Lightened air cooled flywheel

Following on from the post below, The next item up for modification and extensive testing is the flywheel.

On these aircooled engines the original source of air to cool them down when they were being used as agricultural engines was from the finned flywheel itself that draws air in from holes in the pullstart housing and ducts it up to the finned cylinder cooling it somewhat.

On our race bikes for the most part they are moving, and at a decent speed. so they dont need quite so much cooling as they once did. The original units are also heavy and have a huge amount air resistance when turning at 9000rpm  not to mention they are often outrageously off balance from new.

The original type is on the left. it weighs in at 320 grams. 

By lightening the flywheel the engine can rev much more easily and theoretically rev to a higher peak RPM. taking some load off the crank is also good for reliabilty.

On the right of the picture above is a standard performance part made in china as well. this one has had some of the fins milled flat and the edges scalloped. Its quite a bit lighter then the stock one and has much less air resistance while still maintaining its cooling function. However ive found these to be out of balance just as often as the stock ones are.

After a bit of experimenting about i found that the vast majority of the inbalance comes from the edge of the "disk" and the tips of the fins where the casting variations are greatest. So simply lathing the outer diameter down and thinning the fins length wise brought the flywheel into almost perfect balance with no secondary balancing required.

experimenting showed that there was almost no difference in measured operating temperature after a 20 minute ride between the original,  1/2 length fins and 1/3rd length fins, while the engine pickup and peaks revs was notably better with the 1/3rd length version. It is also lighter by some 20 grams over the others and quite a bit more over the chinese performance version.

Here is a complete one. it weighs in at 260 grams vs 320 of the original.

Also tested was a finless flywheel that weighed in at a tiny 230 grams that works better yet again. HOWEVER it will overheat the engine to dangerous levels if left to idle for 1 minute or more and it is extremely sensitive to jetting. even a little off will result in a seizure. so as such the type in the picture above will be the flywheel supplied in my engines.

If you want your flywheel machined to similar specs or want to purchase one new contact me at Glen.M.R@gmail.com  for more info.