Rupp belt, why is this so hard?

#1
OK fellas, this must have already been done and discussed 1000 time before but I,so far , have not found the correct answer,

1970 Scrambler with a knock off Comet 20 driver and the stock Rupp driven.

I have a 200421 comet belt which had bee recommended more than once and it is too long. I don't know how too long it is but I know at idle it rests on the foot pegs.
If you grab the belt and pull it all the forward there is all of an inch between the belt and the bushing on the TC.

current specs are 5/8 x 29 9/32
I know the orig bet was 3/4.

I have found no resource that lists belts by length which would make things easier.

These belts are too expensive to attack this by trial and error.

What is the answer fellas?

Secondly, how do you make this Comet 20 clone engage at a lower RPM. This has to be a 75% throttle before the outer sleeve begins to move inward [engage]
 

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cfh

Active Member
#2
Use this web page. you want the TC88 belt. i will double check my 1970 roadster and see how it measures up too.
https://www.gokartsupply.com/tcbelts.htm

The 200421A belt shows a distance of 7 9/16" to 7 5/8" center to center from the Drive to the Driven. That's the belt recommended for 1970 Rupps. But perhaps that is incorrect. i will measure mine tonight and check against the info on the above web page.
 
#4
Use this web page. you want the TC88 belt. i will double check my 1970 roadster and see how it measures up too.
https://www.gokartsupply.com/tcbelts.htm

The 200421A belt shows a distance of 7 9/16" to 7 5/8" center to center from the Drive to the Driven. That's the belt recommended for 1970 Rupps. But perhaps that is incorrect. i will measure mine tonight and check against the info on the above web page.
I have the 200421 belt, too long for sure. But I looked at the chart you referenced and found the same info you posted, here is the rub, I have a 6 inch driven and center to center is 7 3/4 , by that the 200421 could actually be too SHORT! But it's not too short...looks to be an inch or better too long. Why is this so hard?

Any input appreciated.
 

cfh

Active Member
#9
yea it does look like you have a mix of 5/8" and 3/4" belt driven/driver situation. that probably won't work well. but you can modify the 3/4" belt driver and make it work with the 5/8" belt.
 
#11
OK, here is what I have learned, the driven portion of the TC was FROZEN partially 'open' causing the belt to sit waaaaaaay too deep in the 'V' [Please remember I have nothing to reference this to, I don't know what is right or wrong] So I freed up the driven and now the belt sits much higher in the V and the belt seems to fit way better. Still too long but worth another try.

HERE is a new question, how easily should spring in the driven portion of the TC collapse. Now that I have it freed up I'm almost shocked how little pressure it takes to move the inner portion of the driven TC in and out. Is that correct?
 
#12
OK I kinda just figured this out, there is supposed to be preload on the spring on the driven portion. I'm assuming it's a quarter turn but I'd love it someone told me the correct amount....
 

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