Fox Doodlebug 2-Speed Conversion
- Thread starter ubernoob51
- Start date
Yes and with the Cat where you really felt the difference was going uphill. Other bikes I road with would slow or bog a bit when we hit a good hill but I’d cruise right past them. It worked well with the 4hp.
P.s. You don’t have to engage it. When you get going fast enough the secondary clutch engages and that powers the jackshaft.
P.s. You don’t have to engage it. When you get going fast enough the secondary clutch engages and that powers the jackshaft.
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Yes it does and I do still have a Comet 2 sprocket clutch for it but I think I’m going to drill and tap the crankshaft on the original h50 and use one of the max torque clutch’s I have and preserve the comet. Most guys on here don’t like set screws on clutch’s and though I’ve never had a problem with them they’re right especially with modified high rpm engines.
The two speed clutch was very innovative at the time but was replace by the torque converter. The one way bearing was the downfall because it was very susceptible to contamination and once it got dirt/sand in it then you only had low gear working because it could no longer free spin when the high gear tried to kick in.
The posting by Ginz61 is one of the best illustrations on how the two speed clutch works. I have always sent the one done by Comet to people that wanted to know how they worked but this is a much better explanation and easy to follow. Now I have to figure out how to download and save it which for an 80 year old is a real trial and error and most likely I will have my daughter help me.
The posting by Ginz61 is one of the best illustrations on how the two speed clutch works. I have always sent the one done by Comet to people that wanted to know how they worked but this is a much better explanation and easy to follow. Now I have to figure out how to download and save it which for an 80 year old is a real trial and error and most likely I will have my daughter help me.
Thank you for providing your input @Jim Donovan !
I was hoping you would.
And thanks to @Ginz61 for the correct explanation and illustration !
I was hoping you would.
And thanks to @Ginz61 for the correct explanation and illustration !
My .02 cents...
I have owned bikes with both the 2 speed set up ( a 1970 and1971 Sear's Ropers) and the torque converter set-up (Rupps, Super Bronc). Performance - wise, the former are poor compared with the latter. Those of you who have had bikes with torque converters and are now thinking about doing your first bike with a 2-speed set up will be surprised and disappointed. As Mr. Donovan has stated the 2-speeds were innovative (and cool!) for their time, however, soon became dinosaurs when the torque converters came out.
Michael
I have owned bikes with both the 2 speed set up ( a 1970 and1971 Sear's Ropers) and the torque converter set-up (Rupps, Super Bronc). Performance - wise, the former are poor compared with the latter. Those of you who have had bikes with torque converters and are now thinking about doing your first bike with a 2-speed set up will be surprised and disappointed. As Mr. Donovan has stated the 2-speeds were innovative (and cool!) for their time, however, soon became dinosaurs when the torque converters came out.
Michael
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Having owned old snowmobiles and a Honda odyssey along with a Rupp Roadster with belt drives I have to agree 100% with you. The thing is some of the older mini bike frame designs do not readily accept torque converter setups without major modifications.I test fit an imitation Comet Torque converter my older frames and it just wasn’t worth it. If I build a hot rod mini I’d definitely want a TC setup and look for a frame to accommodate it
Oh, don't get me wrong. Overall, I am not putting down the 2 speeds. I actually LIKE the old 2 speeds and enjoy riding my Sears Ropers that have them. It is fun riding around on these old technology nostalgic relics that were a part of history and how we eventually got to torque converters. The gist of my post/reply was just to prepare and provide a "head's up" to those who have displayed an interest in trying one on what to expect for performance if they have not had one before.
Michael
Michael
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My first mini in the 70’s had the comet 2 speed and once I figured it out and got everything adjusted right it worked great. I of course thought that all minis came that way. I didn’t realize that they were only on the deluxe versions and a bit rare until I needed parts. I agree with you again in that they’re cool to ride around and I like keeping them going too.
I didn’t think you were putting them down at all. Bill
I didn’t think you were putting them down at all. Bill
There are 3 PDF files showing the differences in the Comet 2-speed setup (like my Sears minibike had) and the much better Fairbanks setup.
This link is posted above, my first attempt at remembering how my Sears minibike was built. I rode it as a teen in the 1970's and was trying to illustrate from memory in my 50's.
https://www.parduebrothers.com/minibike/twospeedminibiketransmission.pdf
After more study it became evident this was a Comet setup, so this re-named and re-labeled PDF resulted:
https://www.parduebrothers.com/minibike/2speedcometdesignmminibiketransmission.pdf
The Fairbanks illustration was done last. If you are going to build a 2 speed setup today, this is the easiest and best to build.
OldMiniBikes members contributed to my knowledge, making illustration possible:
https://www.parduebrothers.com/minibike/twospeedfairbanksminibiketransmission.pdf
Now and then someone asks me how to find a one-way sprag clutch today.
You can buy a one-way bearing clutch and press it into a sprocket.
For example https://www.mcmaster.com/products/one-way-clutches/
Another example https://www.formsprag.com/products/General-Purpose-Clutches/Bearing-Envelope-Design/CSK-Series
There are #35 sprockets with one-way clutches, additional looking might turn up more results.
For example this is current in November of 2023:
https://www.daytonsuperiorproducts.com/one-way-sprocket-clutch.html
Hope that helps!
This link is posted above, my first attempt at remembering how my Sears minibike was built. I rode it as a teen in the 1970's and was trying to illustrate from memory in my 50's.
https://www.parduebrothers.com/minibike/twospeedminibiketransmission.pdf
After more study it became evident this was a Comet setup, so this re-named and re-labeled PDF resulted:
https://www.parduebrothers.com/minibike/2speedcometdesignmminibiketransmission.pdf
The Fairbanks illustration was done last. If you are going to build a 2 speed setup today, this is the easiest and best to build.
OldMiniBikes members contributed to my knowledge, making illustration possible:
https://www.parduebrothers.com/minibike/twospeedfairbanksminibiketransmission.pdf
Now and then someone asks me how to find a one-way sprag clutch today.
You can buy a one-way bearing clutch and press it into a sprocket.
For example https://www.mcmaster.com/products/one-way-clutches/
Another example https://www.formsprag.com/products/General-Purpose-Clutches/Bearing-Envelope-Design/CSK-Series
There are #35 sprockets with one-way clutches, additional looking might turn up more results.
For example this is current in November of 2023:
https://www.daytonsuperiorproducts.com/one-way-sprocket-clutch.html
Hope that helps!
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