Help keeping the chain on my sprocket

[5-7HEAVEN]

Here's what happens if you use a 10t sprocket and a 30t sprocket.

a 30t divided by 13t engine sprocket gives you 2.31:1.

your 36t rear sprocket divided by 10t equals 3.6:1.

and 2.31 X 3.6 = 8.32:1. divide that by 4.1 happy time, and it's like having a 20t rear sprocket.

now your clutch burns out before 15mph with a screaming engine, and a 12-year-old girl outruns your bike in a 50-yard dash.

Actually Steve, you need at least a 42t sprocket, if ya wanted just one jackshaft. that is, if you can use an 8t sprocket to link with your 36t rear sprocket.

so 42t jackshaft divided by 13t engine sprocket = 3.23:1.

and 36t rear sprocket linked to 8t sprocket = 4.5:1.

3.23 X 4.5 = 14.535. divide this by happy time gear reduction of 4.1 gets you 35.45, or a 35t rear sprocket on a happy time engine.

the bike will be fast, and the engine is at redline 8500rpm @ 41mph.you MIGHT have trouble climbing steep hills with the 42t sprocket, and may have to swap in a LARGER jackshaft sprocket.

a 48t jackshaft sprocket yields 16.62:1, or a happy time and 41t rear sprocket.

Of course you won't find any 36t-48t sprockets that slip onto the jackshaft. you can't afford the machine work, so you'd be welding bicycle crank sprockets onto the jackshaft.

so there you have it. use 2 jackshafts with smaller sprockets, or one jackshaft with a sprocket the size of happy time rear sprocket.

for 2 jackshafts and easily-available sprockets, use 18t to engine sprocket, 8t to 18t on the second shaft, then 8t to 36t bike sprocket. that's good for14.02:1, like a happy time engine and 34t rear sprocket.

your foolish mistake was welding that 13t sprocket onto your engine, without considering how to attain effective gear reduction. being unable to downsize your engine sprocket limits your gear selections, and necessitates two jackshafts or one huge jackshaft sprocket. if you were able to install an 8t engine sprocket, then a 26t jackshaft sprocket could be used, instead of that 42t jackshaft sprocket.

if you weld in your jackshaft supports, then pivot your engine carrier and make threaded adjustments on your support arms to the rear axle frame dropout. this is to maintain proper tension between rear sprocket and the 8t jackshaft sprocket.

THEN be sure your engine mount is adjustable. this is to maintain proper tension between 13t engine sprocket and 42t jackshaft sprocket.

there is no cheap and easy fix, but then that's what you get for being hardheaded in the beginning of your project.

Myron

 

[MisterSteve124]

Ok I understand it now that I looked at all the math in your previous posts. I'm going to order 2 jackshafts tonight. I just have one more question. I assume having a higher gear ratio like 16:1 opposed to 14:1 makes the speed of the bike slower but it has more power, right? Right now I can't find any 22tooth sprockets for the jackshaft so I am just planning on using 20, unless I can find a 22. By looking at what srdavo posted with his chainsaw and a gearing of 24.9:1 and still with a top speed of 37mph for my case the higher gear ratio for me the better. Since the only difference is my chainsaw is 42cc and his is 36cc. So in that case by my math (feel free to correct me):

20tooth / 13tooth(engine)= 1.69230....

20tooth / 8tooth= 2.5

36(rear sprocket) / 8tooth= 4.5

Multiply those 3 together and i get 17.308.....:1 which seems like it would be great! Now if any of this seems wrong feel free to correct me before I buy my jackshafts and sprockets later tonight or tomorrow. Now 2 more questions that I hope you guys can answer. What size chain do you think I should get for the sprockets #35 or #40/41. Obviously I need to do some measuring to find out what size I need for the ones being connected to the engine and rear sprocket but what about the others. Thanks a lot guys you have been so much help and now I am looking forward to finishing it! Hey atleast I learned something in the process, thanks to all you guys. And thanks Myron for helping me out with all the gear ratio calculations and more.

P.S. Does anyone know what size a typical mountainbike chain is, I'm gonna try and measure but just wanted to be sure.

Update: Just measured the chain and I have a question for roller width is that the width of the actual roller or of just the chain? Because my chain roller width is like 1/8" and #35 and #41/40 are 3/16" and 5/16". If so then I may need to use an angle grinder and just grind down the tips of the teeth so they are a tiny bit skinnier. I hope I won't

 

[5-7HEAVEN]

Steve, 17.308:1 is correct, and comparable to happy time and 42t sprocket. you should have great low-end.

engine rpm of 8500rpm at 39.1mph on your 26" bike.

when you replace a 22t sprocket with a 20t in the formula, you need to recalculate your other sprocket choices. believe it or not, two teeth make a big difference.

it may not seem logical, but the higher the gear ratio number, the "lower" the gearing. so 16:1 is a "lower" gear ratio than 14:1.

whenever possible, take your sprocket and chain with you for "show and tell" to the shops you visit. or take pictures, which are worth a thousand words.

it'd be nice if all the gears and sprockets use the same chain. however, if cannot, just match rear sprocket and 8t sprocket, 13t engine sprocket and 20t, 8t to 8t sprocket.

good luck, Steve. calculate on paper before buying.

Myron

 

[MisterSteve124]

Ok well the only problem I found is I need a #40/41 sprocket so that it will fit the bike chain and they don't have 18t #40/41 sprockets, they just have 17 so then I would have the 13 tooth drive sprocket 17 tooth, 8 tooth, 20 tooth, 8 tooth, 36 tooth rear sprocket. So that's a 14.7 gear ratio. I know it's not 16.8:1 but it's better than 2.76:1. Will it still work? And should they sell #35 chain nearby? At some shop? I don't want to have to order that online too.

 

[Alaskavan]

Hi Steve, looks like you're getting it down. I may be wrong, but I think 14.7 should work fine.

 

[5-7HEAVEN]

Steve, depending on the hills around you, this will work well for speed.

a 14.7:1 ratio is happy time with 36t sprocket.

at 8500rpm, speed of 46mph.

Myron

 

[MisterSteve124]

Ok I wish I could get a Lower gear ratio but I just don't see any way of doing it right now. Maybe later down the road I can try and get a bigger gear for one of the sides to give it some more hill climbing power. And the engine's max rpm is over 10,00 I think it's somewhere between 10,000 and 12,000 I don't think I'll go over 40mph anyways.

 

[5-7HEAVEN]

Steve, at what rpm is your max hp?

at what rpm is your max torque?

you need these stats BEFORE you choose your sprockets! i was calculating using my 8500rpm engine. if you intend to utilize max hp at a sensible mph, then you have to RECALCULATE!! taking maximum rpm range of....

what is max? 10,000rpm or 12,000rpm?

don't buy ANYTHING until you discover where max hp occurs at what rpm.

do more research! if you were to build your jackshafts on the sprockets we've discussed, you'll still be burning clutches, and kids on BMX bikes will be smoking you.

i'm not helping you anymore until you research your engine stats.

Myron

 

[japat100]

i would be temped to go with a belt from the motor to the jack shaft ,, pulleys are easy to get and all sizes ,and cheap and easy to replace belts ,and very smooth running at high speed ,and coming off the motor will be high speed ,, you could gain 4 to 1 on one jack shaft and another 4 to 1 on the main drive with a chain ,that would give you 16 to 1 on one jack shaft , as far as the weld goes on the clutch to remove the sprocket or weld a pulley on not a big deal ,
there must be some other members that tried belt and chain combo.,,,, hope they will pass on there opinion to help you out ,,


japat

 

[MisterSteve124]

Ok this whole project is not worth it I'm officially done. Anyone want a chainsaw?