Engines > Your Own Design

Flywheel Foolishness

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Brian Rupnow:
I'm bored today, and that is not a good thing. I haven't built much of anything since Christmas, but I woke up this morning thinking about a flat-head hit and miss engine. I did a web search and found a few flat-head Briggs and Stratton engines that had been modified to be hit and miss engines, but no "real" air cooled hit and miss flathead engines from "back in the day". Jason was kind enough to send me some information on water cooled flat-head engines, but the flat head was hidden by a ball shaped water reservoir. Okay---if I build one, it has to be air cooled, and I don't want to run a separate belt driven fan. This takes me back to my air cooled twin cylinder which was cooled by a flywheel with vanes attached to the outside, running inside a metal shroud so it wouldn't become a meat chopper. This time I want a flywheel with something similar to vanes, but with the outer shroud built into the flywheel. So---If I started with a piece of 6" double strong pipe x 1" long, I could make the outer rim from steel something like this, and it would be  6 5/8" outside diameter.

Brian Rupnow:
Then, I could build a center hub out of steel, mainly because I'm not fond of using aluminum for hubs because it gets all chewed up by the keyway and the set screws don't stay tight in aluminum.

Brian Rupnow:
The center disc of the flywheel can be aluminum. It doesn't really do anything except hold the outer rim and the hub together. All those small holes are for #10 socket head cap screws. The big holes are 1" diameter.

Brian Rupnow:
And these are the fan blades. They can be made from aluminum and fit into the 1" holes in the center disc, at a 45 degree angle.
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Brian Rupnow:
And when it's all bolted together, it looks like this. The easiest way to attach the 1" diameter fan blades in place is to weld them. The last time I tied to weld aluminum with my tig I just made a horrible mess, but these parts are a lot thinner and don't need a lot of weld to keep them in place. This will move a surprising amount of air, which will be directed over the cylinder, and hopefully keep the engine cool.--particularly if the engine is a hit and miss, because all the time the engine is missing, it is pumping ambient temperature air thru the cylinder and out the exhaust.

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