After having my head gasket replaced and the head redone on my 1995 S320, the engine stopped running abruptly 30 minutes after starting it.

My mechanic turned the cylinders manually a full 360 degrees before cranking it to check for valve clearance; everything checked good. The engine subsequently started, and sounded smooth and steady when idling. He was letting the engine idle to check for leaks, (oil and exhaust) when 30 minutes after starting, the engine died.

He opened the oil cap to look around and found everything appearing to look normal. He decided to take the cam cover off to investigate further. Low and behold, he found the cam shaft, on the intake manifold side, snapped at the sprocket/gear connecting to the timing chain! The whole gear was snapped off the cam shaft, sitting tilted with the timing chain still in the teeth of the gear.

Has anyone ever experienced or heard of this happening? If not, any ideas how this could happen?

My mechanic was able to allocate another Cam shaft and will be installing this weekend. I'm hoping the valves aren't damaged...

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1995 S320
1987 560SEC
1992 300E

timing chain tensioner set to a billion pounds pressure?

thats about the only thing i can think of - thus mechanics fault if you ask me....

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C140 420 CL
W114 280CE pimpmobile
W114 250/8 Hillclimber with M110 and bike carbs - got any hot cams?

I suspected that as well. Does anyone have a manuel handy and know what the proper torque/tension is for the tensioner?

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1995 S320
1987 560SEC
1992 300E

I don't know how M104 cams are held in place but for other engines you're supposed to tighten the cam towers a little at the time. In some cases, there's even a tightening sequence. The risk of not following the procedure is breaking the cam.

Sixto
95 S420
87 300SDL

The tensioner should be withdrawn and carried out a tension reset procedure (dissemble it and install the components in the correct order)

I agree that probably nothing was done with the tensioner. After the chain goes slack, the tensioner moves and will not return to its original position. This will put too much force on sprockets. The tensioner is a combination one-way ratchet and a hydraulic plunger that runs off oil pressure.

I'm not sure if you realize the torque you are asking for has little effect on the tensioner force applied to the chain. It is only a mounting load.

To properly reset tensioner load, the following sequence must be followed:

1. Remove tensioner assembly
2. Install chain
3. Disassemble tensioner
4. Install tensioner outer body
5. Install inner works of tensioner

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95 E320 Cabriolet, 159K

Definitely chain tensioner. Chain tensioner has a one way ratchet that allows it to take up slack and not release tension.

You need to remove the tensioner before you can remove chain/cam gears.

I would say your mechanic has removed and refitted the tensioner as an assembly and hasn't reset the plunger.

Once you have timed the eng you would then fit the tensioner body and torque to 80 Nm, then the plunger, spring and screwplug torqued to 40 Nm.

The engine isn't a free spinner, so unfortunately the head will need to be removed again as the valves will definitely be damaged .

I believe this is 100% mechanics fault and he should pay for all repairs.

Good luck

Hi Iwould think you would hear the valve train screeming if the tension was to tight,sounds more like he for got to fasten the bolts or the adjusting piston and pin on the flange shaft for the advance control was not lined up.joeym

It shouldn't be too difficult to diagnose. If the fasteners weren't tightened at the cam sprocket assembly, they'd show a lot of damage. If the problem was the tensioner, the fasteners should be tight.

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95 E320 Cabriolet, 159K

Ive heard of this before. I believe he probably has the " adjuster " on the left front head not in its proper position before he puts the chain on...if he doesnt figure this out itwill not be proper and will either brake the chain or the cam again. The chains are pretty strong too. It was probably whining when he started it. I can talk to him or you about it if need be. Peace.

Is this what you were told by your mechanic??? Or were you at the shop when this happened???

As long as he is paying to have it repaired and he repairs it "CORRECTLY" I wouldn't stress too much.

I would like to know what your mechanics reason is for the camshaft breaking ???

Either he has left cam bolts loose or he has installed tensioner incorrectly.

As Kestas stated "It shouldn't be too difficult to diagnose" and he should be able to come up with an answer.

Keep us posted

Was this head warped and milled to straighten? Not a good idea for OVC engines as is upest camshaft bearing alignment.

Also I am not sure of the set up procedures for this engine but I belive it has variable valve timing. This may mean that your manual check by rotating the engine was fine staticly but when running at different RPMs the timing will change and possibly cause an interfearance.

Unfortunatly I am sorry to say, you did most likely bend a few valves.

John Roncallo

welcom to the club it happing to me last week on my 1991 300 sl and im looking for cam shaft let me know from where you get it