since 1940

Broken Distributor Gear Teeth on Bendix Magneto

1. Magneto turned while timing lock was engaged in distributor gear.

2. Gear shimmy caused by excessive clearance between distributor block bushing and distributor gear shaft.

Shimmy can be described as what happens when you go to the grocery store and get a shopping cart with a bad wheel or when the nose wheel of an airplane shimmy's. In a magneto the shimmy causes a loud noise but you cannot hear it with the engine running. Out of several thousand worn magnetos we ran on a test bench  we had only two magneto gears that shimmied. The occurrence of shimmy is unknown unless you happen to test run many worn magnetos on a test stand which very few people have done. The results of shimmy are broken gear teeth.

Bendix distributor gear, distributor finger, distributor shaft and distributor block. Excessive clearance between block bushing and shaft causes the shaft to wobble in the bushing. Stress on the gear teeth can be heard as a loud roar on the test bench but probably wouldn't be heard over the aircraft engine noise.

3. For additional information on distributor gear maintenance and broken gear teeth see Continental Service Bulletin 658

4. Loose parts inside magneto such as coil retainers.

5. High magneto temperature

6. Old style distributor gear. See Continental Service Bulletin 658 for identifying new and old gears.

7. Magneto operated without proper venting - especially pressurized magnetos

8. Bent magneto rotor

9. Engine counterweights not operating properly.

 

10. Bushing in distributor block loose allowing shaft on distributor gear to wobble. Notice gap at yellow arrow. This is the bushing that holds the shaft on the distributor gear. It is pressed into the distributor block and not removable.

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Disclaimer: sacskyranch.com contains abundant information relating to aircraft maintenance. The information provided  is not intended to supercede or supplement the F.A.A. approved  maintenance and/or operator’s manuals. Those F.A.A. approved manuals must be utilized when performing maintenance and/or operating aircraft.