Rich250RRacer
12-22-2004, 10:20 PM
In the process of rebuilding a 91 CR250 motor for someone, I got to thinking about a set-up that I heard microsprint racers use.
What most 250R owners don't know is that the 85-89 ATC/TRX 250R motor was designed at about the same time and is based on the 85-91 CR 250 motor. The 85-86 250r crank uses the same rod as the CR and is the same stroke. Microsprint racers were taking 86-91 CR cylinders and using them on 250R bottom ends, since they are a direct bolt on when used with a CR piston. They are, of course, eliminating the power valve set-up since there is no way to drive the system. This looks to be a relatively easy mod since the valve guides can either be welded or epoxied. Longer rear cylinder studs would be required, and there may be some re-engineering needed on the exhaust flange. These CR motors were very potent with the later models producing 51-53 horsepower in stock form. Has anyone tried this yet? If so, what kind of power did it produce and how did it perform overall?
What most 250R owners don't know is that the 85-89 ATC/TRX 250R motor was designed at about the same time and is based on the 85-91 CR 250 motor. The 85-86 250r crank uses the same rod as the CR and is the same stroke. Microsprint racers were taking 86-91 CR cylinders and using them on 250R bottom ends, since they are a direct bolt on when used with a CR piston. They are, of course, eliminating the power valve set-up since there is no way to drive the system. This looks to be a relatively easy mod since the valve guides can either be welded or epoxied. Longer rear cylinder studs would be required, and there may be some re-engineering needed on the exhaust flange. These CR motors were very potent with the later models producing 51-53 horsepower in stock form. Has anyone tried this yet? If so, what kind of power did it produce and how did it perform overall?