User-Agent: Microsoft-Outlook-Express-Macintosh-Edition/5.02.2022
Date: Tue, 03 Oct 2000 00:51:36 -0700
Subject: Re: 320/360 Spinner Backup Plate Fractures
From: Doug Weeldreyer <skyweel@earthlink.net>
To: <lancair.list@olsusa.com>
Message-ID: <B5FEDE18.390%skyweel@earthlink.net>
Reply-To: lancair.list@olsusa.com
Mime-Version: 1.0

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If you place the spinner backup plate on a bench with the flange down and
put a straightedge across the face, you will find that the face is cupped
down toward the center. Therefor the face is not perpendicular to the bolts
going through it and a stress is created as the nuts are tightened and the
face is pulled perpendicular in the small area right around the bolt.
Doublers with rivets simply don't solve the problem. I used tapered shim
stock on both sides of the backup plate allowing the plate to remain out of
perpendicular allignment and unstressed. At Lancair we used self centering
washers from McMaster Carr on both sides of the backup plate and
accomplished the same thing. You will have to make the backup plate spacers
shorter to allow room for the washers if you want the spinner spacing to
remain the same. A bulkhead in the spinner is also a must. After cracking
two backup plates in short order on my 360 and then making the fix I have
had no cracking in 400 hours.

Apparently when the center is cut out of the backup plate during
manufacturing,  stress is relieved and the face becomes cupped.

Doug Weeldreyer 
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Please send your photos and drawings to marvkaye@olsusa.com.
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