912S Worn Prop Shaft

Hi All

I think there is a misunderstanding of what the issue is with AVGAS in the gearbox.  it is not at all related to the friction setting, that is simply wear on the disk springs.  The problem is if you have an engine that is equipped with an overload clutch.  The clutch pack can be contaminated with lead sludge and lose its effectiveness.  The only way to clean it is to remove the clutch pack and have it sent to a qualified shop to be cleaned and reset for the correct breakaway values.  

As a note when you read the text from the heavy maintenance manual it states that any sign of wear on the disk springs when doing an inspection requires that they be replaced.  Shimming a worn disk spring simply limits the travel on the spline of the prop shaft and creates more wear problems.  

Here is the text I refer to: .—If there is visible wear to the disc springs (18) in the contact area

(19), they must be replaced.

Cheers

I have always understood the friction torque test to be an indication of the strength of the disc springs.  Of course, that test only applies to engines with the overload clutch, which have the 30 degree dogs.  I agree that it is separate issue from the shorter internal gearbox inspection schedule necessitated by "overuse" of leaded fuel.

So... in this case really there were two different things going on, both of which really required the gearbox be removed and inspected.  That probably should have been done aroud 600h, given the constant use of leaded fuel; the spring washers coulda/shoulda/woulda also been replaced at that time, so the friction torque would never have been allowed to go so low by this (1000h) point.  Had that all been done at 600h (as recommended), instead of at 1000h, maybe the prop shaft, etc, would now be OK.