"Aircraft has a 600 rpm drop on left magneto during run-up. Otherwise engine operates smoothly."
|10-52949 Impulse Coupling Spring|
Diagnosis: Retarded engine timing caused by broken impulse coupling spring.
Underlying Condition leading to Failure: Corrosion pitting
Prevention: Replace impulse coupling spring on engines that show signs of exterior corrosion and at a maximum of 500 hour intervals or in accordance with manufacturer's recommendations.
|Red rust caused by condensation collecting in magneto.|
Additional Warnings: D-2000 and D-3000 magnetos, broken impulse coupling can lead to severe loss of engine power and forced landing. Replace spring at each annual inspection might be something to consider.
Here are two videos I did that shows you how to wind impulse coupling springs