1983 240D camshaft broken :cry:
 

I hope you're all having a better evening than I am.

I had just left the parking lot at work when the engine just ...stopped. I coasted for a short bit, during which I attempted to restart it; it spun for a second then locked up, after which it wouldn't turn over at all.

I towed it home and pulled the valve cover, half-expecting (from those symptoms) to find a broken timing chain. Fortunately, that was not the case. UNfortunately, I found the camshaft broken on the 6th cam from the front. I don't know if the broken camshaft is the initial problem or the result of something else like a seized piston. I haven't pulled off the oil pan yet to look up from the bottom.. I'm expecting that piston #4 is probably destroyed and maybe #3 as well, but I don't want to dismantle the whole engine (again) just to diagnose a problem that might be unrepairable.

The car has 260k on it, but I rebuilt the engine about 7500 miles ago. I'm really quite undecided on what to do... on one hand, I like the car, the body is in great shape, and I have a reasonable amount of experience with W123s. On the other hand, I need something reliable to get to work every day, and now I'm not particularly confident in my rebuilding ability.

Maybe I'll get a 300D longblock & transmission.. maybe I'll give the body away to my Dad, as his '77 240D recently was put out to pasture and he has more time to rebuild or transplant this one... maybe I can find it another good home. I'm quite distraught about the whole incident.. :sigh:

- Nathan

Man, what a bust! What's the timing chain look like?

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The section of the camshaft over piston #4 slides freely out of the rear bearing, so I suppose it's possible that the valves were both closed and the piston still will be OK.

I didn't try to turn the camshaft by hand (er, wrench). I suppose the timing chain could be broken lower down in the engine, but I would think that the momentum of the camshaft spinning as the engine died would have thrown it off the camshaft sprocket.

If the timing chain is still intact, then pistons #1, #2, #3 should also still be intact, since the cams (even the broken half-cam) should have kept them in sync with the crank & pistons.

I guess best-case-scenario would be that all my pistons are still OK if the chain is intact and the valves for #4 were both closed. But, that doesn't explain why it won't turn over with the starter. :sigh: maybe I'm being too optimistic.

Probably wont turn over because the cam wont spin and open/close the proper valves for combustion. or is it not even making a cranking sound at all (no spin)?

It doesn't spin at all. When I turn the key, the engine twitches a bit due to the torque of the starter, but doesn't budge at all.

I unfortunately expect to discover that a piston is stuck due to debris from a shattered valve.. or maybe one of the bearings on the crankshaft? I just don't know.

I wonder if it'll spin after it has cooled down overnight.

Hopefully nothing is broken like that. It sucks when it happens.

ncarter
 

just curious, what was performed on the rebuild you did?
larry perkins

Practically everything. New pistons, new cylinder liners, new crankshaft bearings, new valve springs. I did not have the head machined or the valves ground as the machine shop said the head was in fine shape. I kept the original camshaft and crankshaft; the machine shop said they were also in good shape. He said the crankshaft balanced to within about a gram, which is practially perfect considering the relatively low RPMs of these engines.

My original reason for the rebuild started with low oil pressure, but I wound up doing more than that because piston #1 had cracked lands around the piston rings.

I did all the work myself except pressing the old cylinder liners out and new ones in, machining the new liners, and changing the valve springs. I followed the big blue factory service manuals at every step, and the rebuild took me many months to complete. The only other (significant) problem I have had since getting it driveable again was that the worm gear that drives the oil pump & injection pump broke.. but at least that didn't take anything else out with it.

I just don't know why the camshaft would just twist apart like it did; there shouldn't be enough rotational resistance to accomplish such a feat unless it got caught on one of the valve lifters (how? they're designed to slide against each other) , or one of the valves suddenly became stuck closed (again, how?).

I have seen broken camshafts caused by the timing chain breaking or jumping time. I suspect that is the problem here.

So you had the 616,617 NA MB Factory Shop manual for your rebuilding guide ?

Looks like something was dragging on one spot (like a metal chip) until it wore down enough to weaken the cam.

I fear your chain is not going to be intact. Shocking to see the cam broken where it is......

[QUOTE=ncarter;1378800]I kept the original camshaft and crankshaft; the machine shop said they were also in good shape.
I QUOTE]

In the 616 manual it shows about three different camshafts...and at least one of them is beefed up at some of the journals.... and it shows where to grind on the journal stands in order to install those larger bearings... do you know if you had the stronger cam in the first place ? The manual may say that if you do a rebuild that you are to upgrade to that stronger camshaft....

Wow....thats an interesting point for it to break at, usually it happens between lobes on most anything I've ever seen broken. It could be possible that the cam just had a flaw in it or got weak there over time. In the first post, you mention when it died you cranked it and it spun a few seconds before it actually locked, sounds to me like it might have not impacted things or not very hard, and only struck the valves when you cranked it, which wont hardly do much damage, it "might" bend a valve stem. Continuing to try to crank on it and force it against whatever locked it wont be doing it any favors for sure. I would pull the head and look, to check the valves, just to do it right. If its toasted then theres no loss in doing it, if its fixable then you know. I have the remains of a 616 from an '80 that tossed a rod, good top end, and 3 good rods/pistons. I was saving them to see if I can use them to repair my "64 190 (busted timing chain), doubt it but you never know, but ....

Will the engine turn by hand?