Broken camshaft: 617 '81 SD. How could this happen? - PeachParts Mercedes-Benz Forum

ROLLGUY · #1 02-11-2012, 12:04 AM

My neighbor called me today and told me his car made a weird sound and just quit. He coasted to the side of the road, and called me (he bought the car from me years ago). He tried to start it, but told me it sounded like it was not getting compression. I suspected that I would find the cam not turning, or something like that. As soon as I got there, I pulled the oil cap, and sure enough, a piece of the cam was sideways under the cover, and a follower was out of place. What would cause this? I had just changed the oil for him a few weeks ago, so I know it was not out of oil, or that the oil was old. The car has been running great for him ever since he bought it, and he has had no complaints. I have not pulled the cover yet, but I may find a broken timing chain, or gear. Would something like this ruin the bottom end, or just the top (bent valves etc)? He has been bugging me for weeks about buying my car ('98 E300) since I let him borrow it while I worked on the brakes on his car. Today after he had his car towed home, he called me and made me a deal I could not refuse. We made a deal, and part of it is I am getting his 300SD. If it is repairable, I will get it back on the road. If not, it will make a great parts car (I already may have a use for the trans). What do you think? Should I just bite the bullet and pull the head? Or do you think the pistons will be toast, and the engine not worth fixing?

barry123400 · #2 02-11-2012, 12:36 AM

Timing chain possibly let go. With a little luck you may get away with a complete used head. Probably cheaper than trying to fix the damage.

You will not know until the head is removed about the extent of piston damage. What it does sound like is the cam towers may have broken away reducing any major damage to the pistons. Of course when the towers failed the cam fractured.

Stretch · #3 02-11-2012, 05:20 AM

I think the OM617 turbo camshafts are a chilled casting which needs to be handled more carefully when fitting and removing - if something else has let go then I guess this type of camshaft will be more susceptible to failure... though let's face it the camshaft could be the least of the worries... a camshaft is surprisingly cheap even from the dealer - but - the new rocker arms you should be fitting / camshaft towers / rocker arm towers / rocker arm spindles / pistons / valves timing chain / timing chain guides / sprockets (delete what's not needed) basically means engine rebuild...

t walgamuth · #4 02-11-2012, 09:07 AM

My first thought was the vac pump faiing and dropping parts into the cam chain breaking it. This stops the cam and then the open vavles are impacted by the piston and it pushes up the cam, breaking it and one or more cam tower, usually.

Minimum 1500 repair if hired done. Depends on the stuff done while in there.

ROLLGUY · #5 02-11-2012, 10:39 AM

I may get a chance later today to survey the damage. I will take photos. If I could get away with just changing the head (I have a rebuilt one in stock), that would be great. However, holes in the pistons would make the entire car a parts car as far as I am concerned. I get calls all the time from my MB parts ads on CL asking for engines. If I had a dozen of them, I could sell at least one a month! I don't have any complete engines to spare, so that is why the car may become a parts car.

t walgamuth · #6 02-11-2012, 11:53 AM

I have never heard of valves making holes in pistons. The cam breaks first. I have had this happen once.

It might be possible to simply fix the chain and cam and not remove the head.

Has anybody fixed a broken chain and cam without removing the head for a look see?

junqueyardjim · #7 02-11-2012, 06:07 PM

Quote:

Originally Posted by t walgamuth

I have never heard of valves making holes in pistons. The cam breaks first. I have had this happen once.

It might be possible to simply fix the chain and cam and not remove the head.

Has anybody fixed a broken chain and cam without removing the head for a look see?

No I didn't, but I wish I would have taken that approach on that 240D that I got out of Florida. Replace the vacuum pump, pick out all the parts and go with the new cam and towers. I think it is a good "gamble".

junqueyardjim · #8 06-17-2012, 07:28 PM

Quote:

Originally Posted by t walgamuth

I have never heard of valves making holes in pistons. The cam breaks first. I have had this happen once.

It might be possible to simply fix the chain and cam and not remove the head.

Has anybody fixed a broken chain and cam without removing the head for a look see?

Tom, I did consider that with the 240D on my Florida car, but it really is not a good practice, but if the vacuum pump didn't drop its balls into the engine (and you have to check this to be sure) and you have all the chain, (the broken links match) it could be done. My 240D block and pistons were perfect. But the chain was in about 5 pieces and there were vacuum pump parts in the chain galley and pan.

Stretch · #9 02-11-2012, 01:02 PM

Assuming the camshaft was broken by the force of a piston hitting a valve and these two (combined) opposing the motion of the camshaft I guess you'd get a bent valve with a bashed in piston crown - I think it would be prudent to remove the head to look for damage rather than just hoping it is OK. From a not spending any money point of view, however, I guess you'd automatically be $70+ lighter for a new head gasket alone...

t walgamuth · #10 02-11-2012, 01:14 PM

I cannot feature anything else that coud break a cam.

I am not advocating fixing it without removing the head, but rather am asking the question if anybody has tried that as yet. It might be possible to use a scope to look insde and see if anything is broken.

The valves can be stested with air under pressure, holes in the piston would also be revealed, though other less severe damage might not show without a scope.

layback40 · #11 02-11-2012, 05:57 PM

Quote:

Originally Posted by t walgamuth

I cannot feature anything else that coud break a cam.

I am not advocating fixing it without removing the head, but rather am asking the question if anybody has tried that as yet. It might be possible to use a scope to look insde and see if anything is broken.

The valves can be stested with air under pressure, holes in the piston would also be revealed, though other less severe damage might not show without a scope.

If the cam bearings are not concentric, over time the cam may fail from fatigue. A poor casting can cause failure years later also.

I have seen pistons (non MB) that only have a slight mark on the crown from a valve but the impact has crushed the piston enough to jam the rings in the lands. I have not seen a piston with a hole from impact with a valve. I think it could happen though.

kerry · #12 02-11-2012, 01:17 PM

I thought someone had in fact simply replaced chain and cam without removing the head and reported on this forum about it. I may be mistaken.

ROLLGUY · #13 02-11-2012, 02:18 PM

I am about 3 hours from being able to tear into the engine. It would be nice to see the chain intact, but I am not counting my chickens yet. If the chain did break, I have no idea how to get a new chain in there without pulling the entire engine apart. If I was able to somehow feed a new chain in, I would still need to time the IP/Vacuum Pump gear correctly. At this point it is just speculation, so I will wait to see when I pull the cover...Rich

dude99 · #14 02-11-2012, 10:54 PM

If the chain became loosened it could have whipped and skipped a tooth, although to my knowledge this usually happens at start up, not while driving as you described. I would have a look at the chain tensioner and guide rails as well.

vstech · #15 06-17-2012, 10:39 PM

this was a good read. I'm hoping I'll have similar luck with my 85SD... my cam gear disintegrated, and the chain is SUPER tight on the cam bolt/gear hub... I do not have a warm cuddly feeling...