Challenger reduction drive failure, Hegar belt reduction drive failure.

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Aircraft:
All ultralight aircraft using Heagar belt reduction drive.

Incident Report:
Several ultralight pilots flying various ultralights using the Heagar belt reduction drive have reported loss of propulsion both on the ground and in the air.

Upon closer examination it was found that;
The top pulley retaining nut had loosened off, transferring the belt load to the 1/4 adjusting bolt which then snapped allowing the belts to slacken and thus the lack of propulsion. In another case the top pulley shaft had severed where the adjusting bolt threads through the shaft.

In another case the top pulley shaft had worn (after approx. 150 hrs.) allowing the belts to slacken off. In another case the top pulley shaft bearings had completely disintegrated, causing the top pulley to lock on the shaft.

Suggestions:
1. the correct way to tighten the top pulley lock nut is to first snug up the belts using the adjusting bold, with the lock nut snug but not tight, then remove the adjustment bolt, place approximately 100 ft/lbs of torque on the lock nut, replace the adjustment bolt. ( this allows tensioning of the nut without fear of bending the adjustment bolt.)

2. Check your top pulley shaft on a regular basis for abnormal signs of wear, and at the first sign of wear replace.

3. Check your top pulley shaft bearings on a regular basis, (some early models had less support bearings than later models, if so then replace reduction drive with newer model)

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