William Wynne

"The Corvair Authority"

Safety Shaft for Corvair Conversion

The Safety Shaft is one of my oldest products, Part No. SS-1, and I recommend putting one in every engine. The full story is outlined in my Conversion Manual, but in short, my Safety Shaft is an up-to-date, precision manufactured component integral to the conversion. Although he called it a different name, and it had different dimensions, Bernie Pietenpol pioneered the concept of the safety shaft. My piece is an evolution on his concept and has been in every engine I've built since 1995. It serves the dual purpose of retaining the crank flange while providing a redundant mount to the prop hub. It is offered in one length, which works with hand prop, front starter and rear starter engines. The Safety Shaft itself is made from aircraft grade 7075 aluminum, and weighs about 8 ounces. The $79 price includes a castle nut, washer, cotter pin, instructions and shipping in the U.S. Installation instructions are contained in the Conversion Manual.

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.

Part Description:

Safety Shaft

Revision: 11-9-10. These Instructions supersede all previously dated or undated Instruction Sheets.


Thank you for buying a Safety Shaft, Part No. SS-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. This Safety Shaft 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.

The Safety Shaft has been with flying Corvairs since the very beginning. The credit for the original design probably belongs to Bernie Pietenpol. My adaptation of his concept has been in continuous production since 1995. I have sold a great number of them, and they are in flying airplanes as far away as Australia. Every engine I have built since 1995 has used one. It is the only system that backs up the Hybrid Studs for mounting the Prop Hub. While the Conversion Manual discusses other methods of safetying the flange, it should be clearly understood that the Safety Shaft is the only method I endorse.

The Safety Shaft is made of aircraft grade 7075 aluminum, and is CNC machined just like the drawing in the Manual. It comes in one length. If you are building a Front Starter motor, use it in its full length. If you are using a rear starter motor, you have the option of trimming the length of the Safety Shaft with a hacksaw after it is installed. The weight savings will be very small, on the order of 1 oz. My suggestion is to use it as is.

Clean the inside of the crank and the end of the Safety Shaft with carburetor cleaner. Do a trial fit to ensure that the shoulder on the Safety Shaft bottoms on the crank snout. To be clear, understand that the side with the shorter threads goes in the crank. When the fit is verified, you can apply Loctite 620 to the threads on both parts. Screw it in all the way, wipe off all the excess Loctite, and let dry overnight.

Early editions of the Conversion Manual have notes about a 1/8" roll pin inserted into the Shaft underneath the crank flange. This is an obsolete idea that I have not practiced since 1998. The Loctite is more than sufficient by itself. When your Prop Hub assembly is in place (follow the Prop Hub installation instructions), the included washer and hex nut can be installed. By reaching into the open Top Cover of the motor, a wooden block can be used under the crankshaft throw to stop the rotation of the motor. Torque the nut to 100 foot pounds. Using a 5/32" bit, drill the hole for the enclosed cotter pin, using the castellations on the nut as a guide. If you have trouble getting the drill to start on the threads, carefully punch the Safety Shaft. This will allow the drill bit to start easier.


Thank you. Happy learning, building and flying.

Copyright 2018 William Wynne