[larryMar]

To save me the math, and trip to measure the starter ring, does anyone know:

how many degrees is each tooth, or the diameter of the ring?

I believe that they are all the same, but specifically on an o-320

Thanks

 

[RV6_flyer]

Going from memory, there are two different starter ring gears. 122-tooth and 149-tooth. Both have the same diameter.

The 122-tooth is thinner (front to back) than the 149-tooth gear. I have put a 149-tooth gear on a 122-tooth support. It will work with most starters but the SkyTec NL starter could have issues.

How many degrees per tooth? I would calculate that as 2.95=360 / 122 or 2.416=360 / 149.

I have a new unused 149-tooth ring gear in the hangar that I can go measure BUT I do not have a caliper that larger so will not be able to come up with an accurate measurement.

 

[rocketman1988]

...and

The shape of the teeth are different between the 122 and 149, too.

 

[hgerhardt]

Depends on whether you have a 149-tooth ring gear or a 122-tooth. See this article to identify yours (so you don't have to count teeth!): https://skytec.aero/aircraft-starter-installation-issues/

As to the math problem, just divide 360 (degrees in a full circle) by the number of teeth. So, 149 teeth: 360/149=2.416 deg or 122 teeth: 360/122=2.951 deg.

 

[larryMar]

Thanks,

I have 149 teeth, but I don't know the diameter. I didn't know that they made the 122 one...

Thanks again

 

[RV8Squaz]

I count the teeth between the timing marks and then do some simple math.

 

[RV7A Flyer]

Somebody can check my math, but a 149-tooth gear has a diametral pitch of 12 (per some Lycoming docs I found), which means a diameter of 12.416", or a circumference of 39".