Crankset or new bb for Octalink 9 speed

[MountainSide]

Currently:
Bottom bracket : Shimano BB-ES50 68E BC1.37x24, L-R 113
Crankset: Shimano Alivio M430/M431 44/32/22

Struggling to find a replacement crankset.

Closest I can find is :Shimano Acera FC-M3000 Octalink chainset, 40/30/22

This is "compatible with 118mm Octalink BB". Would this work if mine is 113mm Octalink? That is the length, right - does that matter?

Would I be better off getting a new BB? What would be comparable, square taper?

Would I notice much difference between 44 and 40 teeth. I am mostly on the roads but do lots of hills.


EDIT: So having looked around a bit more, it seems I can't just buy any octalink chainset as it needs to match my 113mm Octalink? Is that correct? So my options are very restricted without changing the BB. So how do I get the right size BB for my bike - I had thought the 113mm somehow related to the bike frame dimensions. (I mean theoretically, if I wanted to stick With Octalink could I replace the 113mm Octalink BB with a 118mm Octalink BB?)

 

[Ajax Bay]

I'd go for a square taper replacing the bottom bracket too.
Here's a Spa Cycles touring triple (£35) with the same chainrings (number of teeth):
https://www.spacycles.co.uk/m2b0s109p2657/SPA-CYCLES-104-Touring-Triple-Chainset
I have one of the similar Spa TD-2 crankset (48-38-28) and have fitted it and then removed it, ready for when my Tiagra 4403 crankset needs replacing. I guess you wish to keep the climbing ratios a 22t inner offers.
And the best BB for that is a Shimano UN-55 which Tredz are selling for £15 (for a 68-113):
https://www.tredz.co.uk/.Shimano-Bottom-Bracket-BBUN55_50477.htm?sku=186587&utm
Tredz seem to have £5 off one's "first" order.
I have one of these fitted - a replacement for the original after 25,000+ km.

 

[MountainSide]

Thanks, in the end I managed to order 2 complete sets of replacement M430 chain rings for about the price of a new chainset. I kept my previous crankset which was also an M430, so I should be good with 2 working sets with new rings. Have stripped down and cleaned the bolts for when they arrive. Saves having to replace the BB or risking a different crankset that might not work and I keep my familiar gear ratios. Would still be interested if cranksets are compatible between Octalink 113mm and 118mm if anyone knows. I gather it is something to do with a 50mm chainline but I guess a couple of mm's each side is pretty insignificant?? Again with the above recommendation, the crankset says "Use 107mm square taper BB" but If had replaced the BB for square taper would I not have gone for the 113mm to fit the bike?

 

[Ajax Bay]

http://www.sheldonbrown.com/chainline.html
Using a 118 as opposed to a 113 BB will shift the OP's chainline 2.5mm further right making the lower gears Ie large sprockets subject to more cross chaining. Would also increase 'Q' factor and some people's knees are sensitive to that.
If the chainset says 'use 107' then use 107. The chainline is a combination of the BB spindle length and the design of the chainset. The road bike frames these BB's fit are all 68mm (generalisation) so one's not trying to 'fit the bike'.

 

[the snail]

http://www.sheldonbrown.com/chainline.html
Using a 118 as opposed to a 113 BB will shift the OP's chainline 2.5mm further right making the lower gears Ie large sprockets subject to more cross chaining. Would also increase 'Q' factor and some people's knees are sensitive to that.
If the chainset says 'use 107' then use 107. The chainline is a combination of the BB spindle length and the design of the chainset. The road bike frames these BB's fit are all 68mm (generalisation) so one's not trying to 'fit the bike'.

That assumes that the BBs are symmetrical, which they may not be. Cross-chaining/Q factor aren't really the issue imo, more that the chainrings might foul the frame/BB shell, and the FD may not have enough travel, so it may not work at all with the wrong BB/chainset.

 

[MountainSide]

http://www.sheldonbrown.com/chainline.html
Using a 118 as opposed to a 113 BB will shift the OP's chainline 2.5mm further right making the lower gears Ie large sprockets subject to more cross chaining. Would also increase 'Q' factor and some people's knees are sensitive to that.
If the chainset says 'use 107' then use 107. The chainline is a combination of the BB spindle length and the design of the chainset. The road bike frames these BB's fit are all 68mm (generalisation) so one's not trying to 'fit the bike'.

So can I just replace my 113 BB for a 118 BB (if I wanted to) or would that not work? Mind you I just saw that even the M430 says "For use with 118 mm Octalink Bottom Brackets" and I have used two of them over 10 years, probably around 30000 km per set and the two sets of replacement rings should out live the bike.

Incidentally, I put the old chainset back together but with the middle ring (the only one that skipped with a new chain) rotated 180 degrees. Been working perfectly! Will do until the new rings arrive from Germany but keeping the miles down to avoid any potential stress on the new chain.

 

[Ajax Bay]

can I just replace my 113 BB for a 118 BB (if I wanted to) or would that not work?
I put the old chainset back together but with the middle ring (the only one that skipped with a new chain) rotated 180 degrees. Been working perfectly! Will do until the new rings arrive from Germany but keeping the miles down to avoid any potential stress on the new chain.

If you 'want to', yes.
Logically it'd be better to rotate the middle ring 72 degrees (or 90 if 4-bolt) as if the wear is uneven it'll be uneven at the two points 180 degrees from each other (max force at (roughly) 3 o'clock and 9 o'clock).
Chain will not care and cycling like this will not risk any additional stress on it. Get out and get the miles in. Small ring if stomping up hills. Don't be lazy: change down at the front in anticipation of serious gradients.

 

[MountainSide]

Get out and get the miles in.

Would have been nice except I have waited in, all day, only for the rings not to arrive despite being told "The shipment will probably be delivered to the recipient today". P.S. Don't ever be foiled by a .co.uk bike company seemingly being UK based, as I have found out, this is not always true and when they "promise" to despatch same day if ordered by 3pm, be aware that it does not apply, for example, after "we had a busy weekend".

EDIT: They arrived eventually and have been installed and a test ride was great. The shop had a choice of 2 outer rings and one was out of stock. I didn't know what the difference was so took a gamble. It turns out it has a pin as a chain stop and the holes for the plastic chain guard ring (that my old sets had) have not been tapped. No big deal, I can live with that.