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This is a Safety Alert. For more information on Safety Alerts for Corvairs, read that section on the main page of this website.
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Date and Revision : This is dated August 8th, 2026. It reiterates previous warnings from 2019-2022. The information is the same, but being presented here to alert anyone who ignored or missed previous warnings.
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Subject: Corvairs drive the ignition and oil pump through a bronze gear mounted on the crankshaft. The part is assigned #1008 in my conversion manual. The original GM gear has a perfect track record, but aftermarket imported gears have a very high failure rate, and should not be flown under any circumstances.
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Applicability: This applies to 100% of all engines which have, or are suspected to have, an aftermarket bronze gear. Be advised, no matter where they are distributed from, all replacement gears available in the last 20 years are imported. and covered by this safety alert.
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Exclusion: This alert does not apply to engines equipped with original GM bronze gears. !00% of the engines I built, and kits I built used GM gears. However, a very high percentage of engines resold fraudulently claim they were built in my shop. The word of a previous owner is not acceptable proof of having a GM gear. Please note the origins of our understanding of the issue came from aftermarket gears installed on new cranks made and sold by Sport Performance Aviation. When the problem was identified 8 years ago, the purchasers where notified. However, no records were kept on which owners elected to comply with replacing the gears with an original GM gear. Additionally, I had no control over decisions made by builders who attended my training events with their own equipment. No assumption should be made without specific proof. GM and aftermarket gears can not be told apart in typical photographs. .
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Discussion: This subject has previously been discussed at length with builders in several venues. It is being presented again here because we have recently has another builder have an un eventful off airport landing caused by the degradation of an imported bronze gear. He is the original builder of the engine, and he missed the previous warnings. Additionally, he was not utilizing our oil sample analysis program, which has the proven ability to spot the degradation of an imported gear before it stops the engine.
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If an imported gear is installed in an engine, it will operate and give the appearance of normal operation. However, they do not have the correct complex tooth shape, and will wear in operation against the steel distributor gear. The wear particles from this action can not be visually seen in the oil, but the advanced oil analysis system we use can spot it in as little as 5 hours of running time. It has previously caught six engines with a degrading imported gear before any operational discrepancy was detected by the pilot.
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If the issue is not addressed or detected, between 75 and 120 hours the imported gear will wear the buttress style tooth design into a continuous knife edge, This misshapen gear will cause very harsh vibrations to travel up the distributor shaft mounting the steel meshing gear. These vibrations will eventually crack the rotor or dislodge the metal tab on the rotor, either will stop the engine. I have only 4 known occurrences of this. The first was an uneventful off airport landing in a stol aircraft, and the origin of the discovery of the gear issue. The second was a partial rotor failure, and the aircraft flew back to the airport. The original warnings date from this time. The third event was a builder who was aware of the warning, but chose not to change the gear. The rotor failure he experienced at 110 hours resulted in a very serious accident and the total loss of the aircraft. The rotor from the most recent event is pictured below. There was no damage to the aircraft, it was towed back to the airport with the wings on. All four of the aircraft were not utilizing oil analysis.
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All engines which showed a degrading imported gear on oil analysis, and replaced the gear with an original GM unit have never shown a recurrence of the issue. The high time aircraft has subsequently logged more than 550 hours on a GM gear without issue.
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Suggested Action: If the gear is imported, or suspected to be imported, replace it with a GM gear before continued flight. It is highly reccomended that all Corvair operators utilize the oil analysis program offered by Larry Nelson at LNCLabs.com
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Thank you for addressing this matter.
W.W.Jr.
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Above, a worn, sharpened imported gear on the left. On the right, a cleaned original GM gear.
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Above, a GM gear. Although it has 100,000 miles of automotive use, it retains the correct flat topped tooth of a buttress thread, correct for these gears.
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Above, a worn imported gear. Note how the tops of the gear teeth have become sharpened to a knife edge. This causes the extreme vibrations to be transmitted directly into the meshing steel gear on the distributor shaft. That vibration attacks the rotor on the top of the distributor shaft.
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Above, an ignition rotor with the dislodged metal contact. This is done by the vibration. In my 37 years of working with Corvairs, I have never seen this happen, except in the case of the imported gears.
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Thank you.