Hi everyone,I have a 95 C220,with a broken intake cam.[sucks bigtime]
Anyway,I had an indie replace the chain tensioner and 1 day later the cam broke right at the first bearing behind the sprocket.I will have another cam in a day or so but here's my question.Have any of you had this happen?Anything in particular that I have to watch for when re assembling?What is the best way to set the valve timing?I would appreciate any help or suggestions from anyone here.
Thanks

That's interesting I just had the same thing happen on a 92 190e that I just finished replacing the head gasket on and the cam broke in the same place after first startup and running for 30 seconds or so! I would like to know what causes this before I replace the cam and start again?

Sounds like the tensioner was not installed properly. It is a ratcheting tensioner. Once extended it won't back up, it has to disassembled and re-set. If you install it without taking the spring tension out of it first the chain will be WAY TOO TIGHT! Too tight of a chain sounds like a sure fire recipie for a broken cam. BTW, as a 12yr M/B tech, I've never seen the cam break as you describe, though I do install the tensioners properly so that may be why.

Thats what I thought,the tensioner was not installed properly.Dux have you got any tips on re aligning the cam sprockets with the crank?Or any other tips for reassembly?
Thanks again

If the cam broke with the engine running then it is most likely that you now have bent valves and will need a complete valve job. Pull the valve cover and see if you have any lifters that are obviously not in contact with the cam when not lifted by the cam lobes. Even 1 lifter that doesn't maintain contact means the head is coming off. I'd be concerned with damage to the timing covers as well. I'd be holding the shop who did the tensioner liable.

With the tensioner , what is the proper way to set? When you take the cap off and remove the spring inside, does the inner part not just screw in all the way to a stop on the threads. The spring doing the automatic tensioning to the chain? I have had another possible cause given to me of sludge build up blocking oil flow or oil pump losing prime causing lack of lubrication and cam breakage! either way I was told that I now have a boat anchor!! This is not been a good day!

Do you know if he removed the cam(s) at all in order to reinstall the chain? If so improper tightening of the cam bearings could also crack the cam...have seen that happen in a local shop just last week on a BMW...while being done by an ASE certified BMW mechanic.

Dux,I spoke to the shop that installed the tensioner and of course he claims it was installed correctly,so it is my word against his.As far as bent valves,I'm pretty sure I'm OK.I was told that this is a non interference engine.All of the lifters are sitting up at the same height with no cam installed,when I push down on the lifters,they all seem to spring back up ok so I hope I'm ok.Thanks
Oh by the way,does what I said earlier sound right to you for setting the valve timimg?

I have heard of numerous broken cams on MBs. They all occured after a tentioner was installed improperly. Do you know how to tell when a tentioner has been installed incorrectly?? .... It breaks the CAM.

BMWs do break cams from improper installation but I have never heard of a MB cam breaking that way. I have never heard of a MB cam breaking from natural causes.

These are the prices one pays for using inexperienced technicians. Anyone that works regularly on MBs knows what breaks CAMs.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Mercedes cams can be broken during install. I remember the mercedes literature stating that an even tightening of the 104 hollow camshafts was critical as the cams are "very breakable". I remember b/c the wording struck me as odd. I've never seen one break on install but I'm really careful to pull them down evenly.

When setting the cam timing you bring it up to TDC and then align the marks on the cams making sure the intake cam is fully counter clockwise in the advancer. Disassemble the tensioner completely. Install the outer housing first, then the plunger, followed by the spring, damper, and cap.

FWIW, I thought that engine was an interference engine, being based off of the 104 which is an interference engine. If while turning the cams to align them you encounter a firm resistance back them up and turn the crank about 30 degrees. Proceed turning the cam until the lifted valves seat and set the engine back to TDC and continue from there

Thanks for all of the replies.Dux,when you say camshaft timing marks do you mean the holes in the flanges that you line up with the holes in the bearing caps?I don't see any other aligninig marks on them.
Thanks

Yep!

I'll give that a try and hopefully I don't encounter any more problems.