Building a mini from scratch

S

stevinator

New Member
#121
#121
ByB I followed your thread and really like what you came up with.I would like to try some thing similar and have been gathering parts.Or junk according to the wife.I understand the belt and pulley drive because of a tractor I have but do you think a centrifugal clutch pulley on the engine shaft with just a belt to the rear would work ok too.I see they have them just like the sprocket-chain type.I didn't know if you did it if you could get away with the tensioner or not.My old tractor is setup from the motor to a pulley on the 3 speed trans like your mini with a foot operated idler except no jackshaft of course.
 
Last edited:
Oldsalt

Oldsalt

Well-Known Member
#122
#122
It would be difficut to make a belt drive work if just a clutch with pulley was driving a larger pulley on the rear wheel. Without a jack shaft the driven pulley would have to be bigger in diameter than most mini bike wheels to get a useable gear ratio. A common clutch that has a #35 chain sprocket has [usually] 12 teeth. To get a 6 to 1 gear ratio [without a jack shaft] it is generally necessary to use a 72 tooth sprocket at the rear tire. 72 divide by 12 = 6. If a 60 tooth sprocket is used at the rear the ratio would be 5 to 1. Five to one is sorta tall unless you are light and got a lot more than, say, 3.5 HP. I don't know what the "pitch diameter" is on a belt-clutch but I'd guess it to be about 2.0 inches. To get a 6 to 1 ratio a pulley with a 12 inch pitch diameter would be necessary at the rear tire.

I have also been looking at a belt drive set-up for a mini, but I have come to the conclusion that some sort of jack-shaft arraingement will be necessary. Pulleys are more expensive than #35 sprockets.
 
Backyard Builder

Backyard Builder

New Member
#124
#124
I did try this bike without a jackshaft at first, but the engine just didn't have enough torque.

But with a gigantic engine (8hp or more) I think it would be possible. As Oldsalt said, it all depends on how big a pulley you can fit on the rear wheel.
 
S

stevinator

New Member
#125
#125
When you first tried it though you didn't have the clutch type pulley did you? Was it just the pulley on the crankshaft like my little tractor?I thought a centrifugal clutch pulley might help the motor get some steam up.But Old salt is probably right.I just wondered if you had tried that.
 
dave dickson

dave dickson

New Member
#126
#126
Personally, I know a belt set up on a mini is a waste of time, back in the days of childhood, we was playing with the idea, using a belt centrifugal clutch to a big pulley on a jackshaft, from the jackshaft, a small 35 chain pulley to a big pulley on the wheel, now how many mini's after a few rough trails, and races start to leak oil? most will, just a little oil on rubber belt and you have a smokey mess, a slippery belt, a slow bike:thumbdown: I really like the 41 chain with like a 40 something tooth sprocket, got one for my go-cart, and I will be putting a set up like that on my bananza, haven't tried it with the 6.5 yet, but I know my 5 hp briggs scared the %$#@ out of me with this set up, no way would I waste my money on a belt set up, and if someone does here's a better ideal, go to your bathroom, take your money out of your wallet, throw it in the toilet and flush, at least you won't be wasting your time!!!! just my thoughts!!
dave
 
S

stevinator

New Member
#127
#127
Yeah you guys are right I was just curious.I'm always messin with something so I wondered in case I decided to make one out of weird parts or something.I keep getting garden tractors following me home instead of fun stuff.:eek:hmy:
 
5

5hpbriggs

New Member
#130
#130
Backyard Builder,
Got a couple questions for you. I am intrested in the build and I am currently in the proccess of gathering parts for a project like this one.

1. Would pillow block bearings work for this? Rear Axle and Front?
 
You must log in or register to reply here.
Top