Vintage Dirt Bike Q & A

hi i have a 73 elsinore cr250m and in my transmision one of the pawls got knocked off of the fourth gear. and so my dad bought a 74 mt250 transmision for it. do you think that i could still run the transmision with the dawg missing or replace it with the mt?

thanks,
Brad

Hi Brad,

Sure that's fourth gear and not third? Third gear is rather notorious for breaking. I haven't heard of problems with fourth but it doesn't mean it won't happen.

Anyway.... I think you'd be risking big serious major doo-doo if you run that bike with a missing dog. It only has three to begin with. You knock one off and now the remaining two have to bear the drive force that three used to bear. This will likely lead to quicker failure of one of the two remaining. Now you're down to one and guess how long that puppy is going to last. Also a broken dog floating around your tranny can easily get caught in some other gears as you're going full tilt down a straight away and lock the whole scoot up. Guess where you wind up???

The MT gearbox works fine. Wider ratios but just fine. I ran the wider ratios in my bike for desert racing back in the 70's. I don't remember specifically but I think fourth is the same between the CR and MT. If so just take the good fourth from the MT and pop it in the CR. (Maybe someone else can verify this.)

HTH,

Loren

Hi Brad,

I did a little looking in my Clymers manual. 4th gear ratios are different between the CR and the MT. (See below) So just changing the 4th countershaft gear won't work. (You didn't say it was the countershaft gear but that's the only one with dogs on it.) You might be able to use both the 4th countershaft AND the 4th mainshaft gears. You'll have to check how the holes in the 4th mainshaft gear line up with it's neighboring gears as well.

Stock gear ratios:
CR250M
1st - 2.055
2nd - 1.571
3rd - 1.250
4th - 1.038
5th - 0.862

MT250
1st - 2.235
2nd - 1.571
3rd - 1.160
4th - 0.896
5th - 0.718

Like I said prior I ran MT gears in the desert and frankly 1st was way to low. (Good for pulling stumps I guess.) 5th was rather tall but worked fine in the real long flat out stuff. Might be a bit tall for MX though. If you use the whole MT gear set see if the 1st gear set from the CR will work.

HTH,

Loren

For the record, second gear is the only interchangable gear between the two bikes.
I have been told the MT gears are stronger than the CR gears. Anyone???