Crankset Replacement

[The Critic]

I have a 2004 model Specialized HardRock Sport.

About a year ago, I discovered that the original chain was very worn, So, I replaced the rear cassette with a SRAM PG-850 and the chain with a SRAM PC890. Ever since then, I could feel the chain "skip" if I pedaled with moderate to heavy pressure. Not knowing what the problem was, I lived with the problem for the past year and in doing so, accumulated a few hundred miles on the bike.

Recently, I noticed that my front chain rings are getting very worn, so I need to replace those. It appears that my chain rings are riveted together, so I'll need to replace the entire crankset. Currently, I have a Truvativ ISO-Flow crankset, 42/32/22 cr-mo chain rings and a Truvativ 68X113 square-taper bottom bracket-- all of which are original.

So, here are some questions I have:

1) Currently I have a square-taper bottom bracket. Can I switch to a Octalink type bottom bracket? I ask because there are more crankset choices if I switch to an Octalink type bottom bracket.

2) If I decide to stay with a square-taper compatible crankset, should I replace my bottom bracket when I install the new crankset? I don't have any issues with the bottom bracket right now, though it is nearly six years old and probably has 500 miles on it.

3) So, if I stay with a square-taper setup, I plan to buy a Shimano Alivio FC-M410 crankset and a Shimano UN-54 bottom bracket. Or, if I go to a octalink setup, I am going with a Shimano Deore FCM-442 crankset and a Shimano ES-51 bottom bracket. What do you guys think of those choices?

Thanks!

 

[mpvue]

only 500 miles on the bike? and the chainrings are worn? how did you determine that? chainrings should be good for multiple thousands of miles.
who installed your chain? are you sure you don't have any stiff links in the chain?

 

[The Critic]

Originally Posted By: mpvue
only 500 miles on the bike? and the chainrings are worn? how did you determine that? chainrings should be good for multiple thousands of miles.
who installed your chain? are you sure you don't have any stiff links in the chain?


There's at least a thousand miles on that bike, maybe 2.

My friend's dad is a pro bike mechanic and he told me the other night that my chain rings had the "sawtooth" pattern and were quite worn, especially the #2 and #3.

I installed the chain, but I also had a professional tune-up done on the bike shortly afterwards and they did not mention any issues.

 

[mpvue]

ok then. I asked because what some think is 'wear' is really not. riveted cranksets aren't expected to be used all that heavily; some will last forever because of the light use. but when they do wear out, you have to replace the whole shebang.
you could probably get a nice deore setup for cheap, rings are replaceable.

 

[wantin150]

If you are running a square taper BB, you can swap it to an Octalink. Just make sure that the thread type and count is the same. The info should be on the old BB (the 68X113 you mentioned). There are different versions. You are better off doing this as square tapered cranks are becoming harder and harder to find.

You will need a special tool for the Octalink. You need a special tool for the square taper. Either way, you need a crank removal tool. If you choose to stay with the square taper, you can just buy one removal tool and then replace chain rings as necessary. The set-up you mentioned will be fine. If your current BB is OK, stick with it (although I did say the Octalink is better). You can tell when they go bad by grabbing the crank arm and pulling/pushing back and forth. If it moves, it's on it's way out. You can also hear them when they are failing. Remove the chain and spin the arms.

 

[The Critic]

So, my neighbor's boyfriend works at a bike shop and suggested that I purchase one of these:

http://www.pricepoint.com/detail.htm?stylePkey=15769&style_id=100 TRUFT6

What do you guys think? He claims that it'd be the best bang for the buck.

 

[MtnMike]

Yeah, I wouldn't mess with the Octalink system. The state-of-the-art in cranksets is the external bottom bracket style, like the one in the PricePoint link above. Basically that means that you have a bigger crank bearing, which is outside of the bottom bracket shell. They're normally stiffer and lighter than either Octalink or square taper. I have no idea of that Truvative crank is good or not, but it represents one of many models available from various companies.

The very newest innovation by Trek encorporates the external bottom bracket style bearings (which are large) into an even larger bottom bracket cup. This constitutes an entirely new frame design concept, which is out of the question for you. Also, the jury is still out on it's reliability. I've heard mixed reports.

 

[wantin150]

I would jump all over that, as long as there is no conflict with the increased BB length and chain angle.

 

[MtnMike]

Originally Posted By: wantin150
I would jump all over that, as long as there is no conflict with the increased BB length and chain angle.


I'm pretty sure the standard BB lengths (68 or 73mm) are compatible with either. Because of the way the cranks are designed, your chain line should not change with the external system.

 

[NYEngineer]

I have the external bearings on my bike with 175mm long XT cranks. Seems better than the square tapers on my old bike.

 

[cchase]

External bearings are the new thing, however even a standard cartridge bearing ISIS or Octalink will be worlds better than a square taper. Just make sure you keep the crank bolts tight or you'll round out the splines.

 

[The Critic]

So, I saw a Deore FC-M590 on eBay and decided to bid on it...and won:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=320478209096&viewitem=&sspagename=STRK%3AMEWAX%3AIT

What do y'all think? It's an external BB system right?

 

[MtnMike]

Yep, and looks like you got a nice price too

If you're putting it in yourself, there's a special tool that you'll need. Park calls it the BBT - 9 . If you're moderately good with a wrench it's an easy install. Edit, I forgot; you've gotta take the old stuff off, which needs other tools. Anyway, Good luck

 

[wavinwayne]

Bottom Brackets have always given me trouble. I never have been able to get the torque right, and have had problems with the BB coming loose after a couple hundred miles. This is a job that I now leave to my local bike shop mechanic; plus anything related to brakes and cables of any kind.

The crankset you purchased should serve you well for a very long time, assuming you use a decent chain lube, and you clean the chainrings every once in a while. Have fun!