Vintage Dirt Bike Q & A

I'm working on rebuilding a 1980 CR250 engine from a mini sprint car, and converting it for use in a Bonneville salt flats race car.

The first thought I have is doing away with the close ratio gearing. Is it possible to swap gears from an MT/MR from the same period?

there is no swap that i know of.the 78-80 gearboxes are completely different than the 73-76 cr,mr,mt transmissions.i dont think any parts will interchange.i have a 75 model cr250m1 that has the 5th gear mainshaft and countershaft gears from a mt250 in it and it has truly eye watering top end.

_________________
(2) 1968 DT1 1970 RT1M,1970 DT1C 1971 RT1B Enduro 1974 MT250 1974 DT250A (2) 1975 DT400B 1974 DT100,1978 DT175
1975 CR250M1 1979 CR250R 1979 Kawasaki KZ400H1 Jesus is Lord!!

Bummer. Anyone know the tranny ratios for this motor, and max RPM? I need some numbers to tell the guy if the motor will make the speeds he needs or not.

if its anything like my 79 model.i am guessing about 7500,maybe 8k or so.these motors dont have a lot of over rev.my 75 model kills it in revs.it will do 8500 or even 9k.it winds like a hot 125.

_________________
(2) 1968 DT1 1970 RT1M,1970 DT1C 1971 RT1B Enduro 1974 MT250 1974 DT250A (2) 1975 DT400B 1974 DT100,1978 DT175
1975 CR250M1 1979 CR250R 1979 Kawasaki KZ400H1 Jesus is Lord!!

Just going by the Honda advertising of the day 37BHP/7,000RPM and out of the owners manual Primary reduction 3.250 gear ratio 1/ 1.900 2/1.591 3/1.240 4/ 1.000 5/0.839 .Thanks Mark Birkett

_________________
Couple of CR`s