Compression test, what does it mean???
1983 380 SL, ONLY cyl 8 fouls plugs and smokes after startup, idling at red light or any other idle posibility.
Removed all spark plugs and all other than cyl 8 look great, no dark deposits, if anything maybe running lean or hot. decided to test the compression on all cylinders dry and this are the results. 1= 168 2= 178 3= 175 4= 170 5= 175 6= 174 7= 163 8= 200 I tested number 8 last and retested them all. How is that the bad one tested higher? Is it that oil is leaking into the cylinder somehow and it test as if it was a wt test. What do do next. Any ideas? Thanks :confused: |
I expect that it is higher because that hole is oily. The oil will bring up the compression, but usually that doesn't happen because the oil is coming around rings and a cylinder that is not sealing.
I think you might have a seriously bad intake valve seal on that hole. You can verify this by doing a cylinder leak down test and listen for leakage on that hole. I expect that you will not hear any. Good luck, |
thanks Larry, i have been trying to figure out if a stem seal is the culprit or a guide.
your answer says it's a seal and i like your answer, better. :P |
did you try doing a running compression test
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Quote:
Need a leakdown test.....This will let you find a bad piston ring set or leaking valve seats. Need a reading of less than 12% for a health motor. Ideal is 5% or less. As you apply air, you can hear where the air is leaking from. From your discription, it sounds like a valve stem seal popped off. . |
When I say a valve seal I should have said a valve stem that is not sealing. This could be the seal itself or it could be a worn valve guide and/or stem.
If the engine has lots of miles on it, the compression test numbers indicate that the bottom is okay. It would be a good time to pull the head and do a valve job with valveguide replacement. Good luck |
I am half way into replacing the stem seals on cyl # 8, it's the easiest of the possible jobs that could be the problem. I hope it cures it.
Thanks for the responses. |
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