Can anyone help me solve a really frustrating problem please? I have a problem whereby when I am in top gear (largest front, smallest rear ring) and peddle hard, the chain seems to slip off the chain ring. It sometimes happens if I'm in middle front and smallest rear as well (though I know that this will place strain on the chain and was only tried to see if the chain jumped in other gears) If I peddle with a little less force, things are ok. I have SPD pedals so do put a lot of force throught the drive train to get up difficult hills (Its a mountain bike by the way...). I've checked the front changer and it is aligned parallel to the chain wheels and have checked the bottom bracket for play. There is VERY little play in the bottom bracket and I think that this is necessary for the bearings to move freely, certainly not enough to make the chain rings move out of alignment.
Can anyone help? The bike is a Giant XTC 840 cross country.
Sounds like a worn out chainwheel if it's a big jump when it slips.
Look closely at the chainwheel teeth to see if they exhibit a hollow on the driving face (forward facing at the top) of the teeth (kinda like a shark's fin shape) that would indicate a badly worn chainwheel.
Look closely at the teeth on your block for similarly worn tooth profiles (rearward faces of teeth at the top).
Try pulling the chain away from the front of the chainwheel (the 3 o'clock posion) and see that it doesn't lift as high as the teeth that would indicate a badly worn chain.
Measure your chain under a bit of tension and if 12 links measure more than 12 and an eighth inches the chain is worn out.
"BigRab" <[email hidden]> wrote in message news:[email hidden]...
Quoted message said:
Mark,
Sounds like a worn out chainwheel if it's a big jump when it slips.
Look closely at the chainwheel teeth to see if they exhibit a hollow on the driving face (forward facing at the top) of the teeth (kinda like a shark's fin shape) that would indicate a badly worn chainwheel.
Look closely at the teeth on your block for similarly worn tooth profiles (rearward faces of teeth at the top).
Try pulling the chain away from the front of the chainwheel (the 3 o'clock posion) and see that it doesn't lift as high as the teeth that would indicate a badly worn chain.
Measure your chain under a bit of tension and if 12 links measure more than 12 and an eighth inches the chain is worn out.
How long do chainwheels last? I have replaced my rear cassette and chain 5 or more times but am still using the original chainwheels - no hooked teeth visible or other problems. Why don't they make cassettes of similar hard-wearing material?
How long do chainwheels last? I have replaced my rear cassette and chain 5 or more times but am still using the original chainwheels - no hooked teeth visible or other problems. Why don't they make cassettes of similar hard-wearing material?
Think this way, the chain has the load spread over, prehaps, 27 teeth on a 53 tooth chainwheel and, again, maybe 5 teeth on an 11 sprocket. That's why we don't use alloy cassettes for everyday use.
Sounds like a worn out chainwheel if it's a big jump when it slips.
Look closely at the chainwheel teeth to see if they exhibit a hollow on the driving face (forward facing at the top) of the teeth (kinda like a shark's fin shape) that would indicate a badly worn chainwheel.
Look closely at the teeth on your block for similarly worn tooth profiles (rearward faces of teeth at the top).
Try pulling the chain away from the front of the chainwheel (the 3 o'clock posion) and see that it doesn't lift as high as the teeth that would indicate a badly worn chain.
Measure your chain under a bit of tension and if 12 links measure more than 12 and an eighth inches the chain is worn out.
If you see no problems with the rings then the problem is most likely a fault between the cassette and the freehub (maybe the pawl slipping) - easilly fixed at your LBS. If you replace the cassette ensure you replace the chain too.
Why don't they make cassettes of similar hard-wearing material?
They usually make cassette sprockets of steel rather than the softer aluminium alloy that most chainrings (excluding most granny rings) are made of. Apart from the smaller diameter causing more wear as has been pointed out, Shimano for instance, go for shallower teeth to give priority to smooth shifting over longevity.
As an aside, I do sometimes wonder if it's not cheaper to run the entire transmission into the ground & replace the lot in one go rather than replacing chains a lot more frequently than the rest - gone are the days of cheap Sedis chains! Then again, there are some good arguments for not doing so like not being caught out with a worn chain that's snapped far from home. I can't have been the only one to wonder at how much gets worn off the width, let alone the added "stretch", so front shifting may deteriorate more than expected.
I would consider chainring wear 1st as the cause for slip. -- Basically, I hate people who preface nearly every sentence with the word 'basically'!
