Lightened Flywheels

Pushrod Twin

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First you will have to work out how to achieve concentricity on a laser machine. Pity you`re not here, half an hour on the mill, and I could have all three gears done. Hard ? , No problem. Without removing the cams also.
.......... experience has showed me that lightening flywheels has more useful effect on performance. Moto Guzzi & BMW factories have both lightened flywheels progressively over the years & when I chewed a couple of pounds out of my V7 Sport wheel the difference in acceleration was impressive. Any time that I have mentioned this in Vincent circles I receive mumblings in beer & beards to the effect of "I wouldn't do that sonny", I even had one well known expert tell me that top speed would drop! Clearly, Vincent flywheels would need re-balancing because of the weight distribution, but I don't see any other deleterious effects.:)
 
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davidd

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Thanks for the offer Trev, maybe for the next engine I could post them to you? I know PEI recommended lightening valve trains, in M/C Engineering, to reduce inertia & I do see the benefit. But experience has showed me that lightening flywheels has more useful effect on performance. Moto Guzzi & BMW factories have both lightened flywheels progressively over the years & when I chewed a couple of pounds out of my V7 Sport wheel the difference in acceleration was impressive. Any time that I have mentioned this in Vincent circles I receive mumblings in beer & beards to the effect of "I wouldnt do that sonny", I even had one well known expert tell me that top speed would drop! Clearly, Vincent flywheels would need rebalancing because of the weight distribution, but I dont see any other deleterious effects.:)

Top speed will absolutely drop with lightened flywheels. Successful drag racers found their times went down significantly with heavier flywheels. Recently, Stuart Hooper complained to me that he could not get his flywheels heavy enough. He is hoping to break 200 mph on his Velo. Lots of Tungston alloy:

Stuart Hooper 2014 _PB_3.jpg

David
 

roy the mechanic

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David, that's one serious crank! Brian Chapman reconed his best time on mighty mouse was with a "standard" crank. Having a disaster the meeting before, it was all that was readily available! So I went with the standard weight on my "new thing ".
 

clevtrev

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Top speed will absolutely drop with lightened flywheels. Successful drag racers found their times went down significantly with heavier flywheels. Recently, Stuart Hooper complained to me that he could not get his flywheels heavy enough. He is hoping to break 200 mph on his Velo. Lots of Tungston alloy:

View attachment 12414
David
I think you`ve made a typo there.
 

vibrac

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First you will have to work out how to achieve concentricity on a laser machine. Pity you`re not here, half an hour on the mill, and I could have all three gears done. Hard ? , No problem. Without removing the cams also.
Last time I got worried enough to lighten timing wheels I had a set narrowed as well as drilled, it seems to have worked. off hand I don't even know which engine they are in:oops:
 

davidd

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I think you`ve made a typo there.

Thank you Trevor. I don't know why it seemed correct when I proof read it. I had trouble seeing it after you mentioned it.

HEAVY FLYWHEELS WILL INCREASE TOP SPEED not lower it.

David
 

passenger0_0

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In case you were wondering - increasing flywheel mass increases the mass moment of inertia which causes the coefficient of speed fluctuation to reduce which ultimately leads to a higher mean torque over the full cycle. Higher mean torque potentially could increase top speed, all else being the same, so David is right. If in doubt, try reading any good mechanics text.
 

Bill Thomas

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Why is it always me !, I have found that lighter flywheels rev' higher !!, As P.T. always says " how much is too much " !, When I was sprinting , I found the front wheel came up higher, Further away from the start line, I have run very narrow flywheels and now run with metal took off the rims, I was told it would mess up because the rims would be too far away from the scraper in the cases, But have found no problems, Cheers Bill.
 

davidd

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I think this is a tough one to figure out. Bill and PT are right in that the "seat of the pants" results tend to show that lighter is better in terms of performance, but I think if the performance were measured over a wider time period you would find that your results would be the same or worse than expected. So, the front wheel will come up faster and the engine might accelerate momentarily quicker, but the overall elapsed time will be longer.

Originally, it was a post here on the forum that put me on to this. It was a question that came up regarding primary belt drives and whether or not they provided some measure of shock absorption. It turns out they do not perform as an ESA even if they can damp out some vibration that could be transmitted by a solid gear. But I found that savvy tuners all seemed to favor ESA's as well as cush drives. I also knew that Stuart Hooper achieved really impressive speeds using a very heavy flywheel as well as using an ESA on his belt drive. As it turns out, Stuart understood the importance of taming the violent pulses delivered by the engine. The smoother the pulses were transmitted to the mechanical parts the better.

The sprinters found that at the higher rpm's the valves were not following the paths that the cams were describing. Strobe light shots of the valves opening and closing showed that the valve heads vibrated like a metronome needle at full height and kept vibrating while closing, often with the head hitting the valve seat off center and never closing. Additionally, four stroke engines do not make power when the valves are open, and they are open most of the time. Every spark causes a power pulse that must transmit power for the next several engine revolutions by using the energy stored in the flywheel. The lighter the flywheel, the quicker that power is delivered to the valve gear and cam followers (and all that follows) will be accelerated at a much higher rate. It was this high rate of acceleration that was causing the valves to dance around wildly.

Finally, these short fast power pulses were being delivered to the rear wheel. This would in turn cause the rear tire not to "hook up" as quickly or easily as the rider wished, thus reducing speed and lengthening times. These effects can be seen easily in singles, but Dick O'Brien at Harley, and Rob Muzzy at Kawasaki found these effects with their engines.

On street engines, you may only care about low end performance, but, like Bill you may wonder about the oil scavenging when you move the rim of the flywheel away from the scraper, but it probably won't show a problem. But, I can see why some of the grumpy old Vincent guys stick with the original flywheels.

Smoother is better!

David
 

passenger0_0

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Bill - I think we may be confusing acceleration with top speed. These are two completely different beasts I'm afraid.
 
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