Briggs and Stratton build, jackshaft ideas

Cannonball 2 is your man for belt drives. Have a scroll down here, there are a couple of interesting constructions of his that will show you ways to do it.

Belts are handy, you can go through 90 degrees with them with no trouble, and slim the bike right down. Read through this and see.

http://motorbicycling.com/showthread.php?t=57197

Welcome Milo

You might be looking for the older style Whizzer design:

Manual Clutch-Fits Cruzzer, Whizzer
http://www.ebay.com/itm/Manual-Clut...ash=item25a71c0417:g:A2IAAOSwDk5TxYYc&vxp=mtr

You are welcome. Glad to help. A few links of this design (also called Slipper) in action:

Whizzer Moped 1948 Vintage
https://www.youtube.com/watch?x-yt-...ts=1421828030&feature=player_detailpage#t=190

Whizzer 138cc beltdrive from 1950 in first paint
https://www.youtube.com/watch?v=jPWQajZF1mA

1953 Schwinn DX with J model whizzer engine
https://www.youtube.com/watch?v=Vv-y8fKuRt4

Heres a pic of a jackshaft I fabbed on a build similar to a B&S. Uses lock collars to mount it to the frame making it very adjustable. Very easy to make but does require welding. One could fab the parts and have it welded fairly cheaply. This build uses an idler clutch, but a centrifugal clutch could be used. The belt had enough grab to start the 5hp Robin engine. Unfortunately the rear hub wasn't up to the task so rope starting had to be used. If you wanted to go all belt you could use a Whizzer rear pulley that bolts to the spokes. I did that on another build.

This build started with a very similar frame to yours, that had to be stretched to accommodate the larger engine. http://motorbicycling.com/showpost.php?p=389145&postcount=66

I just want to add that in wet conditions if the belt gets wet it will slip a bit till it spins off and drys. When dry still under a lot of torque it may slip if using the regular 4L A section belt, like I built from washing machine pulley.

I had the white metal washing machine pulley unlike 40 years ago when they were pressed stamped steel, they crack if put under too much stress. I resorted to a Whizzer type clone sheave for around 50 bucks made over seas. It needed sanding down the sharp ridge where weld seam was not so nice, but still OK.

Something else, just maybe me in preference is I do not like the threads that are provided in the sheave clamps of some of these. The screws are fine, but to keep from falling out they have deformed bottom threads.

I drilled the threads out and use screw with nylon locking nut and split lock washer. It was prior when I was trying to disassemble the sheave to put on another wheel, taking them out they cross threaded and jammed.

I also opted for stainless steel hardware, but the sheave will rust as the chrome is not very much going to stay put.

You can spend maybe 3 times as much for a more expensive sheave if you want belt drive, but I'm happy with it. Have a way to set tension on the belt, idler, or what ever as belts will stretch and you can only have so many increments of belt sizes.

Very important for less slippage is don't have a pulley anywhere in the drive train that is much less than 3 inches. They may say 2 inches, but they really slip and heat the belt cogged or not.

MT

There's a very old trick as well from the original belt drive days. I don't know what the American term would be, but old time riders here would carry a packet of Fuller's Earth (presumably some sort of absorbent powder) to sprinkle on the belt and pulleys when they got wet.

Interesting https://en.wikipedia.org/wiki/Fuller's_earth ............Curt

I'll see about this and maybe get some. I don't ride in the rain mostly. I go trail riding and when going through small streams, or puddles the splash sometimes get to the belt and pulley. I know for usually 60 seconds it will be at some loss if big enough splash, but then things are OK.

Its fun going through mud, but I know it is probably a bit of stress on parts. I usually know to keep up momentum and the weight of the bike gets me though it. It mostly does not get on the belt, but my back and under the banana seat it cakes on some.

What all I have done once in a while is remove the belt and use mild dish washing soap , rinse with water, and dry the belt. The metal pulley I use acetone and clean all grime off. It grabs really good and is noticeably better. If I have gone out using the bike maybe 3 rough weekends of riding, then I would see if it needs it and only clean if it look like it could benefit.

MT

If you don't want to have pillow blocks you can make the jackshaft a solid non-rotating non-keyed shaft (i.e. 3/4"). Then find a double pulley with a 1" bore, and run it on two needle bearings that have od/id to fit between. This will save you the need to make space between the seat tube and the tire. You'll need some way to prevent the pulley sliding off.. however when the belts are on maybe it won't slide off at all.