Front Mech Upgrade

theblarney

Hi,

I need to replace the crankset on my bike so I am taking the opportunity to upgrade the front mech also. My Scott Aspect 40 is 3 x 8 and I just wanted to check that a 9 speed crankset and 9 speed front mech will be ok?

What I have read so far would say yes but just wanted to check.

Thanks

kingie3105

I do believe (and if I am wrong, i am sure someone will correct me) that a 9 speed mech is a little bit wider that an 8 speed version... Not that thiss will matter much.
As for the cranks, the rings are a little wider spaced due to the fact the chain has to move further when its at the extremes of the cassette, but this spacing is literally mircometers. I ron a 10 speed crankset with an 11 speed cassette and it works perfct..
Hope this helps

theblarney

kingie3105 wrote:

I do believe (and if I am wrong, i am sure someone will correct me) that a 9 speed mech is a little bit wider that an 8 speed version... Not that thiss will matter much.
As for the cranks, the rings are a little wider spaced due to the fact the chain has to move further when its at the extremes of the cassette, but this spacing is literally mircometers. I ron a 10 speed crankset with an 11 speed cassette and it works perfct..
Hope this helps

Yes thanks it helps a lot.

The Rookie

The 9 speed cage is narrower as the chain is narrower, that said it will work just fine with an 8 speed chain but some chain rub is slightly more likely, having said that you can use a 9 speed chain on an 8 speed setup anyway, so that will resolve that issue.

theblarney

Hi,

Just to follow up, I did swap out the front mech for a Deore M590 and continued to use the 8 speed chain and rear cassette and all was fine but as advised I started to get chain rub.

I ordered a KMC X9 73 chain (9 speed) and this evening I measured it up and fitted it but when I connected the master links and started to turn the cranks, I got the following in the picture where the chain links are resting on the teeth. Its almost as if the chain isnt the right speed for the mech but I ordered a 9 speed chain and the Deore M590 ir definately 9 speed also, any ideas?


Thanks

cooldad

The pitch is the same for 8, 9 and 10 speed, only the width of the chain is different, so that wouldn't make any difference.
Was the crankset new?
If not the ring could be worn. How does it work on the other rings?

theblarney

cooldad wrote:

The pitch is the same for 8, 9 and 10 speed, only the width of the chain is different, so that wouldn't make any difference.
Was the crankset new?
If not the ring could be worn. How does it work on the other rings?

The crankset is only 2 days old, haven't tried it in any other rings as I have just fit the chain this evening and came across this

cooldad

Stiff link? Can't see behind the crank.

theblarney

cooldad wrote:

Stiff link? Can't see behind the crank.

Nope, it's a brand new chain

jimothy78

So to be absolutely sure - both the chainring and chain are brand new? Where did you get them?
If both are truly new, then I'd guess that the chain isn't sitting square on the teeth of the ring, but getting caught on an edge.
Check the derailleur limit screws and cable tension - does the derailleur cage actually move far enough out to let the chain sit properly on the chainring?
Also check the teeth of the chainring are straight (even a new chainring could have been dropped and damaged somewhere along the line).

theblarney

jimothy78 wrote:

So to be absolutely sure - both the chainring and chain are brand new? Where did you get them?
If both are truly new, then I'd guess that the chain isn't sitting square on the teeth of the ring, but getting caught on an edge.
Check the derailleur limit screws and cable tension - does the derailleur cage actually move far enough out to let the chain sit properly on the chainring?
Also check the teeth of the chainring are straight (even a new chainring could have been dropped and damaged somewhere along the line).

Yeah well the chainring is 2 days old, I fitted it Thursday evening using my old 8sp chain, indexed all the gears and went out Friday and all was fine apart from a bit if chain rub. Fitted brand new chain last night and found the error.

jimothy78

So have you checked the allignment of the derailleur? Is it making contact with the chain when it's on the big ring?
What about gear choice - does it happen on all sprockets at the rear, or just some of them?
Have you double-checked that the "quick link" is properly engaged, and not only half-closed?

theblarney

jimothy78 wrote:

So have you checked the allignment of the derailleur? Is it making contact with the chain when it's on the big ring?
What about gear choice - does it happen on all sprockets at the rear, or just some of them?
Have you double-checked that the "quick link" is properly engaged, and not only half-closed?

Hi,

Ill try out all the options you mentioned tonight but one thing when I looked again after your last message was I noticed on the big ring that the teeth are wide and narrow, thick and thin and the inner plate of the chain was catching on the thickest part of the ring so I moved the chain around the chainring one link and its stopped but surely you dont line them up like this?

Sorry if I am not explaining this correctly.

jimothy78

theblarney wrote:

I noticed on the big ring that the teeth are wide and narrow, thick and thin and the inner plate of the chain was catching on the thickest part of the ring so I moved the chain around the chainring one link and its stopped but surely you dont line them up like this?

Your explanation makes sense, but the situation you describe doesn't - the ring is obviously designed to work as part of a multi-ringed setup, not single-ring, so shouldn't have narrow/wide teeth - they should all be the same thickness. Are you sure it's the physical thickness of the teeth that caused the chain to "hang-up" and not some other factor? Take the chain off and try wrapping a length of it round the chainring without going through the derailleur, then move it on one space and try again. It should work in both positions. if not, something's definitely wrong with either the chain or the ring.

theblarney

jimothy78 wrote:

So to be absolutely sure - both the chainring and chain are brand new? Where did you get them?
If both are truly new, then I'd guess that the chain isn't sitting square on the teeth of the ring, but getting caught on an edge.
Check the derailleur limit screws and cable tension - does the derailleur cage actually move far enough out to let the chain sit properly on the chainring?
Also check the teeth of the chainring are straight (even a new chainring could have been dropped and damaged somewhere along the line).

I think you hit the nail on the head, see below:

The issue only seems to happen when its in 8th gear (highest) so the chain is at its straightest, it seems fine in 7th.

Is it just a matter of taking a file to it?

cooldad

Get it replaced. That whole tooth looks wrong.

jimothy78

^This.

Looks like a manufacturing flaw - the tooth hasn't been machined properly. Refund time.