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Tech. Advice: Series 'A' 500cc/1000cc Bikes
Main Bearings Clearances for Series A Singles and Twins
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<blockquote data-quote="A_HRD" data-source="post: 84975" data-attributes="member: 49"><p>Post-war Vincents are generally accepted as needing C3 fit main bearings so as to allow for the radial clamping action of the crankcase on the bearing outer ring - causing a slight tightening of the bearing clearances. The C3 looser fit takes this into account and minimises the chance of early bearing destruction. </p><p></p><p><em>However, what is the general view regarding the need for C3 fit bearings in the Series A? </em></p><p></p><p>Don't forget we have the same basic principle on the timing-side of the 'A'; that is the bearings press-in to the alloy of the crankcase (although in my experience there appears to be less interference here than with post-war Vincents). </p><p></p><p>On the drive side, the 2 x bearings are housed in a fairly thick steel sleeve that is a push-fit in to the crankcase. Again, the bearing fit in to this sleeve is little more than a firm push-fit. Moreover, the drive side roller (MRJA1) has a thrust face on the outer sleeve making it an L shape (in section) which would better resist any tendency to closing-up radially. So I contend that the need for C3 clearance bearings in the Series A, particularly those with original 80 year old crankcases, is not essential. But I would welcome other views. </p><p></p><p>Peter B</p></blockquote><p></p>
[QUOTE="A_HRD, post: 84975, member: 49"] Post-war Vincents are generally accepted as needing C3 fit main bearings so as to allow for the radial clamping action of the crankcase on the bearing outer ring - causing a slight tightening of the bearing clearances. The C3 looser fit takes this into account and minimises the chance of early bearing destruction. [I]However, what is the general view regarding the need for C3 fit bearings in the Series A? [/I] Don't forget we have the same basic principle on the timing-side of the 'A'; that is the bearings press-in to the alloy of the crankcase (although in my experience there appears to be less interference here than with post-war Vincents). On the drive side, the 2 x bearings are housed in a fairly thick steel sleeve that is a push-fit in to the crankcase. Again, the bearing fit in to this sleeve is little more than a firm push-fit. Moreover, the drive side roller (MRJA1) has a thrust face on the outer sleeve making it an L shape (in section) which would better resist any tendency to closing-up radially. So I contend that the need for C3 clearance bearings in the Series A, particularly those with original 80 year old crankcases, is not essential. But I would welcome other views. Peter B [/QUOTE]
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Tech. Advice: Series 'A' 500cc/1000cc Bikes
Main Bearings Clearances for Series A Singles and Twins
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