Krisboats Posted January 3, 2008 Report Share Posted January 3, 2008 (edited) You bb is too short then. Yep, thats the prognosis i'd go with too. Either that or he's tried sticking an echo external bb in and fitted a front freewheel to it.If your chain keeps coming off its not lined up properly, especially if you say its got enough tension. If the freewheel is rubbing on the bb shell and the chain on the tyre i think its okay to assume your bottom bracket axle isn't long enough, you'll need a wider one to solve these problems. I'm guessing as you've just started using a front freewheel, the cog that was on there before was thinner, so further away from the bb shell. But then when you fitted the front freewheel its closer to the bb shell as the freehwheels generally have a wider spacing than the single cogs do. If the chainline was slightly out with the cog already, fitting the front freewheel could have been just the final amount of distance needed in order to start causing you all these problems.But yeah, the simple solution should be to get a wider bottom bracket, one that isn't an echo external one (unlikely with the chain/tyre rub but just incase you have one). Luckily its a relatively cheap and fairly simple procedure, not like building a new wheel up anyway. If your not confident you can always pick up a new bottom bracket from somewhere like tartybikes or cleanbikes and then take it to your local bikeshop for them to fit it, shouldn't cost more than about £5-15.If you could take a picture of it though from the rear cog point towards the front of the bike, then one of the front freehweel/bb shell area we'd be able to determine for sure. Edited January 3, 2008 by Krisboats Quote Link to comment Share on other sites More sharing options...
LiamWood! Posted January 3, 2008 Author Report Share Posted January 3, 2008 Its just snapped for a 4th time , i think its down to the bb, mine is an isis and they are fairly expensive(ish) i will atek some pictures tommorw in the line so you can see how the alinment is. Quote Link to comment Share on other sites More sharing options...
Will Arnold Posted January 3, 2008 Report Share Posted January 3, 2008 Its just snapped for a 4th time , i think its down to the bb, mine is an isis and they are fairly expensive(ish) i will atek some pictures tommorw in the line so you can see how the alinment is.how are you joining your chain?ok, put it like this, CRAIG LEE SCOTT rides with a split link in his kmc, look at the mad mad mad dropgaps n stuff he does...split links are strong! (when fitted correctly)Will Quote Link to comment Share on other sites More sharing options...
LiamWood! Posted January 3, 2008 Author Report Share Posted January 3, 2008 With a chain tool? i dont have a split link. when you look up from the sprocket the freewheel looks miles out but i still need a longer bb?? Quote Link to comment Share on other sites More sharing options...
Luke Rainbird Posted January 3, 2008 Report Share Posted January 3, 2008 Kris' post says all you need to know really.If you can get us a picture or two showing your drivetrain setup (from rear sprocket forwards, from above (or below) the freewheel etc) so we can see your chainline and other things that could cause the problems, we will be in a better position to help you, and more likely to be able to pinpoint the issue.It does SOUND like you need a longer BB, though we can't say for certain with the information we have at the minute Quote Link to comment Share on other sites More sharing options...
balfa Posted January 4, 2008 Report Share Posted January 4, 2008 Small point but the smaller the chainring and rear sprocket the more force your putting on the chain as it is concentrated on a smaller area. This also causes chains to wear quicker. It shouldn't cause you to constantly be snapping chains though.What ratio are you running? Quote Link to comment Share on other sites More sharing options...
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