Chain not dropping onto inner ring correctly

Ken Night

I have a Centaur 50/36 compact, which used to work correctly.

Recently, the chain drops onto the inner ring, but without always engaging the teeth-usually when in the sixth smallest cog at the back

I'm using a 111mm BB, and have tried a spacer on the cup on the drive side, to no avail

I've tried changing the outer ring too.


any ideas anyone?

binlinus

What chain are you using? Are you on 9 or 10 speed? How old is the chain and chainset? Has the front mech moved at all? ie has it twisted about the seat tube?

Bin

Ken Night

binlinus wrote:

What chain are you using? Are you on 9 or 10 speed? How old is the chain and chainset? Has the front mech moved at all? ie has it twisted about the seat tube?

Bin

Using KMC 10spd chain, new

Chainset about 18 months old

Front mech appears OK

Changing the chainset back to the old 53/39 results in perfect shifting

The reason I tried a spacer on the drive side cup, was that I thought the hole where the BB axle goes, may have enlarged changing the chainline, as the crank ended up closer to the BB. I don't want to make suggestions, having asked for solutions-but I may try another spacer to check this out

Steveorow

How much difference is there between the big ring and the Mech when you have the compact on ? It should around the thickness of a penny ( however the closer the better without the mech touching the chainring teeth ) .
The diameter of the 53 chainring and the compact 50 chainring will be slightly different . If you have a band on mech then you may want to try moving the mech down the seat tube slightly so its closer to the compact chainring .

Ken Night

Steveorow wrote:

How much difference is there between the big ring and the Mech when you have the compact on ? .

I've used the current front mech with the standard and compact c/ss, moving it up and down as required-so it's not that either

binlinus

Maybe try to take one chain link out? the reason I suggest this is that if the 53/39 works fine then maybe the rear mech is not taking up the slack quickly enough as the chain drops to the inner ring with the 50/36

I also use a Centaur 50x36 C/Set (10 speed), with a Centaur 10 speed compact front mech (minus the resin insert), but am using 9 speed sram chain and everthing else is 9 speed. Only problem I sometimes get is sometimes I overshift the chain when shifting from inner to outer. But I've tweaked the mech now so I hope it's ok.

Bin

Ken Night

binlinus wrote:

Maybe try to take one chain link out?

It is a good chainset-the difference being acceptable, whereas I find 50/34 too much

Alas, I've also tried different chainlengths-keep one for standard c/s, and another for compact

Uranus

Ken Night wrote:

I have a Centaur 50/36 compact, which used to work correctly.

Did you keep the old chain? As you say the setup "used to work correctly" and now it doesn't, and it sounds like the chain is the only thing you've recently changed.

It the chain won't engage on the front sprocket teeth then either it's not being pushed the right distance laterally by the front mech., or maybe it's riding up on the teeth (new chain on worn teeth syndrome)?

Ken Night

Uranus wrote:

Did you keep the old chain? As you say the setup "used to work correctly"

Thanks-should have thought of that
No. But I have changed from Campag to KMC, and I've tried three of their chains (which work on the standard Double, on the FSA compact,and on the Centaur triple, all 10spd on other bikes

Uranus

Ken Night wrote:

I have changed from Campag to KMC, and I've tried three of their chains (which work on the standard Double, on the FSA compact,and on the Centaur triple, all 10spd on other bikes

Well that is puzzling. How about swapping inner rings between the FSA Compact and the Campag one, just to try to isolate the problem?

I had shifting problems with my Campag compact where it would dump the chain on the inside of the small chainring, but it was more a question of me not being able to adjust the original (standard Campag) front mech adequately. In the end I took the easy way out and bought the compact-specific front mech which has sorted it. But it sounds like my problem was different than yours.

Ken Night

Uranus wrote:

[Well that is puzzling.

too right!

spent most of the morning swapping rear wheels (different cassettes), chainsets, and chainrings, and seem to have sorted the problem, in that it's gone.

I can't explain why, but I've put on the original Campag chainrings.

I have a notion that the chainrings weren't in alignment, though why that should affect downshifting is beyond me

Thanks for your suggestion-I would'nt have fiddled so much with the chainrings otherwise

Uranus

Ken Night wrote:

seem to have sorted the problem, in that it's gone.

I can't explain why, but I've put on the original Campag chainrings.

Glad to hear it's fixed, though in the ideal world one would like to know why as well! :?

FWIW I use a mixture of Campag and Stronglight chainrings on my Centaur CT cranks, and the Stronglight rings (they are marked 9/10 speed) have a slightly different offset than the Campag ones but the difference is very small. I get slightly more chain rub and chain noise with the Stronglight rings but not enough to classify it as a "problem". Like you I go for a 14-tooth difference between the chainrings, 16-tooth gives a poorer change and, for me, clumsier gearing.