It seems to me that the kx250 inner clutch covers were too short but I should know on Monday as I have set the hook on a 89 kx250
i dont think that the inner 250 cover would fit directly to the k5 without mods for waterpump and governor drive and the k5 kickstartshaft is also bigger diameter than 250 , but without a try we never will find out ...
my thinking was to use the outer 250 cover and making cuttings on the right places to weld the cutted ring of the 88-91 250 to the k5 clutch housing and we can bolt on the 250 outer cover to the k5 .
without destroying one of the rare 88-91 250 inner cover could the needed weld on adapter copied without cutting and only measure the location of bolt holes and diameters. with the right tool on pc could made a program with the needed dimensions for a cnc-mill , find the right mashine shop and we have it... the outer cover could be easily copied with the cnc- mill . (or maybe a 3d-printer??
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and like i said: at the moment i run a little bit out of my possibilities and it would give a very long session to make this adapter by hand in my garage. there is nothing that not could be made. it needs only time , money , the right material and gives lot of fun.