Re: Distributors are happy now

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Posted by Tim Daley(MI) on September 11, 2017 at 07:44:51 [URL] [DELETE] :

In Reply to: Re: Distributors are happy now posted by Tim Daley(MI) on September 10, 2017 at 07:33:53:

The HEX size on the SHCS is 9/64, not 9/32 as first stated, my bad. If head diameter is .27" the HEX can't be 9/32 ---DOH! I've been looking for something relatively close, even would accept a brass 8-32 HEX HEAD but no such luck, at least not at McM-Carr, and if they don't stock it, it ain't made. The 91A12159 screw was used across many Ford distributor modules, but, like many old Ford parts, is no longer serviced. I have a call out to my Early V8 buddies, specifically 1939 as that is what the 91A Ford Prefix designates when first used, for more info on the part. A true screw machine would be ideal. Here's how I would make them on an engine lathe: Chuck a length of 3/8" diameter brass rod; face & turn major OD at .344" and to a length of 17/32 (.531"); then part off. I calculated a 1/32" wide cutoff insert and leaving a half a millimeter for a finish face cut on the secondary operation to turn and thread the stem. Here's where I'd prefer a CNC Lathe with Live Tooling. After facing and turning, I'd use a 5/16" Ball Nose Endmill and Machine the coil spring well pocket to depth. Next, use a 1/16" endmill to cut the screw slot to size and depth. 2nd Turn Operation: Flip part around, collet chuck the turned end with positive stop on back face. Finish face to overall length of .475" and turn the 8-32 UNC major diameter at .163" for .31" length with a slight undercut at shoulder face. Single point 8-32 UNC thread full length. Without the actual drawing, here are the 91A12159 screw specs as best as I can determine: Head - .344" diameter at .165" width. Coil Spring Well Socket at 5/16" diameter to 1/32" depth. Screw slot - 1/16" width to 1/16" depth from face. 8-32 UNC 2A to .31" full length. A CNC Lathe/Screw Machine could to produce the entire part in one operation. Perhaps Kevin Norman at Carpenter will read this and start repopping them. Unless someone already makes these, I'm kind of surprised DC hasn't already made them.


Tim Daley(MI)

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