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Discussion in 'Board Trackers and Vintage Motorized Bicycles' started by RocketJ, Jun 20, 2018.
I started this project about 6 months ago. It's slowly, but surely getting there.
More and closer pic's please! This looks interesting. Going belt drive?
Yup. It works well, but i need a longer belt.
Engine is it Briggs? Are there faux items? Oiler I think someone said those pump thingies were once used in 2 strokes in the way past. I have a Briggs 3.5 4 stroke used for off roading only. Chain on your bike will still be, just a manual belt tightener I suspect to use to go from stop. Cogged belts I use for less heat and bends better for smaller radius bends. Belt I have has Kevlar in it and they do wear the metal down on the softer aluminum adjustable diameter pulley I use. Possibly one day a steel or cast iron would be better. If 1/2 inch increments of belts are not doing it, adjustable idler pulley or adjustable diameter pulley can help.
Its a 4hp 4 stroke briggs. It has a belt to chain drive, but the belt is used for neutral-to-go. I use steel pulleys and currently an enforced belt.
Also there's no oiler, just an oil reservior. As far as faux items, I'm not quite sure what you mean by that.
Fake for oiling inside 2 stroke crankcase is what I hear that pump up near the gas tank was there to fool. Old time looks they are after use it.
I was using twin jackshafts to get a 20:1 ratio and that ended connected to a 26inch knobby wheel. My three belts then went to 2 belts and 1 short chain between jackshafts when the small pulley diameter was causing too much friction and slipped.
All was well until the prior older 3hp Briggs was intermittently seizing up. It was of the primarily same form factor of the newer in current use 3.5 used engine.
Then I found that did not have enough crankshaft to mount a centrifugal clutch on the stubby legnth crankshaft of a replacement engine I got. Too late to return it, but it runs great.
12:1 ratio is what I get now since the 1st jackshaft is connected 1:1 with a chain and I mount the sprocket drive clutch on that live jackshaft.
I may be seeing if one day I can use crankshaft out of the 3 and put it in the 3.5 engine. Else something I saw at Tractor Supply Company a steel part that I could modify to reduce 3/4 to 5/8 shaft by welding some 5/8 keyed shaft material to the clamping part.
Other already made adapters cost more than a used engine. Also in the works is fixing up the older engine with some save used but maybe better rings and possibly hone the cylinder very very slightly. I was warned hones work fast on the softer aluminum cylinders like in my 80202 series Briggs.
For you, friendo.
Hello. Nice build. some tips that might help you:
Tension the slack side of the belt. You're gonna eat away at the tensioner pulley and belt much faster with your setup. A longer belt won't solve your problems of a bad idle due to the belt trying to become a circle. Make guide pins above+just behind, and possibly also below the drive pulley to force the belt to not contact the drive pulley at the front when in idle. Run an overall ratio or 9:1 to 11:1.. depending on how fast you wanna go. Also get rid of the water pipes for the exhaust, make one that matches the port size. You can gain a lot of power from a lot of simple free mods on those motors. search my posts for briggs 3.5hp mods, or look at some of my build threads. Before I blew it up mine was probably pushing about 5hp.