Clutch Decisions

sparkwizard

sparkwizard

#1
#1
We are building a backyard/farm beater minibike with a Clinton Panther in it. I already know I will need a jackshaft to get the gearing (numerically) high enough to get around the flat, sandy property. One option is to mount a small sprocket on the engine, use a larger sprocket on the jackshaft to slow the shaft down, and mount a clutch on that shaft. I don't like that idea, because it seems to put a lot of stress on the clutch, since it would be pulling about 6:1, mounted on the jackshaft, where it would have closer to 12 or 18:1, if mounted on the engine. I don't want to build problems into the little bike.
Rear tire 12.5 inch diameter, and I have 72 and 60 tooth #35 sprockets.
If I do choose to mount a clutch on the engine, it is a 5/8 shaft, 2 stroke engine, can someone get me close to an engagement RPM target? 3000 might be too low. I think I saw a 4200 on Max Torque's website.
 
J

Jim Donovan

Active Member
#4
#4
Have you drilled and tapped the end of the crankshaft to hold the clutch in place so you don't have to rely on the set screws? The crank is not hardened so you can do it fairly easy. 1/4-20 is fine or go up to the 5/16-24 and I will send you the hex bolt with the clutch. With the 72 rear sprocket and a 10 tooth #35 sprocket it will be fine ratio. Using the black spring she will come in just over 3,000rpm which let you take off easily. When you get down that low on the clutch sprocket it has to be a two piece clutch -shoe assembly is NOT attached to the drum and sprocket and there is a bushing in the 10 sprocket. When it is a 3/4" crank the same sprocket is honed out to ride directly on the crank and it works out fine in racing because you are not at idle very long which is the only time it free spins on the crank -steel on steel.

The heart of all clutches is the spring or springs and the bushing or needle bearing. Stainless steel springs can take more than twice the heat of music wire but few people put them in their clutches because of the cost of the spring. We do it because of the cost of a lawsuit for a run away vehicle because the spring got annealed from the heat and it is useless. When clutch wants to grab at neutral you know right way the spring went south. Door bell just rang so I have to cut this short.
 
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