William Wynne

"The Corvair Authority"



Machined Ring Gear For Use With Low Profile Front Starter Kit

Installation Instructions for Part # 2408 – Ring Gear

Please Read and Follow Entire Instruction Sheet, i.e. To The End of Page 3

Date: 11-3-13. These Instructions supersede all previously dated or undated Instruction Sheets.

Thank you for buying a Ring Gear, Part Number 2408. Your business and trust is much appreciated.

These notes are supplementary to my most current Conversion Manual. This Ring Gear is developed as part of the system that we use to convert aircraft motors. This system is outlined in the Conversion Manual. The parts alone, without the information contained in the Manual, will not allow you to develop as reliable an aircraft conversion. When I develop and market a part, it is fully flight tested, and designed to work in concert with the other parts in the conversion. I take into account the way that most people are capable of installing and operating the part. There’s a great deal of consideration that goes into these issues, and I urge you to utilize all the information in the Manual and the parts in the way that they are intended to be used. Of course, contact me at any time with any question you may have.

To be fair, everyone needs to understand that these are not certified parts, and it's not a certified motor. Experimental is not a misnomer; everything we do in this field is of increased risk. If anyone even suspects that they have a problem, E-MAIL or CALL ME. If you have never worked with torque wrenches and precision fasteners, get help from an A&P. Let's all remember to use our heads and not take unnecessary risks. I have gone to great lengths to make these components as reliable and easy to install as possible within the bounds of affordability. I have personally flown all of these parts, because I have a low opinion of people who market aircraft parts without flying the parts themselves. I believe that each and every part I sell is the best solution to its respective aspect of converting a Corvair engine. Take your time and do good work. The system is proven and will reward you with the same type of reliable flight performance we have always had.

Background and Part History:

We have been putting ring gears on Corvair flight engines for more than 20 years. There have been four different models we have used. The Corvair slang terms for them are “Nissan” (1992-99), “4-Spoke” or “FRA-235” (2000-05), “Early solid” (2006-09) and “Late solid” (2009-present). The part you are working with is a Late solid, and is the only type that we have supplied for a number of years.

We made very few Nissan flywheels; in that era we were a small outfit and many people still built hand prop motors. The Nissan is recognizable by its coarse teeth. The three models we have used since have all been 11.3” in diameter and had 135 fine teeth. Obviously the 4-Spoke has 4 wide spokes. The Early and Late solids are hard to distinguish from each other, but the Lates have a larger flat area that fits the AN-3 bolts better.

Of all of these, the only model that ever cracked was the 4-Spoke. We warned builders that this was possible if they did not polish the stress risers off the edges of the part. We asked that builders polish the edges and frequently visually inspect the ring gear. An additional giveaway of a cracked spoke was a large increase in noise when cranking the engine. The appeal of the Spoke unit was its extreme light weight, and the fact that many with polished edges flew several hundred hours without issue. (We also had a large number of them with razor sharp edges on very smooth engines that never cracked.) In 2005, their sole manufacturer ceased production, and they became unavailable. If your plane has one of these, please read the inspection notice that has been on our FlyCorvair.com Web site since 2006. It is reprinted at the end of the notes. If you don’t wish to comply with it, the easy solution is to purchase a Late solid from us, as it is interchangeable and it has no recurring inspection.

In 2006, we switched to Solid ring gears, which look like a disc. Not a single one of these has ever cracked, and they have no stress risers, nor edges to clean up, and they need only be visually inspected at annual. The small downside is their 1 pound weight increase. On the Early, the edges of the AN3 bolts touched the radius pressed into the gear; on the Late, these bolts are entirely in the flat center area.

Installation Instructions

The ring gear is fully machined and it only needs painting before it is installed. Don’t worry too much about getting paint in the teeth; unless you dipped it in a paint can, the thickness will not bother the starter engagement.

The dished side of the gear faces the engine, not the prop. If the center hole is slightly tight, carefully sand it with 220 paper until it goes on the back of the Gold hub. The system is designed so that the ring gear centers on the 3” hole in the middle, not the AN3 bolts. I bore the holes for these to .200” intentionally so that they have plenty of clearance on the bolt shanks.

Install the six AN3 bolts with the heads facing the engine, and the washers and nuts facing the prop. Torque them to 7-10 foot pounds plus the drag torque of the nut. There is no need to be quite as picky as when torqueing a rod bolt, but do a good job. Any aircraft mechanic will tell you that homebuilders almost always overtorque fasteners. If you are building an engine and a plane, owning a few torque wrenches is a classy move. Other builders will think of you as first class. BUT, if it turns out that you bought Harbor Freight torque wrenches made in the People’s #37 lawn sprinkler and torque wrench factory for imperialist running dogs in Throw-dung province, mainland China, then people will find out that you have no judgment. Don’t do this.

This installation should be checked for torque during the test phases of the engine. You will not be able to hold the bolt heads, but you can put a wrench on the nuts and simply make sure none of them are loose. I have never seen this happen, but vigilance pays, and that's what flight test periods are all about. If you have questions, make sure they are thoroughly answered. Remember, safety is paramount. By choosing this part, you’re taking advantage of our years of flight experience which went into the design of this highly evolved component. Thank you for your purchase and congratulations on your good judgment.

NOTE: In the past 10 years, we have machined several hundred Ring Gears. The total amount of flight time on the 4-Spoke style Ring Gear is in the tens of thousands of hours. About a half dozen Ring Gears have cracked through one of the four spokes in operation. The propagation is slow. The issue was discovered in annual inspections. The part has only ever experienced one failure, and the builder said he only looked at the gear during annuals. More frequent inspections would obviously be prudent, and good risk management. As manufactured, these openings are stamped, leaving sharp edges that are stress risers. For the past several years we’ve recommended that builders take the time to debur and smooth all the edges on the four openings on both sides with 100 through 400 grit sandpaper. Ring Gears with polished edges have been operated for hundreds of hours without issue. Having an out of balance or track spinner, or a propeller that was not dynamically balanced, has shown to be a large contributing factor to cracking.
Again this issue only applies to “4-Spoke” ring gears from 2000-2005. If you have one of these and would like to avoid frequent inspections, just upgrade to Part #2408 as it interchanges.

Please print, complete and return a Liability Statement with all orders. These are available for printing at the Liability Statement Page.

Thank you for your order.


Copyright 2018 William Wynne