Chain Thrower

Dear Ralph:

I’ve got a 2002 Yamaha SX Viper and I threw the chain on it last winter. It wasn’t pretty, and I was shocked that it happened. Do you think the chain or gears were bad, or was it simply a matter of ignorance (I had tensioned the chain back when it had about 1,000 miles on it, but not since then).

Danny Wussem
Duluth, MN

That’s a bummer when you throw a chain. Usually it takes out the chaincase as well, and you will be getting a tow back to the trailer. I’ve only had it happen a couple of times over the years. One of them was on a Polaris Ultra, about 60-70 miles from the nearest anything, and yes, we had to tow it all the way back. That was on the first day of a week long ride, so I had to rent an Indy 500 to complete the ride that week.

Generally, drive chain failure and gear damage is due to improper chain tension and lack of maintenance. There will be cases with modified sleds where the power being applied exceeds the load capacity of the chain for a given width and design, but in your case it is pretty much a matter of a lack of maintenance. Add to this the loads applied if your track is spinning and then catches something and SNAP, something has to give. Especially on a sled that is studded.

Studies show that over one half of drive chain failures occur after 1,000 miles, so this tells us it is a matter of maintenance and not weak or defective chains. As indicated in most every service and owner’s manual I’ve ever examined, the chaincase oil should be changed at least once per season, ideally at the end of the season. Don’t just drain the oil through the drain plug and pour in the new, you should remove the silencer and chaincase cover to visually and physically inspect the chain and gears. Look for damaged link plates and/or excessive wear on the gear teeth. Each chain also has a wear limit as for stretching, this should also be measured if the chain has high miles on it.

But you and I know it was more a matter of chain tension than anything else. Sure, the chain might stretch more with no lube changes, but flat out ignoring the chain tension and letting it slap around in there is going to catch up with you. Most service and owner’s manuals are going to detail this procedure for you, but the rule of thumb is to finger tighten the tensioner and secure the lock nut. Some riders will even back the adjuster off just ever so slightly after reaching finger-tight so as to not place undue stress on the bearings, which occurs if the chain is too tight. You want a small amount of slack in there, not too tight, but not loose by any means.

Always inspect the cover gasket when putting it all back together, and clean the sealing surfaces of the gasket and the matching surface on the chaincase. Make sure the gasket isn’t pinched or folded, or you will be fighting a leak. Add the specified amount of chaincase oil and do it again next season, or after the next 2,000 miles. I like to check the chain adjuster tension after 1,000 miles of hard riding.