Replacing crankset on bike

[palebluedot]

So back in August my sister gave me her old Trek 820 AL (http://www.bikepedia.com/quickbike/BikeSpecs.aspx?year=1999&brand=Trek&model=820+AL) .It wasn't well maintained and probably not used for years. It has served me well though being able to do all my local errands and commuting to my part time job on the weekends.

It has begun to wear down though. I am collecting all the tools I need little by little to do my own maintenance. I want to fix the entire drive train first. I am a little confused about the crankset and bottom bracket compatibility.

According to the spec sheet, the BB shell width is 73mm. I believe most are either 68 or 73mm. Now for the spindle length, should the BB spindle be the size of the current one or one that's going to fit the new crankset? The closest I could find to the 121mm that specifies on the trek sheet is a 122mm BB.

Will this crankset: http://smile.amazon.com/dp/B002I7K5LC/ref=wl_it_dp_o_pC_nS_ttl?_encoding=UTF8&colid=N1TC52IHEYXU&coliid=I3NF8RTDAZMMC1 (170 x 22/32/42)

work with this BB?: http://smile.amazon.com/dp/B00629OC98/ref=wl_it_dp_o_pC_S_ttl?_encoding=UTF8&colid=N1TC52IHEYXU&coliid=I2UCUSQTWBYJQN (73 x 122mm)

Thanks!

[kendallf]

Changing the bottom bracket is probably a good service item if it has play, creaks loudly, grinds, or otherwise shows signs of neglect or wear.  Most modern BBs last for a few thousand miles under normal use.  It's a cheap service item though, so it won't hurt to change it.

Why are you changing cranks?  Unless yours are damaged, I'd keep them.  The chain rings don't wear appreciably until you have many, many thousands of miles on them.   If you do need the new cranks, go ahead and get the 122mm spindle; +/- 1 mm won't be noticeable either way. 

I'd consider a new chain and cassette; these are wear items that wear out more quickly than front chainrings or bottom brackets.

Good luck!

[fodder69]

+1 on not really needing to replace the crank. The BB you picked would be fine, 73 MM english (non italian) threads. You will need the BB tool and a crank puller as well. Those BBs last forever though so are you sure you need to change it?

http://www.amazon.com/Park-Tool-Puller-Square-Cranks/dp/B001VS1M20/ref=pd_bxgy_sg_text_y

http://www.amazon.com/BIKEHAND-Bicycle-Shimano-Bracket-Removal/dp/B00811WQJS/ref=pd_sim_sg_2

[palebluedot]

I have a new cassette and chain ready to be installed. I am awaiting the lockring tool to remove the current cassette.

Sometimes when riding, I tend to hear a snap on the cranks and the cranks start moving loosely/freely without any tension. Could it be a problem with the BB or the cranks/something else?

I will get those tools. I had them on my list of necessary items. Thanks!

[anastrophe]

Sometimes when riding, I tend to hear a snap on the cranks and the cranks start moving loosely/freely without any tension.

Do you mean they're moving independently of each other or that there's no pull on the chain?

[fodder69]

That actually sounds more like the rear freehub is slipping that would. It could just be the chain slipping off the cassette momentarily but it's definitely not the bb or crankset.

[anastrophe]

That actually sounds more like the rear freehub is slipping that would. It could just be the chain slipping off the cassette momentarily but it's definitely not the bb or crankset.

I agree, most of the BB/crankset problems I've encountered feel more like crunching, clicking or play that you can reproduce not under load, not free spinning.

[palebluedot]

Sometimes when riding, I tend to hear a snap on the cranks and the cranks start moving loosely/freely without any tension.

Do you mean they're moving independently of each other or that there's no pull on the chain?

There's no pull on the chain momentarily until I switch gears then it starts pulling again. Although sometimes switching gears doesn't do anything and I end up having to walk heh.

I need to adjust the derailleurs as well. The rear and front don't shift to the highest gear. I will keep reading/watching videos.

[fodder69]

Hmm, that is hard to diagnose without being there. Bikes are not super complicated so next time it happens just look down and see if the chain is skipping around or if it is on the gears but just spinning freely.

[kendallf]

Sounds like a front and maybe a rear derailleur  adjustment issue.  Your chain is probably dropping off of the front chainring and shifting the front sometimes will guide it back on.  Google Sheldon Brown and go read up on how to adjust them.