Compression numbers in the 140-150 range

Low compression. Several possibilities.

 

Could be cylinder liner damage, piston wear, rings. You probably won't really know unless you take the heads off and see what's going on in there. That will not be part of a basic PPI. To rebuild a 355 engine could cost you $20-$25k.

 

If all cylinders showed that I would suspect either valve timing or the gauge itself being off. I would do a leakdown and see how much the cylinders are leaking and where the leakage is coming from if there's a decent amount. That should tell you where the issue is.

 

that is very odd to have low compression and OK leak down.

Valve timing being off is a very good possibility
Not opening up the throttle during compression test is a rookie mistake but it happens
A bad gauge is also a possibility.
Doing the test at very high altitude is a remote possibility.

 

To me it sounds like a possibility that this car has been sitting for some time and the rings are a bit stuck. An Italian tuneup may be in order. I small amount of oil dropped into a cyl is a quick way to see if it is rings or valves. If it is rings, the compression will come up. If it is valves, then you should see no change. I do agree that the throttle could have been left closed during the test.

 

If valve timing is the culprit would the engine out service and timing solve the problem?

 

The figures are a part of a diagnosis. Without knowing the mileage and circumstances (e.g. pressure for leakage, altitude etcc) it becomes a still speculative analysis. On the plus side, it seems to indicate good news, very consistent numbers in both columns, in fact I find the leakdown almost too good! But not having ALL data and history is an issue.

 

cold engine + altitude + throttle + warm engine + guage = ?
What does the tech say?

 

It does seem inconsistent. Typically low compression means there's leakage going somewhere. Brian does have a point that the numbers are pretty uniform overall.

I would recommend more testing before doing anything else.

 

You almost never see a motor with a compression problem that manifests itself equally across the board. Even cam timing issues are almost never done equally bad bank to bank.


My money is on it having a good motor and a questionable method or equipment during the compression test.

 

That is what I thought. Very suspicious all those low numbers being consistent. Engine cold maybe or monkey on the guage.

 

I concur. Try again with a different gauge. If you don't have the right adaptor it won't seal properly. I have had to modify the adaptor on 355s because they are so narrow where the plug gasket meets the head.

I had a car from dealer with similar numbers, it was diagnosed with bad guides. After modifying the adaptor the numbers were normal. 190/200

 

Compression numbers can vary by having the throttle(s) closed or open. If those leakdown numbers are correct and the gauge not faulty, I would bet the low compression numbers are the result of doing the test with the throttle(s) closed.