Jlbarnett

So I had planned to reseal my engine this winter when it gets taken out of the car. Car is a 1995 C2 July 94 build date. Car runs smooth and strong it just leaks a lot of oil. Today a fellow RL member and myself did a leak down and compression test just to be sure the engine is healthy before wasting money on resealing it if it will need to be refreshed again later. Here are the results:

Cylinder 1:
Compression 170psi, 165psi, 175psi
Leak down 1%

Cylinder 2:
Compression 170psi, 170psi, 165psi
Leak down 6%

Cylinder 3:
Compression 160psi, 155psi, 160psi
Leak down 8%

Cylinder 4:
Compression 140psi, 140psi, 140psi
Leak down 52% (double checked this twice, air could clearly be heard leaking from the exhaust)

Cylinder 5:
Compression 175psi, 170psi, 165psi
Leak down 6%

Cylinder 6:
Compression 160psi, 165psi, 160psi
Leak down 4%

This was quite unexpected to say the least. The car feels so good and responsive. The car has 120k miles on it with no previous rebuild history. Even after sitting for a week there is no smoke on startup or acceleration and no clacking of hydraulic lifters. At this point is my only option to have the top end done? Is it safe to drive? Is it carbon deposits or a burned valve on cylinder 4?

gt3'er

Before heading for a top end rebuild, worth getting a "second opinion". Have a pro do it and see if he gets the same results. You double checked twice, but you never know...

sand_man

I agree. I will be following this thread closely, since this car/driver are local to me.

sand_man

Also, when you bought the car (not that long ago), what were the PPI results at that time?

axl911

From the low leakdown and compression, it seemed you have a bent valve?

Or it could be a stuck piece of carbon on the valve. Put the car back together, go for a really hard drive. Test again. Maybe it dislodge the carbon.

Mike J

Funny, the compression looks a bit low but not as out of whack as the leak-down. Sometimes it's easy to get two wrong reading when repeating a test because when repeating you naturally make the same mistake .. :-).

What did the sparkplug look like? As suggested before, start and run the engine and try again just in case something is lodging in the valve given you removed the spark plug, it has happened before.

Did you rotate the engine from TDC and work your way through all firing order when testing? Was the compression test done separately from the leak down? I assume you removed all the plugs and then ran the tests? You double check using the distributor rotor to make sure you are TDC on the compression stroke when doing the leakdown?

Cheers,

Mike

AOW162435

Was the engine cold or warm when you did the testing?



Andreas

sand_man

I chatted with him last night and asked many of the same questions.

-The spark plugs "all looked clean, with no oil or fuel on them"
-And the test was done on a warm engine: compression first, then leak down using the lower spark plug holes.

sand_man

I also mentioned that I once had some inconsistent leak down numbers on my 930, which had been updated to twin-plug ignition. Discovered that a few upper spark plugs were not tight and this caused the poor readings.

Mike J

Hmmm .... given a 52% leak down, i doubt if this is a contributing factor. I would believe a few percentage points though.

Jlbarnett

We did the compression test first when the engine was warm, then directly went to doing the leak down. All the plugs were out of the car and they all looked fine with no oil or fuel on them. We rotated the engine with the distributor cap off at first to find TDC but after finding it on cylinder 1 we used the notches on the crank pulley to locate TDC and went through the firing order 1,6,2,4,3,5.

I think driving the car and then retesting is a good idea, that was our first guess that carbon buildup was causing the valve to not seat properly. Is it still safe to drive? Car runs great...

Jlbarnett

The shop that did the PPI said it didn't need a compression or leak down because it felt strong. Guess I shoulda done one anyway. :/

axl911

If the car is still up on the lift and half taken apart, you can drop the header/heat exchanger on that side and examine the exhaust valve.

Maybe get a plastic tool or brush and go around the valve/head to see if there is any carbon.

Jlbarnett

We put the car back together last night, and I drove it home 30 miles with no issues. I bought some liquimoly valve cleaner so maybe I can run some of that through the gas and recheck

pp000830

Contemplating internal engine repair in absence of any operating issues is a very suspect need.
If you look for love in the wrong places someone is
Can always be found who will be delighted to help you at considerable cost.