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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Black Shadow Crankcase Threads
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<blockquote data-quote="oexing" data-source="post: 177141" data-attributes="member: 1493"><p>Firstly 9/16-20 thread is NOT UNF, that is 18 tpi at 9/16. That is why my tap from Aliexpress is marked UN 9/16-20 and is cycle thread for bicycle pedals - still. And no, it looks like at Vincents they had thread rolling heads for producing cylinder studs. Why : I looked at my 5 studs from the Argentinan engines, two will most likely be standard, the two at bottom of first photo. They got waisted tubes for ca. 13 mm for working with the rolling head, you have to reduce the 9/16 stud for this diameter certainly. The three above them are repairs most likely done in Argentina, by chasers or thread cutting, not rolled . It is very unlikely that in Argentina they had a rolling head for that cycle thread , so the two rolled types are originals I say.</p><p> We do not know today the reasons then to have 60 degrees thread form which I verified by a little use of the microscope. See yourself and draw your conclusions. One reason is the remaining meat around the rolled thread when having 60 degrees AND having a through hole of 3/8 inside with the two part studs post war. That gives less than 2 mm wall thickness, so 60 degrees is better than 55 degrees. . Plus we do not know about equipment at the works, maybe thread rolling heads from cycle threads - which got 60 degree rollers. Or maybe heads from USA that got the 60 degree types from UNC or UNF - unlikely as they don´t offer the 20 tpi type ? But they may have come to that available bicycle pedal thread as best compromise when having the two part studs and maximum remaining meat at threaded ends, not an argument with the later one part studs.</p><p> In my photos a lathe tool with 55 degrees profile is shown , next to the UN 9/16-20 tap and the obviously standard B-type two part studs. Your choice if you can see 55 degrees or rather 60 degrees . . .</p><p></p><p> Vic</p><p></p><p>[ATTACH=full]61234[/ATTACH]</p><p></p><p>[ATTACH=full]61235[/ATTACH]</p><p></p><p>[ATTACH=full]61236[/ATTACH]</p><p></p><p>[ATTACH=full]61237[/ATTACH]</p><p></p><p>[ATTACH=full]61238[/ATTACH]</p><p></p><p>[ATTACH=full]61239[/ATTACH]</p></blockquote><p></p>
[QUOTE="oexing, post: 177141, member: 1493"] Firstly 9/16-20 thread is NOT UNF, that is 18 tpi at 9/16. That is why my tap from Aliexpress is marked UN 9/16-20 and is cycle thread for bicycle pedals - still. And no, it looks like at Vincents they had thread rolling heads for producing cylinder studs. Why : I looked at my 5 studs from the Argentinan engines, two will most likely be standard, the two at bottom of first photo. They got waisted tubes for ca. 13 mm for working with the rolling head, you have to reduce the 9/16 stud for this diameter certainly. The three above them are repairs most likely done in Argentina, by chasers or thread cutting, not rolled . It is very unlikely that in Argentina they had a rolling head for that cycle thread , so the two rolled types are originals I say. We do not know today the reasons then to have 60 degrees thread form which I verified by a little use of the microscope. See yourself and draw your conclusions. One reason is the remaining meat around the rolled thread when having 60 degrees AND having a through hole of 3/8 inside with the two part studs post war. That gives less than 2 mm wall thickness, so 60 degrees is better than 55 degrees. . Plus we do not know about equipment at the works, maybe thread rolling heads from cycle threads - which got 60 degree rollers. Or maybe heads from USA that got the 60 degree types from UNC or UNF - unlikely as they don´t offer the 20 tpi type ? But they may have come to that available bicycle pedal thread as best compromise when having the two part studs and maximum remaining meat at threaded ends, not an argument with the later one part studs. In my photos a lathe tool with 55 degrees profile is shown , next to the UN 9/16-20 tap and the obviously standard B-type two part studs. Your choice if you can see 55 degrees or rather 60 degrees . . . Vic [ATTACH type="full" alt="P1110830.JPG"]61234[/ATTACH] [ATTACH type="full" alt="P1110833.JPG"]61235[/ATTACH] [ATTACH type="full" alt="P1110837.JPG"]61236[/ATTACH] [ATTACH type="full" alt="P1110810.JPG"]61237[/ATTACH] [ATTACH type="full" alt="P1110813.JPG"]61238[/ATTACH] [ATTACH type="full" alt="P1110814.JPG"]61239[/ATTACH] [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Black Shadow Crankcase Threads
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