Prop Tracking Issue

[Aviaman]

I have a prop tracking issue. I have a Cato 3 blade FP on my RV-9A.
I have one blade which tracks 1/8?, or slightly greater, aft of the other 2 blades. I re-clocked the prop 60 degrees, then checked tracking again. It turned out the SAME blade was still 1/8? aft of the other 2 blades. This implies that either the blade itself is warped or that the aft mating surface of the prop is not parallel to the plane of the 3 blades. These 2 situations would cause the same blade to be aft upon the second tracking check. However, If the hub front surface itself was not parallel to the rotation plane of the crankshaft hub, another blade would have been aft upon the second tracking check.

If I assume either the 1 blade is warped or the mating surface of the prop is not parallel to the plane of 3 (true) blades, it would be tempting to shim the prop mating surface. However, I believe the mating surface should be an intimate contact across the entire surface, and not have a washer or shim causing voids and local concentrations of force. Or could a very thin shim, like paper be acceptable? Any opinions on this ?

 

[D Weisgerber]

I would call Catto, I've always heard good things about them. I would never shim it!

 

[lr172]

My understanding is that the resistance to rotation of the prop is via friction between the hub face and the flywheel face, accomplished via proper bolt torque. Catto once showed picture of the severe, heat-based fretting of the hub face when the bolt was allowed to loosed just 10-20 degrees.

I absolutely would not put shims in their!!

Larry

 

[Aviaman]

I hear you guys 5 x 5. No shims!!

 

[lr172]

I would get catto's opinion. Beyond balance, I can't see a reason this issue would cause any real performance issues, assuming it is not warpage that also caused a change in the pitch of that blade. But I don't know a lot about props and Catto does.

Larry