It is important to nail down the gear train as it dictates the engine geometry. The gear mesh tolerance has to be perfect and the distance between the gears defines the position of everything else. I think I finally have a solution I am happy with.
These are the Constraints I laid out earlier for the gear train:
- I would like to use a “standard” gear pitch. The smallest that can be considered standard is either a 48DP or a .5 Module (which is about 50DP). Use .5 Module
- The camshaft has to turn 1/2 the speed of the crankshaft. Yes
- Would like to have a single plane gear train for simplicity. The Mighty Midget has a dual plane gear train as can be seen in the photo above. Use Dual plane gearing, that is, use a cluster gear to allow the use of a larger pinion on the crankshaft, 32 tooth instead of 16.
- The camshaft gear, as well as all of the others, has to fit in the gear tower housing Yes
- The crankshaft pinion should have as many teeth as possible. 32 is a good number
- There should be as few bearing sets as possible. There are a lot of bearings, but I think this is the minimum possible.
- A plus would be to have as few gear types as possible, also “standard” tooth counts would be preferred. Yes, 4 gear types and they are standard: 28, 32, 36 and 56 teeth.
- There are other mechanical constraints such as the 88 degree inclusive angle between the two valve banks and the distances between the camshaft and crankshaft. All met, went with 90 degree inclusive angle on the valves
- Also the magneto needs to turn at the same speed as the crankshaft. Yes
- Use an inexpensive involute gear cutter set. Yes, used .5 Module. these are inexpensive and readily available. so are the gears if one want to go that route.
Below is the final(?) solution:
The Camshaft gear can be no larger than 36 teeth, otherwise it would be too big for the gear tower. If I used a single plane gear train the crankshaft pinion would have to be 1/2 of that, 18 teeth. Not the end of the world, but the crankshaft would be pretty small and I had a hard time defining a gear arrangement that met all of the dimensional requirements. By using the cluster gear set as shown above, I am able to keep the camshaft gear to 36 teeth and have a crankshaft pinion of 32 teeth. In the picture above you can see I can have a larger crankshaft diameter at the pinion. The engine geometry worked out spot on with the .5 Module gear pitch.