Please educate me on Lycoming starter ring gear supports (flywheels)

[Sam_B]

All,

I’m in need a a starter ring gear support for my O-360 A1A (narrow deck), and I don’t really know what my options are due to my inexperience with Lycoming engines to date. I’m hoping to be at a point to overhaul my engine this year (under supervision, but I really want to learn more so I want to do it and I own another flying airplane, so finishing the build is 2nd priority to enjoying the build and learning) but I’d need to source a few of the things that were missing from the engine I bought. I see from the parts catalog that my engine calls for either an LW-16064 or a 75221. See screen shot from the parts catalog.





What is the difference between the two?

Some clues might come from the wide deck parts catalog:




It seems like the difference is a “1.91:1 drive” vs. a “2.5:1 drive”…. I’m not really sure what that is referring to. Is that referring to the alternator pulley?

If I were to purchase a ‘lightweight flywheel’ would it work on my engine?

 

[Mcmark]

Sam, not knowing part numbers I can't say which is which. There are 2 ring gears available for the Lyc. 122 teeth or 149 teeth. If you have the starter that will likely dictate which ring gear. If you have neither part, most find the 149 tooth to be superior.

Mark

 

[RV6_flyer]

As Marks says, there are two different ring gears. The "Support" assembly is different for both but either ring gear will fit. The problem is that the front to back dimension on the ring gear is different and depending on the starter, can be an issue if you place the 149 tooth gear on the 122 tooth support. I have a 122 tooth support on my O-320-B2B narrow deck but I have a 149 tooth gear and starter. When you do this, there is a possible issue with clearance between the starter gear and the ring gear. Many, not all, of the SkyTec NL starters have had issues with the ring gear rubbing the starter gear and there was a notice of that on the SkyTec website before Hartzell purchased the company.

I have both supports with ring gears installed in my hangar. I have posted photos before showing the difference.

I have volunteered to help the EAA with setup for an event this morning. IF I have not posted photos by the end of today, send me a PM / "start a conversation" with me to remind me.

Bottom line, you need the ring gear to match the starter. IF you change ring gear and starter to something other than what Lycoming had, you may have an issue with the clearance when the starter is not engaged.

 

[RV6_flyer]

Here is a photo with a 149 tooth starter ring gear on a wide deck support (LEFT side) and 122 tooth starter ring gear on a narrow deck (STD cylinder flange) support.



Notice that they both are at approximate same aft location (top of photo) but that the front / forward end on the wide deck is more forward than the narrow deck support. (down in the photo)

 

[Sam_B]

Ah. Wonderful, thanks for the information, I appreciate it!