Quite a few options with the $ going to be dropped. Assuming the engine was well cared for the last 100k, a top end redo with head gaskets and valve guides and seals may restore the compression. This would entail a mild valve regrind which would increase costs with labor. And when the heads are off, a good mechanic would use a bore gage to determine if the cylinders are worn; especially on the weak cylinders.
If I remember correctly, the cylinders have a unique silica base, hence gives them ultra durability. Someone correct me, as I am not sure if MB blocks can be bored to oversize or not? Most of the time, these engine bores are within spec and simply honed. Then pistons are reringed. With a checked crank and new bearings and such. And that is just the bottom end. If you could do this work yourself, you can save $!!. best option may be to find another well cared for motor with <120-150Kmi. OR, if you plan on keeping forever, a rebuilt motor with a warranty may be an option.
Bottom line is cost. Either way: top end, rebuilt motor, or engine replacement is
a major decision. If you spent for a quality top end: t chain/rails, valve job and gaskets with labor, you're going to into thousands$ and still have a gas motor with 212k. A lot to think about. Sorry for the long reply, hope this helps:thumbsup:

 

Janos,

Personally, I'd consider replacing the valve stem seals first. It's not that hard and may postpone the rebuild for quite a while. Even if you have to pay a mechanic to do it, you'd save potentially thousands.

Beyond that, I've heard good things about Metric Motors in LA for replacement engines. Don't know of anyone here in the Bay Area yet who I would trust with the job of rebuilding.

Mike

 

I just got my heads back from the machine shop; my car has petty similar mileage, and the valve guides were shot (one even came loose in the head). You might get some improvement out of just doing the seals, but at this point it would make more sense to me to bite the bullet. You don't need to pull the motor, the heads can come out with the engine in, but if it did have to come out I would replace every seal and gasket. Timing chain is recommended unless it (and more importantly the upper guides) have been done recently.

By the way, once the heads are out the rebuild isn't too bad as long as the valves and seats aren't completely worn out. I spent just over $500 on parts and machining the heads, and really the biggest concern was some erosion from previous owners not using the right coolant and/or not keeping up on the maintenance. Still got a ways to go (doing most of it myself), but can't wait to fire it up and see how she runs!

 

Thanks for the advice, all. After talking to my mechanic for a bit, I decided to keep the original engine but go for the whole top end rebuild. I wish I could tackle a job this big myself, and I think it would be a fun experience if I had the space, time, tools, and expertise. Sadly, I have none of those.

I'm curious to see how the car will drive after the rebuild. It had pretty good power still, but the idle was a bit lumpy. So I'm guessing there won't be a big change.

BTW, the timing chain/guides/tensioner were done about 70k miles ago, so I'm leaning towards having that done while the engine's apart -- or, at least, new guides put in for sure. Car will also need a new EHA and water pump.

Will keep you posted, and maybe upload a few pics, too.

 

Here are some photos I took today with my phone.

 

Looks great, Janos. Please keep us updated.

Who did you finally decide to let do the work?

Mike

 

Thanks, Mike. Fingers crossed...

I'm doing the work through my usual mechanic shop, Pete's Inc. They strongly recommended Star Machine Shop for the head work. They used to work with Metric, but decided to part ways a few years back.

Since a lot of the work will be done by Pete's itself (assembly/disassembly/peripherals, etc), I thought it would be best to let them choose whom to outsource the machine work to, especially in case something goes wrong and I need to lean on them for warranty repairs.

 

This is just my $0.02, but even in a W126, with more room in the engine, I think that a more thorough/better job can be done with the engine out of the car, even if you are just going to do "the top end". Whatever time is lost doing this will be gained in convenience. I am rebuilding an engine for my 380SL, and the amount of crap on and in it was absolutely astounding after 30+ years. And, there is a real risk in pulling the threads out of the block when reinstalling the heads. With my luck, I guarantee that this would happen on the 32nd bolt, so I time-serted the block first as insurance. Doing this with the engine in the car would take a mechanic of the very highest levels of skill and patience. Also, you don't have to bend over the hood for hours with the engine out, which is even WORSE on a W126. If you have ever had back issues, you know what I mean. Torquing all those bolts properly, stooped over in weird positions with extensions on the wrench? Maybe...but you are having them do it, so it's their problem.

 

This is just my $0.02

Gorgeous work. :thumbsup:

Excuse my ignorance but, how do you polish all that and why are the throttle linkage pieces and other bits gold?


.

 

Wow, that engine looks beautiful!

Yeah, ideally, I'd have the engine removed and every bit of rubber or plastic replaced, as well as all hoses, belts, etc. But since I can't do it myself, and since even this way I'll be spending a huge amount of money, I had to make some compromises and hope that my mechanic knows what he's doing. But in an ideal world, yes, you're right: I'd pull the whole engine, too.

 

Well, at the very least, I hope they change a goodly amount of the rubber and all the vacuum fittings. I am of the opinion that these things represent a lot of little vacuum leaks that collectively represent one BIG vacuum leak. I had problems with my car, and I changed the injector holders, the distribution hoses, and the fittings around the idle controller. Vacuum immediately improved and I am getting the rated MPG of the car as when it was new, 185K miles ago.

 

Janos,

It sounds like you have a solid relationship with Pete's. I'm sure you'll be happy with the results. Would love to see it after.

Mike

 

After the head work with new valve guides which are the main culprit to wear on these motors, have every piece of rubber replaced with OE parts. The Plenum boot, doughnuts, vaccume fittings and lines will ensure the car will run properly! Don't use Uro brand/ cheap lines or you will be spending $$$ to hunt down the causes of poor idle and performance.

Do it right the first time and don't worry about it for another 10-20 years.

 

Yes, I was thinking about the plenum boot also. An ugly surprise awaits people with older M116 and M117 engines; the original boot had a molded-in aluminum frame; that's no longer available, now there is a rubber part with a separate aluminum frame; the frame is amazingly expensive. This is why I took the time to acquire a few from the boneyard for virtually nothing.

The iron-block M117 had an aluminum cast/machined "boot", which of course will last forever; I have one of these also, but its flange won't fit the short rubber adapter between it and the (well, at least the 380's) throttle body.

I recently installed the doughnuts, and I used a lot of rubber grease (Syl-Glyde) on them before installation. Someone on the 107 board didn't, and cracked several of their retaining rings. I believe that a lack of heating parts in hot water and use of rubber lubricant causes many new rubber parts, genuine or not, to fail during installation. It's a good thing the guy on the W107 board discovered what happened before he assembled everything!

 

Just closing the loop on this thread...

Picked up my car from Pete's a couple days ago; all is well so far. There's nothing dramatically different about the way the engine behaves, but then again, the car was running fine except for the occasional cloud of white smoke spewing out of the tailpipe.

Maybe it's a little smoother on acceleration, but it could just be my imagination and latent wish to have something tangible to show for the $$$ I just forked out...

There's a bit of a lumpy idle (which was there before, too), being chalked up to the injectors, which are apparently original to the car but were not replaced at this time.

Anyway, a couple more pics attached -- not that they show much of anything.

 

Janos,

Congrats on the car being done.

It's amazing how fast this went compared to those of us who have to do it ourselves.

Glad it's done and you can get back to enjoying it.

Mike

 

Thanks, Mike. I'm glad to have it back.

BTW, I have the utmost respect for the real do-it-yourselfers. I can change out the odd relay and stuff, but taking the engine apart is a whole other ballgame...

 

.

How much did it set you back?


.

 

It was very expensive. Let's leave it at that

Now that I've been driving it more, I'm noticing some subtle improvements. No more fumes coming into the cabin from the leaky exhaust manifold and EHA and a bit more midrange power, mostly.