Anyone know what the engine compression was new for a 72 280SE V-8 engine when new and what's considered reasonable for a 32 year old vehicle now? The car I just got is about 140 straight across..
Thanks...

All that is on the CD for the 8:1 US engine is that the test value should be 8.5 bar, which is about 125 psi. So if you have an even 140, stop and take your SO out to celebrate.

Bob Neuberth of TMC, who tests engines before he sells them, once told me that he sees 180 psi in a fully rebuilt engine.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Wow..that is great to hear..thought it was supposed to be around 150 for each cylinder..any other owners out there who know what their numbers are or who have recently run a compression test on their engines?
Thanks!

you're looking more for even compression across all of the cylinders more than the actual #, although that does matter too

This is the result of a compression check on a 90K+ mileage 1963 M127 6 cylinder engine :

PSI Dry: #1-125 #2- 122 #3-125 #4–125 #5– 125 #6 - 125
Oil Wet: 150 152 155 150 153 155
Sparkplug tan tan tan tan tan tan

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Gregg:
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Should the compression be checked with the engine hot or cold?

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Litton
'90 420 SEL (sold)
'72 280 SEL 4.5
'98 ML320 (for sale)
'86 560SL
'05 Jeep Grand Cherokee Ltd (offroad in style)
'87 Chevy Blazer (AZ Pin Strips)

my autoshop class is failing me here. i think you want to do it hot, but i'm unsure

Saw this thread and the last post so will put in my two cents...

My auto shop lessons all advised to test hot with the throttle blocked open to ensure the fullest possible charge into the cylinder. In addition, I was advised to run the engine over about five or six times (choose one, be consistent) watching the rate the needle climbs. If on the first pump of compression it runs up the gauge significantly, i.e. 75 - 80% of eventual maximum, the engine is sound and tight. If it runs up slooowly, small steady bits of increase with each compression stroke, then it is becoming somewhat worn. You should look for reasonable uniformity across the cylinder readings, like in Bambo's example. Likewise you should carefully analyze off-spec numbers for what they are telling you. One cylinder reading low may be a valve leaking or if it is an end cylinder a leaking gasket. Two adjacent cylinders down may be a leaking head gasket between the cylinders, or two leaking valves that are exessively worn from the same cause.

The final number is somewhat less important that the relationship between the numbers. And, bear in mind that compression is greatly influenced by several factors. Among these would be condition of the camshaft or whether it has been replaced with a long duration shaft (not usually an issue with MB owners), cam timing changes due to chain stretch (an issue for MB owners), and also your elevation. Potential compression pressure is directly influenced by elevation. Results in Denver at 5,000+ feet elevation will be about 80% of that you will get at sea level. Handbook specs are always referring to sea level results.

Much can be learned from compression and vacuum readings. You might want to invest in a copy of Martin Stockel's "Auto Service and Repair" which is a superior basic text. I have his original and also one of the later editions which covers newer systems in more detail. Both are chock full of valuable information for the non-professional who wants to play the game better while still retaining his amateur status.

Good hunting,

230/8

As a 30 year Mercedes mechanic those readings seem fine to me. Remember that is a low compression engine designed to run on regular gas. The important thing is the #s are even. I would be concerned if the compression is too high. Basic compression test starts with a dry test and then you put oil in the cylinders to see if the compression comes up. If it comes up sgnificantly, it is an indication of worn rings. You can get the same high readings from an engine that is pushing oil. Enjoy your new charge. The EFI 4.5 was a good engine. Fuel mileage sucked, but at least you can run on regular.

Peter

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