Simple Question ?

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Philip Justice

New Member
Nov 14, 2014
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East Coast Florida
Phil Here, My first build is in the planing stage right now. I have already purchased a HF 79cc engine that I am mounting vertical in a custom BTR loop frame. I would like to keep my drive set up quite simple, I am not looking for speed or long range driving. My questions are:

Can I run a Centrifugal clutch on my 4 stroke directly to a Rear sprocket, using a chain like the 2 stroke engines do?

Can I run a Centrifugal clutch on my 4 stroke directly to a rear sheave using a belt drive?

As you can see I am trying not to have to build or buy any type of jack shaft.
I don't understand the need for Jack shafts anyway?

If the solution is not simple for me than I might pack up the 79 cc 4 stroke and return it to HF. I will than purchase a Good 2 stroke that will be able to install with a simple drive set up.

I am reluctant to do that because the HF engine is so nice and also good looking. The 2 strokes look so puny sitting in a nice loop frame.

I hope someone will chime in on my problem, I have a engine and I am picking up my custom frame tomorrow from the welder, after that I am at a stand still.

Thanks in advance Phil Justice [email protected]
 
Mike B

Mike B

New Member
Mar 23, 2011
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Central CA
You could do it with a belt and a centrifugal clutch, but you need 10-12 : 1 reduction. With a 2 inch clutch pulley, the sheave will need to be 20-24 inches.

Some builders use a rim. It can be done and it looks clean & awesome like the old machines.
 
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Imthegrt1

New Member
Nov 8, 2014
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USA
Most the times a jackshaft is used because when the motor is center. The shafts to far out for the chain to go to the rear.
So jackshaft is needed or you have to moth ur motor over no the side for the shaft to line up.which now ur bike weight sits of sides.
 
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Philip Justice

New Member
Nov 14, 2014
10
0
0
East Coast Florida
Re: Simple Question answered.

Phil Here. Thank you guys for your quick and informative replies. Now I know why we need Jack shafts. Now Jack shafts would be my last ideal set up.

The Bike that I am building is a retro of a early 1900's BTR, so a 'Belt drive setup would be apprepoe to that era type bike.

Well now maybe Mike B can help with other questions pertaining to this belt build?

Parts supplier and location of a Centrifical Clutch with a 5/8 shaft belt pully of the right size, also the best way obtain and mount a 22-24" sheave to my rear 26"wheel.[ I have seen the on Ebay ] I have noticed in old photo's that the pully belt seems to be made out of "leather" I am wondering if this is a option [would look cool] or would have to settle for a rubber belt?

Another question would be how to get a belt size to match the distace between the Pully and the Sheave? I'm sorry for all the questions, I am a very old Dude and I have to farm out all the welding and mecanical work on this bike.

I am building this bike to carry on the back of Motohome, I'll have a differant mode of transportation to ride around the camp grounds.

Thanks again for the info and looking to have these other questions answered

Phil Justice
 
Ludwig II

Ludwig II

Well-Known Member
Jul 17, 2012
5,071
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UK
I have a question. Do you want the drive to at least appear to come off the engine shaft?
 
Ludwig II

Ludwig II

Well-Known Member
Jul 17, 2012
5,071
783
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UK
This is thinking out loud, on the fly.

There was a recent discussion on toothed belt drives. The manufacturers have tables relating to the width and sprocket diameter required to transmit a given amount of power. If you can tolerate a wide enough belt, you might be able to get down to a small enough engine sprocket diameter to achieve a good amount of reduction. I don't know, I've never done toothed belts. The pulley on the back wheel won't need teeth, as it will have a lot of area for the belt to run on.
 
Mike B

Mike B

New Member
Mar 23, 2011
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As I said, you can use a bicycle wheel rim to make the sheave. How you attach it I haven't a clue. Some people cut slots, some rivit brackets to the wheel spokes. I've never done it, I dunno.

But I have seen it done and done here. You will need to search to find it.

After you build it and install it you can wrap a tape measure around it all and measure it.

Good luck!
 
Ludwig II

Ludwig II

Well-Known Member
Jul 17, 2012
5,071
783
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UK
The other thing that comes to mind is to use a small output gear inside a bigger internally toothed gear. This means the rotational speed of that gear is slower than the crankshaft. A pulley of smaller diameter can sit on one face of that gear, and then the drive can go to the back wheel.

What about a planetary gear arrangement, either at the engine end, or as a reduction drive in the rear hub? Several early bikes used that.
 
cannonball2

cannonball2

Well-Known Member
Oct 28, 2010
3,682
221
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Colonial Coast USA.
I have seen builds from ages ago where they welded/brazed a matching size rim to the rear wheel. It certainly provided a low enough ratio for direct drive.
 
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Philip Justice

New Member
Nov 14, 2014
10
0
0
East Coast Florida
Phil Here

I think I have got it together for my BTR Belt drive, Thanks for lending hand.
I have located a 3.20 Pulley Clutch for a 5/8 engine shaft, I will secure a 22 or 24" Sheave to my rear wheel and build a Belt tension system. My build will have no bicycle peddles and the HF 79cc is pull start. I will try to post the Belt Pulley Clutch. Thanks again................................
 

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