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I have a Shimano Altus 8-speed on my hybrid/commuter bike. I have to put in a new cassette and a new chain as well and looking at the teeth of the largest chainring cog in the front, it looks like the teeth are pretty worn as well.

I expected the chainrings to be replaceable individually but was puzzled to see that they are one solid unit. It kind of looks like a chainset but the pedal part seems so be attached by a screw and does not appear to be part of the chainring-set.

The largest cog has 48 teeth and has 4 extra holes to attach a chain protector.

Does anyone know the name of the part and a supplier in the UK?

Would it be advisable to invest in a chainset where I can replace individual cogs? What would be a possible part combination?

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Shimano are generally pretty good for publishing their tech docs, and there is a whole page on Altus at techdocs.shimano.com/techdocs/…. However it doesn't appear to have details on the chanirings. Or I missed it. But from your photo this looks identical to something I used to have on an old Raleigh hybrid. I bet if you took it to your lbs they'd know instantly. –  PeteH Nov 15 '12 at 16:27
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up vote 1 down vote accepted

While cleaning I found the part number printed on the inside of a crank handle. It is a FC-M191. This part seems not to be available in the UK anymore so I decided to buy the MC-M411, which has the same teeth number for all three cogs, is suitable for 8-speeds and has the same Shimano rectangular axle fitting as the FC-M191.

I also bought a Tl-FC10 crank pull to disconnect the cranks from the bearings.

It appears that the derailleur is an Altus but other parts have been used for the Chainset in the front. This makes it difficult to find the matching parts.

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This looks like a pretty good replacement. Don't see any reason why it wouldn't work for your purposes. It's not a performance upgrade, but it's nice to have the ability to swap single rings. –  Benzo Nov 15 '12 at 20:25
    
This would be the ideal time to service the bottom bracket while everything is apart. –  mikes Nov 15 '12 at 20:59
    
Once the parts arrive I will take everything apart and clean it. The derailleur cogs look quite worn as well but I will clean them and try not to change them just yet. As the parts served me well for three years, I was not looking for a performance upgrade at this point. Especially because I have to lock the bike sometimes in public places and I do not want to to look too fancy –  Martin H Nov 19 '12 at 15:31
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