Ring Gear replacement?

[airguy]

Follow up question for the knowledgeable A&P types...

Reading through all the ring gear and flywheel literature I have found, there are obviously many different part numbers for the flywheel/ring assembly - like maybe 3 dozen different ones - but it appears to me that there are only 2 different rings gears, a 122-tooth and a 149-tooth, is that right?

Are there various different models of the 149 (or 122) ring gear itself? Or is this more of a generic gear that fits any of the flywheels intended for that size gear?

[C. Brenden]

I did this to my RV6 O360 engine years ago. Followed all the instructions and went according to plan. I was impressed at the precision of the fit.
If I remember right there are only two ring gears, each with a different tooth count. Just make sure you put the gear on the correct side - you won't get it off in one piece if it cools on the wrong side.
Have fun!

[drone_pilot]

Not all ring gears are the same. I purchased a 149 tooth from Superior for my Lycoming flywheel. It is about 1/32 wider than it should be. It should sit flush to the back of the flywheel when installed.

[lr172]

Originally Posted by drone_pilot

Not all ring gears are the same. I purchased a 149 tooth from Superior for my Lycoming flywheel. It is about 1/32 wider than it should be. It should sit flush to the back of the flywheel when installed.

+1 on this. Skytech has a nice paper explaining the different styles of rings and how to identify them.

Larry

[RV6_flyer]

Originally Posted by airguy

Follow up question for the knowledgeable A&P types...

Reading through all the ring gear and flywheel literature I have found, there are obviously many different part numbers for the flywheel/ring assembly - like maybe 3 dozen different ones - but it appears to me that there are only 2 different rings gears, a 122-tooth and a 149-tooth, is that right?

Are there various different models of the 149 (or 122) ring gear itself? Or is this more of a generic gear that fits any of the flywheels intended for that size gear?

Here is a link to Lycoming Service Instruction 1141A that lists all the different ring gear supports and how to change the ring gear. As near as I can tell, there are only two different ring gears.

SkyTec published a web page that gives a warning about changing from one to the other. Their NL starter is manufactured to a very close tolerance and may not work when changing from a 122 tooth gear to a 149 tooth gear.

[airguy]

I had some emails exchanged this morning with Richard Condy of Skytecair, he confirmed that there are multiple part numbers for the flywheel itself and these translate to multiple part numbers for the flywheel/ring gear assembly, but the actual ring gear itself is only available in 2 variants - the 122-tooth and the 149-tooth. They are not interchangeable on the same flywheel due to differences in the mounting depth of the support.

The upshot is that if you need to replace a 149-tooth ring gear, you can buy one from any of the sources selling them, they are all the same.

[DaAV8R]

Originally Posted by airguy

I had some emails exchanged this morning with Richard Condy of Skytecair, he confirmed that there are multiple part numbers for the flywheel itself and these translate to multiple part numbers for the flywheel/ring gear assembly, but the actual ring gear itself is only available in 2 variants - the 122-tooth and the 149-tooth. They are not interchangeable on the same flywheel due to differences in the mounting depth of the support.

The upshot is that if you need to replace a 149-tooth ring gear, you can buy one from any of the sources selling them, they are all the same.

I didn't know the 122 and 149 were not interchangeable. Mine is a 122 and I have planned on changing to a 149 as I have an overhauled 149 starter on the shelf.

If someone could post the width of their 149 tooth gear I will measure and post the width of my 122 tonight.

[airguy]

Originally Posted by DaAV8R

I didn't know the 122 and 149 were not interchangeable. Mine is a 122 and I have planned on changing to a 149 as I have an overhauled 149 starter on the shelf.

If someone could post the width of their 149 tooth gear I will measure and post the width of my 122 tonight.

You'll need to exchange the flywheel also, for one intended to take a 149-tooth ring gear, since the depth of the ring gear support is different.

[RV6_flyer]

Originally Posted by airguy

I had some emails exchanged this morning with Richard Condy of Skytecair, he confirmed that there are multiple part numbers for the flywheel itself and these translate to multiple part numbers for the flywheel/ring gear assembly, but the actual ring gear itself is only available in 2 variants - the 122-tooth and the 149-tooth. They are not interchangeable on the same flywheel due to differences in the mounting depth of the support.

The upshot is that if you need to replace a 149-tooth ring gear, you can buy one from any of the sources selling them, they are all the same.

Swapping from a 122 to 149 may or may not work with your starter. There may be an issue doing this with the Skytec NL starter but it may work. I had the 122 tooth ring gear swapped with a 149 gear 20-years ago. I used a Skytec PM starter without issue for a number of years. It worked perfect. When switching to the Skytec NL starter a year ago, there was minimal clearance between the starter gear and the ring gear when rotating the propeller one or more revolutions.

IF you change from a 122 tooth to a 149 tooth ring gear, make sure you rotate the prop at least one complete revolution before trying to use the starter or fly the airplane.

[airguy]

Originally Posted by RV6_flyer

Swapping from a 122 to 149 may or may not work with your starter. There may be an issue doing this with the Skytec NL starter but it may work. I had the 122 tooth ring gear swapped with a 149 gear 20-years ago. I used a Skytec PM starter without issue for a number of years. It worked perfect. When switching to the Skytec NL starter a year ago, there was minimal clearance between the starter gear and the ring gear when rotating the propeller one or more revolutions.

IF you change from a 122 tooth to a 149 tooth ring gear, make sure you rotate the prop at least one complete revolution before trying to use the starter or fly the airplane.

The profile of the gear teeth is very different between the 122 and 149 ring gear. The starter gear should match the profile of the ring gear. Skytecair specifically calls out which starters should be used for 122 and which ones for 149 ring gears, I would suspect all the other starter manufacturers do as well. Go look at the link on post 15 above (Skytec link), the document linked there shows the difference.