Just had mechanic give me results of compression test on my "73 1.7.
#1 100 psi
#2 120 psi
#3 120 psi
#4 150 psi
He is recommending valve job. I realize the readings are all over the place, but is this guy right?
Car was in for valve adjustment, small miss at 2800 RPM, and backfire under decell. Timing and fuel mixture were adjusted. Backfire is still there, but not too bad. Still not smooth accel at 2800 - 300 RPM.
During last oil change, I noticed some black soot around the left exhaust pipe on the cylinder head. Can't remember if it was the front or rear cylinder.I suspect small exhaust leak. Would this leak have any bearing on the compression reading for that cylinder?
I would appreciate any and all comments on the valve job recommendation and your thought on the compression readings.
Thanks for listening!

i don't have answer for you but you don't need to start a new post after 3 minutes give it some time.

Ah, George- stop baggin on the new guy! Three minutes is a long wait for a response around here...

ejm914- I do not know either, but an answer, correct or not, will appear here SOON.





John

P.S. I hope SirAndy does not run out of either ones or zeros due to the 'double post' .

I'll give it a shot,
Surely the numbers are disappointing at best. I would really want to be sure the test was administered correctly. I would wonder about the seal in-between the cylinders and the heads. That would surely make a difference in compression readings if there was a leak. It may not change the overall outcome as its likely the heads would have to come off but at least you would be more prepared. I would want to check that as well as preforming a compression test and add some oil to see what the outcome would be. By adding some oil to the cylinder (just a real small amount) if the rings are skewed the readings will jump up to a more normal state, if not then theres another cause / valve or head sealing.
My 2 cents
Now some real Porsche guy needs to chime in and help me out

Does the engine feel weak when you drive it?

I would personally do my own compression check (after the engine is fully warmed up). After you do one cyclinder you can remove the tester, squirt a little oil in the cylinder and then test again. The oil will might help seal the ring. If the compression goes up then you know the problem is rings. If the compression stays the same then the problem is in the valves. How many miles on the engine? It may just be time for a new engine or a big bore kit and some new heads.

Those numbers look like a half-assed compression test to me, at first glance.
If the engine's running mostly OK, I might expect to see 1 cyl a little low, but every compression check I've done was more like 120, 122 118, 125,
or 125, 124, 130, 85. Either all pretty close, or one lower. The test they did could be bad, I'd have someone else do another, with the engine warm, and the butterfly open for the test on all 4 cylinders.

I suggest you perform a leak down test.

This test will REALLY let you know the condition of your rings and valves without tearing the engine apart.

It is the next step I would perform after another compression test. (Do that your self..!!)

Search Leak down test on this forum...

Twystd1