Diesel Engine Front Crank Bolt Failure and Loss of Pulleys - PeachParts Mercedes-Benz Forum

markho · #1 02-28-2010, 02:52 PM

The old 616 and 617 diesel engines produce a lot of shake and vibration and over time that can loosen the front crank bolt. Hard to believe since that big bolt it torqued to over 250 ft. pounds. If caught early enough you can save yourself a lot of grief. If it happens on the freeway (as it did with Kaia) the pulleys can fly off- you will immediately lose your power steering, the dash warning lights will come on and the engine will start to overheat! I would recommend you check the tightness of this bolt at your next service. Certainly check it at the first sign of any strange front engine clicking or clanking noise. Ignore this and I guarantee you will be sorry.

To the high mileage club here (250k and over) anyone preemptively rebuild the crank bolt?

kerry · #2 02-28-2010, 05:52 PM

Never heard of a preemptive rebuild. I think most people leave well enough alone because the pins that hold the crank pulley and balancer on the shaft are not the best design and are difficult to reinstall. There was a recall on the pulley on early 116's. Some people have successfully rebuilt without major problems after a failure but other have found the pin grooves damaged and have to to redrill the nose of the crankshaft.
I've actually never heard of anyone attributing the problem to a vibrating engine.

tangofox007 · #3 02-28-2010, 06:09 PM

Quote:

Originally Posted by markho

To the high mileage club here (250k and over) anyone preemptively rebuild the crank bolt?

How do you envision that a bolt might be "rebuilt?"

Quote:

Originally Posted by kerry

Never heard of a preemptive rebuild. I think most people leave well enough alone because the pins that hold the crank pulley and balancer on the shaft are not the best design and are difficult to reinstall.

The crankshaft bolt can be removed and replaced without disturbing the balancing disk or pins. The pulley (along with the vibation damper) is attached to the balancing disk by cap screws.

layback40 · #4 02-28-2010, 06:24 PM

I guess you could check the bolt torque if you were concerned. It may have stretched over the years. Never had a problem with my 2.

markho · #5 02-28-2010, 08:19 PM

Quote:

Originally Posted by tangofox007

How do you envision that a bolt might be "rebuilt?"

pardon my semantic use of rebuild. i guess i meant replaced? the paragraph makes a novice like me nervous...

Stevo · #6 02-28-2010, 08:54 PM

The pulley that attaches to the balancer came adrift on my '79' 240D, not too much of a big deal to fix, that crank bolt would have been a different story.

t walgamuth · #7 02-28-2010, 10:25 PM

I would not touch the large bolt or the harmonic balancer unless there was a need to fix something.

If it Ain't broke....don't try to fix it!

Sbean · #8 03-03-2010, 08:04 PM

Not the crank, but the alternator pulley bolt came out in my '99 E300 last year when my wife was in town 15 miles from home. The alternator shaft was chewed up requiring replacement, and a couple of fan blades broke. No damage to radiator. My mechanic (29 years Mercedes experience) said he's seen it before and used to routinely tighten that bolt on every E 300 that came in his shop.

Steve

pawoSD · #9 03-03-2010, 08:18 PM

None of our 617's have had that problem, and I've removed the balancer/pulley on two of them and reinstalled. I used new bolts (the smaller ones) when re-installing. No issues so far. I also keep my belts more loose than tight to prevent excess strain.

I would never do "preventative" on it though. If it is fine leave it alone! And make sure the belts are not too tight!

mwoodland · #10 03-05-2010, 11:20 AM

I had all of the small bolts shear on my 240 last year. From the presence of rust vs shiny steel, it was evident that they had been shearing over a period of years, and when the last 1 or 2 gave up, the pullies popped off. I was able to pull the harmonic damper and slot all of the bolts with a dremel, and either turn them out the front, or out the back of the damper. Replaced all with correct hardness, and loctite..

SirNik84 · #11 03-05-2010, 12:05 PM

Dieselkraut23 should really chime in here. hes tried several fixes to the crank, new woodruff keys, new balancer, and at the moment he has the crank out getting the groove machined. I helped him order new bearings, they should be here on monday.

Dieselkraut23 · #12 03-05-2010, 01:11 PM

For the record my story is different.....my mentors car that i now have (1985 euro 300tdt) was in a front end wreck where the HB was tweaked and the bolt snapped. He had the bolt extracted, but every two years he would have to re-tighten the bolt.

The reason for this was because the HB isnt just held on by the bolt and pins but it is really pressed on for a tight fit where as some other car seem like they are pressed on but not this tight.

I went through 3 HBs and two bolts but the shaft had been spun so it just was never tight enough.

In the end i had to have the crank out and to the machine shop to have it built up and machined back to spec.

Shims do not work.......WELDING does not work. Nothing will last but having it machined to stock.

Some 617s and very few 616s with very few miles on them had a loosening problem.

If caught in time they dont need to be repaired just tighted to spec with new bolt and spring (or cone forgot the name) washers.