New crankset help, please

Slurp

Following a service at my local bike shop -- one of the larger chains -- during which the sharp-eyed mechanic noticed a small crack on the drive-side crank and suggested a fairly rapid replacement, I need some help on cranksets. To their credit, the shop suggested it would be cheaper for me to source an OE crankset than to get them to replace just the offending spider. But before I dive in, there are some questions:

1. How easy is it to change a crankset? It sounds fairly straightforward, but does adjusting the gear spacing make the whole thing a minefield?

2. Current crankset is Specialized's own triple; I'd be looking to replace it with similar at Shimano Tiagra level. But my current cassette (also Tiagra) is 8 speed and it seems that the latest Tiagra cranksets are 9 speed. Is that a problem? Do I also need to replace the chain and cassette, both of which are brand new?

3. What glaringly obvious problem have I failed to ask about?

Underscore

Having replaced Specialized's own crankset on my Sirrus with a Deore, I can probably provide some insight.

1) Changing crankset is a bit involved but is certainly doable without resorting to the LBS. The one exception to that is if you are proposing to go (as I did) from an internal to an external bottom bracket - in which case you will need to get the BB shell "faced". This cost me £15 but I had to hunt around a bit to find an LBS with the tools to do it. To remove (and fit) an internal BB, you will need a crank extractor and the appropriate splined socket. These aren't horribly expensive but, if this is your only bike and you are going external, I would get the shop that does the facing to remove the old crankset as it will likely not cost any more. To fit (and remove) an external BB, you will need the preload tool (£3) and I would recommend a socket for the cups (yours for for £10). Ideally you'll fit with a torque wrench. Again, getting the shop doing the facing to fit the cups may be attractive, but it's probably useful to have the tool for future maintenance so I fitted it myself. Once fitted, you'll probably need to adjust the front mech (park tool website was invaluable) as the chainline will probably have changed. As the outer chainring was the same size (48-tooth) for me, the existing mech was suitable but, if the chainline and/or chainring sizes have changed too much, it may not be.

2) The Deore I fitted was 9 speed but everything else is 8 speed. It shifts better than the Spesh crankset ever did, so you should be fine. I've heard that a worn chain on a new chainring will always slip but, if your chain is new (as you say) there should be no problem.

3) If you are going from Shimano MTB to road ranges, bear in mind that you won't be able to use a road front mech with you existing shifter (the pull ratios are different) so you may be better sticking (as I did) with a 48/36/26 MTB chainset as you'll be able to get a compatible mech, should you need one. If your bike is already build around road components (which it sounds like could be the case), you should be fine.

HTH,

_

nicklouse

well without knowing the make model and year of bike it is hard provide the correct info.

as spesh have made more than one triple crankset over the years.

But Parktools have all the info and also list what tools are needed.

you say the spider is cracked? so it is not the crank arm as mentioned in line 2.

again some spiders are replaceable some are not. but then i wonder is it the spider or the chain ring that has cracked?

so more infos please and pics will help muchly.

Slurp

nicklouse wrote:

well without knowing the make model and year of bike it is hard provide the correct info.

OK, didn't want to overburden with too much info. It's a Specialized Allez, bought in 2004.

you say the spider is cracked? so it is not the crank arm as mentioned in line 2.

It seems to me that the crank arm and spider are one-piece. See attached photo, which clearly shows the crack just where the crank emerges from the spider. (Actually, attaching doesn't seem to work, but the link does)

nicklouse

Ok. yep the arm is trash.

Ok looks like a square taper fitting

http://www.parktool.com/repair/readhowto.asp?id=103

if you want to keep the current BB you will need to measure the axle length and get new arms that work with that axle length.

to remove the BB

http://www.parktool.com/repair/readhowto.asp?id=94

if replacing the old with a new External crankset you will need the BB shell facing.

But if you use another internal type you wont need to and it will use the same tools for fitting as the old one did for removal.

have a read of those Parktools links and if you are happy to give it a go have fun.

Slurp

I still have questions, though: the later Tiagra, even the square-taper ones, seem to be 9-speed so will I need to replace the chain from the current 8 speed or is the width difference not as signficant? If I do need to replace the chain with a 9-speed, will it work OK with my 8-speed rear cassette?

I've replaced a crankset before, so have a little experience, but that was on an old singlespeed bike, so there were no complications with setting front derailleurs.

And I see that the picture attachment did work, but yuk -- that's an eyeful. Must work out how to shrink it down for next time.

Underscore

As I said (somewhere in my post!), I'm running 8-speed everything (including chain) with a 9-speed crankset and have no problems. Of course, YMMV.

_

Slurp

Thanks, Underscore. Very helpful and detailed post. Must have just read over that bit.

Slurp

And the next problem is that it seems the cranks I need -- Tiagra triple for 118mm spindle, square bottom bracket (i believe that's model 4404) don't appear to be made any more. so it's either off the bike shop for a `facing' or finding an alternative quality non-Shimano option. Any suggestions as to the latter any one?

CarlosDSanchez

Chain reaction have the tiagra square taper crankset on their sale. About £28 I think.