The co axle chain drive, "reduction gear" which really isn't, is really quite simple. I use two 14 tooth go cart type sprockets which are "keyed" as a basis for the drive. The key way isn't used for the operation of the chain drive system, but is used to mount the two sprockets together on a short piece of keyed 3/4" shaft that I use to mount the sprockets to the lathe chuck during the machining operation. First I bevel the inside of the entire circumference of each sprocket in preparation for welding them back to back. I didn't have to surface the two as they were flat & as luck would have it the correct thickness to line up the primary & secondary chains. Next I weld the two together in two passes while they are still mounted on the 3/4" inch shaft to retain perfect alignment. I then bore first one end then the other on the lathe...still using the 3/4" shaft (keyed) for alignment and "chucking"...boring deep enough to accept the bearings for a moderately tight press fit. After boring I remove the keyed shaft & mill the remaining length of 3/4" sprocket hole to 13/16"...then press fit the bearings & that's all there is to it. I use thrust washers to space out from the bracket bearing if required to line up the secondary sprockets for a straight chain line and I've plenty of adjustment for the engine side to side. That being said I've been very careful in determining the width of the reduction sprocket so that only minimal adjustment should be necessary...maybe 3/16" or so at most. I use shaft collar on the outside to locate everything in place. Included photos aren't comprehensive, just a point of reference.
This is not the only way but it works well on the Simplex and it's simple, rugged & really inexpensive as well, so I'm making another for the Harley. The sprockets just happened to be the perfect width for the CG125 & both the Simplex and the Sportsman frame, but I was prepared to cut one or both the sprockets if they were too wide or add a spacer plate to widen if required. No big deal either way, just have to ensure that both, sprockets remain perfectly parallel.
Rick C.
This is not the only way but it works well on the Simplex and it's simple, rugged & really inexpensive as well, so I'm making another for the Harley. The sprockets just happened to be the perfect width for the CG125 & both the Simplex and the Sportsman frame, but I was prepared to cut one or both the sprockets if they were too wide or add a spacer plate to widen if required. No big deal either way, just have to ensure that both, sprockets remain perfectly parallel.
Rick C.
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