ATK / Rotax 4 Stroke Crankcases/Main cases

I have been told that the main engine / crankcases on 4 stroke Rotax motors are not interchangeable in some cases.  Could anyone elaborate on that? Some of my questions are:1) can i swap my pre-1990 cases for post 1990 cases on 604cc motors?  2)Can cases for smaller than 600cc motors be used to house crank and internals for larger than 600cc motors?


 If anyone could share what they know I have to either repair or replace the cases on my 1988 604 Rotax engine. The internals are in great shape and I have a heavily modified cylinder I use but the cases could stand some work. Does anyone have some 604 cases available for sale or know of a good place to have cases repaired?

Edited by soapman626

For the most part the differences in cases on the 604 Rotaxs are between the kick only and the ES.  When looking for differences between the 604 and 605 there are many differences.  the 604 engines from 1986-1992 are identical, model to model.  You can find out which cases are compatible by looking at the clutch basket.  I can't remember which one it is, but the main change was the clutch was much smaller. as for the bottom end. the 350's have the same motor, but the top end is sleeved down.

Edited by 07ATKEnduro

The 604 cases cannot be replaced with cases from a 500 motor without a bit of work as the piston sleeve has a bigger outside diameter on the 604.  The 500 cases can be used but you need to have a machine shope bore out the sleeve hole which means removing all the internals and bolting the 2 crank case halves back together first.  This might help though.

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