since 1940

Camshaft followers, tappets, not rotating in Continental or Lycoming aircraft engine

Evidence of non-rotation of a camshaft follower can be caused by:

 1. Camshaft lobe ground straight. There should be a .001 to .003 taper ground on the face of the lobe to provide the rotational force required to rotate the follower.

2. Crankcase tappet bore worn. If the tappet bore is worn "egg-shaped" it can prevent tappet rotation. Evidence of a worn bore can be seen on the contact face of the tappet. The camshaft lobe doesn't contact the very edge of the tappet face. The tappet face will therefore have an area on the edge where no contact has occurred. This area should be the same thickness around the entire circumference of the follower. If the crankcase tappet bore is worn it allows the tappet to deflect sideways in the bore. This causes the camshaft lobe to contact the tappet closer to the edge in some areas than others. An uneven wear pattern on the edge of the tappet face indicates the crankcase tappet bores are excessively worn and should be repaired.

 Notice black edge on right is wider than edge on left. The camshaft follower is loose in the crankcase tappet bore causing the follower to wobble. This is a sign that the crankcase tappet bore is worn out. Also notice numerous black spots that are corrosion pits. If allowed to remain in service, small chunks of the surface will break-off. Rough surface will damage camshaft lobe. This type of damage will usually not be detected in a pre-purchase inspection, and oil analysis inspection. It can be detected by removing a cylinder and taking a look. Pitting is typically found in low time - low usage engines. 

Copyright 2003 by Sacramento Sky Ranch Inc. All rights reserved.  Prices subject to change without notice. Not responsible for typographical or misprint.
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.