Das MZ Forum für MZ Fahrer

Hello,

I'm looking for factory papers about crankshaft balancing factor they used for ETZ 150 and 250. Some manufactures writes it in service manual, even DKW/MZ did it at the begining as I remember but for ETZ models they didn't. I do not have any oryginal crankshaft with complete new piston with oryginal bearing to weight that and calculate, but even with oryginal parts there could be a difference becouse of inaccurate manufacturing proces. It's good to know, what was the designed percentage.

Hope in Germany you have this knowledge somewhere and it's not gone forever.

Greets
Roman

For ETZ250 balancing is a problem. You have to increase the weight of the crankshaft if you use the original piston.
For detailled information ask Steffen Uhlmann from ORP --> mail to www.oldtimerracingparts.de He is an expert for balancing crankshafts (my point of view)

Best regards!

Thanks for the link. But generally I do not want to change balancing of the crank. It's designed to be at specyfic balance factor for example polish bike shl have 35%, sfm junak 350 have 68%, jawa 250 - 72%. As they did in MZ, this designed balance factor by engine designer is a mystery becouse the do not write it in service manual. Measured value could not be accurate, becouse of imperfections and tolerances of parts.

hey roman,

look at this.

It seems as if there are various balancing factors on original crancshafts. In this thread, you can read values from 10% to 32% for ETZ250.
The advice from user smu (professional) is to choose 50% for ETZ250.
An original factory paper is not known. Christof doesn't upload any papers in this thread. So you can be sure, there are no papers.

It leaves a question "why they did it that way" unanswered and open forever

Thank for your reply. I know something more now

I know: They did it that way, to minimize vibrations in footpegs and handlebars. The factor the junak has, is quite normal for a more or less vertical zylinder in a closed-slope-style frame, and a stiff mounted engine (without rubber-blocks like ETZ)
For the ETZ-Engine can turn around a pivot at the rear-mount, and is hanging on a rubber-block with the cylinder, balancing-factorshould only compensate horizontal forces.

Cheers,
Hans

This is the point for sure, but when I said "mystery" I meant designed balance factor in factory. This 68% value for junak comes from factory paper, because there are available fortunately. If you took oryginal crank and measure it, you will have result for example from 40% to 80% becouse of wide tolerence... That's the point. Research must be done about who worked there at the time, still lives and could still remember that. All engineers could not be dead till now...

In junak for example as far I as know the history of it, they made a crank with changeable balance factor. They could made a difference just by taking a cylinder with head off. And they do a lot of experiments and pick up 68% value that way. That's the value that gives best feeling for a rider. Of course in practice it wasn't that great becouse manufactured cranks were poor quality and the real value was way off this 68% sometimes but the research was done and when you balance your crank or make new with this 68%, you will have a result in smoothest possible engine feeling in junak's frame.. I'm pretty sure they did it that way in MZ factory, and the best value, in the opinion of an engine designer was picked. This value is a key here