Broken camshaft: 617 '81 SD. How could this happen? - Page 2 - PeachParts Mercedes-Benz Forum

t walgamuth · #16 02-11-2012, 10:58 PM

I believe the only way for it to break things without a broken chain is if it slipped a tooth or more on the sprocket.

You need to really look at the sprockets and see if the teeth are wave shaped. If they are they will need changing too. IN order to achiev correct mechanical compression is if the enigne is timed correctly with the cam.

Once you can verify that and verify good compression then looking at the pump makes sense.

The only reason I suggest the idea of trying it without puling the head is that nobody i have heard of here has found any piston damage from valve impacts. The valve hit the pistons squarely.

Also the cost in time and materials is very high for removing the head. It is not a side valve engine after all.

ROLLGUY · #17 02-19-2012, 03:27 PM

I fed in a new timing chain yesterday, thinking that was the problem. After feeding in the chain and connecting the master link (the old chain was connected with a master link, not crimped, and besides it was worn out!), I turned over the engine, and the chain started doing the same thing the old chain did (riding up on the gear). I can only assume the chain was not the problem, but something else deeper inside the engine. I have decided to replace the engine with another good one. I will probably tear down the bad engine to see what might have caused the problem in the first place.

ROLLGUY · #18 02-19-2012, 03:48 PM

Quote:

Originally Posted by t walgamuth

The only reason I suggest the idea of trying it without puling the head is that nobody i have heard of here has found any piston damage from valve impacts. The valve hit the pistons squarely.

After finding out that a new chain would not fix the engine, I decided to pull the head. It appears that the piston tops are perfect, and have no visible damage. I will pour some lacquer thinner into the ports in the head to see if any of the valves leak.

whunter · #19 02-20-2012, 01:28 AM

Quote:

Originally Posted by ROLLGUY

I fed in a new timing chain yesterday, thinking that was the problem. After feeding in the chain and connecting the master link (the old chain was connected with a master link, not crimped, and besides it was worn out!), I turned over the engine, and the chain started doing the same thing the old chain did (riding up on the gear). I can only assume the chain was not the problem, but something else deeper inside the engine. I have decided to replace the engine with another good one. I will probably tear down the bad engine to see what might have caused the problem in the first place.

Two points.

Warning, Danger: Please read this thread FIRST...
Need Automotive Grade Prozac
Need Automotive Grade Prozac = timing chain - PeachParts Mercedes ShopForum

The second point is that the chain tensioner should prevent the issue you describe, unless it has failed.

.

ROLLGUY · #20 03-11-2012, 12:00 AM

Well, I found the cause today. The car has been sitting, waiting for me to do some digging to find out what caused the cam to break. I pulled the lower pan (it was badly dented, so I thought something might have gone wrong with the oil pump chain), and found no problem down there. I decided to pull the vacuum pump. Here is what I found:

Evidently parts from the bearing got wedged between the chain and gears, and caused it to jump time and break the camshaft.

ROLLGUY · #21 04-12-2012, 01:23 AM

I got the engine put back together with a new chain, upper guide, rebuilt head, good used (un-dented) oil pan, used cam and towers, and of course vacuum pump. The engine runs great! I was glad the engine was not a total loss, as then the car would have been scrapped. It is a decent car, and it only cost about $800 for parts and my labor.

layback40 · #22 04-12-2012, 03:41 AM

Quote:

Originally Posted by ROLLGUY

I got the engine put back together with a new chain, upper guide, rebuilt head, good used (un-dented) oil pan, used cam and towers, and of course vacuum pump. The engine runs great! I was glad the engine was not a total loss, as then the car would have been scrapped. It is a decent car, and it only cost about $800 for parts and my labor.

Thats great to hear !!!!

Will be interesting to see how it goes after say 1,000 miles. Hope you get a good run for a few years at least.

LNGfish · #23 04-12-2012, 05:30 AM

I love a good ending. TY for the story.

ROLLGUY · #24 06-17-2012, 03:57 PM

Quote:

Originally Posted by layback40

Thats great to hear !!!!

Will be interesting to see how it goes after say 1,000 miles. Hope you get a good run for a few years at least.

My friend bought it from me, and has put several thousand miles on it so far. He really loves the car!

junqueyardjim · #25 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.

vstech · #26 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...

ROLLGUY · #27 06-18-2012, 01:08 AM

I pulled the head not knowing for sure, but ended up not needing to do so. I would suggest pulling the lower pan, removing all the metal pieces, and replacing all the broken parts. You will need to remove the IP to re-time it, as it probably is not in time with the crank. If you replace all the parts and then do a compression check, then you will know for sure if the bottom end and head are still good. Be sure to check for small pieces of metal in the teeth of the lower gear. Even the smallest piece of metal will cause the chain to become tight. Once everything is back together, timed, and the engine turns freely, a compression check will tell you if you can go further and get the engine running again. I wish you luck....Rich

barry123400 · #28 06-18-2012, 08:19 AM

Periodically taking a mechanics stethosope or large screwdriver even and listening to your vaccum pump may pay dividends. They just might get substantially more noisy well before letting go.

On the otherhand they may go out very quick with no precussors at all. Certainly it would not hurt anything to follow that policy say at every oil change interval. It would only take a minute to do afterall. Could concievably save you hours later and many dollars as well.

ROLLGUY · #29 06-18-2012, 11:58 AM

Quote:

Originally Posted by barry123400

Periodically taking a mechanics stethosope or large screwdriver even and listening to your vaccum pump may pay dividends. They just might get substantially more noisy well before letting go.

On the otherhand they may go out very quick with no precussors at all. Certainly it would not hurt anything to follow that policy say at every oil change interval. It would only take a minute to do afterall. Could concievably save you hours later and many dollars as well.

Good idea. I have a mechanics stethoscope, and can compare the sound of a known good VP to a suspect one.