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Gearing Options?

Merlin

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Medicine Hat, AB
Hello & Merry Xmas,


I'm currently running the stock, 2.44:1(16/39), gearing in our long tracked(136" X 1.75") Indy Lite.

Being my son(9yrs / 100lbs) is riding this machine in the mountains, it is no surprise that we are finding the "big" track puts a pretty good load on the lil' 340.

According to the service manual 2.56:1(16/41) is lowest recommended combo for the 6.625" chain case. That said, the service manual lists P/Ns for 13, 14, & 15 tooth top sprockets.

Anyone have any experience running lower gearing combos such as 15/41, 14/41, 13/41?

IMO, being geared for anything over 45MPH in this application is too much.

Thoughts?


TIA

Glen
 

Merlin

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VB, I've been running it on the factory recommended setting(B2).

This year I rebuilt the primary & installed the Gold spring with Thunder Products Glide Washers & 10M Blue weights(47.5g). The factory calibrations were the Gold/Silver spring & 10 weights(51.5g). I also replaced the ramp buttons in the secondary with the newer 5450873 buttons that have a different profile which will add to the initial spring preload.

I'm going to test this set-up to see how it works. If not satisfactory, I plan on cranking up the secondary spring to B1 or even B0 before dropping the weights to the 10M White(46g).


That said, I think that even if I can get the machine to run good with clutch tuning, it'd even do that much better with lower gearing. A good example of that is the proven lower re-gearing of the Pro chassis that TRS and many others have advocated.

FWIW




Have you added more tension on the secondary clutch spring to keep it effectively in a lower gear (higher rpm's)?
 

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C

cowboy181d

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Burns oregon
I am running the 15/41 combo in my 79 txl 340 long track (133) seems to pull it around great top speed is about 40mph with untouched clutching. I cannot remember the chain I ended up running I know it was a bit funky to get together though.... funny i seen this on here today as I am getting ready to go out and dig my old txl out of its 6 year slumber for my daughter to ride this season!
 

Merlin

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Thanks for the info.!

Do you recall what size drivers you are running?




I am running the 15/41 combo in my 79 txl 340 long track (133) seems to pull it around great top speed is about 40mph with untouched clutching. I cannot remember the chain I ended up running I know it was a bit funky to get together though.... funny i seen this on here today as I am getting ready to go out and dig my old txl out of its 6 year slumber for my daughter to ride this season!
 

Merlin

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Thanks!

I'm running 7 tooth drivers & found them to be a significant improvement over the factory 9 tooth.

After looking a little closer at the gearing chart, I could swap out my 16T top sprocket with a 14T & be at 2.79:1 which is pretty much the same as you're running. The bonus would be keeping my factory bottom sprocket(39T) & chain(64P).


7 tooth I think..... I will have it in the shop this week I will roll it over and see....
 

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retiredpop

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Don't forget the effective increase in ratio because of the smaller track sprockets when you are figuring your gearing out. Reducing from 9T sprockets to 7T sprockets gives the same effect as changing the gear ratio from 2.44 to 3.13 because of the smaller diameter. Keep that in mind when you go even lower on the top gear. 15T top gear would be 3.34 with the 7T sprockets. 14T top gear would be 3.58. You do need to maintain a reasonable amount of track speed in the mountains.
 

Merlin

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Thanks,

I think I have taken the effect of the smaller drivers into account.

With stock gearing & factory 9 tooth drivers theoretical top end is 60 MPH +/- at 7000 RPM according to the chart in the service manual.

Top end drops to 47 MPH +/- with the 7 tooth drivers.

If I go with the 14 tooth top gear to end should drop to 40 MPH +/-.


40 MPH top end is pretty darn slow but I think it's asking a lot of 35 - 38 HP engine to pull a 136" X 1.75" track through deep snow with anything even close to that for track speeds. I'm thinking it's better to be geared for the power & traction I've got to work with.


Thoughts?

Don't forget the effective increase in ratio because of the smaller track sprockets when you are figuring your gearing out. Reducing from 9T sprockets to 7T sprockets gives the same effect as changing the gear ratio from 2.44 to 3.13 because of the smaller diameter. Keep that in mind when you go even lower on the top gear. 15T top gear would be 3.34 with the 7T sprockets. 14T top gear would be 3.58. You do need to maintain a reasonable amount of track speed in the mountains.
 

Merlin

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I hear you. There will be a point of diminishing returns, the question is where though....

I just thought I'd canvas the forums to see if anyone had been down this road before.

I'll try the machine with the mods. I did this season, maybe play around with the clutching(secondary spring tension & primary weights if needed), & see how it runs. Then revaluate for next year.



I hope you are not over-doing it.
 
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