Due to some impending speed limit rules it was time to do something about the Cromwell's slightly higher top end! To slow the tank down a reduction ratio adjustment is applied. Since increasing the reduction ratio was impractical with the current belt drive first stage, ANSI 25 chain and sprockets are used to increase the ration from 9 to 1 to 11.8 to 1.
During the gear change I pulled everything out from the rear end and gave it a good cleaning and lubrication. This was the first time the transmissions were pulled since construction in 2005.
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Though there's some superficial damage to the plywood drive sprockets, overall, they are functionally as good as the day they were first fabricated. This goes to show that plywood is a viable construction material for these vehicles.
The Cromwell's sprockets have more mileage on them than most, the TiteBond coating is mostly still intact. Note the wear in the inner surface from the track guide teeth.
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So what do you do when you want to mount a sprocket to a shaft and you don't want it to slip? Here's what I do, first mount the sprocket to the shaft with one of the setscrews and remove the other setscrew. With a bit that fits within the teeth of the setscrew hole, drill a shallow hole. Switch the set screw and then drill the other hole.
The shaft with the two guide holes drilled.
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With a bit the same outer diameter as your setscrews drill a couple of holes into the shaft. In this case I'm drilling these holes 1/8" into the shaft. That's about .000003175 kilometers for you metric types.
Here's the final holes drilled into the shaft. Their perfectly aligned with the sprocket and once you Locktite the setscrews in place the sprocket isn't going anywhere.