charlesb2003

2005 E320 with M112 V6, but I'm sure this applies to multiple different engines with MLS head gaskets.

After doing 250,000 mostly trouble free miles, my M112 is ready for a top end refresh. I know I've got a blown head gasket, most likely a delayed reaction from a mild overheat that happened about a year ago. While I've got the heads off I'll be doing valve stem seals and hydraulic lifters, and of course cleaning everything I touch and replacing all gaskets. I'm also replacing my factory torque to yield head bolts with ARP head studs. Probably overkill for this engine but I don't ever want to have to redo this job anytime soon (hopefully ever) and I do plan on keeping this car for the long haul. Hoping to hit the magic million mile mark one day.

Anyway my question is in regards to the use of Loctite 5900 on the head gasket mating surfaces. I've done a lot of reading on this forum and on some service bulletins and it seems like the M112 and M113 engines came factory with sealant applied to both the heads and the block, but it's not recommended to use sealant when replacing head gaskets unless there are pits or damage to the mating surface. If there turns out to be, should I apply sealant only to the damaged areas, or to the whole mating surface?

I've also read where some people have had their heads machined, but others don't recommend it stating that the clamping force of the head bolts is sufficient to create a good seal even on a mildly "warped" head. Is this true? Would it be advisable to go ahead and machine the heads anyway? And what about the block? Wouldn't machining the heads and not the block mean that they are no longer matched in a way?

Lastly, if I don't end up machining any parts, what is the best way to clean the mating surfaces? I know not to use any abrasives, but I want to make sure I get every last little but of crud off.

Thanks in advance for the advice! I've done lots and lots of work on lots of different cars and changed many parts on this one, but this will be my first head gasket job and I want to make sure I do it right.

chassis

Good luck on the project. Keep us updated on the progress towards 1 million miles!

I'm not familiar with using sealant on the cylinder head-block interface. If it isn't specified by Mercedes, I wouldn't use it. Do you have the factory manual (WIS)? It's on ebay, but I don't know if it covers your model/year.

Loctite 7200 is specified by MB for old gasket removal. Abrasives are not permitted to clean the mating services. I would use Loctite 7200, microfiber cloths and elbow grease.

If you are good with a machinist's straightedge, you can check the cylinder head and block surfaces for flatness. Machining either independently is permissible. Flat within specifications is the goal, not a "match" of the surfaces.

charlesb2003

Thanks for the advice!

I don't have WIS, thinking I should get a copy. I've come across the relevant pages for the head gasket job in the past but I can't seem to find them again.