New chain question .

[mak]

I fitted a new chain today, picked it up from the shop that did my download this morning, my old chain has 1600 miles on it but the gears are slick and never mis a cog, I have however kept on top of adjustments and tweaks to keep it shifting smooth.

After removing the old chain and lying it down next to the old one the only option after breaking the new chain to length was either a link to long or a link to short , after counting the links I decided to go the link shorter option but keep the same amount of links as per the old chain, is it possible the chain has stretched a complete link ?

Providing the pitch is correct you can see the old chain running out of sink with the new one the further down the length you follow.

Incidentally the gear change has gone to pot with the new chain so will be tweaking it tomorrow . Its not catastrophic but not as good as before.

 

[steve_sordy]

You did the correct thing to keep the same number of links.
As a chain wears, it gets longer, often expressed as a % wear, for example 0.5% wear. What is really meant is that the chain is 0.5% longer

Lets assume that you have 120 links (my bike does). If you wear your chain to the standard 0.75% length extension then the old chain will be 0.9 of a link longer. (0.75% x 120 = 0.9)

What wears is the pins, where they rotate in the side plates. It is very gradual and very small, but when you get over 100 of them all wearing, it adds up. The big problem is that nothing wears out gear teeth faster than a worn chain. The chain ring pitch is 0.500" and when you run a chain over it that is longer than that, then bad things happen. The rollers on a new chain plop into the valley between the gear teeth and sits there, not moving and not wearing the teeth. A worn chain with its pitch that is longer than 0.500" slides around trying to find the place of least stress. This sliding causes friction and wear. This is worse when the teeth and chain are contaminated with grit (thinking grinding paste).

The worse the imbalance between tooth pitch and chain pitch, the faster the wear.

If you let the chain wear more than 0.75%, the tooth profile can rapidly deteriorate. This can happens to such and extent that a new chain will no longer run on the gears. What happens is that the chain slips under power, which can be disconcerting to say the least! Some people run a chain to say 0.5% then replace it, but keep the chain to use after the second chain has worn to 0.5%. Proper high mileage riders can have 3 chains on the go. Once the third chain has been fitted, the transmission is run into the ground and the whole lot is replaced. Before starting again!

 

[mak]

Cheers Steve, i think the main problem now is the B tension screw, tweaking it to compensate for the stretched chain. I've managed to get it changing fairly slick on the bike stand. Going to give it a run out tomorrow evening when I get home and try out the new software update for the bosch motor as well

 

[steve_sordy]

I can't say that I have ever had to adjust the B screw because the chain was worn, can't think why it would be required. If your new chain is running worse than your old chain, then it sounds as though the gears are worn too, which is why they didn't run well with your new chain. In which case refit your old chain and buy a new cassette for when the refuse to work together any more.. Have a good look at your chain ring too. Be aware that the longer you run your old chain and old cassette together, the worse your chain ring will become.