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Date:  7-1-2017
Number of Hours:  2.00
Manual Reference:  
Brief Description:  Mandatory Service Bulletin

A Mandatory Service Bulletin was received from SPA a couple of days ago, relating to shearing of the tail wheel assembly mounting bolt; experienced by another builder.

The Bulletin called for inspection to see that the bolt was a tight fit in its hole, and if not to replace it with a NAS bolt, or a first oversize bolt, to insure a tight fit. If any movement was detected after this work, a second bolt was to be added ¾” behind the original, using tight fit practices.

My tailwheel assembly was very tight, but I decided to insure it didn’t become a future problem by installing the second bolt anyway. I did not want to remove the entire assembly or freehand the drilling operation. So, I decided to make a drill fixture that could be securely clamped in place. The fixture consists of an AMERICAN VALVE 3/4-in dia. Galvanized Split Ring Hanger, from Lowes, costing $1.72, a 5/16 bolt, and nut. A minor amount of grinding the clamping radius with a Dremel tool was needed to achieve a good fit to the tailwheel shank.

The bolt with the nut at midpoint of the bolt was mounted in my lathe and an 11/64” hole was drilled through the center, yielding the fixture shown in image #1. This assembly was tightly clamped around the tailwheel shank as shown in image #2, and an 11/64” hole was drilled through the aluminum shank and the stainless steel spring. I used a new cobalt drill bit at a low speed, with lots of pressure to complete the hole.

The bolt and nut were then removed from the fixture and remounted in the lathe and the through hole upsized to a #14 drill. The bolt and nut were re-assembled to the fixture and the hole in the tailwheel assembly was updrilled to #14. The Process was repeated again to upsized the bolt hole and tailwheel hole to 0.187” with a reamer. The hole was cleaned, both ends beveled, and an AN-3 bolt was inserted using a plastic mallet to drive it through.

The inexpensive drill fixture worked very well.
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Drill Fixture

Drill Fixture

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Drill Fixture In Position

Drill Fixture In Position

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Service Bulletin Compliance Completed

Service Bulletin Compliance Completed

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