71 Rupp Roadster Torque Converter Question

#1
I have a 71 Rupp Roadster 2 roller frame. I have just about everything to make it move except the torque converter. I know it takes a 20 series torque converter.

Will any comet torque converter with a 1" secondary and 3/4" primary work?
 

cfh

Well-Known Member
#6
i've heard you can put a series30 on a 1970s rupp. personally i always run the stock TC1 torque converter. but if a series30 could be implemented without modification and using the original TC1 black cover, that would be pretty cool. probably a good upgrade. the series30 units are a lot cheaper and frankly i like how they perform compared to series20 units.

by the way the driven rupp side jackshaft is 5/8" on the rupp, like nearly all torque converter mini bikes use. at least that's what i remember. and obviously the drive side on the motor is 3/4"
 

f4radar

Well-Known Member
#7
i've heard you can put a series30 on a 1970s rupp. personally i always run the stock TC1 torque converter. but if a series30 could be implemented without modification and using the original TC1 black cover, that would be pretty cool. probably a good upgrade. the series30 units are a lot cheaper and frankly i like how they perform compared to series20 units.

by the way the driven rupp side jackshaft is 5/8" on the rupp, like nearly all torque converter mini bikes use. at least that's what i remember. and obviously the drive side on the motor is 3/4"
I wanted to try the 30 series because I’m cheap and so are they. It looked to me like the 30 series driven would need to be flipped to keep the flat side of the belt to the inside. I’d need a longer jackshaft and spacer to get the driven to lineup. Maybe you could make up some of that by moving the motor right using the slots on the mount plate.
 

cfh

Well-Known Member
#8
you can't flip a series30. the whole point of a series20 is it expands inward. likewise the whole point of a series30 is it expands outward. it has to match the drive portion. series30 drive is flat towards the motor. so the driven has to expand outward, away from the motor. series20 works opposite. also series20 is symmetric where series30 is asymmetric. Series30 has better engagement (quicker) so it tends to wheelie off the throttle. More violent take offs. also series30 has overdrive. series20 is smoother takeoff. but series30 is more efficient, more motor power transferred to the torque converter.

but i have heard you can use a series30 on a rupp. and yes you'll probably have to make a custom jackshaft for that to work. which frankly isn't that difficult. i just have not tried this.

you can get reasonably priced series20 clones here... my understanding is that a comet clone series20 system will bolt right on a rupp without modification. but i have not tried it. this is a 3/4" belt comet series20. so you'll need a different belt than the stock rupp 5/8" belt. unfortunately i do not know the 3/4" series20 belt number.
https://www.vmcchineseparts.com/col...4-bore-for-go-karts-and-mini-bikes-version-70
https://www.vmcchineseparts.com/col...5-8-bore-torque-converter-go-karts-mini-bikes
 
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#9
i've heard you can put a series30 on a 1970s rupp. personally i always run the stock TC1 torque converter. but if a series30 could be implemented without modification and using the original TC1 black cover, that would be pretty cool. probably a good upgrade. the series30 units are a lot cheaper and frankly i like how they perform compared to series20 units.

by the way the driven rupp side jackshaft is 5/8" on the rupp, like nearly all torque converter mini bikes use. at least that's what i remember. and obviously the drive side on the motor is 3/4"

You are correct it is 3/4" on the jack shaft I'm not sure what I was thinking
 
#12
I do not want to disagree with anybody here. Especially any of the highly respected and knowledgeable experts on the vintage stuff.....BUT...
I have on my desk a 6 inch asymmetrical driver that says COMET Richmond Indiana and the number 20 on the front. The flat side is stationary, the beveled side moves. It looks like it will take a 5/8 asymmetrical belt, and it came off of a 5/8 shaft.
If your jackshaft is 5/8, not 3/4, you are welcome to this part. I will never use it.
I plan to put it in the classified section on Wednesday if it's still here.
I am sure this one did not come on a Rupp.
 
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f4radar

Well-Known Member
#13
I do not want to disagree with anybody here. Especially any of the highly respected and knowledgeable experts on the vintage stuff.....BUT...
I have on my desk a 6 inch asymmetrical driver that says COMET Richmond Indiana and the number 20 on the front. The flat side is stationary, the beveled side moves. It looks like it will take a 5/8 asymmetrical belt, and it came off of a 5/8 shaft.
If your jackshaft is 5/8, not 3/4, you are welcome to this part. I will never use it.
I plan to put it in the classified section on Wednesday if it's still here.
I am sure this one did not come on a Rupp.
I might be getting lost here but it sounds like you have a 6" driven (not a driver) that fits the 5/8 jack shaft.
 
#15
Dodgecharger -- did you get the driver and driven you needed? Was your engine crankshaft size 3/4" or 5/8" ? Still talking about the series 20 which is the only one we made. Our driven was 7" since the market we went after was go karts, mini-bikes were no longer in production back in 1996 in the US.
 
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