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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Piston Choice
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<blockquote data-quote="Flo" data-source="post: 107945" data-attributes="member: 3744"><p>Prof Higgins has stated some semi clever snippets in the link:</p><p><em>The four cylinder in-line engine which is the most common on our roads can be made fully in primary balance, but <span style="color: rgb(235, 107, 86)"><u><strong>also has secondary out-of-balance forces which rotate at twice engine speed. These can be partially balanced by adding weights to the crank</strong></u></span>, and it is this and the reduction of main bearing loads which mainly concern the car engine designer. The in-line four can, of course, be completely balanced by using </em><span style="color: rgb(184, 49, 47)"><strong>one or two balance</strong></span><em> shafts rotating at twice engine speed, and this technique is used by a number of modern manufacturers. However, our old fashioned single cylinder Comets generate major primary out of balance forces which rotate at engine speed, and we can only partially balance these by adding weights to the crank, so manufacturers chose to ignore secondary out-of-balance forces, which are only small in comparison to primary ones anyway. As we saw in a previous article on Breather Timing in MPH 608 the Twins, which have 50 degree out of phase pistons running on a common crankpin, are very similar to a big single, and can be treated in a similar way for balancing purposes, though</em></p><p><em>the ideal balance factor is different. </em></p><p></p><p>Mostly the confusion arises by mixing components of the proper and complete dynamics of the crank-slider mechanism - one of those is the balance of forces and another one the non uniformity of rotation!</p><p></p><p>F</p></blockquote><p></p>
[QUOTE="Flo, post: 107945, member: 3744"] Prof Higgins has stated some semi clever snippets in the link: [I]The four cylinder in-line engine which is the most common on our roads can be made fully in primary balance, but [COLOR=rgb(235, 107, 86)][U][B]also has secondary out-of-balance forces which rotate at twice engine speed. These can be partially balanced by adding weights to the crank[/B][/U][/COLOR], and it is this and the reduction of main bearing loads which mainly concern the car engine designer. The in-line four can, of course, be completely balanced by using [/I][COLOR=rgb(184, 49, 47)][B]one or two balance[/B][/COLOR][I][COLOR=rgb(184, 49, 47)] [/COLOR]shafts rotating at twice engine speed, and this technique is used by a number of modern manufacturers. However, our old fashioned single cylinder Comets generate major primary out of balance forces which rotate at engine speed, and we can only partially balance these by adding weights to the crank, so manufacturers chose to ignore secondary out-of-balance forces, which are only small in comparison to primary ones anyway. As we saw in a previous article on Breather Timing in MPH 608 the Twins, which have 50 degree out of phase pistons running on a common crankpin, are very similar to a big single, and can be treated in a similar way for balancing purposes, though the ideal balance factor is different. [/I] Mostly the confusion arises by mixing components of the proper and complete dynamics of the crank-slider mechanism - one of those is the balance of forces and another one the non uniformity of rotation! F [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Piston Choice
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