bummed.... engine running but accessories not turning. 1982 300CD Turbo - PeachParts Mercedes-Benz Forum

lutzTD · #1 09-29-2009, 08:02 AM

got to work this morning and had an alt light and no power steering. the sinking feeling in the pit of my stomach said sheared crank. I verified it under the hood but have not removed anything, I am still at work. I am going to have the wife pick me up and go get the trailer to take it home. whats the best and worst I can expect? is it simply a key or is there some other big problem lurking?

found this thread, hopefully it is just the cap screws

Engine running; no belts turning, no pulleys turning

LNGfish · #2 09-29-2009, 08:58 AM

Now I'm bummed too, good luck you'll get it!

kerry · #3 09-29-2009, 09:17 AM

Not an uncommon problem on 617's. Should be fixable. Even if the pin slots on the crank nose are bad, new pin holes can be drilled.

bobodaclown · #4 09-29-2009, 11:45 AM

I lost an alternator key once. Though the alternator sized. Lost the pulley and everything. (going from San Francisco to Elko, Nv. it happened on 80 outside Fallon NV) Got towed back to Elko pulled the Alternator. It was a $10 fix. new key and pulley. Never figured out why. But it was good t go.

Hopefully it will be a relatively easy fix. Good luck.

lutzTD · #5 09-29-2009, 02:40 PM

well its the worst. the keys on the crank nose are bunged along with the id of the balancer. I am going to go get a new balancer from the pnp, not sure how much material is gone from the crank nose. when drilling new holes, is the hardness of the crank and balancer similar? is it better to drill new holes or enlarge the current ones?

kerry · #6 09-29-2009, 02:56 PM

There are a couple of threads which describe drilling the crank. My recollection is that the new holes were drilled 90 degrees away from the existing ones.

pawoSD · #7 09-29-2009, 03:01 PM

Yikes....how tight did you have the belt tension set? I keep mine all quite loose to prevent this issue....

kerry · #8 09-29-2009, 03:06 PM

Does belt tension have any effect? I'm pretty sure MB knew there was a weakness and if my memory serves me correctly, even recalled the early W116 SD turbo engines because they were throwing off their balancers.
Any idea why it failed in this instance?

tangofox007 · #9 09-29-2009, 03:09 PM

Quote:

Originally Posted by kerry

I'm pretty sure MB knew there was a weakness and if my memory serves me correctly, even recalled the early W116 SD turbo engines because they were throwing off their balancers.

What corrective action was taken in conjunction with the recall?

barry123400 · #10 09-29-2009, 03:15 PM

Possibly locktight on any fastenings? They have been known to loosen off I think. Miserable experience to have. Especially if damage has occured.

I cannot think of anything else they might have done during the recall except perhaps harder pins as well if they suspected shearing was an issue.

kerry · #11 09-29-2009, 03:40 PM

Quote:

Originally Posted by tangofox007

What corrective action was taken in conjunction with the recall?

Not sure. I'll do some searching.

Haven't been able to find anything. Can't remember where I read about the recall.

lutzTD · #12 09-29-2009, 08:19 PM

yeh looks like I will drill 2 holes 90 degree off. The engine was making a clattering noise for 3 weeks. I searched and searched and couldnt find it. I finally decided it was the motor mounts. looks like that guess was wrong. I think the last straw was turning the engine by the crank bolt to do the valve adjust and my own inexperience with these engines. the bolt was loose when I was turning the motor over, but it didnt clue me to the bigger issue, I just retightened it

winmutt · #13 09-30-2009, 03:31 PM

.

Any chance the balancer had been pulled off by a mechanic recently?

lutzTD · #14 10-01-2009, 08:00 AM

Quote:

Originally Posted by winmutt

.

Any chance the balancer had been pulled off by a mechanic recently?

no, I had some wicked vibes from the transmission for a long time until I fixed it a while back. From what I have read the failure path is: Vibration from bad/old mounts causes the bolt to come loose which in turn allows the dowels to move making their fits progressively looser until they finally shear. I had noticed more noise from the engine that disappeared at 900 RPM, looking back it must have been the balancer making the sound. Since I had no idea this was an issue, I am used to working on US V8's, I did not even think to check the balancer bolt. I noticed it was loose, which was I guess my last chance to fix it, when I did the valves 2 weeks ago. I should have torqued it then but I tightened it and forgot about it. seems like a poor design for a joint, but I guess if all is right it will last a long time. not sure why they didnt just make the crank snout longer. I rule of thumb for a good shaft fit is 1.5 times the diameter for the length of engagement. this one is not long enough to be a good joint.

t walgamuth · #15 10-01-2009, 08:19 PM

I'm not sure why they used round keyways, maybe because the section at the shear line is maxxed out without weakening the hub much. The way that they fail is that folks pull the harmonic balancer and bugger up the pin holes when they reinstall.

I am skeptical of drilling new holes successfully because getting a precise hole seems very very difficult to me.

When I had the wobbling hb my favorite machinist advised me to get another crank. If he couldn't drill a proper new keyway I don't see how a hobbiest can do it in their garage with hand tools.

It doesn't hurt to try though.

The alternative is to tear down the entire motor and put in a new or good used crank. Just the labor to tear it down and reassemble is probably 2K.