Chainring replacement for 3 x 9 Deore

[Rob D]

Hi. I've had a few problems with the chain jumping off at the front. The chain was worn somewhere between 0.5 and 0.75% and was causing a chittering noise around the derailleur. So I swapped the chain for a part worn one, still not yet at the 0.5% wear.

But that led to another problem: the inner ring (24T) had become a little 'hooked', causing the chain to be hung up on the slightly hooked teeth (as the chain leaves the chainring), jamming everything. So I replaced that, but then found the new chain was jumping off the middle ring (36T) when I changed up, causing the chain to come off inside the inner ring. I'm not sure if it's doing the same thing as the inner ring had been doing?

Whilst the middle ring does not look too worn, I'm looking to replace it. It's stamped 'shimano m9 t36'. But I can't find a replacement with that number.

Does anyone know what would fit?

I'm keen to sort it pronto as we're off to France for 3 weeks soon.

Many thanks

Rob

[Eyebrox]

This archived Shimano compatibility chart lists the company's 9sp MTB style triples and their chainring configurations. You need to find the FC code which should be engraved somewhere on one of the rings. You can then see what's available and check with the supplier on whether the replacement ring or rings fit the numbered crank.

[Rob D]

Thanks for this. I can't find the code, but am yet to strip it down. It may be hidden?

[AndyK]

It may be easier to find the code on the crank arm. It will be on the inside of the arm (i.e. the side facing inwards towards the bike) and will start with "FC-". Was the inner ring always a 24T, or did it replace a larger ring? The 24T-36T-whatever combination seems pretty unusual for Shimano.

[slowster]

I have the 42/32/22 version of the Octalink FC-M540 chainset, and recently replaced the middle ring which was badly worn. The ring is stamped M9 N-32, but that is not the actual part number, and I had to do a lot of online research to make sure I was ordering the correct replacement.

The problem I found was that Shimano made various 9 speed triples numbered FC-M4xx and FC-M5xx all using the 104mm BCD, but they did not all use the same chainrings. In particular those chainsets that were the two piece Hollowtech 2 design used different chainrings to the three piece Octalink chainsets. I think that I read on a forum that someone who ordered the wrong one was able to file the chainring so that it would fit on the crank, but obviously it is better to get the correct chainring.

The following EV docs are for three Octalink chainsets:

FC-M540 - http://www.sjscycles.com/Instructions/S ... ctions.pdf

FC-M440 - http://www.sjscycles.com/Instructions/S ... ctions.pdf

FC-M510 - https://si.shimano.com/en/pdfs/ev/FC-M5 ... -1873A.pdf

The part code for the 32t silver is same in all: Y-1DS98010. It also looks like there are other cross compatible Octalink chainsets per this link - https://www.bike-components.de/en/Shima ... ng-p21682/.

I had no luck searching for a 32t chainring for FC-540, but I did find it by searching for a 32t chainring for FC-510.

You should be able find a suitable 36t ring by searching for the relevant part codes and/or by searching for one or other of the compatible chainsets.

If do you have an Octalink chainset, I **think** that that this might be what you need, but you absolutely need to double check everything for yourself:

https://www.amazon.co.uk/gp/product/B001EIG704/ (out of stock, but sometimes re-stocking is very quick)

https://www.amazon.co.uk/Shimano-Deore- ... 0075I9678/ (ditto)

https://www.freemanscycles.co.uk/shiman ... -m510.html (photo is of 32t, not 36t)

If instead you have a Hollowtech 2 chainset, then you will probably need to do the same thing and find and compare part numbers for the chainrings.

[peetee]

I think that I read on a forum that someone who ordered the wrong one was able to file the chainring so that it would fit on the crank, but obviously it is better to get the correct chainring.

It was me and I agree, the correct chainring would have been easier but it was not available and, even if it were, it’s possible that the price disparity would be such that 10 minutes spent with a hand file would be worth the effort as, once adjusted and fitted, it worked faultlessly.

[Rob D]

It may be easier to find the code on the crank arm. It will be on the inside of the arm (i.e. the side facing inwards towards the bike) and will start with "FC-". Was the inner ring always a 24T, or did it replace a larger ring? The 24T-36T-whatever combination seems pretty unusual for Shimano.

Thanks all. Just arr work, so will look into the other helpful posts later.
Yes, it was a 26. We've been reducing our gears as we get older - and do more adventurous stuff! Currently 24 - 36 seems ideal. My wife has 22, but I think the bigger jump causes the occasional chain-off. Mine had been ok til now...
Flippin' complicated stuff, trying to get replacement cogs!

[Rob D]

I managed to get a suitable Shimano 36T ring at the LBS. It's improved things but I've still had a couple of chain-offs - but that was when doing a lot of changing to check it. I think when changing up. I know it's a 'piece of string' question, but is there anything I ought to be looking at? The inner stop for the front mech is set correctly.
Or is it just one of those things?
Thanks,
Rob

[rareposter]

Flippin' complicated stuff, trying to get replacement cogs!

It's often cheaper and easier to just get a whole new chainset; 3 individual rings often work out more expensive than an entire new chainset.

I know that rings wear at different rates depending on usage but you end up chasing chainsuck problems around the whole drivetrain and a mix of badly worn, part worn, and new rarely works well together.

[peetee]

I managed to get a suitable Shimano 36T ring at the LBS. It's improved things but I've still had a couple of chain-offs - but that was when doing a lot of changing to check it. I think when changing up. I know it's a 'piece of string' question, but is there anything I ought to be looking at? The inner stop for the front mech is set correctly.
Or is it just one of those things?
Thanks,
Rob

Your post is contradictory. The inner shifter stop should not come into play when changing up from the middle ring.
Can you clarify please?

[Rob D]

Thanks both. I didn't think I said it came off when changing up from the middle ring? I was only ever talking about the inner and middle. I added about the stop in case anyone queried it. No probs with going middle to outer and back, thankfully!
Didn't know the term chainsuck - very appropriate, and helps describe things.
And re getting whole new chainset etc, I agree - and accept I may have to take that route. There's lots to be said in knowing everything is working correctly.

[nosmarbaj]

Two things worth considering if not already checked:

• You say you replaced a 26t ring with a 24t one. Does this mean the capacity of the rear mech has been exceeded, leading to a slack chain when on a small cog and inner ring?
• Has the front mech been bent or knocked so that it isn't in line with the diameter of the chainrings?

[Rob D]

Thanks. I went to a 24 about 18 months ago and it's been fine, just the very occasional chain-off. So I'm sure that's ok.
I'm pretty sure the front mech has not been damaged either.
Went for a 17 k hilly ride yesterday, so lots of changing on the front. All seemed fine until near the end, when it sounded like the chain was coming off but it didn't. So maybe it'll improve as the 2 new rings wear in?