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Tech. Advice: Series 'A' 500cc/1000cc Bikes
Series A large idler thrust washer
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<blockquote data-quote="A_HRD" data-source="post: 103263" data-attributes="member: 49"><p>Mark,</p><p></p><p>I'm glad you asked this question because I needed a reason to go searching for mine which went AWOL...</p><p></p><p>Like most things with the 'A', the answer isn't so easy. Early Singles - yours, and also mine built Oct-Feb 35/36 - had a 2 piece thrust washer comprising a hard steel ring which fitted partially over the bronze bush flange before fitting the assembly in to the crankcase with a 1 to 2 thou interference fit (heat case first -and ensure oil-hole lines up). </p><p></p><p>Later singles used a one-piece bush (top of pic) to save all the hassle of the earlier variant. This new bush was made from cast iron and had a thicker top-hat brim at 0.218" (same as the earlier steel piece). Let's face it, I don't really see much input to cause any significant longitudinal thrust from the large idler, so this "production easement" must have seemed more logical. Overall length is 15/16", ID is 0.625", OD is 0.8765". Bob S mentions the later variant in "Ab Initio" - which of course is also widely featured in the imminent <strong>new book - Back to 'A' </strong>(plug, plug). <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite8" alt=":D" title="Big Grin :D" loading="lazy" data-shortname=":D" /></p><p></p><p>I think you and Greg are both right about idler end-float. It does need some of course, but not much, 4-10 thou max would seem right to me. I don't believe there were ever any figures published for this - but I stand ready to be corrected. </p><p></p><p>Peter B</p><p></p><p></p><p>[ATTACH=full]25505[/ATTACH]</p></blockquote><p></p>
[QUOTE="A_HRD, post: 103263, member: 49"] Mark, I'm glad you asked this question because I needed a reason to go searching for mine which went AWOL... Like most things with the 'A', the answer isn't so easy. Early Singles - yours, and also mine built Oct-Feb 35/36 - had a 2 piece thrust washer comprising a hard steel ring which fitted partially over the bronze bush flange before fitting the assembly in to the crankcase with a 1 to 2 thou interference fit (heat case first -and ensure oil-hole lines up). Later singles used a one-piece bush (top of pic) to save all the hassle of the earlier variant. This new bush was made from cast iron and had a thicker top-hat brim at 0.218" (same as the earlier steel piece). Let's face it, I don't really see much input to cause any significant longitudinal thrust from the large idler, so this "production easement" must have seemed more logical. Overall length is 15/16", ID is 0.625", OD is 0.8765". Bob S mentions the later variant in "Ab Initio" - which of course is also widely featured in the imminent [B]new book - Back to 'A' [/B](plug, plug). :D I think you and Greg are both right about idler end-float. It does need some of course, but not much, 4-10 thou max would seem right to me. I don't believe there were ever any figures published for this - but I stand ready to be corrected. Peter B [ATTACH=full]25505[/ATTACH] [/QUOTE]
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Tech. Advice: Series 'A' 500cc/1000cc Bikes
Series A large idler thrust washer
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