1970 Rupp Torque Converter replacement please

longlongtimeago

longlongtimeago

Member
#1
#1
It's has been slow at work so yesterday I finally started to assemble this 70 Scrambler basket case [big order to Black Widow]

I know this has been asked and answered but before I order more parts, I figured it wouldn't hurt to confirm...

'70 Rupp Scrambler, using hssk40 for an engine.

I don't have the driver portion of the TC. Still have the original driven... I think I read a Comet 20 was the best choice if I just wanted to replace the driver. Yes? What will I use for a belt? Anybody have a part number?

Any modifications I will need to make?
Will the Rupp Plastic belt guard fit ok?

Can I get away with the cheapo '20 series' converters off ebay?

Thanks for all the great help I have already received from you fellas....
 

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E

ELT

Active Member
#3
#3
I have tried to make a comet clutch work with the oem rupp secondary clutch and have never had any success. The rupp secondary doesn't have a strong enough spring in it to backshift correctly. I would like to know a way to make the comet work myself.
 
C

cfh

Well-Known Member
#4
#4
You can read all about this conversion, and the pitfalls involved, here:
http://www.pinrepair.com/minibikes/ruppinfo.htm#tc1
unfortunately there are some pitfalls, especially if you are using the series20 clone driver. But the biggest pitfall is the comet/clone uses a smaller brass idler. this means the rupp belt Gates 6061 for 1971-1975 models is too big to work really well. There is a solution... i am working on it... but it will be a couple weeks before i publish it (i'm still testing the concept, and it's winter here, meaning it hard to find time for good testing.)

and yes the stock rupp clutch cover works fine with a comet/clone.
 
colt 1911

colt 1911

Active Member
#5
#5
longlongtimeago said:
It's has been slow at work so yesterday I finally started to assemble this 70 Scrambler basket case [big order to Black Widow]

I know this has been asked and answered but before I order more parts, I figured it wouldn't hurt to confirm...

'70 Rupp Scrambler, using hssk40 for an engine.

I don't have the driver portion of the TC. Still have the original driven... I think I read a Comet 20 was the best choice if I just wanted to replace the driver. Yes? What will I use for a belt? Anybody have a part number?

Any modifications I will need to make?
Will the Rupp Plastic belt guard fit ok?

Can I get away with the cheapo '20 series' converters off ebay?

Thanks for all the great help I have already received from you fellas....
Click to expand...
use a comet 20 driver from china for $45. the cover will fit fine. the belt length will vary but it will be 5/8 inch wide. the comet uses a 3/4 inch so the 5/8 will help with early engagement if you have the engine idle a little higher then stock. you measure center to center between the driver and driven to use the chart. you should find a belt on ebay for around $15. the vendor for the clutch has been rock solid in the past for me. good luck.
 

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delray

delray

Well-Known Member
#6
#6
if a guy could still find a tc88 driver...big if. would that be a better choice replacement unit? belt length might be different in size still because the bronze/oil bushing would be smaller then a rupp or just machine a new bushing to the correct size?
or can a guy just modify a 20 to only open up to a 5/8 width? like a tc88 unit.
 
C

cfh

Well-Known Member
#7
#7
again refer to http://www.pinrepair.com/minibikes/ruppinfo.htm#tc1 discuss this exact issue with a 5/8 versus 3/4 belt. Also alignment issues with the clone driver to the original rupp driven. and belt considerations. there is no belt smaller than the rupp/Gates. None of the comet 5/8 (or 3/4) belts really support this set up. Now on a 1970 Rupp, this is not an issue (because the motor is in a different spot, compared to the 1971-1975 rupps.)
 
C

cfh

Well-Known Member
#9
#9
Yeah but you replace both the driver and the driven so you got a matched set. That is the optimal thing to do. You also went with the 3/4 inch belt which again is a good thing. But some people want to use the original Rupp driven, and that’s where you get problems, mixing it with a comet/clone driver.

When you installed this set up did you have to make a new jack shaft for the driven side? Or did it just bolt right on without any modifications to the original rupp jack shaft?
 
Skipp

Skipp

#12
#12
I personally found that with any type of modification to the motor the stock torque converter slipped way too much...made riding a chore and not fun..even mixing them was not beneficial to me...MAY work for you...but with the set up I have, albeit not stock by any means, it does make for a real sweet rider and that is what it is truly about right??
 
delray

delray

Well-Known Member
#13
#13
Skipp said:
Works awesome...but I’d buy a comet....not china crap...screams down the road View attachment 255968
Click to expand...
skip I am assuming with the driven flip around you have a 20 series on it.
i would think if a guy had to replace your stock rupp driver with a 20 series modified? at that point you might as well replace the driven with a comet like skipp did. not like you going to go bank up with the new setup and just replacing the driver at that point it's not original anymore. so if your trying to keep it original? thats out the door.
i'm not a real big fan of the 20's or 30 series, in this case where it's being use on a low rpm motor and low HP motor too and a heavy aluminum flywheel. i would think it would work good.
 
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