E320 W211 - 2005 - M112 Valve Train Questions...

[DrLou]

Just bought the above car - with the M112 engine. Starting with addressing misfires on a couple of cylinders - and cover gasket leaks...

Among other projects - and while I'm in there, Looking at doing a general update on the heads - Definitely needs valve cover gaskets, doing valve guide seals, and I don't think plugs have ever been changed on this 170k+ car... !

Am assuming(?) the bolts on the valve train are the torque-yield (on-time use) type? Do these bolts pass through completely? IE, are they actually head bolts? Anyone have specs on these bolts? Exact dimensions? want to order all I need before starting the project.

Should I replace the head bolts while I'm doing this? Alternatively, is there a high-mileage re-torquing spec on those bolts?

[paul roberts]

Originally Posted by DrLou

Just bought the above car - with the M112 engine. Starting with addressing misfires on a couple of cylinders - and cover gasket leaks...

Among other projects - and while I'm in there, Looking at doing a general update on the heads - Definitely needs valve cover gaskets, doing valve guide seals, and I don't think plugs have ever been changed on this 170k+ car... !

Am assuming(?) the bolts on the valve train are the torque-yield (on-time use) type? Do these bolts pass through completely? IE, are they actually head bolts? Anyone have specs on these bolts? Exact dimensions? want to order all I need before starting the project.

Should I replace the head bolts while I'm doing this? Alternatively, is there a high-mileage re-torquing spec on those bolts?

I'm just curious to know why you're doing valve stem seals. Unless you have plugs that are extremely oil fouled, I don't know if I'd go through the trouble of replacing valve stem seals. Especially on the M112. If you're concerned about a misfire, I would start with plugs and a wire set for a random misfire and one of the coils for a dead miss. We've worked on these for years at my shop. Never had to do anything more serious than valve cover gaskets on the top. Even with over 300,000 mile on the clock. The first generation v-6 is the best engine that Mercedes ever bulit. Just my 2 cents.

[engatwork]

I agree with what Paul says.

[DrLou]

OK; Well I welcome your inputs - and take it all under advisement... Am particularly encouraged for yet another reinforcement that these engines will survive to high-mileage old age. This is my goal!

More data: Car's oil changes have been good/frequent. Runs/ran! beautifully - before it started misfiring. PO told me it consumes a bit of oil, but was not very specific as to quantity... Obvious oil leaks around cover gaskets. In addition, bit of oil smoke on startup and acceleration from dead stop. At 172k, stem seals seemed like an easy - if perhaps partial - answer.

Few plugs I've pulled out to inspect. One was pretty fouled, and did correspond to occasional misfires on that cylinder. Others/all are 'gap-burned' to pretty open gaps. With two per cylinder, I'm guessing there is still 'pretty good' firing. Is plug replacement overkill in such context?

I did swap positions on two coils, with no clear resolution.

However, misfires are 'floating - and I see no evidence that camshaft position sensor has ever been replaced. This also seems like an obvious culprit. Starting with that.

Thanks for feedback, guys. Happy to hear more...

PS - I would argue that my Diesel 617 engine is the best they ever made, but a topic to discuss over a beer!