Ed Anderson - 02/MAY2001

Problem: It is relatively easy to place the 13B oil-pump chain drive sprocket on the oil pump shaft without having the woodruff key correctly positioned. Sliding the sprocket on the shaft can push the key out of its slot in the shaft and trap it against the oil pump aluminum housing. The torque (30 ft/lbs) of the oil shaft nut can provide sufficient clamping force on the drive sprocket, pressing it against the oil pump shaft shoulder, that it will drive the oil pump - at least for a while. I flew approx. 10 hours with the oil pump in this condition - until a fortunate event caused the sprocket drive to break lose from the clamping force of the nut with resulting drop in oil pressure to 20 psi. Fortunately this happened on the ground and investigation led to discovery of the problem.

Recommendation: Use some method to ensure the key is properly position before placing washer/nut on the shaft. Here are two suggestions:

1.) Visually ensure that the key is in the shaft by looking down the shaft keyway.

2.) Use a paper clip with one leg bent 90 degrees, insert the end of the bent leg in the woodruff keyway and ensure that it does not extend all the way. In other words, the leg of the clip should encounter the key before the leg is fully inserted into the keyway.