundred miles or is it time to tear it down and do a Valve job? Thanks for any suggestions.
I forgot to mention the engine is a 2.0L out of a 1975 Porsche 914.
Those are shit numbers.
Was the engine hot, and the throttle wide open?
You want to see 100 psi in each cylinder, engine hot and throttle open. If you can't get that it's time to start saving for a top end rebuild.
Zach
Engine was cold, throttles (dual Weber 40s) were closed!
Agree numbers are bad, and agree it has to be done on a hot engine with throttle wide open. However, I thought 120-130 was on the lower end, but I can't seem to find any definitive numbers right now.
You also don't like to see a spread of more than 10% or so.
Valve adjustment can affect numbers also.
Sounds good, we will get the engine running, let it warm up then recheck compression! Thanks
Don't be too quick to judge. The #s didn't real look good on my wife's 1.7 when we first tested it, but decided to let it be for the time being. One day I decided WTH and adjusted the valves - found #3 & 4 were tight (#3 was way too tight).
Interestingly, those were the low reading cylinders. The engine was really peppy after adjusting all the valves.
Make sure the valves are adjusted properly first.
Adjust the valves and get it running. If those are the cold numbers, the warm numbers will probably be just fine.
--DD
Check the valves for sure.
Engine needs to be hot so everything is expanded. Throttle needs to be open so the cylinders are getting air. Valves need to be right so you are not leaking air out of a partially opened valve (valve too tight).
After that, you can try a thick oil to bring up compression as you said. But at that point, you are ordering parts and saving money for the head rebuild.
As DD said, just getting the engine adjusted and hot will bring your numbers up considerably.
Zach
The fault with those numbers is mostly the closed throttle.
Do like the others have said with all plugs removed
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