Help with front derailleur/outer chainwheel woes

[hawker]

I would very much appreciate help with a problem I'm experiencing with my front derailleur/outer chainwheel since I fitted new chainwheels. I have just fitted a new cassette, new chain, and new outer and middle chainwheels to my Deore Hollowtech 9 speed (27 gears) setup (existing Deore XT front mech used). I have replaced drivetrains many times over the years, including on this present bike, but never experienced problems before.

1) With the bike mounted on my workstand, the gears change smoothly on the cassette with the chain on the middle chainring.

2) The old outer chainwheel was a 44T Mega Drive. I have replaced it with the closest match I was able to find (44T Mega Drive, but not identical: these 9 speed components seem to be getting harder to source), but the front derailleur (still mounted in its previous position) now seems to be far too high. Also, the gap between inner and middle ring I think looks rather wider than the gap between middle and outer.
When I rode the bike, and changed gear on the cassette, the chain crashed down onto the BB. I could, with care, manage to use about two of the rear cogs, and even then, nasty crunches happened at times, though the chain didn't actually fall off again.

3) The thickness of the old and new outer chainwheels looks pretty much identical, but I'm now thinking the maybe the old outer is shaped such as to offset the teeth further out from the midline than is the case with my new outer. I think that the new chainwheel is maybe flatter.

4) The positioning of the front derailleur with the recommended 2-3mm vertical gap between tooth and outer plate seems to mean that the chain is now too high up in the derailleur cage, causing it to foul on one or other side of the cage, and causing it to be knocked off the rear cassette.

5) Might the fitting of spacers (maybe 2mm) between the outer chainwheel and the crank spider be the solution? (The old chainwheel didn't need spacers). I have looked at the setup ad infinitum and can't see that I have done anything obviously stupid, and the outer chainwheel is the only different component.

At present I am running the bike with the front derailleur removed, and using a restricted gear range with the chain mounted on the middle chainring.

[Cugel]

I would very much appreciate help with a problem I'm experiencing with my front derailleur/outer chainwheel since I fitted new chainwheels. I have just fitted a new cassette, new chain, and new outer and middle chainwheels to my Deore Hollowtech 9 speed (27 gears) setup (existing Deore XT front mech used). I have replaced drivetrains many times over the years, including on this present bike, but never experienced problems before.

1) With the bike mounted on my workstand, the gears change smoothly on the cassette with the chain on the middle chainring.

2) The old outer chainwheel was a 44T Mega Drive. I have replaced it with the closest match I was able to find (44T Mega Drive, but not identical: these 9 speed components seem to be getting harder to source), but the front derailleur (still mounted in its previous position) now seems to be far too high. Also, the gap between inner and middle ring I think looks rather wider than the gap between middle and outer.
When I rode the bike, and changed gear on the cassette, the chain crashed down onto the BB. I could, with care, manage to use about two of the rear cogs, and even then, nasty crunches happened at times, though the chain didn't actually fall off again.

3) The thickness of the old and new outer chainwheels looks pretty much identical, but I'm now thinking the maybe the old outer is shaped such as to offset the teeth further out from the midline than is the case with my new outer. I think that the new chainwheel is maybe flatter.

4) The positioning of the front derailleur with the recommended 2-3mm vertical gap between tooth and outer plate seems to mean that the chain is now too high up in the derailleur cage, causing it to foul on one or other side of the cage, and causing it to be knocked off the rear cassette.

5) Might the fitting of spacers (maybe 2mm) between the outer chainwheel and the crank spider be the solution? (The old chainwheel didn't need spacers). I have looked at the setup ad infinitum and can't see that I have done anything obviously stupid, and the outer chainwheel is the only different component.

At present I am running the bike with the front derailleur removed, and using a restricted gear range with the chain mounted on the middle chainring.

A problem of this sort manifested for me when I attempted to install a new but different brand chainring on to a double chainset. The new FSA ring replacing the older Shimano ring was "flatter" as you describe it - moving the big ring chainline inwards towards the frame by 1 -2mm.

I solved the problem (mostly manifesting as the chain unshipping off the big ring and down the chainset crank arm) by buying another new chainring with the same chainline as the original.

So, it seems that some apparently suitable chainrings (right teeth number, BCD and thickness) are not really suitable for some cranksets. Staying within brand helps but even here there are differences in that "flatness" or chainline of rings from different crankset models, even those of the same brand.

I suppose putting in spacers might fix the problem but ..... what a faff! And who knows what other subtle difference might be lurking that'll then manifest as another issue?

I'd just find a better chainring. Figuring out which has the right "flatness" or chainline will be the difficulty. You'd probably need to do a by-eye comparison of the original worn but unproblematic chain ring with the new one, perhaps also laying both on a flat surface that supports only the crank connection tabs to make sure the teeth themselves are at the same height.

[Cyclothesist]

Some pictures and ideally a video of gear changing on a bike stand would help understanding what exactly is going on. If the replacement outer chainring is the same diameter as the previous one (same tooth count so it should be) but of a shape that means it's a little further inboard the FD will need adjusted. The FD moves up as it moves out. The new ring being further inboard will likely need the FD moved *up a mm or so. Go for the FD outer cage being 1mm above the tallest chainring teeth (a 10p piece should just fit the gap). The FD outer stop (Hi stop) will need screwed in to stop the FD overshifting the chain on to the cranks.

*Edited - correction of down to up.

[hawker]

Thanks both. I've tried re-setting the position of the FD, but still been unable to resolve the issue. I called in at a LBS to see if they had any FD bolt spacers, but they hadn't (a LBS crammed full of all manner of bits and pieces, and smelling of rubber tyres, no longer exists in my neck of the woods .) However, the chap in the shop, who was pretty helpful, did think that I needed to move the chainwheel about 3mm towards the pedal, so I've sourced some 2mm and 1mm spacers online.

The problems with trying to find a more compatible chainring are, firstly, that such things seem to be very difficult to source, now that 9 speed is old hat, and secondly, that I'd have to order the chainring online, and would then quite likely have to return it if unsuitable. Therefore, though fitting the spacers is a bit of a pain, it might be the lesser of two evils. It occurs to me now, that given the narrow gap between middle and outer rings, the mech probably isn't able to swing far enough up to lift the chain up onto the outer ring. Fingers crossed that the spacers do the trick.

[Cugel]

Thanks both. I've tried re-setting the position of the FD, but still been unable to resolve the issue. I called in at a LBS to see if they had any FD bolt spacers, but they hadn't (a LBS crammed full of all manner of bits and pieces, and smelling of rubber tyres, no longer exists in my neck of the woods .) However, the chap in the shop, who was pretty helpful, did think that I needed to move the chainwheel about 3mm towards the pedal, so I've sourced some 2mm and 1mm spacers online.

The problems with trying to find a more compatible chainring are, firstly, that such things seem to be very difficult to source, now that 9 speed is old hat, and secondly, that I'd have to order the chainring online, and would then quite likely have to return it if unsuitable. Therefore, though fitting the spacers is a bit of a pain, it might be the lesser of two evils. It occurs to me now, that given the narrow gap between middle and outer rings, the mech probably isn't able to swing far enough up to lift the chain up onto the outer ring. Fingers crossed that the spacers do the trick.

Your next problem may be that the spacers make the chainring retention bolts too short!

Have you considered looking at 10 and 11-speed chainrings? In many cases they aren't significantly different in tooth or body thickness and work with 9 - 11 speed chains. Many manufacturers, such as Spa, sell chainsets and rings suitable for more than one "speed" of gear systems. It may make it easier to find a suitable chainring of the right chainline.

I have seen tech data for some chainrings that does mention their chainline .... but this isn't info generally found in product descriptions and one has to go digging on manufacturer's websites, where the info may still be missing.

[Cyclothesist]

Just a thought...are you sure the rings are mounted the correct way round? Apologies if this sounds basic but it's v easy to do with a middle and inner. The outer ring graphics usually make the orientation obvious.
Again some pics would help.

[hawker]

Just a thought...are you sure the rings are mounted the correct way round? Apologies if this sounds basic but it's v easy to do with a middle and inner. The outer ring graphics usually make the orientation obvious.
Again some pics would help.

Thanks. In fact, I did initially mount the middle ring wrong way round, but did correct that error, without actually improving the middle to outer shift.

[Cyclothesist]

Good luck with the spacers. It might be worth trying just the 2mm first.

[hawker]

Thanks for your suggestion, Cugel. I can see that it might be fine to mix a 9 speed chain and rear cassette with 10 speed chainwheel, but would it actually be O.K. to have a mix of 9 and 10 speed chainrings mounted on the same crank, as opposed to buying an entire new 10 speed triple?

I must say that, having removed the front mech, the bike now actually looks neater (pity it's obviously also slower .) I'm now tempted to think about a Rohloff-equipped steed... (Well, there's no harm in dreaming.)

[Brucey]

...The FD moves up as it moves out.....

Not always. The exact path of the FD depends on it's design, chiefly whether it is top swing or bottom swing. However, there is more than one bottom swing mech where the linkage has gone overcentre by the time you are over the big ring in which case the trajectory is downwards with further outboard movement.

The OP's issue may well be that he has a chainring that is meant to be part of a 2x setup not a 3x setup. Chainlines are still separated by ~8mm or so, despite modern chains being much narrower. So the chainlines in a double setup are ~4mm different to a triple. This discrepancy could either be taken up in the design of the chainrings, cranks or both. Chainlines that differ by ~3mm on the big ring are to be expected. I am also rather sceptical that this could be adjusted out using spacers alone.

[hawker]

...The FD moves up as it moves out.....

Not always. The exact path of the FD depends on it's design, chiefly whether it is top swing or bottom swing. However, there is more than one bottom swing mech where the linkage has gone overcentre by the time you are over the big ring in which case the trajectory is downwards with further outboard movement.

The OP's issue may well be that he has a chainring that is meant to be part of a 2x setup not a 3x setup. Chainlines are still separated by ~8mm or so, despite modern chains being much narrower. So the chainlines in a double setup are ~4mm different to a triple. This discrepancy could either be taken up in the design of the chainrings, cranks or both. Chainlines that differ by ~3mm on the big ring are to be expected. I am also rather sceptical that this could be adjusted out using spacers alone.

I've managed to find the order details of the two chainrings.

The old chainring was: Deore M540 44T 9spd

The new one is: FC-MT 300 44T 9spd

Do you happen to know if the latter is a viable replacement?

[Brucey]

I don't know if that chainring can be made to work or not. I suspect that you will run out of chainring bolt sleeve length. Years ago, several chainsets (eg. stronglight 99/100) were sold as triples where all three rings use the same bolts. These bolts had very long sleeves, ideal for cutting down. I think you can buy bolts and spacers from spa cycles.

[gregoryoftours]

Have you physically counted the teeth on the new chainring to make sure that you were sent what you ordered? The fact that the front mech was higher in relation to the ring when the ring was fitted makes it sound like you may have a 42t. A 44t replacement would be exactly the same diameter and would therefore have the same mech clearance. Photos would help, both from the side and top.

[Cyclothesist]

Have you physically counted the teeth on the new chainring to make sure that you were sent what you ordered? The fact that the front mech was higher in relation to the ring when the ring was fitted makes it sound like you may have a 42t. A 44t replacement would be exactly the same diameter and would therefore have the same mech clearance. Photos would help, both from the side and top.

Not necessarily but definitely worth checking. Assuming the FD adjustment and position isn't touched:- If as the OP states the new outer ring is a few mm inboard of the original and the FD is of the usual modern type that swings up as it moves out then the FD will sit too far out. Adjusting the hi stop would then bring it in a bit too low.
I can envision a couple of problems with that kind of setup:
- The gap between middle and outer rings may be too small to allow sufficient FD cage rise to move the chain from middle to outer. Conversely if the FD is height adjusted for the outer ring there may be too little distance for the FD to move down when shifting from outer to middle leaving the chain riding on the FD cage.
- In the middle ring changing up gear to the smaller sprockets across the cassette will move the chain angle such that it catches and rides up the inside surface of the outer ring. Possibly even autoshifting noisily from middle to outer chainring.

Brucey hinted that chainrings for doubles and triples are not the same shape. Never knew that. If it's not indicated on the sites selling them how is the buyer supposed to know?

[Cyclothesist]

I'm thinking we're missing something here. The new chainring is for a Shimano hollowtech MTB triple. It's going on a Shimano square taper MTB triple. Are hollowtech chainrings dished differently? We really need some photos to help further. I can't get away from the thought that the outer ring may be on with the wrong side facing out. That would reverse the dishing of the ring and explain the spacing problem.
The new ring doesn't appear to have the protective short metal pip that stops the chain going between the ring and the crank. That pip is also a useful orientation guide!