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Dan Smith's Latest Project

Little Honda

Well Known and Active Website User
VOC Member
Same trail and fork length as Domy. The trans is in stock position with the engine squeezed in, leaving enough room for the exhaust pipe to clear the front down tube. Primary chain is the same length as my A +twin.The frame is stock with the exception of a small cutaway on the top right rail to clear front intake rocker cover. The bike is very smooth up to 67 mph when a vibration starts. I balanced each 1/2 of the 270 deg. crank at 67%. Looks like it'll come apart some day to raise the balance factor. Neat riding bike at this point. I need more miles on it but our good riding weather in nearing an end for this year.
Is there a head-clamp fitted to the frame? As felt vibrations are a product of resonances, a higher balance factor may not always help. PEI gave some good explanations on balancing and focussed on this special
problem of engine manufacturers like JAP, whose engines were fitted into many different frames, showing
a very different vibration profile (with the same engine). See "Motorcycle Engineering", p.280: "....found in the original Vincent-HRD. singles. These engines ran very smoothly in the standard spring frame with a
factor of 66 %, but the speedway versions,......, vibrated badly in a cobwebby dirt-track frame until the factor
was reduced to 61%, this not very large reduction making all difference between a machine which was
passably smooth and one which shook itself out of your hands."
 

Nigel Spaxman

Well Known and Active Website User
VOC Member
What a fantastic achievement. That type of crank always interested me. I have a Honda VT500 Ascot. It is a 50 degree V twin with a forged crankshaft with two throws. I am not sure what the angle is between the pins. Honda had a way of off setting the pins that they said achieved the same perfect primary balance that the 90 degree V twin can achieve. The 90 degree V twins like Ducati and Moto Guzzi are very smooth. They need a 50% balance factor. The Hondas like the VT500 are very smooth as well. I understand the balancing of the 90 degree engines. I have neve quite managed to figure out the balancing on the Hondas. I think it might be possible that if you get the balance factor just right that this engine could be as smooth as a Ducati. I am pretty sure the right balance factor is going to be 50%. With V twins like the Vincent the balancing is always a bit of a compromise, just like with a single or vertical twin. With engine layouts that can't have perfect primary balance, you are always trading horizontal vibrations for vertical ones. I have one very unusual bike, a Triumph with a 0% balance factor. That might seem wrong but that particular bike has a rubber engine mounting system that can only isolate vertical vibrations. This system works pretty well on this bike.
 

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