Easy Variable Pulley

cannonball2

cannonball2

Well-Known Member
On my last FD build I had designed in the ability to change ratios by a simple pulley swap. The short run of the belt would not allow the use of a double type pulley due to alignment issues. A pulley swap is no big deal and done in a minute or two, but who wants to carry around an extra pulley? I have had this variable pitch pulley laying around for years, so dug it out to see what it might offer. It allows a half inch of variation, doesnt seem like much but is a 4.8 mph difference on top end versus hill pulling power. Its a simple matter of loosening the set screw, relieveing a little tension on the idler pulley and "screwing" the pulley which ever way is necessary. It will adjust in my case to any size betwen 3.5 and 3" as long as the locking flats are aligned. This allows me to over/under/1:1 drive the roller with one pulley. All I need is an allen wrench which I plan to carry under the engine frame on rare earth magnets. The pulley in the pics is the wrong size, but I found one on the net for $14, cheap enough. If you are building a belt driven jack shaft might be something to consider.
 

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I like this idea. Variable pitch pulleys are a common item on evaporative coolers out here in the desert, so finding them cheap is pretty easy. The local Home Depot sells them for about $8.
 
Cool idea Cannon! The worlds first manual 2 speed FD. (I think)

Been following a couple of your threads and was thinking about an engagement system where the engine sits stationary and drives sheaves that rotate down to engage the wheel. (just a thunk) But a variable pulley would be a great adjustment-er

The goal being have the engine center mounted above the rear wheel with an easy to change ratio.


.flg.
 
Thanks Dan, on the latest FD, since its an auto clutch I just leave it engaged all the time. Its real easy to push around that way. I can still raise it in the event I need to pedal the bike freely. Just found this pulley@ Grainger. It adjusts from 2.9-3.9" for a 1/2" belt. That varies my speed range from 23.4-31.4mph. At the low end it should be a hill climbing monster as it is under driven by nearly 1K rpm. Is over driven on the high end by about 500 rpm. More "screwing" with this pulley than the first one.
 

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LOL Cannon. I misunderstood the last line until I looked closely at the pic and saw how it worked.
 
Got and installed the variable pulley today. Required a few mods like an inch longer belt, but was basically a bolt on. What this does is to quickly allow the change of the roller speed and the overall ratios to allow for top end, or climbing/load capabilities. Speed wise this changes the speed range from 23.2mph top speed on the low to 30.9mph top speed on the high. This is like changing from a 1 5/8 roller to a 2.16(slightly bigger than a 2 1/8) with semi infinate adjustments every 180 degree rotation of the pulley. All I have to do is loosen the set screw relieve the pressure on the spring idler and screw the pulley in or out to the desired ratio/speed. Maybe not as easy as jumping a belt to another pulley but dang close, and there are many ratios avalible. This was kind of hard to show in pics, but look at the pulley size, the red reference mark, and the idler position and you will get the idea.
 

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Tested the Vari-pulley this morning. Started in the 4" position. Man this thing is a tractor with that ratio, would easily pull a trailer. Went down to the monster test hill. With the 3.5" pulley it would climb the hill just fine, losing 4-5 mph but climbing with authority at 15-16mph. The twisted up top speed at this setting was calculated to be in the 23.2mph It actually did 22.7 GPS corrected computer, but man was it wound out!. Comfortable cruise speed was 15mph. From dead stop at the bottom I twisted it to 20mph and it climbed it all the way at 20, too wound up for my taste. Same again but accelerated to 15, climbed all the way to the top at 15. So with this ratio it will climb with power in excess. Thought this would work on trails. Took it down to my pasture and rode slowly over the terraces and other rough areas. Worked great. Clutch engagement speed is around 3
mph. Allows you to poke along with out riding the clutch. Top end was less thrilling. Calculated top was 30.9 actual was 29.4. This is because I cant reach the lowest pulley setting until I redo the idler slightly. So really it works exactly as expected. All adjustments are less than a minute, and easy. Also there are a ton of multiple ratios every 180 degree rotation of the pulley. Soo if you are building a jackshaft something or other, and you can get at the pulley easily, might be something to consider. I am very glad I went this route.
 
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