This means your compression gauge is leaking somewhere.

I'm in the middle of head r&r because of what you read below. I believe someone even said he was surprised the car ran with 100 on one and 120 on the other. But damn if the car didn't run pretty good. It'd even start down to 27F. I did the compression test three times, same numbers. I fashioned a fitting onto the HF adapter to get air into the cylinder. I felt a wafting breeze at the intake on every cylinder. When I covered the intake with my hand, the air squealed out of the valves up top. It was the poor man's leakdown tester, but I figured it told me enough of what I needed to know.

I doubt your car would run well with actual 0 compression in one cylinder. But who knows. I think in my car, the 100 cylinder fired when hot because the operating temperature could compensate for a burned valve here or there. It did run rought when cold and smoked furiously for 5 minutes or so in the a.m.

But I did my stuff cause the car smoked bad--embarrassingly bad at stop lights. It burned a little oil, but not much--qt per 900 miles I think. So I wanted to fix something. I think others have made the point that testing blowby and compression are useless unless something's wrong that you need to fix.

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Car: 85 300d turbo diesel, 260k, no signs of any major engine work (I've had it the last 6k miles), but I have replaced injectors, valve seals, timing chain, adjusted valves.

Sympton: Blowing blue smoke mostly only at idle, tea kettle test dances the filler cap, but doesn't totally blow it off--so could be worse; using about 1 qt rotella 15/40 per 900 miles. At initial takeoff, I observe a pretty impressive puff of blue smoke in the rearview, but then it dissipates underway. So tested when parked--I give it the fuel, puffs blue initially, then I hold rpm's at 2k or so and smoke dissipates.

Car performance: Really quite good--15 sec. 0-60 times consistently. Idles well when warm and burning either bio or Cetane 45 diesel. I've fooled with ALDA and have it to where I get a small puff of black under heavy load and then it dissipates. Doesn't use coolant to signify head gasket.

Here's the kicker: Ordered up my Harbor Freight compression tester off of Ebay ($35 including shipping) to really see what I'm up against. Did the dry/wet (squirted 1 tsp. oil in cylinder) in a semi warm engine (got up to operating temp., then sat maybe 40 min.s in 50F weather (yeah, beautiful day yesterday!). Numbers as follows:

#1 - 360, 420
#2 - 260, 300
#3 - 220, 220
#4 - 100, 120
#5 - 260, 320

Howdy GRIESL:

Best of luck and please to share your results with the head R & R - iam actually doing same on a 6.9 International tomorrow

time has passed since I first started this post - now am a wiz at the compression test - did you test at glow plug or at injector

I have read over the years on this board that the only compression test that matters is a cold start- if you no.s improve the hotter the engine i believe this is more a sign of rings- and if I recall correctly - if you have switched oil lately - say from dino to Synth - you will have ring issues for quite some time as the engine gets used to the synthetic oil -

i am most interested to hear what shape you valves are and if any of your precups are loose

Good luck

Cheers

It's hard to tell just by looking if valves or seats are burned, but a visual inspection reveals that they are shot. LOTS of carbon buildup above the seat and on the shaft of the valve. At least two guides were worn enough to feel some play when giving the valve a side-to-side pressure. By precups, do youmean precombustion chambers? None were loose, but looked nasty. Metric Engines convinced me to replace the chambers with the new head. A severe case of the may as wells. Anyway, I pulled the head with an engine hoist (damned thing weighs in at 80 lbs. by itself, and I left the manifolds and turbo on there). It's really not that hard a job--just time consuming. I wonder if MB designs it so that you don't even have to get under the car once to do the head. Love that!

I've heard both opinions on the compression test. Apparently MB recommends it warm, but then there a lot of folks who say a hot engine can damage the gp holes if you're sticking them in and out with the engine hot. I used the injector hole. I can't imagine it makes any difference at all which one you use. I also squirted the oil in the chamber, which gave me further evidence that the problem is with my valves. The one thing I'm terrified of is that I get the whole thing buttoned up and it turns out that rings are bad as well as the valves. You know what I mean? The valves, sure, are shot, but maybe they're just letting the majority of the compression out the cylinder before the rings get a chance to. Who knows. I'm just doing a lot of praying to the Benz gods! Good luck wrenching on your Int'l. I think once I get this project done, I may look for a cream puff with a blown engine and just do the whole damned thing at once.

while you have the head off i suggest getting a machinist to measure the taper in the bores to see how it is. there is a go no go ratio between the top and bottom.

good luck

tom w

Howdy GRIESL:

Good job - yes is easy on the 617 engine - just heavy and consuming as you know

How much ridge do you have on cylinder walls?

Dunno how much I am qualified to say - but I would imagine if you are not burning that much oil - your rings may be in pretty good shape-

Think replacing the Pre Cups- Combustion chambers - is a good call- you have good instinct there -

How technical will you get ? i.e. - do you know if you need to increase the thickness of head gasket yet?

Good luck -

cheeers

Hey there, I didn't measure cylinder walls--kind of wish I did. Visual inspection looked fine though, and you're right, not much oil consumption so rings probably OK. I'm going to get the timing chain on soon and I'm going to do another compression check then just for kicks.

Metric Engines said their new heads do not need thicker gaskets. Something like they reface and then machine the head surface. I'm going on that recommendation.

About to test
 

I am about to compression test my OM617. I had the injector lines off and tried to test it. (in the injector plugs) Totally spaced that one out. took me 2 attempts before I realized I was just letting all the pressure out through the injectors.

I already have all 5 glow plugs out because they were all bad. Do I have anything to gain by pulling out the injectors? I have the glow hole adapter and the injector adapter. I could throw the injector lines back on pretty quick, or should I stick the plugs back in and test from the top?

It does not matter where you test. If you have glow adapter by all means use that.

Tom W

Howdy SGT John:

have you adjusted your valves of late ? Really better to do this once engine has been running about 15 minutes to warm up - and you 99.990% likely have to do this with fuel pipes off --to get valve cover off at least ---- depending on how clean is your head - I prefer glow plug compression test - also , again - many will say to do a compression test after engine has been idling for 15- 30 minutes and then cooled a bit
There should be plenty writ here discussing every option
and do report your procedures and tallies - I for me like to hear everyones experience
cheers:

This is for you also nibiru,

I will have to pull the injectors. I can not get the compression tester attached to the fittings for clys 5 4 and 3. #5 the oil filter housing is in the way. #4 and #3 the injector pump is in the way. I don't have a garage and I am too cold to mess with it any more tonight. I pick up new bosch glow plugs tomorrow at 2ish, so I will throw them in and then pull the injectors to test compression from the top.

I have had a valve adjustment about 10k miles ago. Anything else anyone would suggest I do while I have the injectors out? I figured I would give them a little bit of a brush because I have used veggie in the car, but other than that I'm at a loss.

I have read here that WVO can cause your rings to stick.

Tom W