Author Topic: converting 50/60 transmissions  (Read 130 times)

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Offline JackA

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converting 50/60 transmissions
« on: March 13, 2018, 04:36:32 PM »
I have edited this post because I guess I was asking the wrong questions -- nothing new for me! -- to which 57 readers had no answer.

I am looking to build a couple of 50cc engines for vintage roadracing.  For openers, I am leery of rotary transmissions for that use.  Looking at the parts diagrams (what a helpful site this is, just for those and the other manuals!), it looks like the Tora has only about 4 more parts than the Chibi to make the shifter a return type instead of rotary, and my next step will be to ask Richard if he has those parts. 

The drums are also different, presumably for 3 vs. 4 speeds (?).  They both appear to differ from the Sport 50 drum, but query whether that could be used with the Tora stopper parts.

As an alternative, does anyone have any experience and/or photos of shop-made solutions for this?

« Last Edit: March 15, 2018, 08:07:24 PM by JackA »

Offline OldSwartout

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Re: converting 50/60 transmissions
« Reply #1 on: March 16, 2018, 09:35:40 AM »
I'm not familiar with the specifics of the small bike transmissions, but on the 175, the change from rotary to return change is just whether a moveable guide pin in the 5th gear shift fork hits a stop in the groove in the shift drum.  I would think something similar could be accomplished by simply drilling and installing a stop pin in the shift drum groove for 4th gear shift fork guide pin so that the groove didn't go all the way around.  I agree that a rotary shift would be a bad idea for a road racer.

What racing organization has a class for 50cc?
Karl Swartout
Mooresville, IN
BS175 Roadracer

Offline JackA

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Re: converting 50/60 transmissions
« Reply #2 on: March 16, 2018, 06:38:34 PM »
Thanks, Karl.  I will study the parts pictures for the 175 (again, it's great to have those douments available on this site!).

The USCRA -- United States Classic Racing Association ( to be confused with the Court Reporters or the Calf Ropers) -- which currently conducts most of its races at NHMS and the Canaan Motor Club track, both in New Hampshire, has 3 classes for 50cc machines:  Classic, Super Vintage and Modern.  Craig Hirko is a member and races his Bridgestone 175 there very competitively in 200GP (while the crank holds together), and Hiroshi Murata is at least a former member, but I don't think he has been around lately.  We also cater to multiple classes of sidecars (a B'Stone 350-engined rig would be eligible...).  It's a great club!  Many members also race with AHRMA and VRRA, but neither of those has 50cc racing as far as I know.




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