433k mile headgasket job?
 

So finally after 433k miles I am seeing slight symptom of failing headgasket. I have a small oil leak at the front passenger side of the engine, just right under the timing cover. I checked the U shaped timing cover and even replaced it a few weeks ago, but there was still oil leaking and the new seal was bone dry. tracked the leak to the front of the block/head. I have read the how to article for the w124 on this forum and just went out and purchased the 12 mm xzn bit. I have a new water pump coming and I have valve cover seal, even though I just replaced that about a month ago, and I have all new hoses and seals for the entire cooling system. Anything else I need other than the cyclinder head gasket/bolts or anything else I should replace? Valve stem seals were replaced 3/2015 @ 360k miles.....maybe I should do those too? Also, I have somewhat of a unique situation. I actually have another m103 engine sitting in my garage. So what I was thinking of doing was disassembling that one before diving into the one on my car. Then I can send that head out to be machined and when I get it back I can just take off mine, clean up the block, and put the other one on. I welcome any tips and advice anyone can offer. Thanks.

Might as well hone cylinders,and rering pistons,and change bearings,go another 400k

Suggest a leak down test before disassembly to identify any problems such as rings. Valve seals, definitely replace if disassembling the head. Use new bolts or measure the old as per factory specs. Replace the timing chain.

Read up on how the chain tensioner gets disassembled and reset unless you already understand how it works.

Use an inch pound torque wench on the rocker arm to head bolts, the threads in the head pull out easily.

Good luck!!!

I found that an engine hoist to lift the head out makes the job a whole lot easier for one person. At a minumum, remove the valves and check the valve seats for damage. You should replace the valve stem seals and guides, as you don't want to be back in there soon. Not a bad idea to send the head out for light surfacing. If they have to take off a lot of material, there should be thick headgaskets available.

You have to replace the head bolts, they're designed to stretch once and shouldn't be reused. Also, a tip for aligning the head on the way back in: take one or two of your old head bolts and grind the head off. Turn them in finger tight before you drop the head in, it makes it much easier to get everything in line without damaging the new gasket.

Should the head gasket be coated with anything or just applied as is? Also, regarding tdc of engine....does that mean piston#1 and #6 are at the top? I am turning the crank and watching for the small drill-like hole to line up with the notch on the head.

This is just my experience and I think it's the easiest way to reinstall the head and I know other people say differently. I didn't use a host and did it by myself with no help. I took everything off the head before I installed it, including the exhaust manifold and especially the studs to fasten the intake manifold to the head. Set yourself in the engine bay, it's heavy but with everything stripped very manageable and align the front of the head with the front of the engine block where the chain is. If you do have a hoist it's the best way to go off-course and you can disregard my post.

Just applied as is and yes on the TDC. This is a great tutorial on how to reinstall the timing cover. If you take your time, it's an easier job than you think it is. But you have to pay attention to the details to do it right.

PeachPartsWiki: How to reseal the front top timing cover

Ismalley, TDC of Piston #1 which is closest to the radiator. Of course, you know to turn the crankshaft CW only (when viewed from the front) with a 27mm socket. Be sure to follow re-assembly instructions exactly. Turn the crankshaft a few turns by hand (after you think everything is aligned properly to ensure there are no interferences) before attempting to start the engine the first time.

I'd find a low mile 3.0L and reseal it, I mean if you want more power that is. You've got a few years of options to deal with Cali emissions if I am understanding them correctly.

And don't be like me and turn the engine by hand without the chain tensioner installed, it will make the timing go out of whack.

My M104.980 has just been redone at 420k Kms (not miles). As you say, they fitted new bearings and rings and overhauled the head etc.

They said no need to touch the bores as they looked perfect, retaining the original machining marks. I was happy with that.

RayH

I did the HG on my M102 about 1.5 years ago. Wasn't too hard, but yes the head is heavy. It's difficult to get in the correct position for heavy lifting. I remeber I climbed on the strut towers or something. If you do this, remember that you'll have to get down with the head in your hands... Definetly do the stem seals again since they are so cheap and you'll have to remove them when cleaning/machining the head.

Hey guys, need to back track for a minute. I stated in the original post that the head was leaking oil from the front passenger corner....like right at the corner where the front timing cover meets the head. Anyways after searching online here and speaking to a few friends, everyone seems to think it is actually the timing cover and I need to double check that. I looked at a post on the forum from S Class Guru and he recently did a m103 in November I believe, and stated that the rear passenger side of the m103 is the area where an external oil leak head gasket failure is likely to occur and that there weren't even any oil jackets near the front cylinder one to cause an external oil leak from HG failure. I pulled my plugs today and all are bone dry with no signs of oil, so I'm assuming even the valve stem seals are still good. I just replaced that timing cover gasket last month, but I have several of those and valve cover gaskets as well because those parts are likely to develop leaks and they are so inexpensive. I guess what I need to know is that, is it likely that there is an external oil leak from the HG in the location I mentioned or is it most likely the timing cover gasket? Also, can anyone confirm that there is no oil passages/jackets near the front passenger piston #1. Thanks guys.

It could be either the head gasket or the front cover again. I have read that the head gasket leading edge in the area in question can recede/deteriorate creating the leak described.

Oil pressure passage location is on the right rear of the head/block, not in the front.

It may be worth doing the front cover again and putting a very small amount of sealer on the leading edge of the head gasket, assemble everything and let the sealant dry for a couple of days if you can.

Good luck!!!

Ok, so I redid the timing cover and valve cover gasket yesterday. I cleaned everything up and now going to see if it continues to leak and pinpoint it. I couldn't see where it would leak from at the headgasket, but the timing cover corner looked pretty sketchy. I hate that corner, what a poor design. And then to have the engine tilted towards that corner so oil can just run out....$#@!