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Old 03-01-2010, 09:19 AM   #1 (permalink)
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output shaft on Genesis 80Fi

On the 2007+ Phazers, there is a large cylindrical part on the output shaft to the CVT. It appears to have a floating outer shell which is gear driven by the crank, and an inner part that bolts to the CVT. The part is listed as 'Primary Sheave Drive Shaft Assembly' in the service manual, and is half of the 'Drive Gear Set' in the OEM catalog. Does anybody know what this thing is? It looks like it may be some kind of torsional damper, but it is attached to the CVT instead of the free end of the crank. I need to know exactly what this part is, but don't want to cut it apart to find out. It may also be on other sled motors, but I'm not sure.

Any help would be great.

Here are some pics of it in the manual:
This thing:


and part 3 here
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Old 03-01-2010, 11:00 AM   #2 (permalink)
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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?
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Old 03-01-2010, 11:46 AM   #3 (permalink)
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Quote:
Originally Posted by Jerrys1 View Post
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.
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Old 03-01-2010, 01:09 PM   #4 (permalink)
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I know on the atv engines they always ran a somewhat heavy counterbalance shaft on the single and twin cylinder engines because of their inherant problem of stumbling or occasional "cough" caused when the throttle is opened and they arent at the compression/ fire stroke the 3 and 4 cylinder engines dont have that problem because of having additional cylinders the time between cylinders firing is reduced. This engine has a lightweight counterbalance shaft so I think your right its being used as a dampner/flywheel to eliminate the stumbling problem that persists in the 4 stroke engine.

That is a pricey part to be cutting up I agree but I cant give a definitive answer I wish I could be of more help. My personal thought would be that you probably need some of that weight to keep enough momentum in the engine to keep it running at low rpm's how much would be the question? Given the application that your running it in I dont think low rpm operation is a very big deal since most of the time it will be running wide open but it must stay running when the clutch is pushed in.

Have you tried to contact anyone from yamahas office's in CA. they used to have a pretty good program with racers such as yourselves its been a few years and I dont know if they still do this but they used to give a lot of technical support to cart racers that I knew.

Again would love to see some pics of that driveline setup when your done!
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Old 03-01-2010, 05:27 PM   #5 (permalink)
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Ill try and give Yamaha a call, see if I can find anything out. Thanks for your help.
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