3.0 engine compression figures after 1+ year of not running
 

Have a question for you engine gurus here on the forum....I bought a '79 SC a few months ago and just got around to getting a closer look at the engine in the car. The prior owner told me that the engine hasn't run in over a year and he got tired of working on the engine and wanted to get rid of the car because of it. Long story short, I did a compression test on the cylinders and they all came back with readings between 50 and 65 PSI. My question is, does that mean all pistons/cylinders are on the way out, or would the compression numbers be so low because there us no oil left on the cylinder walls to provide a proper seal between cylinder walls and pistons? I haven't tried squirting some oil into the cylinders and then taking a new reading. What do you guys think is the most likely cause of this? Would the oil pump circulate enough oil into the engine to lubricate the cylinders after cranking the engine a couple of times for each cylinder? Should the readings improve the more I crank the engine?
Any insight would be greatly appreciated....Bernd

You sure the compression gauge is not faulty?

Pretty sure, I hooked it up to two compressors and the gauge was showing the same readings as the compressor itself....

How many miles. I'd run it and see if the compression comes up.

Sounds like you didn't hold the throttle wide open

The car has around 65k miles on it. Before driving it I was planning on dropping the engine and replacing all fuel and vacuum lines(and whatever else needs fixing), just to be on the safe side. I checked the insides of all cylinders with a bore scope and didn't see anything glaringly wrong with them. I'm just stumped by the consistently low compression figures on every single cylinder.

Good point, but the throttle body is off the intake and there shouldn't be anything restricting air inflow into the cylinders as far as I can tell....

I bought a mid year that had a 78 sc engine in it and it had the issue of excessive oil in number 6 or 4 cylinder. It had sat for a while. At least a year or more.

I have been to the track, driven the heck out of it and have no problems. If everything works drive the car for a few months then take stock. Forgot to add that was 4 years ago, car starts like new and goes like the wind.

Compression readings on a cold non-running engine have little value. I would work on the running issues, and perform a compression check after the car is on the road. Rob

This ..

I brought back to life a car that sat for 10 years The compression was absolutely horrible but it ran and ran well.

I would try & get it running in its present condition. Then you have a baseline to work up from.
For such a low mile engine to have consistently low compression is very unusual, do you know what the PO did to it before he gave up? Could he have set the valves/timing wrong - consistently wrong - does it look like the valve covers have been off recently?

When 911s sit for a long time they usually get some oil leaking into the cylinders past the valves (& you have a smokescreen for a while after it starts).

Squirt some oil in the plug holes, spin by hand a few times, then do a leak down.

I NEVER hold the throttle open. even did a comparison of holding it open vs closed and there was no difference. besides, it does not really matter as long as they are measured under the same conditions.

I think comp numbers on a cold engine do have value. it has to build compression cold,. I have done both hot and cold, really no difference.

if all cylinders were 60'ish then you either did something wrong, your tester was bad or likely someone did a bad valve adjustment. I think the odds would be pretty hi for all 6 to be bad and read that consistent at that reading. even a bad valve adjustment and all be low and the same might be pushing it.

if you still have bad comp numbers do a leak down and listen for where the air is coming out.

I agree with others here, try getting it running and drive it some then test again.

After I got my 3.0L running I did a compression test cold and came up with 115-120 psi. I did it on a hot engine after running it on the road for 15 min or so and came up with 165-175. Just a data point for you.

Baseline the car and run it before you start assessing the compression. Who knows what the PO did - your valves, timing, etc. status has to be confirmed before you can proceed with speculation. Sounds to me like a jewel and I'd bring this back slowly and with some caution, but mindful that the 3.0 is a very robust engine unless it has been criminally flogged.

Best of luck and let us know what happens. North Tejas has a lot of very good Pcar shops if you need one.

cam timing can make it hi or low. if the intake closes sooner as in advanced then the comp will be higher.

his car should be 150-165.

check the valve adjustment.
check the head bolts while you are in there.
try another gauge if you can.
try some oil in the cylinder.
try to get it running.
if the compression is really that bad and it is not a valve adjustment and it does not get better after running then you are looking at a top end at the least.
I would try to get it running and check oil pressure hot. depending on oil pressure and miles would determine if I would split the case.

sometimes carbon can fall into the exhaust valve and keep it from closing but all 6? go buy a lottery ticket. a leakdown will at least tell you where it is leaking from. even 6 bent valves might be pushing the odds.