Uber race crank

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RinB
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Wed Jan 07, 2009 4:46 pm

Basically this is whats being done to crank

As you can see very simular to Vespa cranks and alot of bike cranks

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Smiffy
If its made of Metal Fettle it !!

RobD
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Wed Jan 07, 2009 4:50 pm

That's what I'd pictured, at BDC wouldn't you have a cavity behind the webs with only the area around the big end for gas flow to occur?

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sean brady scooters
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Wed Jan 07, 2009 4:52 pm

yep.....thats the idea.........but the remaining webs will be chamfered on ours...... :D
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drunkmunkey6969
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Wed Jan 07, 2009 4:52 pm

RobD wrote:That's what I'd pictured, at BDC wouldn't you have a cavity behind the webs with only the area around the big end for gas flow to occur?
I'm trying to visualize what you mean?

Have you accounted for the metal removal from inside the crank case, as per my earlier post?

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sean brady scooters
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Wed Jan 07, 2009 4:53 pm

its the chamfere that will allow flow all around.............
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RobD
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Wed Jan 07, 2009 5:04 pm

I see what you mean about the chamfering lessening the bottleneck to the gas trapped behind the crank with this race design. Can't get my head around the advantage of bell shaped webs though. What advantages do they bring? All I can see them doing is creating lots of turbulence and trapping charge behind them :?: Then you're chamfering them to ease trapped gas flow caused by having bell shaped webs. Only benefits I can understand are the lowering rotating weight and primary compression on the full circle but just lowering weight on the race design. Won't primary compression be all over the place as opposed to lowered with a full circle crank due to the constantly changing effective volume of the crankcase? Sorry if I'm being thick :D

I could sort of understand if the bell wasn't exactly opposite to the pin and you were using the turbulence to create a pumping effect to charge the cylinder?

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sean brady scooters
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Wed Jan 07, 2009 5:11 pm

......nothing would be trapped as such anyway...........so no bottle neck prob....
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RobD
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Wed Jan 07, 2009 5:29 pm

Captain Pedantic here ;)

Ok I can see that if you remove the crankcase neck web you'll lessen ;) the bottleneck on the driveside but what are advantages are you expecting other than a reduction in rotating weight?

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drunkmunkey6969
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Wed Jan 07, 2009 5:33 pm

RobD wrote:Captain Pedantic here .......... but what are advantages are you expecting other than a reduction in rotating weight?
.......decrease in rotating mass, improved gas flow, lower primary compresion, increased lubrication.

We're just cutting a bit off a crank.....what more are you expecting? :lol: :lol:

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Wed Jan 07, 2009 5:42 pm

I'll wait and see the results ;)

I've got you down for decrease in rotating mass (which will increase revs, but an increase in vibration due to the crank inbalance which will decrease revs), disrupted gas flow and fluctuating primary compresion. Can't argue with the potential improvement to big end lubrication though, you've got me there :lol: :lol:

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