William Wynne

"The Corvair Authority"

Hybrid Studs for Corvair Conversion

Hybrid Studs, Part No. S-1, have been with us since 1999. I designed them a year earlier, as a means of simplifying the method of converting the Corvair motor. Prior to this, the crank flange had to be re-threaded, a time consuming and expensive machine-shop-only job. The Hybrid Studs thread right into any Corvair crank flange, and allow the Prop Hub to be mounted on a threaded crank in a matter of minutes. They required working with one of America's leading manufacturers of studs through two stages of prototyping and testing. The Studs have rolled threads, and are manufactured with several stages of heat treatment under precision quality controlled conditions. The term "Hybrid" refers to the two different threads on each Stud: the 11/32"-24 flange thread is an obscure, Corvair-only thread used by General Motors; the other end of the Stud uses an aviation standard 3/8"-24. Their alloy is heat treated to match the same characteristics of AN bolts. I have sold hundreds of sets, and they have functioned flawlessly in service. They go in every Corvair engine I convert. The six Studs and nuts weigh 13.5 ounces. They come in one length that works with hand prop and front and rear starter engines. Includes six washers, installation instructions (reprinted below).

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Installation Instructions for Hybrid Studs

Thank you for buying a set of Hybrid Studs, Part No. S-1. Your purchase makes possible my further research and development on the Corvair. In this way, you’re investing in the future development and perfection of your chosen motor.

These notes are supplementary to my most current Conversion Manual. These Studs are 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.

Hybrid Studs

The Studs are heat-treated 4140 steel, (the same alloy was used to make .50 caliber machine-gun barrels in WWII) and have rolled threads. The small thread end (11/32"-24) is the crank flange end and the large end (3/8"-24) is the prop end. The overall length of the Stud is 4.410". If you are building a front starter motor with one of my Pucks, you will use the Stud at its full length. If you are building a rear starter or a hand prop motor you will need to cut the Studs down to 3.700" by cutting off some of the 3/8" thread. (Front Starter engines need the extra length to account for the thickness of the Puck.)

Cutting the Studs is no big deal. Put two 3/8" nuts on the threads, run them down an inch. Butt them together and then clamp them in a vise. This way the vise holds the nuts, not the Stud. Mark off and cut with a good quality bimetallic hacksaw blade. Clean up the end of the thread with a belt sander or a file. If you're concerned, practice on a few Grade 8 bolts. After they’re trimmed, or used at full length, a test fit is in order. You’re making sure that absolutely no threads protrude into the plane of the prop flange face. If they’re a little long, sand them down. If they stick out, they’ll interfere with the proper mounting of the prop. The easiest way to check this is with a straight edge.

Using the double nut technique, install the Studs permanently in the crank. The holes and threads must be very clean. Use LocTite 620 to hold them in (if you don't, they will leak oil). Make sure the shoulder on the Stud squarely contacts the crank flange. You'll notice that the flange is slightly countersunk at the threads. Years ago, a batch of replacement crank gears was sold on the West Coast that did not have this countersinking. All original GM gears and good quality replacements have it. Torque the Studs into the crank with the same setting you would use on a 3/8"-24 bolt (20-24 foot pounds). Remove the two nuts. Let it harden overnight. Make sure that there is absolutely no LocTite oozed out onto the surface of the flange. This would interfere with the seating of the hub, and eventually you’d lose torque on the studs. A successful installation must be very clean, and metal to metal.

When bolting on the Hub, use the same technique as outlined in the Manual. Make sure that the 3/8" washers do not bind in the holes or on the Studs. Included with the Studs are six AN washers. Torque them to specs taking into account the drag torque of the nut on the Stud. Use a good torque pattern, like putting a wheel on a car. Check the torque frequently. Again, all of the parts and mating surfaces should be spotlessly clean and free from defects.


Thank you. Happy learning, building and flying.

Copyright 2018 William Wynne