SKS 800 2016 geardown

Xeiscountyduke · May 15, 2019

I'm trying to gear my SKS 800 155" down a little bit. currently installed is 20T/40T and i want to try 19T/42T. Does anyone know if this will work? and does anyone know if the big lightweight sprocket part no. 3221142 (2900139) will fit or does i have to take the part no. 3222192. for the small sprocket i take the part no. 3221095.

sledhed · May 19, 2019

Same chaincase as in the 3" Axys RMK sleds with a 3" track, which has stock gearing 19 top 44 bottom. With 74P chain. With a 72P chain which is stock in the SKS, might be a little tight on the chain even with the gears you are thinking of using. They used to list what combinations give you what ratios and what chain is required in the owners manual, assuming gearing down for elevation, but they don't do that any more. I know the 19/44 with 74P chain has a fairly good dog-leg in the chain.

Xeiscountyduke · May 19, 2019

Thanks for the interesting info. now i calculated the estimated top speeds of all gear ratios. original with 20T/40T gear is 78mph. that is truly correct, i reached this on snow with my sled. with 19T/42T gear the speed will be 70mph and with the 19T/44T gear the speed will be 67,7mph. Now i have to decide which one i will try....

BeartoothBaron · May 20, 2019

I haven't tried a ton of combinations, but on my sled I went from 19/39 to 19/41 to 19/43 and it was better with each step. I may go further in the future. Until you get on the extreme ends, there's just nothing to lose off-trail. People have gone too far, but most gear-down reports I see are positive. Like sledhead mentioned, try to keep the dog-leg small (meaning the most teeth recommended for a particular length of chain). You'll maximize the chaincase efficiency; probably just a percent or two, but it's there. Don't take it too far; pretty sure there are combinations that bolt up but leave no slack, and you don't want that. Not sure if you can go to an 18T sprocket on the AXYS, but an 18/43 might be the ticket for you. I have to doubt a 19/44 is even possible with the 72p chain: in my case (perfect pun there), 19/41 is approved with the 74t chain, and it takes up 90% of the adjuster, but the 72p chain wouldn't even physically fit.

Xeiscountyduke · May 20, 2019

Thanks for the info about the chain length. i try to get a original setup from a 850 pro. there is the 19T/44T setup with the 74p chain installed. than i can try what would better fit. my original 72p chain, or the 74p chain from the 850....
i think a 18T/43T would be difficult to get, because i don't know if there are original parts available. a complete 19T/44T setup with 74p chain you can get for 50$ with a minimum use on it...but i try to find out if there is a 18T/43T possible...i also try to ask a good friend of mine. he is in the R&D of BRP Rotax and he knows very much about clutch and chaincase tuning (probably is not the right manufacturer, but he's a guy that tries all different setups to find the best solutions) ...

Xeiscountyduke · May 20, 2019

now i calculated the estimated speed for the 18T/43T setup. with this the speed will be around 66mph compared to the 19T/44T setup with 67,7mph top speed.
i think i'll try the original 850 setup, because it's the cheaper variant and the differnce is not that much in top speed...

BeartoothBaron · May 21, 2019

For me, the cost of buying two sprockets would be the only downside to the 18/43 (and you'd have to check on whether that's approved with a 72t chain, but it's pretty close to 20/40 and effectively the same as 19/42). If you ride trails with lots of long straights, I guess top speed is a factor though. Mine has bigger drive sprockets, so the final drive ratio is different; I top out in the mid-70s. I wouldn't mind giving up another 6-8 MPH for more low-speed response and track speed in deep snow, but that's personal preference. If it's that cheap, it'd be worth trying the 19/44 setup to see how you like it. From there, going to 18/43 would just be optimizing (slightly lower, less dog-leg); not 100% on the availability of the gears, but should be possible.

sledhed · May 21, 2019

I saw a complete 2017 RMK chaincase setup on facebook mountain sledder swapmeet (included chain, sprockets, tensioner, cover) for like $75... that is a deal if it doesn't have a million miles on it... if you are interested I will see if I can find it again. It was a sled that got converted to TKI belt drive.

Xeiscountyduke · May 26, 2019

made a list with possible gearing options. just have to decide which i want to try...

formula used for calculating:
8250 (TopRPM)/(LoSp/ToSp) x (driveshaft 7T/pitch 2,86) / 12 x 60 / 5280 = mph

Setup original: 20T/40T = 78 mph / 125,5 kmh original in Pro RMK 850 155" with 2,6" track, 7T driver and 2,86" pitch
Variant 1: 19T/40T = 74,5 mph / 119,9 kmh original in SKS 800/850 146" with 2,25" track, indeed with 8T driver and 3"pitch (89,3 mph / 143 kmh)
Variant 2: 19T/41T = 72,4 mph / 116,5 kmh
Variant 3: 19T/42T = 70 mph / 112,6 kmh
Variant 4: 19T/43T = 69,2 mph / 111,4 kmh
Variant 5: 19T/44T = 67,7 mph / 109 kmh original in Pro RMK 850 155", 163" and 174" with 3" track, 7T driver und 2,86" pitch
Variant 6: 20T/42T = 74,5 mph / 19,9 kmh original in RMK 600 155" with 2,4" track, indeed with 8T driver and 3"pitch (89,3 mph / 143 kmh)
Variant 7: 20T/43T = 72,7 mph / 117 kmh
Variant 8: 18T/40T = 70,4 mph / 113,4 kmh
Variant 9: 18T/41T = 68,6 mph / 110,4 kmh
Variant 10: 18T/42T = 67,1 mph / 107,9 kmh
Variant 11: 18T/43T = 66 mph / 106,2 kmh

Xeiscountyduke · Aug 29, 2019

now i got gears (19T 41T) and a chain from a 2010 RMK 800. Yesterday i installed it with the original 72P chain of my SKS and it fits perfect. Now I'm really interested how this will work...

kanedog · Aug 29, 2019

As someone else said, each step that you gear lower the performance will improve each time.
The lower you go, the better you go.
As an example, I run a belt drive 23/84, 3.65 on a 16 800 stock motor Doo 174. It beats some turbos and other NA sleds are not even close. It’s unbelievable.
You are going in the right direction. This is assuming mountain riding.

Xeiscountyduke · Aug 30, 2019

i hope it is the right direction.
A Turbo kit is not useful for me, because i run my sled at Low elevation around 3000' and so i would have to run it with a high percentage of avgas and thats not the cheapest way. the turbokit is about 3500$ and the avgas is also expensive here in austria, about 10,9$/gallon.
If i will mod anything in the future, i think i will go with a 860cc big bore kit... that would be the best way for me

shagsmc · Sep 3, 2019

So with these changes have you considered any clutching changes to go with it?

Xeiscountyduke · Sep 3, 2019

yes. i also have added a complete SLP single Pipe kit, so i changed the primary clutch spring from the original black to the blue-red SLP 40-71 spring. i run my sled around 3000' elevation. i have the 68g weights in it. i will check at first ride tests, if i need to change the weights...

raleigh111 · Sep 30, 2019

19 41?? I tried that with 72 chain and was too tight??? I will double check tomorrow but i was sure 19 41 72 chain was hammer on tight??

Xeiscountyduke · Sep 30, 2019

i put in the new sprockets with the original chain of my SKS and i don't think it's to tight. the tensioner is nearly on the same position as original was and there is enough space for the cahin... i think this will work...

Xeiscountyduke · Sep 30, 2019

here are also pictures of the complete sled after the modifications...

raleigh111 · Oct 1, 2019

BeartoothBaron said:
19/41 is approved with the 74t chain, and it takes up 90% of the adjuster, but the 72p chain wouldn't even physically fit.

Xeiscountyduke said:
i put in the new sprockets with the original chain of my SKS and i don't think it's to tight. the tensioner is nearly on the same position as original was and there is enough space for the cahin... i think this will work...

I am boggled? I tried 19 41 72 chain hammer on tight 16 sks..... He shows it fits in picture??? LOST HERE?

raleigh111 · Oct 1, 2019

I am running 19 40 72 now and it takes up 85% of adjuster. Not liking that part..

Xeiscountyduke · Oct 1, 2019

As you can see on my picture the 19 41 sprockets with the 72P chain fits perfect in! i just can say, that i did have no problem with mounting and adjusting that

SKS 800 2016 geardown

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