upper gear bushing

[ROCKERDAN]

Dan, 21 tooth 15 wide upper sprocket with oil holes = Cat p/n 1702-490. Think there might be a backorder right now?

Thanks Brother!

 

[ROCKERDAN]

Dan, 21 tooth 15 wide upper sprocket with oil holes = Cat p/n 1702-490. Think there might be a backorder right now?

Anyone got the stock chain part number by chance? (for stock YAM 21/41)

Thanks gang
Dan

 

[ROCKERDAN]

IMO - things that contribute to load on upper sprocket bushing:
- size (weight) of that sprocket
- length (weight) of chain
- chain tension
- RPM
- amount of traction of track (unstudded vs. studded: more traction = higher load on chain case & belt)

I would think traction is a big one here....If you are hooking hard, that has to be a massive amount of force(with big tune) vs a guy with trail studs.

Dan

 

[Turboflash]

Yup! If track can't spin much, I think the load on the chain case goes up exponentially!

 

[ROCKERDAN]

I would like to hear more about the shims(thrust washers) that are on either side of the gear...

Has anyone been able to add another, to lend more support to the gear? Maybe hold it tighter? Or would side loading the snap rings cause problems?

Dan

OUTER

INNER

 

[Turboflash]

I'm running 21/38 w 84 pitch chain. Hardly any dog-leg at all.
I ran 22/37 for a season. Big speeds but hard on belts so I went back to 21/38 for best all-around IMO.

 

[ROCKERDAN]

Here is where my Chain tension was about 1000 miles ago....(approx 3000 odo)

Dan

Shown with 3/4 turn backed off.

 

[Turboflash]

Need to remember the top gear should theoretically be held "straight" on jackshaft by the reverse gear collar that slides over those short teeth on the side. Based on how much counterclockwise force one has to apply to the reverse servo when you're installing it, seems like the inside snap ring can stand allot of force without becoming dislodged. I think that counterclockwise force on the servo ends up directly on the inside snap ring?
So your thought is more shims should hold the gear straighter on shaft?

 

[ROCKERDAN]

Need to remember the top gear should theoretically be held "straight" on jackshaft by the reverse gear collar that slides over those short teeth on the side. Based on how much counterclockwise force one has to apply to the reverse servo when you're installing it, seems like the inside snap ring can stand allot of force without becoming dislodged. I think that counterclockwise force on the servo ends up directly on the inside snap ring?
So your thought is more shims should hold the gear straighter on shaft?

I just felt like there was "play" on that top gear when installed with thrust washers(in/out) and thought less play would lend support vertically to the gear. Probably not enough play for another thrust washer(too thick) but maybe a thinner-same ID/OD washer to take up the play....just thinking out loud.

 

[RAMSOMAIR]

With the shims on either side, could this limit the amount of oil getting in to lubricate?

 

[ROCKERDAN]

Need to remember the top gear should theoretically be held "straight" on jackshaft by the reverse gear collar that slides over those short teeth on the side. Based on how much counterclockwise force one has to apply to the reverse servo when you're installing it, seems like the inside snap ring can stand allot of force without becoming dislodged. I think that counterclockwise force on the servo ends up directly on the inside snap ring?
So your thought is more shims should hold the gear straighter on shaft?

There is no snap ring on outside extent of the reverse gear, when going into reverse, the fork just stops it.

Dan

 

[Turboflash]

I see how you're thinking. I don't think it would hurt to add a shim of the right thickness. I don't think you'd want to take ALL the clearance out. I think there needs to be some room for thermal expansion?

 

[4strokes]

There is no snap ring on outside extent of the reverse gear, when going into reverse, the fork just stops it.

Dan

View attachment 147560

quite sure I read on hear the other day someone said they added a shim. I know I would. remember the nytros popping the bolt head off? solved with a spacer.

 

[Turboflash]

Yes, that top outside gear has that collar (on the inside) that slides over those teeth on the side of the main top sprocket, theoretically centering that inside gear on the shaft.

 

[Turboflash]

Most top gears sold now have 3 holes drilled through into center bushing from outside. Should allow more oil to get into bushing? Plus, with the 12 oz. of oil in the case, I think there is a tornado of oil being sprayed all over so I think that bushing gets plenty of oil.