1983 380 sl
 

After performing a cylinder leak test I discovered that the piston on #8 cylinder leaks more than the others and thats where the plug fouling occurs.

Can the piston be remove:( without removing the engine?

Yes....and no.
Quicker to remove the engine/trans' complete.
Trying to remove the oil pan assembly will take as long or longer as removing the engine.
...'sides, you need to remove all the pistons and re ring them all.

You'll be glad you did.




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Thanks for the reply guys, the piston does not have a hole. I did take the head apart a few months ago and replaced the guide seals, the guides seamed tight but the problem that I thought was repaired by replacing the guide seals did not go away. I think maybe a ring on #8 piston is not working properly.
Does the guide could leak by if the piston is on TDC and the valves are closed? :confused:

Premature
 

Why would you assume that it is a piston?you may have a valve that is the cause of your leak down or poor compression. If you are set on pulling the 8th piston,TRy pulling the head first look into the valve if it is OK you are not behind because you are still going to pull that head!JNT:D

the guide doesn't seal anything. it guides the valve so that the sealing surfaces of the valve and head align properly and actually seal. so no, with the valves shut the guide should be just sitting there and doing nothing.

a worn guide is often the source of some smoke on startup or on decelleration. being bad enough to cause plug fouling seems to be too much to be just a guide to me.

did you have any expert look at the cylinder walls when your head was off?

if i had a head off i would ask my favorite machinist to come look at it and perhaps measure for taper. a broken ring might also leave tell tale marks on the cylinder wall.

if the problem is just from wear, marks might not be evident to observe.

tom w

Well, i performed a compression test and a leak down test yesterday gain to reasssure that what I was seeing on Sunday was correct.

Cyl compression at 175 within 10 % of the rest. GOOD.

Leak down test at TDC is 20% at 15deg before TDC 1% same as cylinder number 2. Which is weird, but I have hi hopes that the piston is OK.

A few months ago, when I took the head apart and replaced the valve stem seals i checked the stem play inside the guides but did not notice anything different on cyl #8 than on 5 6 7. This test was very un-professionaly performed and I assumed the guides were fine. The cylinder looked good and no grove was noticed at TDC or walls. The cylinders looked good to plain eyesight.

The car runs great ather than smokes after it reached operating temp. and fouls #8 plug, I installed a anti foul extension on it to keep it firing.

Question I do have, is it normal to have less leakdown at 15deg than at TDC
it happend on both cylinders 2 and 8 when I tested and retested to confirm my findings.

At this point I am suspecting a worn out valve guide on Cyl # 8. Any opinions.

I will install the new/rebuilt head but I wanted to try and dismiss the possibility of a bad piston or cylinder before re doing the 1/2 ass work I had already performed. What do you guys think.

I do have a rebuilt head that I purchased from a garage that was closing out about a month ago, they had a 380 sel with a just rebuilt head that never was fired up. Repairs were never finished. Lucky me. with it I got a distributor, an intake plenum, a fuel distributor all 8 injectors, a new water pump, a camshaft, black valve covers and a few misc.

Anyone needs 380 parts, I may have extra after I'm done. The donating car has gone to the recycler.

the max wear on the cyl will be at the top where the max combustion occurs. so yes, leakdown would be more there.

fouling plugs might mean a broken ring. just guessing really.

i guess i would be thinking of going thru the motor or looking for a drop in used motor.

tom w

Since I have a professionally rebuilt head and gaskets already, I will take the monster apart again and try it, I will post the results for future refs. I hope the smoke goes away.
Thanks.