Hello awesome forum members,

I am currently restoring a neglected '84 300TD and recently had a compression test performed by a local MB mechanic. These are the numbers he gave me after he adjusted the valves:

#1 420
#2 340
#3 400
#4 360
#5 360
#6 340
#7 370

Why are there 7 values instead of just 5?

Initially, I thought these were good numbers, but then I read on another thread that too much variance in compression across cylinders is bad compression. So is an 80-point range an ominous sign?

Any recommendations?

Thanks!

And many thanks to all Pelican Parts folks for providing such a great info resource and parts supply! I'm in way over my head with this and loving every minute of it!

Where the valves adjusted prior to the test? Maybe 1 through 5 are the first pull, 6 could be a recheck of #2 cyl., and #7 after adjusting tight valve clearance on that suspect #2 cyl. Just a guess, but call them up and ask why only 7 I thought it was an eight cyl, and see what their response is. I have read that 10% variation is reasonable on a >250K engine.

I would have asked him, but he's Austrian and barely speaks English. I am very confident that he adjusted the valves before compression testing. The odometer reads just over 100,000, but it tends to pause intermittently so I'd guess its true mileage is <110,000. It was sitting for probably 5-10 years. Do you think the engine will improve once it gets running more regularly? It does have some "blow-by", but I've also heard most do. The power seems alright, even at high speeds (70mph), but its the only w123 I've ever driven.

So as is, the engine has 20% variation, which is twice as much as an engine should have with over twice the mileage. What should I do to prevent further harm and extend the life of the engine?

I would adjust the valves again yourself and redo the compression test before I went any further

__________________
2004 F150 4.6L -My Daily
2007 Volvo XC70 -Wife's Daily
1998 Ford F150 -Rear ended
1989 J-spec 420SEL -passed onto its new keeper
1982 BMW 733i -fixed and traded for the 420SEL
2003 Volvo V70 5 Speed -scrapped
1997 E290 Turbo Diesel Wagon -traded for above
1992 BMW 525i -traded in
1990 Silver 300TE -hated the M103
1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
1979 Silver 300D "The Silver Slug" -Sold

Well the compression reading is not what you were hoping for. But let me say that before you become to attached to the mileage shown on that speedometer, and it isn't reading correct right now, that these Mercedes speedometers are the worst at recording mileage. So unless you have a good paper trail the mileage, you don't know what the mileage is, and it could very well be 410,000 miles . You just will never know, but 100,000 miles on a 1980 wagon is just not realistic.

__________________
Junqueyardjim
Christianity, if false, is of no importance, and if true, of infinite importance. The only thing it cannot be is moderately important. C.S. Lewis



1983 Mercedes W123 240D 4 Speed 285,000 on the road with a 617 turbo, beautiful butter yellow, license plate # 83 240D INDIANA

2003 Jaguar Type X, AWD. beautiful, good mileage,
Mom's car, but I won't let her drive it!

Or maybe the sixth was a recheck of #2, and seventh after adding some oil to that cylinder? I'd try to ask the mechanic ... I think that's the only way to really know what the last two numbers are.

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)

The compression looks ok to me.

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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.

X2 X2 after reading that it sat for an extended time. i would try a valve adjustment after a thousand or so miles if it is starting easily and then recheck it, but only if you need to be reassured. If you do not need proof that the engine is fine, and is running to your satisfaction drive it like you stole it.
P.S. Seeing you were from Chicago IL I grew up around North Av. and Cicero circa 1970s hows it lookin?