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How many Degrees in a Window?

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Post Tue Sep 28, 2010 7:06 am

Posts: 1676
Location: Interlaken, NY USA

Right, somewhere along the line someone quoted the width across the timing window as being "x" degrees. I suspect it was Panic who provided the figure. Point is, I can't remember how many degrees, and I haven't found it in my admittedly halfhearted search. Can someone help me out? I'm just being lazy so I don't have to get a degree wheel out and mounted to measure the sweet spot that the bike is running at.
Forgetful DD

Post Tue Sep 28, 2010 7:45 am
Pa Site Admin

Posts: 5843
Location: Ohio USA

Don't know that off hand either but pi of flywheel diameter is a good place to start Doc. From that circumference pi data, you can break it down into inches verses degrees. The flywheel being 360 degrees. The distance across the window, in relation to the flywheel circumference surface, will be the inch data to compare to the calculated pi inch data. How many inches of circumference [ pi of flywheel diameter ] are there in 90 degrees if there are so many inches in 360 degrees of the circumference ? Pa

Post Tue Sep 28, 2010 7:54 am

Last edited by panic on Sun Nov 28, 2010 12:23 pm, edited 1 time in total.

Post Tue Sep 28, 2010 8:15 am

Posts: 1676
Location: Interlaken, NY USA

Thanks Pa, Panic,
Now you make me feel lazy. I should have dug up a flywheel and gotten there myself :lol: But I appreciate the effort. 7degrees is what I believe you quoted last time, and that's close enough for what I'm doing. I'm investigating my two 84" U motors, one with drag pipes, one with 2-1/punched out harley muffler. They seem to like different amounts of advance. I believe the original marks from T&O were at 36 deg (for ohv's). With that, the TDC mark and 7deg, I should come up with a reasonable estimate without pulling the primary drive apart.

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