Vintage Dirt Bike Q & A

Hi I am almost reasy to reassemble my 75 mt250 engine. I was going to put in a 74 cr250 crank I have but when I took out the mt crank and measured it it was 8mm wider than the cr crank which puts the crank shafts 4mm further out than on the cr. I am assuming this will make it not fit properly. If anyone knows anything about this swap please let me know if its gonna work or not.

the wider crank is for the electrics.you can put the cr crank in but you wont be able to use your ignition or lighting you will have to use cr ignition or go electronic
hope this helps.just look at the lhs engine cover for both bikes als cr to mr there is a bulge in the cover mt/mr and flat on the cr
cheers
jimg

_________________
Jim Garvey
1x honda cr250m 1973 in bits
1x honda cr250 champion dirttracker
1x yamaha tt500 dirttracker 1976
1x yetman triumph dirttracker
1x tt500 longtack speedway bike
1 x 1940 350 ariel speedway bike
1 x bultaco astro grasstrack bike antig

You are right about the lighting but the bearing races are set out 4mm further on the mt crank as the weights are thicker so I really think it would cause problems on the top end was. A mechanic told me the cr crank could move back and forth and possibly cause the wrist pin to crack the piston.

hi
i have a mr250 motor and i was told the crank would fit in my 73 cr but i would need to use the mr ignition and side cover.i didnt do this i fully recoed my cr250 motor.you could br right about the 4mm i didnt pull my motor apart.no it is spares for my 76 cr250.

_________________
Jim Garvey
1x honda cr250m 1973 in bits
1x honda cr250 champion dirttracker
1x yamaha tt500 dirttracker 1976
1x yetman triumph dirttracker
1x tt500 longtack speedway bike
1 x 1940 350 ariel speedway bike
1 x bultaco astro grasstrack bike antig

I believe the MR250 crank might fit the 76 CR250M, but the 73/74 has a shorter rod than the MR.