Wardog's Balloon Tire Scratch Build - Anything Goes

#62
Ah, somebody's doing the hair raising two speed calculations. Use this chain length calculator and remember to set the proper pitch--
Sprocket Center Distance and Chain length Calculators

Here's the deal on this--you'll never get the two chains absolutely perfect AND an idler will NOT work because that extra link or two will cause one chain to start skipping cogs. What you have to do is calculate several distances center to center from the PTO to the jackshaft, then calculate chain length with the sprockets of choice. You may have to adjust your engine plate forward as a result. You want to get within 0.004 or less (with a #35 chain). See this starting at post 325 from my bike last year: https://www.oldminibikes.com/forum/...rs-lil-indian-model-600-vintage-class-33.html

Awesome project and I'm glad I caught up on this one.:thumbsup: Glad to help you if you get stumped on the chain calculations.
 
#63
War dog are you going to gusset the rear wheel arm ? Will it just be attached buy the single weld connecting the tubes together?
If left like I see it in my opinion it will eventually break , especially if hard or rough riding is done .
 
#64
War dog are you going to gusset the rear wheel arm ? Will it just be attached buy the single weld connecting the tubes together?
If left like I see it in my opinion it will eventually break , especially if hard or rough riding is done .
Yes, the plan is for another tube front and rear to provide some triangulation and also gussets...... I'm definitely not worried about frame strength.


Ah, somebody's doing the hair raising two speed calculations. Use this chain length calculator and remember to set the proper pitch--
Sprocket Center Distance and Chain length Calculators

Here's the deal on this--you'll never get the two chains absolutely perfect AND an idler will NOT work because that extra link or two will cause one chain to start skipping cogs. What you have to do is calculate several distances center to center from the PTO to the jackshaft, then calculate chain length with the sprockets of choice. You may have to adjust your engine plate forward as a result. You want to get within 0.004 or less (with a #35 chain). See this starting at post 325 from my bike last year: https://www.oldminibikes.com/forum/...rs-lil-indian-model-600-vintage-class-33.html

Awesome project and I'm glad I caught up on this one.:thumbsup: Glad to help you if you get stumped on the chain calculations.
Wow, it is really involved. Thanks for the info. I think I follow most of what you are saying except the idler not working. With a clutch on both the engine and the jackshaft they can freewheel independently from each other so it doesn't bind. I am using a regular single sprocket clutch on the engine with another sprocket instead of a dual sprocket clutch, so maybe that keeps it from binding? Anyway, mine seems to spin totally bind free with the idler installed.....
 
#65
Two speed options--

I'm not sure how you have yours set up but you do have to have two sprockets on the PTO--
See: https://www.oldminibikes.com/forum/photopost/data/500/My_version_of_a_2_speed_clutch_web.jpg

The entire thread is here: https://www.oldminibikes.com/forum/mini-bike-discussion/77596-buiding-2-speed-clutch.html

You definitely need to have a sprag sprocket on the jackshaft for the clutch on the PTO. What you presently have may spin freely now, but once both clutches lock up, it seems to me all H*LL will break loose. That's when things start jumping.

I do have a Comet 24 tooth sprag that may work but the engineered version is Black Widow's with their custom made sprag and Max Torque clutches engineered for the application (it ain't cheap but there are vendors who stock sprags in various teeth counts). If you need different sprockets for the clutches, Jim Donovan at Max Torque saved my sanity on the Lil Indian.:laugh::laugh::thumbsup::laugh::doah:
 

red baron

Active Member
#66
Wardog do you think that you'll get going fast enough to utilize that high gear? If it was a pavement pounder I'd think differently but all that rugged terrain you plan to go through. I didn't go much faster than 10mph on my XR-400 on single track, heck I had to drag the bike over fallen trees etc..
 
#67
Wardog do you think that you'll get going fast enough to utilize that high gear? If it was a pavement pounder I'd think differently but all that rugged terrain you plan to go through. I didn't go much faster than 10mph on my XR-400 on single track, heck I had to drag the bike over fallen trees etc..
Probably won't get going very fast, which is why I'm gearing it down so low. With the current 72 tooth sprocket at the wheel and the 1500 rpm spring in the jackshaft clutch it will shift into second at about 12 mph and top out at 30 mph at 5000 rpm. I still feel that this is a little faster than the 79cc will push it, so I am considering an 80 or even 96 tooth rear sprocket. With a 96 tooth at the rear wheel it will shift into second at about 9 mph and top out at 23 mph at 5000 rpm. I found an 80 tooth on Amazon for $25, but the 96 is $50.... Anyone know where to get a cheap 96ish tooth sprocket?
 
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red baron

Active Member
#69
when I was building motorized bicycles there was a business used to advertise on the board called King's that made custom sprockets for cheap. I haven't been on those boards in years so I have no ideas if they're still around
 
#70
Probably won't get going very fast, which is why I'm gearing it down so low. With the current 72 tooth sprocket at the wheel and the 1500 rpm spring in the jackshaft clutch it will shift into second at about 12 mph and top out at 30 mph at 5000 rpm. I still feel that this is a little faster than the 79cc will push it, so I am considering an 80 or even 96 tooth rear sprocket. With a 96 tooth at the rear wheel it will shift into second at about 9 mph and top out at 23 mph at 5000 rpm. I found an 80 tooth on Amazon for $25, but the 96 is $50.... Anyone know where to get a cheap 96ish tooth sprocket?
Am I reading you're going to run that 79 cc engine to 5k? Wow. I'm not sure it'll last long at sustained high rpm. I'd be thinking 36-3800 and gear accordingly. You're going to need some serious low gearing to get those big tires moving and shifting up at 1500 rpm is probably too low--2000 or a little higher might be a better place to upshift. Just my thoughts--the project is great and I definitely want so see you successful.:thumbsup:
 
#71
Am I reading you're going to run that 79 cc engine to 5k? Wow. I'm not sure it'll last long at sustained high rpm. I'd be thinking 36-3800 and gear accordingly. You're going to need some serious low gearing to get those big tires moving and shifting up at 1500 rpm is probably too low--2000 or a little higher might be a better place to upshift. Just my thoughts--the project is great and I definitely want so see you successful.:thumbsup:
Maybe you are right in that sustained 5k rpm might be too much for the 79cc. After all, it doesn't even have bearings on the connecting rod, just aluminum on steel :doah:. An 84 tooth sprocket would put me at 20 mph at 3800 rpm which is a little more reasonable. The high gear clutch engages at 1500 jackshaft rpm which because of the first gear reduction is about 3300 engine rpm.

I want this bike to be able to drag my big ass up a steep hill and I'm willing to sacrifice top speed for torque.
 
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#72
Maybe you are right in that sustained 5k rpm might be too much for the 79cc. After all, it doesn't even have bearings on the connecting rod, just aluminum on steel :doah:. An 84 tooth sprocket would put me at 20 mph at 3800 rpm which is a little more reasonable. The high gear clutch engages at 1500 jackshaft rpm which because of the first gear reduction is about 3300 engine rpm.

I want this bike to be able to drag my big ass up a steep hill and I'm willing to sacrifice top speed for torque.
Absolutely...My 3hp Lil Indian hauled my butt pretty well after shifting up. :thumbsup:
 
#79
Hands down this has to be one of the most creative and well executed mini bike builds I've ever seen.

Excellent work and would love to see it in action!
 
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