QT50 Yamaha MJ50 Towny two-speed crankcase swap?

Trevor Buonaccorsi /

Wikipedia mentioned that some people convert QT50s to use a Yamaha MJ50 Towny two-speed crankcase.

"Popular modifications include: Yamaha YT60 cylinder, piston and rings. Yamaha MJ50 Towny two-speed crankcase and right-side swingarm. Yamaha PW50 rear gears. Mikuni VM15 and VM18 carburetors. Jemco exhaust, etc."

Does anyone have more info on this swap? How hard it is? the parts required? Cost? Having a hi and low gear woudl wake the QT50 up a lot I think.

Re: QT50 Yamaha MJ50 Towny two-speed crankcase swap?

Jack Rutherford /

Hard part is finding one. I don't think there's much involved in swapping engines. It's 2 speeds vs 1 speed btw.

Re: QT50 Yamaha MJ50 Towny two-speed crankcase swap?

I sold off my yamaha pile before I moved. Had 2 mj50 and one qt50.

Mj50 has 2 shocks and 2 clutches. They kinda look like za50 clutches. Parts are super hard to find as only a subset are shared. Lots of unique transmission parts and the crankshaft is longer.

Qt50 one shock and one clutch. Pw50 parts are compatible. (edited)

Re: QT50 Yamaha MJ50 Towny two-speed crankcase swap?

Jack Rutherford /

I'll look closely at my Towny but I would think you wouldn't "convert" a QT50 to use a Towny two-speed crankcase.

I think you would just take the entire Towny engine, transmission and swing arm and transfer it to the QT50. I imagine the toughest part would be attaching the right side shock. But I've never tried it so can't give a definitive answer.

Re: QT50 Yamaha MJ50 Towny two-speed crankcase swap?

There are lots of other differences I didn't mention. Its an engine swap to switch between the 2. The missing shock mount isn't a big deal.

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