20 Series Torque Converter Replacement

[Kartman01]

I have a vintage Terra minibike I am restoring and the original primary and secondary belt drive clutches are beyond saving.

The bike originally used the equivalent of a 20 series clutch (Fairbanks Morse primary and 6" Horstman secondary) and I would like to stick
with that general set up - not the least of which, the room for everything is super tight!

The engine is a 3.5 Tecumseh with a 3/4" shaft that is approx 2.97" long and tapped for a 3/8" fine thread bolt. The secondary goes on a 5/8" dia
jackshaft.

My question: what would be the best 20 series primary/secondary set up I can purchase new for this particular type of minibike?

Are there any good options for 20 series belt drive setups that I might be able to find in good/used condition?

Thanks for any help!

 

[cfh]

Original 50 year old Torque converters are hard to find. Not worth the trouble in my eye. I use standard replacements today which work very well, and are fairly inexpensive. Also they use a 3/4" belt (instead of 5/8"), so everything lasts longer. Torque converter series 20 is harder to find than series 30, but this is where I get them...

Series20 Drive (3/4"):
https://www.vmcchineseparts.com/pro...4-bore-for-go-karts-and-mini-bikes-version-70
Series20 Driven: (6" diam 5/8" bore):
https://www.vmcchineseparts.com/pro...5-8-bore-torque-converter-go-karts-mini-bikes

 

[Kartman01]

Thanks CFH, much appreciated!

I actually purchased a 20 series torque converter from VMC, but when I received it I discovered the bolt to mount it to the crank was
5/16" and my crank takes a 3/8" bolt. There is not enough material to safely bore the VMC torque converter to accept a 3/8" mounting
bolt.

Do you have any other recommendations? Thanks!

Original 50 year old Torque converters are hard to find. Not worth the trouble in my eye. I use standard replacements today which work very well, and are fairly inexpensive. Also they use a 3/4" belt (instead of 5/8"), so everything lasts longer. Torque converter series 20 is harder to find than series 30, but this is where I get them...

Series20 Drive (3/4"):
https://www.vmcchineseparts.com/pro...4-bore-for-go-karts-and-mini-bikes-version-70
Series20 Driven: (6" diam 5/8" bore):
https://www.vmcchineseparts.com/pro...5-8-bore-torque-converter-go-karts-mini-bikes

 

[cfh]

Yeah I’m sorry you’re wrong on this. I do this all the time without issue. And all my Tecumseh motors have 2 1/4 inch long PTO with either 5/16 24 or 3/8 24 drilled and tapped

 

[Kartman01]

Yeah I’m sorry you’re wrong on this. I do this all the time without issue. And all my Tecumseh motors have 2 1/4 inch long PTO with either 5/16 24 or 3/8 24 drilled and tapped

Thanks CFH, help me understand exactly where I am wrong? Is it possible to order a primary configured to take a 3/8” bolt?

Thanks

 

[cfh]

I guess i don't understand what the issue is here. Again, i've done this *exact* replacement probably 40 times. I have about 50 bikes, and damn near all of them are series20 torque converters. And all of them are Tecumseh HS50 (a few HS40) motors. All motors have a 3/4" diameter PTO (2 1/4" length), with newer HS50 engine PTO tapped with 3/8-24, and older motors have PTO tapped for 5/16-24. But either works fine. it makes no different. what is the problem? are you talking about the black shoulder washer? that may be drilled for 5/16 but you can open it up with a 3/8" bit. Or hell, just don't use it at all!