I have tested for compression on my 1990 350 SDL with 220000 miles. I have a range of 320 psi to 420 psi. What am I to expect on this motor?

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Who needs spark plugs.

is correct. the higher readings indicate carbon build up.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

how do you do a compression test? and what is good for a 560SL

ive heard of this test before

Tom, is that right? I thought 400 was normal. Spec is 26-32 bar which is 377-464 psi with 3 bar or 43 psi difference between cylinders. Min is 18 bar or 261 psi.

Chain, maybe a leakdown test to provide more info. That much spread isn't good.

Matt, I don't have V8 specs. For a similar vintage 300E normal is 175 psi, 110 psi is low, difference should be within 20 psi. Specs for a 560 won't be much different.

Sixto
95 S420
87 300SDL

thanks Six,


so how do you check it?

With a compression tester. It's a device that fits into the spark plug hole. You crank the engine and read compression in a gauge.

Typically you cut power to the fuel pump, remove all spark plugs, wedge the throttle full open and fit the tester to each cylinder one-by-one noting the max pressure reading after about 10 full cranks. There's a rhythmic sound to cranking. Count 10 cycles of the rhythm.

The easier gauges to use thread into the spark plug hole and have a peak hold feature. Don't forget to release pressure before removing the gauge. Other, usually cheaper, gauges have to be held against the spark plug hole and read while cranking. When cranking stops the gauge goes to zero.

Sixto
95 S420
87 300SDL