PeachParts Mercedes-Benz Forum - View Single Post

Tomguy · #3 12-30-2004, 08:40 PM

It's probably your timing chain being stretched, and not a bad tensioner - when the chain is hotter and the oil is thinner with age, it might slap against the heads a bit on startup.

I'm going to do the heads and chain on mine (eventually) but that's where I'm going to stop. I don't want to put new rings in, especially because I dont want to have to lift the engine out and remove 50 or so allen-head bolts from the oil pan(s), first off; and secondly, I wouldn't put new rings into a worn bore and piston... they've worn together, and new rings might not "fit" quite the same.

It almost certianly doesn't need ANY bottom end work - rings or otherwise - unless it was overheated to the point where the cylinder walls are damaged. I haven't experienced it firsthand but rumor has it you can often see the cylinder crosshatching in the 3.5 and 4.5 engines at 150k miles.

If you see your cylinder walls have damage (some marks are almost certian, but not deep ones), then you might want a rebore, although I'd advise against it unless its pretty severe. You don't want to ruin the block's integrity and special cylinder wall hardening process, get new pistons and rings, and then rebalance the whole thing to original specs so you don't get horrid vibrations at 3000+ RPMs.

Basically, I'd stop at new stem seals, valve guides, and POSSIBLY a VERY slight valve seat lapping (and subsequent replacement of the 16 valves, which is quite costly). Clean the carbon out of the heads, use all new gaskets, torque it all down properly, and make sure to rematch the cams to the proper rocker arms (You may want to buy a few rocker arms if you see they have worn down through the hardened surface, before your cams suffer).

Of course, I'm going to assume you want to do all this for fun. I think I might have burnt valves, thus why I'm going to do it, but if you don't need to, and don't have $250 over budget just in case something goes wrong (IE Machine shop "drops" your head or finds out it "was cracked"), don't even attempt it!