Crankcases

[squirrel_hunter]

If for example you have made a monumental fuckup is it possible to change the crankcase lower with one from another engine?

I see Yamaha list the crankcase upper and lower as one part, but if I were to use the upper from my 2MA and a lower from another am I going to get into difficulties?

[silverstrom]

Typically, upper and lower cases are a matched serial numbered pair as they are line bored.

[jools]

I'll let you know - my RD350 resto has a mixed pair due to sever bottom end corrosion with some goose leaving the motor outside with no top end on it !!
I checked for any crankshaft and bearing tightness and that the sealant was squeezed out uniformly.

Until I have it set up properly & racked up a few kms on it I'm not going to know for sure

[squirrel_hunter]

Thanks for that. A bit to think about. Once I get the rest stripped back down I'll be off to the local engineers to see if its repairable.

[Rik]

Generally it's more critical to have matched cases with 4 strokes as the shells for the mains have to be 100% in line.

With a 2 stroke there is always a little clearance in the outer crank bearings (especially C3 type) which can mean you get away with mixing cases.

[Toop]

It is very easy to lose grip of power in approximation 
Clearance is necessary to master work well, hard, long time