Author Topic: Compression Checks  (Read 1859 times)

Cole

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Compression Checks
« on: July 16, 2023, 22:28:40 »
Hi,

I did a search on this site and got a lot of word matches, but not for "compression check" per se, so I have a couple questions regarding this:
1. What was the compression in all six cylinders when the car left the factory? Was this the same for all three models?
2. Was this always measured in PSI or other units?
3. After many years, can a pagoda's compression come in higher at 160 - 175 PSI and be ok?

Thanks!
Cole
'69 280SL, 40G Black/Burgundy Interior

Vander

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Re: Compression Checks
« Reply #1 on: July 16, 2023, 23:44:32 »
Are you experiencing compression that you think is too high? What year/model are you working on?

Fluid getting into the cylinders is one common cause of compression being too high.

PSI or POUNDS Square INCH, is an American unit of measurement. Hence pounds and inches. Other units would be kg/cm or Bar. But they're all the same.

Think measuring the length of something...what's longer 1 inch or 2.54cm? Answer is neither, they're the exact same. Same with measuring pressure.

3 tips I would have before even trying to do an accurate compression test...
1. Re-torque the head
2. Adjust the valves
3. Perform test on a warm engine
1969 280SL

Lorsar

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Re: Compression Checks
« Reply #2 on: July 17, 2023, 00:56:57 »
If you searched for "compression check in the General Discussion board then that might be why you didn't get results.  I searched for "compression test" in entire forum and got 8  pages.
 
https://www.sl113.org/forums/index.php?topic=34683.msg253956#msg253956
Lori
1968 280SL (US)

wwheeler

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Re: Compression Checks
« Reply #3 on: July 17, 2023, 15:57:10 »
A rise in compression indicates there is less space in the combustion chamber. I would say an easy answer could be carbon build up.
Wallace
Texas
'68 280SE W111 coupe
'60 220SE W128 coupe
'70 Plymouth Roadrunner 440+6

MikeSimon

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Re: Compression Checks
« Reply #4 on: July 17, 2023, 20:50:00 »
If the engine has ever been worked on and bored with oversized pistons, compression goes up. Same is true for cutting/planeing cylinder head.
1970/71 280SL Automatic
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Cole

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Re: Compression Checks
« Reply #5 on: July 18, 2023, 01:22:23 »
Thanks for the good feedback!
Is there some MB documentation on what the compression was on a pagoda when it left the factory?
Cole
'69 280SL, 40G Black/Burgundy Interior