Replacing triple chainwheel

[deanE]

I have bought a secondhand Specialized Sirrus, which I am doing up for a JOGLE next year. It’s about 8 year old. I have replaced the cassette, to give me a lower gear ratio and the rear derailleur to accommodate, using Shimano Alivio. I have been impressed with the one I fitted to my road bike and it was easy to set up and changing smoothly, with Alivo shifters fitted. However, the chain is slipping on the chainwheel under load and so I have bought a new, Alivio, front chainwheel. The price was right and I thought that it might be better to have the same group throughout. However, this appears to go further on to the taper than original chainwheel, with the result that the front derailleur is not functioning. There is not enough adjustment on the front derailleur to ensure that the chain will shift off the mid to the small chainwheel, it is hard against the frame, and shifting up has the chain on the large chainwheel when the shifter is still mid way. The original equipment on the Sirrus was Nexave and the front derailleur still is. The cross section of the chain wheel / crank arm looks about the same so I am perplexed. If anyone can understand what I have described, and suggest possible solution, I would be appreciative. I have looked at Sheldon Brown, but it just gave me a headache.

 

[e-rider]

when you say you replaced the cassette, did you replace the chain too? If not, that is probably why it was slipping. Shimano Alivio is basic kit but should work reasonably well if set up correctly.

 

[deanE]

Yes, replaced the chain. The front chainwheel was probably the original, fitted in 2004, and looked a bit worn, so thought best to replace it.

 

[simon.r]

It sounds as if you need a bottom bracket with a longer axle.

Having said that, Sheldon's table suggests a 110 - 113mm axle, which isn't particularly long. Can you measure the existing BB axle length?

Edit - that table refers to older chainsets - maybe the newer Alivio needs a longer axle?

 

[deanE]

The guff that came with the chainwheel said 113mm BB needed. I will have to try to get an accurate measurement tomorrow.

 

[simon.r]

That's odd, I'd be surprised if the original BB axle is significantly shorter (assuming the Nexave is a triple chainset).

Silly question, apologies if I'm insulting your intelligence here, but the Alivio chainset is designed to fit a square taper BB? It's not a splined fitting?

 

[deanE]

Still having problems in that new, Alivio, front derailleur fouls the mudguard. Might have to go back to using the original Nexave changer. Does anyone know whether you can mix Shimano gear. Will the indexing be the same? - Alivio shifter, Nexave changer.

 

[Lee_M]

I see a trip to your LBS coming on