Crank Bolt advice for the 603.950 please.
 

Hi there, I was wondering if any one may be able to help me with some info.
I work for a company in the U.K. that has recently won a contract to repair approximately 250 Mercedes OM603.950 engines that have been fitted into a modified off road vehicle.

I work in the workshop and it has recently come to my attention that our engines have 2 types of Crank Bolt and washer fitted.

Some engines have an 8.8 bolt and 3 disc spring washers fitted, others have a 10.9 bolt and a single (10mm approx) washer fitted, and we have seen combinations of the two. These engines were refurbished by a previous company.

I'm trying to ascertain which is the correct/best combination to use as I believe it is well known for the Harmonic Balancer to have a habit of falling off, indeed we have seen several already that have damaged crankshafts due to the front crank pulley having come loose.

From my research on this excellent forum I see that this subject has been discussed several times, but I can't find a definitive answer.

From my research I have seen a torque setting of 200Nm + 90 degrees for the 8.8 bolt with 3 disc spring washers in an online Mercedes workshop manual. I tried this torque procedure today and was surprised by how much effort (and a long bar) is required to achieve the + 90 degrees. That bolt is TIGHT ! Possibly too tight ?

The torque setting of 320Nm for the 10.9 bolt and thick single washer is waayyyyy easier to achieve and is the procedure we have been using up until I started looking into the differences of the 8.8 bolt and 10.9 bolt.

Is the 200Nm +90 degrees with an 8.8 bolt and 3 Disc Springs (Bellville Washers) the recommended advice or is there a new procedure?

Do Mercedes recommend replacing the 18mm bolt each time ?

These engines having been out of production for so long make finding information difficult, or am I not looking in the right place ?

I appreciate any help you could give.

Thanks Fred.

Hmm, I cannot offer much help but I can say that I have had my crankshaft bolt come loose from both of my 603s. My mechanic at the time said he had never heard of that happeneing but to me it had.
You might want to check YouTube, dieselmeken the swedish pump builder had a video for a 606 where he came up with a better bolt solution but it did not provide much information.

Well, I found it
https://youtu.be/2ybRI1wKafo

Thanks for that. Getting an extra 90 degrees out of that bolt is a struggle :-)

Just before Easter we ordered a new bolt and washer from our local dealer. They arrived yesterday, an 8.8 bolt and a single thick washer. It would appear that the three Belville washers have been replaced with the single thick washer/spacer.

It looks like 200 Nm + 90 degrees is what we will go with.

Thanks again.

This is correct, per my copy of the factory service manual.