gears?

[EagleJason]

I have a 2001 Yamaha SX700F (SXr) redhead. The chain broke today and I was thinking of lowering the gear ratios while I have the crank apart. The drive gear has 21 teeth, I counted, but forgot to count the driven gear before I sealed it back up. How many teeth should it have stock and how many can I add without having to buy a non OEM chain? how common is a chain break? is there a stronger than OEM chain I can use?
thanks

 

[snowdad4]

22/39 would be stock with a 70 link chain.

i would say that chain breaks are more a rarity than a norm. with anything in the drivetrain, mileage and maintenance will factor in, as will ratio efficiency(chain bending) along with gear condition.

to clarify chain bending, if someone put the 21t in there with the stock 70l chain, there would be alot of bending in the chain at the tensioner. 21/39 would need a shorter 68l chain. hopefully a 40t replaced the 39t.

 

[A couple of bucks]

I personally like a gearing set up somewhere around 2:1 ratio. That's good for us ditch bangers and jetting from fence line to fence line here in northern Illinois. I see you are in AK. What's your riding style. Are you at WOT much.
60 total teeth & under need a 68L. 61 and up need a 70L. The chart below will tell you what you need as far as a chain goes.

 

[EagleJason]

I am in rural bush alaska and use the machine to tow and haul, it often tours as well but typically with a sled. it's more likely to have a sled than not, usually with 2-400 lbs although occasionally more than that. i was empty and just popped over a berm when it broke and doing <15 mph. my assumption is that it was already worn. i think i have a 10 tooth driver (i counted at 1 point, but don't remember right now), but this is my first machine ever and i just bought it in October so am no super familiar with it yet. if 22 is stock, then 21 is a lowered ratio already. i'll have to double check then before i change anything as the lower may have been changed as well. Yes, the tensioner seemed well screwed in, however i'd just assumed that was from chain stretching. the machine is 14 y/o with 5k miles on it.

 

[jt specialties]

Having a real good idea what you are doing. Me personally, I would start with a 20/40 gear and 68 link chain. Than see how it works for you. You might even try a 19/40 and find it more workable for the way you are using the sled. Chain failure, not common but not unknown to happen. Probably dirty lube, miles, abuse, etc. Wouldn't worry to much. Make sure final drive seal is good. Good maintenance and you will see way past 10k on that sled. By the way check the bearing on the left side of the final drive shaft as they seem to need attention every couple of years. Inexpensive and easy to replace. Just my .05 worth