Probably a head gasket? - PeachParts Mercedes-Benz Forum

birkhoff · #1 03-28-2011, 03:29 PM

The car: 1982 300SD 455,000 km. CANADA

The BAD symptoms: Hard starting, won't idle 'till fully warm. Some 'nailing' when cold. Blue/grey smoke when cold. Lacking power compared to my previous 300SD. 10% down perhaps? PO's mechanic clearly not familiar with the 300 series diesel.

The GOOD symptoms: Very little oil consumption. No coolant consumption. Good fuel mileage. Blowby beginning, but not bad. Very clean engine (!) as PO liked to wash stuff. (Edit: valves adjusted to spec and known good, balanced injectors in the last 200 km. This in response to some questions below.)

Compression: (hot) 410, 420, 350, 360, 400

Diagnosis? Head gasket leak between #3 and #4

The plan: Pull the head, clean and replace HG.

The question: Before pulling the head, is it worth pumping up cylinder 3 and listening into cylinder 4 to confirm the leak? I'd hate to pull everything apart and find no evidence of a HG problem. Does anyone know of another reason to find low compression in these two cylinders?

The car is drivable by dropping the idle stop a bit, starting with WOT and giving a little time to warm up before driving off. Could just leave it this way, but the rest of the chassis/drivetrain/engine is in such decent shape it seems a shame.

whunter · #2 03-28-2011, 03:36 PM

Quote:

Originally Posted by birkhoff

The car: 1982 300SD 455,000 km. CANADA

The BAD symptoms: Hard starting, won't idle 'till fully warm. Some 'nailing' when cold. Blue/grey smoke when cold. Lacking power compared to my previous 300SD. 10% down perhaps? PO's mechanic clearly not familiar with the 300 series diesel.

The GOOD symptoms: Very little oil consumption. No coolant consumption. Good fuel mileage. Blowby beginning, but not bad. Very clean engine (!) as PO liked to wash stuff.

Compression: (hot) 410, 420, 350, 360, 400

Diagnosis? Head gasket leak between #3 and #4

The plan: Pull the head, clean and replace HG.

The question: Before pulling the head, is it worth pumping up cylinder 3 and listening into cylinder 4 to confirm the leak? I'd hate to pull everything apart and find no evidence of a HG problem. Does anyone know of another reason to find low compression in these two cylinders?

The car is drivable by dropping the idle stop a bit, starting with WOT and giving a little time to warm up before driving off. Could just leave it this way, but the rest of the chassis/drivetrain/engine is in such decent shape it seems a shame.

No, further diagnosis is not needed.

The head gasket is failing at #3 - #4 cylinder.

You should replace it soonest.

.

vstech · #3 03-28-2011, 03:37 PM

have you adjusted the valves in the motor?
hard starts are usually glow plug related, but they can also be valve adjust problems.

bustedbenz · #4 03-28-2011, 03:40 PM

Quote:

Originally Posted by vstech

have you adjusted the valves in the motor?
hard starts are usually glow plug related, but they can also be valve adjust problems.

That's what I was about to say. I'd for sure at least adjust them before I tore into a head. Costs relatively little to rule it out.

birkhoff · #5 03-28-2011, 07:11 PM

Quote:

Originally Posted by bustedbenz

That's what I was about to say. I'd for sure at least adjust them before I tore into a head. Costs relatively little to rule it out.

OOps, sorry. I should have put that in original post. Valves adjusted to spec in the last 200 km. They were quite far out. There was an improvement in power, but not in starting or idle when cold.

I should also add while I'm here that I have a set of balanced, overhauled injectors in there -- that's why I did the compression test this weekend, while I was swapping new injectors in.

Not that that has anything to do with compression, but I thought the smoke and nailing might have been a leaking injector and I had known good ones on hand.

Thanks for your ideas.

vstech · #6 03-28-2011, 07:32 PM

how many times did you adjust the valves?
if they were driven tight, debris, and wear will require them to be adjusted again within 100 miles.
so if they were not adjusted a second and third time, I'd pull the cover and do them again.

are you sure of the glow plug condition? have you tested each one to verify they glow well? they should not affect compression numbers, but bad ones sure will make it hard to start!

Diesel911 · #7 03-28-2011, 08:08 PM

I agree it is a good idea for you to adjust the Valves again; if only to rule it out as a source of your problems.

Next, you could adapt one of your compression tester adapters so you could hook up compress air to one of the bad cylinders and simply listen for the hissing sound in the other cylinder; assuming the Head gasket is no good.

birkhoff · #8 03-28-2011, 09:42 PM

Quote:

Originally Posted by Diesel911

I agree it is a good idea for you to adjust the Valves again; if only to rule it out as a source of your problems.

Next, you could adapt one of your compression tester adapters so you could hook up compress air to one of the bad cylinders and simply listen for the hissing sound in the other cylinder; assuming the Head gasket is no good.

Yes, well that was my question. Has anyone done this? Keep in mind that with only 50 psi difference from the good cylinders, the failure at the HG must be minimal. I'm not sure if I should expect to hear any airflow at all. I'm certainly not going to pump 350PSI in there!

vstech · #9 03-28-2011, 10:17 PM

never put more than 5 or so psi in there, it's flow you need to listen for.
the 617 is a pretty robust engine. head gasket failure is rare problem. it does happen.
be sure and readjust the valves.

Diesel911 · #10 03-28-2011, 10:33 PM

Quote:

Originally Posted by birkhoff

Yes, well that was my question. Has anyone done this? Keep in mind that with only 50 psi difference from the good cylinders, the failure at the HG must be minimal. I'm not sure if I should expect to hear any airflow at all. I'm certainly not going to pump 350PSI in there!

Most air compressors will give you 100-125 psi.
I know you can hear a pin hole leak in an Air Hose.

I have one of those Harbor Freight Compression Testers. The Injector adapters have 3/8" npt threads. They brass fittings that you can bump that up to 1/4" npt insid or outsid threads and you can use that to thread the Air compressor Hose Fitting into.

You can search our Forum or even the internet for how a Leak Back Test works and is done.
Of course that is with the Leak Back test set-up. In your case you only want to listen for a leak so I do not think you need the whole set up.

I do not know if reducing the Air Pressure as suggested is going to do the job or not. You could try it at any pressure you want if your Air Compressore has a feature that you can adjust the Pressure on it.

Diesel911 · #11 03-28-2011, 10:35 PM

At 455,000 km how is your Timing Chain doing?

birkhoff · #12 03-29-2011, 12:19 AM

Quote:

Originally Posted by Diesel911

At 455,000 km how is your Timing Chain doing?

Now there's someone on the ball! I don't know. Checked at the front cam tower it is spot-on. But I didn't pull the cam gear to see if there was an offset key on the camshaft nose. Timing could be far out, or it could be a new chain. It cannot be neither at 455 whatever the units.

To be honest, I was assuming compression would be even and low, and pump timing would be the next step (valve timing having been corrected earlier with a simple offset key, but pump timing is such a pain . . . and PO's mechanic had no idea.)

Does anyone know where I can still source a timing chain master link with the clips? All the vendors seem to have conspired to kill them. I would wind in a new chain the next time I'm in there, but having to have the expensive tool to put in the master link is not in my budget. My old technique was to use the clip link and then the next time I was in the shop, have them swap in the crimp master link. I have the new chain sitting in a box here.

birkhoff · #13 03-29-2011, 01:02 AM

Quote:

Originally Posted by Diesel911

Most air compressors will give you 100-125 psi.
I know you can hear a pin hole leak in an Air Hose.

I have one of those Harbor Freight Compression Testers. The Injector adapters have 3/8" npt threads. They brass fittings that you can bump that up to 1/4" npt insid or outsid threads and you can use that to thread the Air compressor Hose Fitting into.

You can search our Forum or even the internet for how a Leak Back Test works and is done.
Of course that is with the Leak Back test set-up. In your case you only want to listen for a leak so I do not think you need the whole set up.

I do not know if reducing the Air Pressure as suggested is going to do the job or not. You could try it at any pressure you want if your Air Compressore has a feature that you can adjust the Pressure on it.

I have a leak-down tester and I'm prepared to use it! My question is, if the HG is losing, say, 10% of peak compression, am I going to hear something at 100 PSI? I can certainly put #3 at TDC and run that pressure in there. If I get something interesting, then the remaining 4-6 hours of dirty work will be more appealing.

It's academic really. The head needs to come off unless for some strange reason the valves went out of adjustment big time almost right after I did them, which is a bit of a stretch. Starting symptoms and smoke did not change pre or post adjustment. Power at speed did. And if it's valve lift, why two adjacent cylinders? Coincidence?

Diesel911 · #14 03-29-2011, 02:47 AM

Quote:

Originally Posted by birkhoff

I have a leak-down tester and I'm prepared to use it! My question is, if the HG is losing, say, 10% of peak compression, am I going to hear something at 100 PSI? I can certainly put #3 at TDC and run that pressure in there. If I get something interesting, then the remaining 4-6 hours of dirty work will be more appealing.

It's academic really. The head needs to come off unless for some strange reason the valves went out of adjustment big time almost right after I did them, which is a bit of a stretch. Starting symptoms and smoke did not change pre or post adjustment. Power at speed did. And if it's valve lift, why two adjacent cylinders? Coincidence?

If you connect 100 psi to one cylinder and there is a leak into the other cylinder I would expect to hear it (of course the Injector needs to be out in both of the Cylinders) if there is a leak.
You will need to get your Ear as close to the Prechamber as possible or stick a Mechanics Stethoscope down inside of the Prechamber.

In any event I am curious to see what the real answer is.

whunter · #15 03-29-2011, 11:07 AM

Quote:

Originally Posted by birkhoff

Does anyone know where I can still source a timing chain master link with the clips? All the vendors seem to have conspired to kill them. I would wind in a new chain the next time I'm in there, but having to have the expensive tool to put in the master link is not in my budget. My old technique was to use the clip link and then the next time I was in the shop, have them swap in the crimp master link. I have the new chain sitting in a box here.

There is a TSB from Mercedes, it states that the clip style of master link is NEVER to be used on any of their diesel engines.

Warning, Danger: Please read this thread FIRST...
Need Automotive Grade Prozac
http://www.peachparts.com/shopforum/showthread.php?t=193675

There are several timing chain crimpers in the tool rental program.

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