Originally Posted by Jerrys1
I think you will find that you are thinking along the right lines I used to be a yamaha tech though I dont have a lot of wrench time on these new motors. But that said all of Yami's new motors are somewhat based off of their motorcycle/atv lines and the rpm range of these smaller motors are not exactly suitable for snowmobile use so they use a secondary shaft setup like the one pictured to produce an rpm range to suit the needs of the cvt type transmissions. Also I would think your right in thinking its also being used as a dampener and even somewhat as a flywheel to smooth the operation of the motor when being used to drive a cvt. The loads on this engine being used in a snowmobile are much different then what they would be in a bike or atv its sort of like comparing an io boat engine to a car engine they may share many things but most all the internals are different.
The bigger cc engines based off of the R1 motorcycle have an rpm range that is much wider and is easier to adapt to the cvt drive system on the sleds over the smaller 2 cylinder engines like the one you are using. But I am guessing that they also have to add some type of dampener/flywheel to help smooth the engine to keep it from coming apart during long periods of sustained high rpm operation.
I saw your post about what you are doing with these engines very cool stuff would love to see some pics of how you setup the final drivetrain. are you running a cvt final drive or motorcycle style trans as I know you mentioned you were building a trans out of motorcycle gearing?
The part is definitely heavy enough to be a flywheel, and is the only part on the engine that looks like it may be a damper. The only thing that makes me think it is not a flywheel or damper is that this part is only on the 2 cyl model-the 3 and 4 cyl versions don't have one.
The transmission is going to be transaxle style, with the differential and final drive built into the same casing as the rest of the gearset. Everything is gear driven, much closer to a indycar or F1 layout than anything else. This damper thing is terrible for the transmission because it is heavy, adds more gears to the system, and adds an extra gear reduction that I really don't want. I would like to drive the clutch directly off the crank, and throw this damper thing in the garbage. If I can figure out what it is, I want to make a custom one that will go inline with the crank before the clutch instead of gear driven. I would like to just cut it open and find out what it is, but a new one is $500.