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Yesterday was one of those gusty bright Fall days. The leaves were falling, probably why it’s called “Fall,” and because of the conditions and leaves all over the place, we kept it simple.
Here’s what we learned about the gear train. These gears are at the very back of the engine, behind the cam and the tappets. There is no propeller reduction drive for this engine, and the maximum speed is 1,300 rpm.
1. The crankshaft gear has 20 teeth and is held on with a nut that has left-hand threads.
2. It drives the oil pump gear. This 40 tooth gear directly drives the oil pump at half engine speed. For future reference, the oil pump plunger runs at a maximum of 10.8333 pulses per second at maximum engine speed. You can see the oil pump gear in the left-hand picture below.
3. The oil pump gear, in turn, drives a small 15 tooth idler gear. This idler gear, the only one in the engine, runs at 1.333 times engine speed.
4. It drives the cam gear. The cam gear has 40 teeth, and rotates at half the engine speed just like the oil pump gear. The cam is attached directly to this on its forward face. The cam gear itself is located coaxially with the crankshaft, forward of it, and rides on a bushing on the crankcase itself.
Those gears are all inside the crankcase and are lubricated. The crankshaft sticks out of the back of the crankcase, and the accessory drive housing fits up to that. The accessory housing holds the oil pump, which you can see in the right picture, and supports the single magneto on the shelf
This whole housing assembly is mounted aft of the engine mounting points. Since the engine usually was mounted to a formed steel forward bulkhead, as was the usual practice in WW I, that means that the magneto and oil pump are probably in the cockpit.
Above the shelf, to the right of the oil pump in that right-hand picture, you can see the hole where the crankshaft fits through.
5. The final gear on the crankshaft is attached to this crankshaft stub. It’s a 21 tooth gear. I couldn’t find the nut that holds it on, and this worries me a little.
6. And it drives the 14 tooth magneto drive gear. The magneto, then, turns at 1.5 times crankshaft speed. In the right-hand picture, the magneto drive gear is placed down and to the right of the hole, in that open space there.
Roger pointed out that there’s a gear to snag a shoelace on each foot.
These gears, being external to the crankcase, will need to be lubricated before each flight. On some of the early aircraft, you can see an access panel on the right side, low and forward. It’s probably to let the mechanic do this. Also, since there’s no way to retain the lubricant, that whole area will probably get messy. It would make sense to provide some sort of light cover assembly that can be removed for cleaning, if that wouldn’t adversely affect the magneto cooling.
I wonder what was used to lubricate those gears?
We determined that the magneto fires twice each revolutions, for three sparks each time the crankshaft revolves. As this is a four-stroke engine, with each of the six cylinders wanting and needing to fire once every two crankshaft revolutions, it works out perfectly.
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