Monday, March 20, 2017

OM603: Loose Crank Bolt Damage

A little while ago an 87 300SDL came in to repair some previously diagnosed suspension problems and a front main seal replacement. Little did I know what I was in for!

If this picture is a testament to what was pulled off the engine, I don't know what is.

On the left, is a new key for the harmonic balancer to slide into and be held in place on the crank. On the left, is what came off the engine.... At some point prior, the crank bolt had worked itself loose. This is the SECOND time (on 2 cars) it's happened on an OM603 for this particular owner. I've personally never had to deal with an OM603's front crank bolt working itself loose. Not even on those that have had front seal work done.

Removing the pulley usually requires a small puller to yank it off. It's not a press fit, but it is a very tight fitting pulley. This one just fell into my hands.....not good. Upon further inspection I found a few problems. 

Namely, a totally cracked off portion here which was somewhat held in by the rubber around it. A small screwdriver to catch it and I was easily able to pry it out.

The 2nd crack - same deal. The balancer show's no signs of abuse in these particular areas. Maybe this was throwing the pulley off balance and allowing for the bolt to work loose? No idea.

Broken key as in the first picture had a portion stuck in the key slot on the balancer. I think I've diagnosed the pulley wobble - the damn thing was shaving itself down! You can see the small lip on the inner section and the scoring on the inside of the pulley.

Another close up.

The outside of the pulley - the wobbling had worn through the front seal and the spring that's found in the seal was wearing a groove into the seal seat.

This story ended with me finding a good used balancer assembly and Mercedes apparently overnighted (I didn't ask for it to be) a new key for me to complete the work. Miraculously the crank snout had no serious damage and was able to accept a new key and pulley. The new pulley fit on the crank with no wobble and everything buttoned up beautifully. New oversize front seal went in, so should this car come back in the near future it'll give me an opportunity to check if the bolt had lost torque or if the engine is still leaking profusely. The only other fix for this would be a new balancer and a new crank - which is completely out of the question for this car.

Thanks for reading!


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