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Farm Machinery
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High horse power four cylinders can’t sustainably do the same job as a larger six pot of similar HP. Tell me I’m wrong
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<blockquote data-quote="Cowabunga" data-source="post: 7478506" data-attributes="member: 718"><p>No it wouldn't. All engines from the same family sound similar except that a four cylinder engine fires every 180 degrees of crank rotation and the three cylinder every 240 degrees. Thats 720 divided by three. Deduct 180 from 240 and you find that the three cylinder engine is only without a power stroke for 60 degrees out of a revolution. Problem is that secondary forces make a three rock backwards and forwards, not side to side.</p><p></p><p>Far a four 720/4=180. So it fires at every 180 degrees of crank rotation. Deduct 180 [a piston's travel from top to bottom] from 180 = 0 This means that an in line four is always on a power stroke. Therefore it is better than a three cylinder and will not rock backward and forwards as a result of always being on a power stroke. Also it has a perfect primary balance because two pistons going up are always balanced by two going down. The secondary balance is poor though because all four pistons actually stop at the same time. The two outer cylinders will be at the top at the same time as the two inner ones are at the bottom with all four transitioning to the reverse direction at the same time. This means that the four needs two balancing shafts, counter-rotating, at twice the crank speed, because the pistons stop twice in every 360 degrees [one revolution].</p><p></p><p>A six cylinder engine 720/6=120. So a firing stroke happens every 120 degrees. Deduct 180 from 120 and you a 60 degree overlap of firing strokes. There is always a piston on the power stroke and for part of every power stroke there are two. This means that both primary and secondary forces are eliminated. No tendency to rock either side to side or back to front. Due to pistons travelling further and faster at the top of the stroke compared to the bottom, sometimes compounded by offset gudgeon pins to minimise side thrust [piston slap] on the power stroke, there may be torsional vibrations which try to speed and slow the crank, or twist it if you like, hence the almost universal fitment of torsional vibration dampers at one or other end of the crankshaft.</p></blockquote><p></p>
[QUOTE="Cowabunga, post: 7478506, member: 718"] No it wouldn't. All engines from the same family sound similar except that a four cylinder engine fires every 180 degrees of crank rotation and the three cylinder every 240 degrees. Thats 720 divided by three. Deduct 180 from 240 and you find that the three cylinder engine is only without a power stroke for 60 degrees out of a revolution. Problem is that secondary forces make a three rock backwards and forwards, not side to side. Far a four 720/4=180. So it fires at every 180 degrees of crank rotation. Deduct 180 [a piston's travel from top to bottom] from 180 = 0 This means that an in line four is always on a power stroke. Therefore it is better than a three cylinder and will not rock backward and forwards as a result of always being on a power stroke. Also it has a perfect primary balance because two pistons going up are always balanced by two going down. The secondary balance is poor though because all four pistons actually stop at the same time. The two outer cylinders will be at the top at the same time as the two inner ones are at the bottom with all four transitioning to the reverse direction at the same time. This means that the four needs two balancing shafts, counter-rotating, at twice the crank speed, because the pistons stop twice in every 360 degrees [one revolution]. A six cylinder engine 720/6=120. So a firing stroke happens every 120 degrees. Deduct 180 from 120 and you a 60 degree overlap of firing strokes. There is always a piston on the power stroke and for part of every power stroke there are two. This means that both primary and secondary forces are eliminated. No tendency to rock either side to side or back to front. Due to pistons travelling further and faster at the top of the stroke compared to the bottom, sometimes compounded by offset gudgeon pins to minimise side thrust [piston slap] on the power stroke, there may be torsional vibrations which try to speed and slow the crank, or twist it if you like, hence the almost universal fitment of torsional vibration dampers at one or other end of the crankshaft. [/QUOTE]
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High horse power four cylinders can’t sustainably do the same job as a larger six pot of similar HP. Tell me I’m wrong
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