Bicycle Mechanics - Newbie: Crankarm/Set

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Stuart111
07-21-12, 11:41 AM
Hello,

I am pretty new to cycling and have recently purchases a Giant TCR which although is in beautiful condition (2nd Hand) the right arm has no thread left in it. The bike was fairly discounted as I need to replace that part but the rest is lovely, recent service, new chain, cables etc.

My question is that the bike has a Shimano Tiagra 4503 triple Crankset as per picture. The rings on my current one are spot on, it really is only the arm. Anyways I ordered a replacement which is on its way, though it comes as a set. both arms, rings etc. Would it be possible to simply take the right arm off via those allen key bolts and replace with other arm and just leave current rings on (So that in month down the line i have a spare set of rings )? I have not tried to take aprt as dont want to incase something goes worng or it should not be done etc,

Any help much appriciated.

S

Stuart111
07-21-12, 11:55 AM
Secondly the reason i was warey of just waking the whole new crankset on is my local bike shop advised i should change the casette if changing the front rings. even though the cassette is pretty new.very confusing
Bill Kapaun
07-21-12, 12:25 PM
If you are asking if you can swap your current rings to the new arm, no problem.

Stuart111
07-21-12, 12:33 PM
Yes I am. Though i guess when the new set arrives i will have to dismantle it along with the one on the bike, unless it arrive in bits. Then just keep the spare new rings and left arm for future use (or ebay)
JanMM
07-21-12, 01:00 PM
No reason to change cassette when chainrings are replaced.
dsbrantjr
07-21-12, 01:31 PM
If the missing or stripped threads you are referring to are the pedal threads they can be repaired easily and economically by drilling them out and re-tapping them for a Helicoil insert. This will make the new threads stronger than the original. Any good bike or machine shop should be able to do the job.
dabac
07-21-12, 02:58 PM
I ...purchases a Giant TCR ...the right arm has no thread left in it. ...Would it be possible to simply take the right arm off via those allen key bolts and replace with other arm

No.

Those visible Allen bolts only hold the two biggest rings. That type of crank, the BB axle is permanently mounted to the right crank. You have to remove the left arm, pull the right and axle as one unit before mounting your new right crank.

But yeah, you can keep the rings as spares. Or move your old rings to your new crank, maybe sell the unused rings on to cover some of the cost for your new crank.

Or go for the Helicoil option, keep your old crank.

And while cassettes and chains can be a bit partial to the company they keep, it'll take a lot of wear before the chainrings start making a fuss.