Re: Broken Skytech pinion tooth (Q200)


Kevin Fortin <kfortin@...>
 

Guys,

I forgot to include in my previous email that a major deflection of the
pinion shaft was detectable because the pinion was pushed far enough off
center to put a gouge in an aluminum "shroud" that wraps around the "open"
side of the pinion (the shroud is part of the starter casting). Skytech knew
immediately what I was talking about when I mentioned this. This deflection
is what made me believe that the gears are off center to begin with. I know
from experience that improper centerline distances, on the plus side,
increase gear separation forces dramatically.

I don't think there is anything intrinsically wrong with the pinion itself.
Apparently it is supplied by Hitachi and is used for other starters in the
aircraft industry.


Kevin

-----Original Message-----
From: britmcman@aol.com [mailto:britmcman@aol.com]
Sent: Tuesday, February 22, 2005 9:02 PM
To: Q-LIST@yahoogroups.com
Subject: Re: [Q-LIST] Broken Skytech pinion tooth (Q200)


Hello All:

There is a lot of available science out there regarding failure analysis.
The broken gears that so many of you seem to have produced should be looked
at
by a metallurgical analytical lab. In order to solve this problem there
ought to be someone at Skytec doing all of this anyway. When something
isn't
right, there is a reason. Consider defective metals, castings, forgings,
heat
treatments, case hardenings, etc. A look at the fracture with an electron
microscope may reveal the real reason that gear tooth broke off.

I would insist that the manufacturer conduct a thorough root cause and
corrective action investigation. They should insist on doing it if they
want to
stay in business. The starter's design and materials should be robust
enough
to survive routine occurrences such as kickback.

Phil Lankford
N870BM
B&C Starter


[Non-text portions of this message have been removed]




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