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  1. #1
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    Help upgrading Shimano 8spd IG crank to 9spd HG crank.

    Hello,

    I'm hoping I can get some help and advice upgrading from Shimano 8 speed IG only crankset to 9 speed HG crankset.

    Background:
    I ride a 2005 Rocky Mountain Fusion that was originally an 8 speed bike. In '08 I decided to upgrade to hydraulic brakes and since my shifters and brake levers were one piece I had to get new shifters as well, so the end result was upgrading to 9spd drivetrain. At the time I got 9spd shifters, cassette, chain and already had 9spd Deore rear derailleur. I skipped on upgrading front chainrings.

    Present:
    Some parts worn out or broke and were replaced since, but I'm still stuck with IG only crankset. I'm able to pick up a brand new Deore FC-M590 44-32-22 crankset with BB for $75 which is tempting. Currently, bike has FC-MC20 42-32-22 IG only crankset.

    Rest of the bike specs:
    Rear Derailleur: SLX 9spd (SGS long cage I think)
    Front Derailleur: XT FD-M770
    Chain: Deore HG-53
    Cassette: Deore HG-50 11-32
    Shifters: Deore 3x9
    Crankset: FC-MC20 42-32-22 to FC-M590 44-32-22
    Brakeset: Deore M596

    Bike was tuned-up for free by LBS in fall and not ridden since, so I'm a bit reluctant to start fiddling with things.

    Will this be a straight bolt-on swap and minor adjustment of the front derailleur via limit screws?

    I understand I will have to swap bottom brackets aswell. What about 42 to 44 ring, will I have any issues with that? The XT mech should handle that, just minor adjustments right?

    Is this upgrade worth it?

    Thanks in advance and I apologize I'm a noob!

    Edit: Just realized I will have to add some links to my chain, won't I? Which I don't even have...

  2. #2
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    In general, it's a direct swap with the following caveats:
    - You may have to move the front derailleur up to accommodate the larger ring, which could also require fiddling with the cable since it may get looser/tighter depending on whether your cable routing it top or bottom. The M770 can accommodate a 44t big ring.
    - You may also have to fiddle with the limit screws as the new cranks may be a bit wider due to outboard bearings although that is not necessarily always the case.

    Are you going to do the work yourself or have the LBS do it? The M590 is an upgrade but if your current stuff is functioning, it may be best to ride it as is. If it shifts okay and is not slipping, I would not spend the money, but would add it to the "new bike fund". However, if it is not functioning, then the price seems okay, go for it.

  3. #3
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    I would be doing the work myself in a volunteer run shop where I have access to tools and advice from techs for like $2 an hour I did the same with my bigger upgrade in '08. If I have to pay LBS to do the work, it would not be worth it anymore in my eyes.

    It was shifting ok, not great imo. I was never really able to tweak it 100% of my liking myself though. The problem is I don't know if it is because of my lack of skills and experience and no bike stand (makes it a PITA to tweak this by myself), or if it is because of the IG to HG compatibility. I sometimes drop the chain from the big ring, and fiddling with the limit screws didn't help much. Last time when I tweaked it, it was with Alivio top swing derailleur. Since then I got a brand new XT bottom swing derailleur I picked up for $5 from a Shimano rep at my LBS. I could not pass that up and told them to put it on as part of the free tuneup. Since then I haven't ridden the bike, except just around the parking lot after the tuneup, but that is not worth anything.

  4. #4
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    If your keeping the bike and no immediate plans to upgrade the M590 will do well, they are stiffer than the Alivio (less flex). The 44T will work better with the M770, they were designed to together. I always found it more difficult to tune an 8 speed FDR on a 9 speed and vise-versa. The cages have a slightly different height. It can work, just required more work.

  5. #5
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    Thanks for the input.

    No plans to upgrade in the next three seasons. Even then I'll still keep this bike for commuting etc since a 10 year old HT won't be worth much. Based on that at least I feel like I'll get some moneys worth from this upgrade.

    I guess stiffer crank arms is a good thing, but I probably won't see the difference. I never even broke a chain yet.

    I wonder if Deore's are lighter too.

    These are 175mm, just like the old ones, so apart from the 42 to 44 ring, they are almost the same.

    I have BB-UN25 bottom bracket now, so this SM-BB51 will just bolt on correct? Thanks again.

  6. #6
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    You should see some weight loss, the UN25 is a boat anchor. To remove the UN25, you need something like this:
    Park Tool Co. BBT-22 : Bottom Bracket Tool : Bottom Bracket
    To install the Shimano SM-BB51 you need this:
    Park Tool Co. BBT-9 : Bottom Bracket Tool : Bottom Bracket

    Incidentally, the Parktools website has great tutorials.

  7. #7
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    Perfect, thanks again. I will watch those video tutorials on Parks website.

  8. #8
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    My parents have a $300 kind of department store bike in the garage that is currently not ridable. It is a CCM HT that needs a 7spd rear wheel and a new crankset. I can't get to it right away to check as there are too many things in the way, but would it be safe to assume the UN25 and FC-MC20 will fit it ok? It has Shimano Tourney drivetrain, any guesses if there is a good enough chance I could get it all to work ok? The FC20 Alivio crankset was originally paired with 8spd cassette.

    That will make it easier to justify spending money on new parts if I can be a hero too and revive an older bike for them.

  9. #9
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    There's a good chance it will work. Older dept store bikes had open bearing square taper cranks, but once removed the threads were the same. You may find out you can leave the existing bb since it may be square taper like the UN26.

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