Hello,
I posted here a few days ago about my '75 240d with a broken valve guide. Well I've dug deeper into the problem and think that I may be getting close to the bottom. I sure hope so because I want to be driving this car again soon. The car was burning a lot of oil so I went to replace the the stem seals as a first step and found the broken guide. I've suspected all along that something was underlying the broken guide. Well I took the head off and apart and brought the valves and head to a machinist. He put the new guide in and ground the valves and found out that two of the exhaust valves were bent. The bends are not visible to the naked eye but fairly obvious when you spin it on the grinder. I can't see any damage to the top of the pistons. Also the idler sprocket is badly mangled. I suspect the chain was riding on one side of the idler. The cam sprocket is visibly worn, but not mangled. The intermediate sprocket and the crankshaft sprocket(from what I can see peering down the hole) are worn, but not nearly as badly as the camshaft sprocket. Here's the interesting part. I measures the chain with dial calipers over a length of eight links. It was dead on within .001" to a pitch of .375". The rollers are .250". I thought it was very interesting to have a chain with imperial measurements on a mercedes. Also the chain seems to have no stretch, and looks to be in good shape. So all I can guess is that the chain broke on this car before I bought it a month ago, bending a couple of valves and breaking a guide. Someone simply rolled another chain on and probably didn't get it on the idler sprocket right. The car, amazingly ran very well, it just used a lot of oil. Incidentally the cylinder walls look very good. I will replace the idler and the camshaft sprocket. I would probably like to replace the intermediate and crankshaft sprockets too, but I'm not sure if I will since they look a bit better. What is involved in replacing the crankshaft sprocket? Do you all think I'm interpreting what is going on decently, or am I missing something. Thanks for all the help I've received in the past, this is a great forum. Sorry for the long post.

Colin Kenny

Bent valve stems seem like rarity to me, but would expect snapped timing chain to do more damage. It would be interesting to pull the sump and check for metal bits which might support your theory. Or maybe the new chain was incorrectly installed at first - and then corrected after bending a couple of valves. BTW, those are sodium filled, self-rotating valves which are said not to be grindable and must be replaced.

". I thought it was very interesting to have a chain with imperial measurements on a mercedes."

What do you mean by that ?

I just put a 300SD turbo five engine back together and during the rebuild found the keyway for the crank sprocket wallored out. This engine had always had rough idle on start up. Replacing the crank resolved this issue. I would try to get as close to that crank sprocket and perform a thorough visual inspection.

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Jim

ckenny,

I replaced a crankshaft timing chain sprocket on a 190D engine and it wasn't too difficult. You have to have the chain loose enough so it falls below the sprocket. After removing the harmonic balancer, the sprocket slid off the crankshaft.

I suspect your 240D engine should be the same.

P E H

Hello all,
I did pull the sump and found no "bits" only some really fine metal particulate. I put the new idler and cam sprockets, and new valves on yesterday and put everything back together. Things lined up pretty well the timing is 2 degrees slow acording to the marks. What I meant about the chain dimensions suprising me is that I expected them to be some nominal metric measurment instead of 1/4" rollers and 3/8" pitch. Just my ignorance P E H thanks for the info. I was wondering if it could be done that way or if I would have to drop the oil pan. I didn't know if the valves could be ground but the machinist that did the work said it was no problem. He seemed to really know what he was about unlike the other machinist that I talked to. The valves look like new (two of them are).

Thanks,
Colin Kenny