OM602 Head Gasket Replacement Questions - PeachParts Mercedes-Benz Forum

casioqv · #1 01-22-2011, 03:40 AM

My 190D Turbo (1987) has a blown head gasket, and I'm trying to begin the daunting task of replacing it myself and have a few questions. I have the factory manual CD, and have searched the forum but am still confused.

Questions:
1) Is it really necessary to remove the pre-chambers before removing the head, or can they simply be left in?
2) Is it really necessary to remove the radiator?
3) Which special tools are required to do this job properly?
4) What else should I replace when I'm in there?
5) What is the best way to clean the head and block surfaces to ensure a good seal?
6) Should I have a machine shop inspect the head for warpage and/or cracks while it's off?

The car has 225k miles and runs perfect other than overheating and failing the bubble test. I'm not inclined to rebuild the head, but just replace the gasket since it runs so well, doesn't burn oil, etc. It was never overheated badly or ran without coolant.

GregMN · #2 01-22-2011, 10:24 AM

1 - no, leave them in along with the injectors, glow plugs, return fuel lines
2 - no, protect with a piece of cardboard, remove fan and shroud for access
3 - long reach socket for head bolts so you do not have to remove the cam towers
4 - nothing
5 - scrape carefully, do not gouge the aluminum head, finish cleaning with 400 grit wet/dry sandpaper and wd-40 as a lube, wipe often with a rag
6 - no - if everything was perfect and you confirm that it is the gasket that is bad

Measure your head bolts and check that they are within factory specs for reuse. They do not need to be replaced unless they are out of spec.

Jeremy5848 · #3 01-22-2011, 11:27 AM

Take pictures as you disassemble as guidance for re-assembly.

Put the engine at OT and use tie-wraps to secure the cam chain to the sprocket before loosening the tensioner and removing the sprocket from the cam. Chain and sprocket can then drop down into the timing cover and be out of the way while not disturbing the timing.

Sixto suggests using a hammer handle in one of the intake ports to break the seal of the head and gasket to the block. The head can then be lifted off. You should be able to disconnect the exhaust pipe and leave the turbo on the head. Remember to remove the turbo oil lines.

Have something soft ready to put the head on -- prechambers and some valves will be protruding.

casioqv · #4 01-22-2011, 12:47 PM

Thanks... the factory service manual says to remove the radiator (quite a long job on a W201) and the prechambers (which require special tools). I'm glad those steps aren't truly necessary.

I have 2 more questions:
1) In GSXRs OM602 pictoral he uses a crank locking tool. What is the purpose of this? Do I need it?

2) Once the timing sprocket is zip tied to the chain is it okay to let the chain go slack? IE, if the chain is slack can it slip off the crank or injector pump sprockets down inside the engine?

04 Diesel · #5 01-22-2011, 01:19 PM

Dont forget you also have 2 pins to pull out in the front of the head. That can be a pain.

GregMN · #6 01-22-2011, 01:54 PM

1 - no - not needed - set to TDC and don't move it, same goes for the cam
2 - yes - okay to let the chain go slack

Use one of the valve cover bolts to draw the chain guide pins out of the head using a stack of washers and socket. Make sure the pin can pass through what ever you use as a spacer.

Jeremy5848 · #7 01-22-2011, 02:31 PM

There's a special puller tool (about $30) for the pins but Greg's technique works well and is a lot less expensive. The flywheel lock tool is nice but not necessary. Just don't move the engine off of OT. Disconnect the battery so the starter motor doesn't get accidentally bumped. The timing chain cannot disengage as it's held in place by the other guides and sprockets. Chain and sprocket can drop down into the timing cover and no harm done.

BTW, the head bolts take a special "triple square" 12-point bit. Good ones are expensive and cheap ones are . . . cheap. Additionally, you'll need the extra-long version (to pass through the cam towers) if you won't be removing the camshaft. I bought a set of 4 ("OEM" brand, PepBoys, $13) for my planned 603 head project but I'm removing the cam (to swap to the new head) so I don't need the long bits. Someone here should be able to steer you to the correct length.

Jeremy

GregMN · #8 01-22-2011, 04:12 PM

Head bolt socket is a "Hazet 2751". 10mm, 12point, 140mm long, 1/2" drive.

http://chadstoolbox.com/hazet2751screwdriversocket.aspx

casioqv · #9 01-22-2011, 05:05 PM

Quote:

Originally Posted by GregMN

Head bolt socket is a "Hazet 2751". 10mm, 12point, 140mm long, 1/2" drive.

Thank you! You guys are all so helpful. I'm also into Volvo (VW) diesels and was hoping the hex bolt was 12mm so I could re-use my Volvo tool, but apparently not.

babymog · #10 01-22-2011, 08:40 PM

I don't suggest the cheap bit for the head bolts. I removed a head using one from autozoo, the tool is badly worn and I'm not sure it would torque the bolts without failure. I have a better quality bit that I've used for several heads, which is holding up much better.

Also, if you have the original head, they are prone to cracking. Some cracks in the combustion chamber, look it over and vac/pressure test it http://www.peachparts.com/shopforum/showthread.php?t=289965

casioqv · #11 01-22-2011, 09:02 PM

The Hazet head bolt tool looks like it's on a 6 week backorder, so I ordered this Assenmacher (ASTS3054X10) which appears to be basically the same thing. I'm not *sure* if it's as good of quality, but it usually sells for about the same price as the Hazet tool.

I was planning to do the timing chain at the same time- but amazingly my motor has less than 1 degree timing chain stretch after 225k miles!

//edit: This is just for my own reference or anyone searching for reference data, but I didn't want to bump it. The head bolt tap and die are M10 x 1.5 for cleaning threads. My motor also has the original OM602 Turbo head casting (602 016 06 01), not the later improved one although these don't seem very prone to cracking the the original OM603 heads.