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I have recently purchased a Merida 2015 7500 One-Twenty 3x10.

Link to bike specs: http://online.fliphtml5.com/pvouz/azox/#p=12

The crankset chain rings are very worn and need replacing.

enter image description here

More Pictures of Crankset: https://drive.google.com/folderview?id=1sHKCdlJYe0ygDfoz3sI7e0QFI-eXPZkE

The current crankset is an Shimano M523 Octalink 40-30-22T 10s. This seems to be quite hard and expensive to purchase here in the UK.

Do you have any recommendations replacing this worn crankset ?

I could replace just the chain rings or the whole crankset.

I could also change the bottom bracket as well to be open up my options.

Any help would be very much appreciated.

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If you're just riding casually, then a simple chainring replacement is probably all you need. You don't have to match the styling, just the Bolthole Circle Diameter (BCD) and number of boltholes. It looks like a 4 bolt pattern, but there are a number of standard sizes (naturally)

Personally I use a 100% printout of the PDF at https://cdn.shopify.com/s/files/1/0230/9291/files/Measure_BCD_5ad6ccfa-f146-4048-ac0f-e2279602c9e1.pdf and then overlay the chainring on the page. You can see what BCD you need. From https://www.wolftoothcomponents.com/pages/how-to-measure-bolt-circle-diameter-bcd

The four chainring bolts can probably be re-used without issue, provided you remove them without damage.

Staying with the same toothcount makes things simpler too, though you might choose to change things if there's a need, like if you're spinning out in 40:11.

There's a good chance you need a new chain too. Based on the wear on the big chainring, its really quite worn. Depending on how you ride, the middle and grannie ring teeth might be okay, but that big ring needs replacing.

I see no point changing a working octalink BB for something else, until it breaks down, and then you look at what options are available. You have matching cranks already. If the bike us for a long distance trek or all-day MTB in the back country, you'd want to have decent options so replacing working parts might be reasonable then. Or if the BB was crunchy and not suitable right-now, then a replacement might be in order.

However I'm firmly in favour of wearing it out - otherwise you're throwing away parts with life left in them still.

Do let us know how it goes too - final followup is always useful.

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  • +1 to this, the steel Deore or Alivio rings for this crank are very good value compared to replacing the whole thing. – Nathan Knutson Sep 22 '20 at 16:52
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I would recommend you to replace not only the chainrings and crankset, but also the bottom bracket.

Octalink is getting rare because it is a big honking design flaw. There are not one but two flaws in it. The first flaw is that it lacks press fit, so the left crank is free to rotate in its splines minutely forwards and backwards. If you rest your weight by standing on the pedals left foot backwards and right foot forwards, it transmit reverse torque causing these minute rotational movements. These rotational movements cause a tendency for the left crank bolt to self-loosen. The only way to keep the left crank bolt tight is to periodically tighten it. In contrast to this Octalink design flaw, good cranks lacking design flaws do not need periodic retightening but stay tight naturally.

Secondly, Octalink uses in-shell bottom bracket bearings. The shell is very small. This problem is made worse by Octalink having a large diameter spindle (thus solving the fragile and flexible spindle problem of square taper bottom brackets), but the large diameter spindle unfortunately leaves practically no space for the bearings. The small bearings have a tendency to wear prematurely.

Replace the obsolete Octalink bottom bracket with a Hollowtech II bottom bracket. Hollowtech II has a proper crank retention mechanism not prone to self-loosening, and because the bearings are outboard, there is enough room for both large bearings and large spindle.

The Hollowtech II bottom bracket anyway costs only $10 - $20. In contrast to the price of a new crankset, this is nothing. Also, Hollowtech II cranksets are more common on the market, so you have more freedom in selecting a suitable crankset. Octalink cranksets are getting rare due to their two design flaws.

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  • Thank you for the helpful advice. In your view would using a square taper 22-32-44 crankset make much difference if I were switch the bottom bracket to square taper. Does the difference in number teeth make much difference? – Samuel Lopez Sep 20 '20 at 13:31
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    There are still new bikes sold with Octalink and new cranks for Octalink produced by Shimano (the company you seem to be endorsing uncritically otherwise). I do not believe it is such a bad design it would need to be replaced., the cost of buying a new crankset is high. The design works (even square taper still works fine) and if the cranks are fine, I would just buy a new piece of the Octalink BB if the existing one breaks down. The track Dura Ace 7700 is still Octalink BTW so I do not believe anyone saying the BB is not stiff enough. Track riders can create very large torques. – Vladimir F Sep 20 '20 at 15:18
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    As one can see for this crank, the user managed to wear out the chainrings before the crank became loose. Thus I would not overthink the loosening problem. It is easy to tighten from time to time, the tool necessary is simple. – Vladimir F Sep 20 '20 at 15:23
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    If you are going to replace the bottom bracket and crank go with a Hollowtech outboard bearing type for an upgrade rather than a square taper. – Argenti Apparatus Sep 20 '20 at 17:30
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    the Altus crankset HT2 is 9 speed. The chainrings are different from 10 speed. They will probably work, but it doesn't seem like an upgrade in the context of the OP's question - lightweight crankset with replaceable chainrings to heavy non-replaceable one. – thelawnet Sep 20 '20 at 20:00
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I replaced the BB on this crankset recently.

I have a spreadsheet here with all Shimano 9/10/11 speed cranksets & BBs

https://docs.google.com/spreadsheets/d/1HdcNgmQKFA-lAqQJ3lXQ8SwA4tblAKiOXe9XYJJHYN8/edit

The M523 is the only crankset with these chainrings and bottom bracket. However, the M522 is almost identical with 42/32/24 chainrings & no need to replace BB, and should work with your FD (44t or larger may not work well)

If you change the BB, then there are HT2 options:

MT500-3, M612, M622 are much the same thing, and then M6000 & M7000-10-3 have hollow crank arms ( a bit lighter, but who cares really) are much the same thing but a bit higher spec. M782 is a few grams lighter again, but it's irrelevant really.

Any of these are good, but do check if they come with the BB.

In terms of the chainrings, you have an 'AN' series. The things to note here are:

  • The two larger rings are 96mm BCD. This is unique to 40/30/22 chainsets as compared to earlier/trekking designs, which use larger outer rings and are therefore 104mm BCD
  • The chainrings are ramped and pinned and the big rings work with specific smaller rings, although I think that as a 96/64mm BCD you might not have any other options here. You won't want to replace 22 with 24, for example.
  • I think different AN chainrings should work here (e.g. Deore, SLX, XT), but I'm not promising 100%, you might like to remove yours and inspect them carefully against images online
  • It might be more expensive to replace all three chainrings than buy a new chainset.

To replace the crankset you'll need:

  • Crank extractor (not necessary if you just want to remove chainrings). Octalink is almost the same as square taper, but it goes in a bit more, so if you have a square taper crank extractor, it won't work and you'll destroy the thread on the crank arms, UNLESS you buy a crank extractor that comes with an extra octalink extension (little metal plug). Cost is about £3 for a cheap Chinese model.

To replace the BB:

  • Octalink BB tool, which looks something like a cassette tool but it's not. Again around £3.
  • HT2 BB tool, which comes in three sizes, best I can tell this for the weight weenies, but essentially the more money you spend you save 10 grams or something, but anyway, there's a HT2 for everything up to Deore, and then two progressively smaller ones, so if you buy a slightly more expensive BB (which might or might not be better sealed), then you'll need both the Hollowtech II BB tool (which is in the form of a spanner) and an adaptor (TL-FC25). More expensive tools can be purchased.

I had a look on Ebay and both M522 and M523 are around £50 but maybe availability is poor. This likely INCLUDES a BB, depending on where you purchase.

M6000 is certainly more expensive, and you'll need to add a new BB and the tools for that as well. The other HT2 cranksets might be a bit cheaper.

I suggest you inspect the current BB for play and if it's not bad, considering the chainring wear, there doesn't seem to be much benefit in replacing the crankset with a HT2, if it's your chainrings that have worn, not your BB.

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