numpty question about replacing crankset

hunnymonster

Sorry to come on looking to take advantage the cycling forum. the threads on my cranks have been worn away (I think my keo's were not not on tight enough and this has sheared the threads on the cranks). The bike is a specialized ruby and google tells me the cranks on it are "FSA SL-K MegaExo, 2-piece carbon crankset"

Will I be able to replace them? If so should I get the same again or are the other (better or cheaper) options? The bike is starting to show it's age (2006 - what's that in human years?) so if it's going to be a very expensive job I may have to start a new-bike piggy bank. I usually only do the most basic mechanics myself, is this something I can attempt?

Sorry again for all the questions.

jlang

I had a similar question on Sunday. I was hoping I'd be able to replace the arm only but ended up needing a new crankset. Bike is quite new so considered changing brand from FSA to Shimano 105 as the rest of the set is 105 but with the shop's advice I went for the same again. I'm looking at 200-ish which is nearly half what the bloody bike cost me but it's no use at all with only one pedal.

blorg

This thread may be of interest, it starts off with DA 7900 but quickly degenerates into analysing crank stiffness vs weight.

The pertinent figures come from a test Tour Magazine did:



FSA SL-K comes out around the same weight as Ultegra SL but Ultegra SL is a lot stiffer.

Having said that I don't really know if this makes a big difference. My cranks are all alloy and very happy with them (DA 7800 standard and Ultegra SL compact on my road bike.)

Carbon is more bling.

TinyExplosions

I like how high Rival comes in that list....

hunnymonster

Thanks Blorg that's really helpful.

rottenhat

TinyExplosions wrote: »

I like how high Rival comes in that list....

I like how price comes nowhere in that list.

sean_d

And to answer your other question - yes it is something you can do yourself, provided you've got even a modicum of mechanical ability. Instructions here.
Shouldn't take you any more than 15 mins..make sure you grease the bottom bracket shell and pedal threads when reassembling.

blorg

Regarding Sean's link above, you probably won't have to do any of the inital steps like facing- and if getting the same brand cranks you won't need to replace the BB cups. If switching to Shimano cranks you MAY be able to use the same BB cups but I am not 100% on this, there is mixed information out there. Certain FSA MegaExo cups are compatible with Shimano Hollowtech II so you could be able to choose between FSA or Shimano cranks without having to change the BB cups. This is at least what I gathered when looking for a compact that I could swap onto my Shimano Hollowtech BB cups, e.g. that FSA carbon cranks were an option.

If you are looking for a standard double, a Dura Ace 7800 crankset can be picked up for around £200 on special, lighter and stiffer than what you have now. Really lovely crankset. They can be reduced now with 7900 coming in. One off a new bike went for £140 on eBay recently, with the BB cups. Ultegra SL would also be a good option, stiffer and lighter if you use the Shimano BB cups.

sean_d

Thanks blorg - forgot to mention you won't need to do any of the preliminaries.
Changing the cranks is an ideal time to swap out the BB too though, unless you've already put in a new one fairly recently.

AFAIK - most external BB cups are interchangeable across brands, but Shimano are reputed to be more reliable...but thats just anecdotal.

DirkVoodoo

Might want a torque wrench too when tightening the bolts, over torque and you could damage the pinch bolts, under torque and you could damage the splines.

doozerie

hunnymonster wrote: »

Sorry to come on looking to take advantage the cycling forum. the threads on my cranks have been worn away (I think my keo's were not not on tight enough and this has sheared the threads on the cranks).

I think it unlikely that the pedals being loose could shear the cranks threads - at least, I can't imagine how this would happen (for the pedal to be loose enough to cause such damage I'd expect that you would have been aware of it while using the bike, and probably for some time). Could the pedal have been put in badly at some stage maybe, as that can certainly damage the threads. Obviously, you should double-check the threads on the pedals too for any signs of damage.

Whichever crankset you go for, be wary when fitting the pedals. The gorilla approach to fitting pedals, whereby you swing out of the spanner until you've squeezed every last bit of life out of the pedal and crank, is very common. It also makes the pedals a nightmare to remove later. I've snapped spanners in the past when trying to remove pedals that were fitted by gorillas. It's a matter of judgement as to what is "tight enough", unless you have a torque wrench that is, so it's worth tightening them to what you think is enough and come back a day or two later to see if you can undo it again - it is likely to be easier to re-do an overtightened pedal sooner rather than later.

Lumen

Pedal/crank thread problems are more likely due to lack of grease causing seizing than overtightening damaging the threads. That said, I don't tend to apply much torque when tightening pedals since they're threaded "handedly" to stay on.

jlang

Lumen wrote: »

Pedal/crank thread problems are more likely due to lack of grease causing seizing than overtightening damaging the threads. That said, I don't tend to apply much torque when tightening pedals since they're threaded "handedly" to stay on.

Which was why I felt so stupid as I had the pedals on correctly before and only took them off to put some grease in there! Three rides later the cranks were screwed (or not, in this case).

blorg

I managed to sheer off my threads from an impact on the pedal- parked bike was knocked over and whatever way it landed on the pedal. Cycling home it became pretty obvious that something was wrong (pedal started sort of moving out of plane) but by that time the damage was done. Thankfully it was a left hand crank so cheap to replace. I do normally lock my bike so this isn't possible BTW