Prop balancing

[Thomas Augustin]

Why do props have .008 to .010 thousands clearance over the shaft diameter (.250)? I think a balanced prop that is not a slip fit to the shaft would not run concentric and result in excessive vibration and wear on the strut bearings/bushings. Any advice or suggestions?

 

[Wasted wages]

I guess that it's needed to be able to slip over the threads of the shaft. The threads raise the metal to some degree as they are cut or rolled.

If the props were honed to exact fit of the shaft, I don't think you could get it past the threaded portion on all different shafts..

IMHO, leaving the prop nut backed off a half turn from tight, allows the prop to float on the shaft, and finds its own center...forward thrust keeps it engaged with the drive dog.

 

[Terry Keeley]

Sorry Frank. I havta disagree.

In my opinion the prop should be a good slip fit on the shaft, otherwise every time a blade "bites" the prop cants throwing everything out of whack. It's bad for vibration and can beat out bushings and bend and/or break shafts.

What prop(s) were they?

 

[justaddwata]

Most every prop I have is snug or better. Occasionally I have to ream one out to fit. Then again not all shafts are the same. I find the German stern drives and European cables tend to be a tighter fit overall.

Is the shaft measuring .250 exact?