1987 300SDL, Cylinder head problems - PeachParts Mercedes-Benz Forum

drivfour · #1 01-04-2003, 04:41 PM

I am new owner to sick 87 300SDL- bought it with antifreeze leaking into #5. Removed and replaced head gasket- no improvement. I have worked on many and various cars but do not know what to look for regarding this problem. I was excited to see the wealth of info I have found in just 1/2 hour. I struggled with the timing chain master link item for example-wish I had found this site earlier. My question is really what does the group suggest- rebuilt head, replace liners and pistons while engine partly dissembled? Who best to get head from and expected cost? car has 220,000. my objective was to repair and bring vehicle to a good condition and sell it- I will not stick someone else with the problem(s). My hobby is repairing things/cars. Any help is greatly appreciated
JD

#2 01-04-2003, 04:54 PM

Most likely the head is warped or cracked. There are shops that can repair cracked or warped heads.

I believe that this is the engine that is known for bending rods, so if there is enough force for that to happen, I would think that cylinder walls could also fracture under such conditions. You need to thoroughly examine cylinders for cracks while the head is off. This would be a very odd thing to happen, but you should check thoroughly while everything is apart.

Good luck,

rickg · #3 01-04-2003, 06:55 PM

I'm not absolutely positive, but am rather certain that the rod-bending thing didn't start until they made the engine a 3.5 liter in the early 90's, whenever it was.
But I agree with Larry about the warped and/or cracked head possibilty. I'm not the expert on these 6 cyl engines, but hear alot that they did have a problem with this. One reason i went for the 5cyl. (But that's a whole different thread again).
Good luck, and welcome aboard!

engatwork · #4 01-04-2003, 07:07 PM

The '87 300SDL is not the one with the "rod bending" rep - that came later with the 350 series.

#5 01-05-2003, 02:00 AM

220k is nothing. The car was probably run hot at some point in it's life, it's a common problem with these cars if you don't watch the temperature gauge. Your going to need to put on a new head, I don't think there is any way of getting around that. I hope you got it cheap because parts are expensive.

rwthomas1 · #6 01-05-2003, 07:10 PM

Everyone here always says replace the head..... Pull the head and find a good head shop that works on drag race stuff. I've seen amazing repairs to heavily damaged racing heads. Likely they will be able to fix a small crack and warping. RT

Motorhead · #7 01-05-2003, 08:36 PM

There are outfits that can "Pressure Test" the cyl head. They clamp it up on a jig and block off areas and pressurize the head and dunk it to ck for leaks. Also carefully ck #5 cyl liner for a crack.

md21722 · #8 01-06-2003, 09:23 AM

The heads on the 603.96x are known to crack. The head was redesigned 4 times and the head gasket at least that many. New oil runners were fitted to the later model heads. The bottom ends on these cars are indestructable as long as they don't run out of oil. The 350SD/350SDL in the early 90's were the rod-benders.

I'd say from all the reports I've seen that it needs a head, every one that's pulled the head has found cracked. Rebuilt heads are not available from normal suppliers for these engines as they have known head problems. But, rebuilt heads are available for many other engines.

sixto · #9 01-06-2003, 04:18 PM

Quote:

Originally posted by md21722
Rebuilt heads are not available from normal suppliers for these engines as they have known head problems.

Exactly. Anyone who knows these heads knows that you're better off with the latest design. Plus anyone who knows these heads knows that your old head, if it has cracks, isn't worth anything as a core.

If you get a new head, just about everything from the old head can be transferred. My SDL head had cracks all over the place and all I couldn't reuse was a couple of intake valves. Look for the posts by Dave M./gsxr that describe how to modify the prechambers to work with the later head. It'll save you a bundle over getting new prechambers and possibly new injectors.

If your engine is together now, do a compression test and leakdown test so you know where you stand.

Figure around $2000 in parts and $500 in machine shop charges to transfer the valves and prechambers.

Sixto
91 300SE
87 300SDL
83 300SD

sixto · #10 01-06-2003, 04:21 PM

You know, I'm curious about the coolant leak into #5. The typical symptom of head cracks is pressure leak into the cooling system. Are you sure the motor didn't hydrolock somewhere along the way?

Sixto
91 300SE
87 300SDL
83 300SD

drivfour · #11 01-22-2003, 01:11 AM

Head shop reports "gusher" around #5 exhaust valve. Said they would weld and pressure test for $300. I agreed-

sixto · #12 01-22-2003, 11:29 AM

JD,

What's the part number on the head? It'll be on the intake side in the area of the #2 and #3 cylinders. The number will begin with 603.

How is a cylinder head pressure tested? Maybe I should ask what is pressure tested? The combustion chamber?

Thanks,
Sixto
91 300SE
87 300SDL
83 300SD

gsxr · #13 01-23-2003, 08:36 PM

Sixto is right, $2500-$3000 for a new head plus parts & machine work (bare head is $1500 at cheapest current source). New prechambers will NOT necessarily work with a new head, you may need to modify new ones as well, might as well modify your old ones and save some $$$!

The pressure test is outlined in the Mercedes factory OM602/603 engine manual. I do hope JD has this manual and is using it (perhaps the CD version), because attempting this job without it is just BEGGING for trouble. Let us know how the weld/repair works out.

Photos of my head replacement are here:
http://www.meimann.com/images/mercedes/head_gasket/

Regards,

dieselsteve · #14 02-04-2003, 05:18 PM

Dave M,

What other symptoms did you have on your car?
I know you multiple cracks in your head, but what other symptoms where there?

I am oil seeing oil leakge issues, Maybe only a head gasket?

thanks
Steve

1992 300SD oIl leaks

gsxr · #15 02-04-2003, 05:47 PM

The main symptom is very high pressure in the cooling system even when stone cold. In the morning before you start the car, squeeze the upper radiator hose. It should be soft. If it's so tight you can't squeeze it, that's bad. Remove the radiator cap and try again, it should be soft now. That means combustion pressure is entering the cooling system.

I had no oil in coolant and no coolant in the oil. I also had zero coolant loss.

The odd oil leak shown on my website, coming from the #6 exhaust port, was AFTER the new head went on. It is due to some problem with the valve guides or seals. Either the head was bad from the factory, or the machine shop screwed up. I haven't pulled it apart (again) to see what happened.

HTH,