Should Crank / Crank assembly be neutral balanced?
 

Talked to a place in California that rebuilds Mercedes motors. They said that the front pulley should be neutral balance separately, They also said that the crank assembly should be neutral balanced. However, they say that the way mercedes does it (and they do it) is to neutral balance the crank, hub (the thing with the timing marks), and flywheel as a one piece assembly.

So theoretically, if everything is zero balanced, than the assembly as a whole should be zero balanced . . .

They mentioned possible "static" balance issues. I didn't know what this meant so I looked it up: "By static balancing, one means that you insure that the crank shaft is in balance while it is stationary in any position; that is, that the shaft is actually the center of gravity when it is stationary. Put another way, there is no tendency for a static crank shaft to rotate from it own imbalanced weight." from http://answers.yahoo.com/question/index?qid=20090316165052AANKWCL . This is different from dynamic balance - i.e., balance around a central axis when the crank is spinning .

I don't think this will be an issue though since my crank was already neutral balanced and I didn't have to mess with it . . .

Most of the 123 cars have neutrally balanced fw and crank. Some do not. I believe that they balance the cranks neutrally as a matter of course and if the crank cannot be balanced neutrally it is balanced with the fw. In this case any fw that is put on that crank needs to match the one from the factory.

To be sure you need to mark the fw and crank before removing them and then have the fw tested for balance. If its not neutral the new fw needs to be matched to it and replaced in the same position on the crank.

My 84 280e euro had a crank that was match balanced to the crank and not neutral. It was out a lot so if we had not match balanced the fw in a conversion on it it would have been disasterous.

It turned out mine had a match mark on the face of the flanges where the crank and fw meet. It was very very light though and difficult to see...almost like a hologram.