Why?
This is a long list, with many things to consider.
First - any Corvair crankshaft is at least 50 years old and we have no real idea of many factors:
1. How much time is really on the crank?
2. How was this engine treated?
3. What is the metallurgy of the crank?
4. Was it repaired or reground in the past?
A new crank shaft of known origin would answer these questions.
Second - Corvair engines were produced in a cost constricted environment. They are good units but the quality assurance in auto manufacturing is totally different in Aircraft engines. The attention to detail in things like surface finish just wasn’t financially viable. With a new crank shaft we can control these aspects.
The Plan: Our current thoughts, after talking with many people in the industry and several metallurgists:
-
Maximize strength and fatigue resistance while maintaining compatibility with the stock Corvair components.
-
Increase all critical fillet radiuses to maximum possible. We are still working through this but, .250 is the standard in high stress crankshafts. We cannot get near that big and still be able to use stock bearings rods etc. More info as we have it.
-
Throws will be increased in width to increase section area. Thickness would be better, but that cuts into room for large fillets which are critical!
-
Material will be US sourced 4340 Timken QA steel.
-
The Crank will go through a extensive metallurgical process to include heat treat, stress relief, ion nitriding etc.
Our primary goal is to offer a replacement crank that will require no major changes to the existing setup to install, while maximizing strength and service life. Second to that goal is to keep the cost down as much as possible.
Status -
Click here for the latest status and ordering information. Pricing depends solely on the number of cranks made at a time. Volume keeps the pricing down. Once we have firm volume increment pricing we will be contacting everyone on our list to see how many of the Corvair builders/owners are ready to pay and then we will start taking orders. At this time delivery date (to us) is 16 weeks from the time the order is placed.
THE BIG QUESTION “DO I NEED ONE?”
This is what everyone asks, but there isn’t a definitive answer for that question. You have to ask yourself what your guideline of acceptable risk is. The circumstances listed below should be the guidelines for running a stock crank:
- If the crank had been Nitrided
- Crank has been reground with attention to detail and as large a radius as possible
- If the crank has a 5th bearing installed
- The engine setup for a front starter and front alternator
- Wood prop dynamically balanced
- Ignition timing set below 30 degrees , use 100 ll only, and a good known carburetor set up (MA-3, Stromberg and Possibly Ellison) to eliminate any chance of detonation
*** Any "trauma" to crank like a prop strike (regardless of magnitude), or a balancer issue etc would be cause for replacement.***
With the above guidelines the remanufactured stock GM crank should perform well and have an acceptable service life for most users.
All that being said; if a new manufactured, extremely high quality crank as above is available, we will use one. If the new crank cost $1500 more than a reworked stock unit then it is well worth the money and the Vair would still be an excellent value in the 100 hp engine market!