Vintage Dirt Bike Q & A

I just put a '76 tranny in my '74 and it now pops out of second gear when I pin it. I put in the whole gear set, shafts and shift drum/forks from the newer bike. When it pops out of gear the cogs ride up out of the slots of the gear it is to lock into and then the tranny locks up and kills the motor.

Is there something special to do when doing this conversion? My old gear set (another '76 set) did not use the center case gasket but the tranny bound up when I did not use the gasket on this set. The old set did not bind up like this but it did not always catch the up shifts to 3rd and 4th. I haven't tried all of the gears under hard shifts, just second. It seems to shift well but pops out under throttle...

Any ideas? I have another '76 set but don't want to use it unless I have to.

mailto:rampman@fmxramps.com

Hi Rick. All these old Hondas use a center gasket. I don't think your problem is the swap, but rather the gears themselves.
Sounds like you have a typical worn second gear problem. When you take it back apart, check the dogs on the gears. I'll bet they're worn. Also take a good look at the drum, especially at the sharp bends of the slots. You may have to make a good transmission out of two. Get a manual and just make sure all the washers are in the correct places. Pick the best of each piece.

Hi Rick,

Tom. H is right on the Money! You do need to run a center case gasket on that motor (which I'm assuming is a 125?) Follow Tom's advice check those gears.

Good luck!

Thanks Tom. It is a 250. The gear set is used and it was worn some but I didn't think it would matter much. The old set was worn more but it did nto pop out like this one does.
I have a box of gears/parts and maybe I will be lucky and have some better spares. If not, I will dig into the newer '76 lower end that I have and switch the whole set again.

What about grinding the cogs? Anyone do this or is there a science to this? I have the tools...

I think if you grind the dogs it will just make it worse I tried that on a kickstarter it did not work trust me on this one but what you could do is sand blast it which would make it rought so they would catch better and save you having to take the other tranny appart

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1974/75 Honda MT 250

Rules are put there to be broken.