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Magneto timing

alcladrv

Well Known Member
I flew a little over 100 hrs. in my RV-7A in the past year. In checking my magneto timing during my condition inspection, I found the timing had advanced by one tooth on the ring gear. How many degrees does that equate to?

Those 100 hrs. were on a newly overhauled magneto. Is that timing change typical for 100 hrs. of use?

Thanks.
 
If there are timing marks on your ring gear, such as TDC, 20°, and 25°, it would be easy to count the teeth in between the marks. If your ring gear is 149 teeth it equates to 2.4° per tooth, if 122 teeth then 2.95° per tooth. It’s not completely unreasonable for it to have drifted that much in 100 hours. However, it would be worthwhile to open the mag and visually check the points and check the internal timing.
 
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360 divided by number of teeth on the ring gear = number of degrees per tooth.

If you have the common 149 tooth ring gear it works out to be slightly less than 2.5 degrees per tooth.
 
I believe I do have the common 149 tooth ring gear on my O-360, although I've never actually counted them.

Thanks for your responses.
 
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