high compression

[bjudd]

Will Samples wrote in a technical article:

"Compression above 170 psi is probably due to carbon buildup in the cylinder."

Mine cylinders average around 200.   Would the car sitting undriven for 10 years be a factor in this buildup?  What will help?  Italian tune up?   The car is only recently safe to drive at freeway + speeds because of completing the front end work.   Thoughts?

bjudd
1969 280 SL 5 sp

[hauser]

I believe that the compression on a freshly rebuilt engine is 160.  As for the carbon build up I'm not sure.

1969 280sl 5 spd
Gainesville, Fl.

[Chad]

Really 200 ??

I don't know. Compressions were about 160 in the cylinders on this 230 when I purchased it, now it had been driven less than 1,000 miles in twenty years before I bought it, and it was certainly not a freshly rebuilt engine. I have no idea. It is interesting to hear what the experts have to say.




-CD-
1967 230SL, 113.042 10

[ja17]

Hello bjudd,
Yes compression this high is not normal. Getting the ignition timing correct without pre ignition detonation will be nearly impossible unless you are using fuels with octane ratings over 100.

The cause can be carbon if it is high in all the cylinders. Italian tune-ups will help. Try driving in a lower gear with rpms over 3,000 rpms for a time. It can also be an over-cut cylinder head.

It the compression is only high on the end cylinders and it decreases on the middle cylinders, the problem may be a warped head which has been over-cut flat again. This situation will be more difficult to fix.  



Joe Alexander
Blacklick, Ohio

[norton]

Hi Brian  You might also try another gauge, I have seen gauges that read funny.

Mike Halleck
Chesterfield Mi
71 280SL
68 250SL (parts car)
94 E320 Coupe

[TheEngineer]

I had my cylinder head off. Measured the cylinders for wear. Found .0015 inches of wear including some taper. Got a NEW head. Put it all together by the book. Measured compression: 185 - 190 PSI. I'm using regular gas from COSTCO. (and have since I got the car 2 years ago) the timing is set to 34º because I adjusted the flyweights. When I set it to 40º it pings. Idles at 625.