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426f motor in stock R frame????
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Posted by: KY250r

how hard would it be to put a stock 426f or 400f or 450f yamaha motor into a 86 stock 250r frame? like would i have to do alot of cutting, welding gridning etc? i am a welder so welding and all that isnt a problem. do they make mount and stuff to make it easier?

Posted by: JessetheKid

man those frames didnt hold up with and R motor in them let alone a yami....try doin some searches you may find some stuff

Posted by: LT250Racer609

its been done but like said above, they are just too weak due to their age. If you have it gusseted and nice thick motor mounts made up i dont think there would be much of a problem....and since your a welder you could even mock up your own gusset kit and do a nice job on it, get it power coated and call it a day

Posted by: KY250r

well its already gusseted and painted. i just want to kno ho much fabricating id have to do to get the motor in it.

Posted by: LT250Racer609

none besides maing new motor mounts.

Posted by: KY250r

so the motor would set right in? all i need is mounts?

Posted by: Slinky

that motor is a lot taller than a stock R motor...you'll probably have to widen the lower frame rails and lower the motor in the frame...its gonna take a lot more than just motor mounts...

Posted by: LT250Racer609

the YZ426 motor, YZ400 motor and YFZ450 motors do not require any frame mods to set into a stock R frame....the motor that you hafto widen the frame is the CRF450 Motor which is taller then the Yamaha motors i just listed....The 426,400, and yfz450 motors are all the same height etc...

Posted by: KY250r

so all i would have todo is buy the motor set it in,measure and cu new mouns,mount a oil cooler and run my stock r radiator?

Posted by: matt250r21

I can tell you from experince, YZ426 motors in stock 250R frames don't fit that great. The main problem is the carb and upper rear shock mount want to be in the same space at the same time. This is the case when you put the YZ motor in the 250R frame the way it is ment to be. By this I mean using the 250R swingarm pivot bolt thru the rear YZ motor mount.