Upgrading bottom bracket
 

I got a cheap bike - a basically brand new bike that someone had initially gotten from Bikes Direct. I am pretty sure it has one of those cheap Chin Huar bottom brackets. And I've read about several CH BB failures. At least one resulted in injuries - the BB broke and a pedal fell off and the guy ended up on the ground.

I've already had a cheap bike's rear axle snap on me - and if things were slightly different that day I might not be here right now.

So - I know the crank is a "Lasco FR670." Does anyone know what sort of bottom bracket this accepts? I am pretty sure that the BB is a square taper type. How can I make sure? What sort of after market bottom bracket may I use? The drive train is a 8 speed Sora/Claris mix. The width of the BB also appears to be on the low side of 70 mm (or in other words, 68mm). So will any 68mm square taper BB work with the existing crank?

Maybe take it apart and look at it? You'd have to do that anyway to replace it (and confirm your assumptions).

Ah yes. I guess I'll have to make a trip to the bike shop as I just found out that the local bike co-op is closed for the next 4 weeks. I was hoping I could do it at home!

I just watched a video on YouTube and learned that it's not only shell width which matters but also the length of the spindle in the bottom bracket ... if only there were an easy way to measure that!

I managed to find Lasco's catalog, and according to them, if it's a square taper crank, you want a 113 spindle, and if it's ISIS you'll want a 118 spindle. If you don't know what ISIS is, it's a splined interface, so you'd be able to easily tell the two apart

Thank you! But doesn't the spindle length vary with the number of chain rings you have? I've seen suggestions of 118 mm.

I'm also pretty sure this isn't an ISIS BB. I see a lot of teeth which seem to correspond pretty well to the Park Tool square taper crank removal tool.

The spindle length would vary, but it looks like that crankset only comes in a triple configuration. Your comment of "a lot of teeth" sounds similar to what an ISIS crank would look like. About how big around is the bolt that attaches the crank arm?

It's 14mm. Here's a pic of the crank teeth. There are 16 of them in groups of 4.
http://bikeforums.net/attachment.php...hmentid=453393

http://sheldonbrown.com/images/bbsx4-labeled.jpg They all use the same tool to remove, just the spindle is different

While it is pretty common for lower end cranks to loosen on the bottom bracket spindle, it is very rare for a spindle to break. Your cranks are probably more at risk than the bottom bracket. I wouldn't change it unless the bearings develop play. Just make sure that your crank bolts are tightened to the proper torque.

If you are Keeping the drive train the same, not changing the crank, then a visual comparison of the overall spindle length, and relative length of each of the 2 side's lengths

may be adequate. The Shimano UN series cartridge BBs are cheap enough that you are not out Much if you guess wrong and are ordering parts online

IF you Remove the existing BB and Bring it into the LBS, then the replacement will be less Guesswork..

From your pix, you have a square taper crank with a BB that has splined retainers for the bearings, which have been almost universal over the past 20 yrs or so
for BB. The sq taper BB axle is less common as most riders on this forum use newer BB axles which are larger in diameter, hollow and have splined ends.
Sq taper BB are readily available, I agree with alcphil, your axle is unlikely to break, its most susceptible part to breakage is the axle-crank retention bolt if
you overtighten it.

http://www.bikeforums.net/road-cycli...-injuries.html

http://www.bikeforums.net/road-cycli...kes-again.html

http://www.pardo.net/bike/pic/fail-001/FAIL-202.html

I can't trust the bottom bracket. I've already suffered a crash (fortunately not from component failure) but I have had a component fail before That time I was not wearing a helmet and had things turned out differently I could easily have ended up under the wheels of a bus. I'd rather dance on the side of caution this time.

Also even if the cheap BB doesn't fail it will almost inevitably end up useless within a few months of use. I've had a similar cheap square taper BB on an old bike and the BB developed tons of play within two months of riding. You could easily swing the crank arms side to side. The bearings were shot. I had the bearings replaced and the entire thing tightened up but it was still a bit loose. Might as well bite the bullet now and switch to a reliable, durable bottom bracket.

You could start worrying about the bottom bracket failing but you might as well worry more about the brakes. You may have fallen but that's not surprising. If you're not going to accept the "possibility" of falling, maybe cycling is not for you.

If you change the BB, you'll probably gain peace of mind but that's about it. You'll just move on to the next component that's likely to fail. IMHO, you'd be better off riding the bike.

Cycling - where it's okay to spend hundreds of dollars to think one is going faster - but not okay to spend tens of dollars to get not only a more reliable part but also some peace of mind.

I also don't know what other component might fail and cause me to fall as readily as a known cheap BB. Sure my frame might snap in half but I'm not too worried about that.

You must be new to this sport. I've been in it for about 50 years. You simplify things by comparing my comment regarding the waste of money on unnecessary parts with the waste of money on "bling". Not fair.

Peace of mind can't be bought. Just sayin...

Simple "truism," simple mind.

Please do tell me about your bike handling skills, aged and perfected over 50 years, and how they managed to keep you upright.

I would install a new one.

It looks like these broken ones are all the hollow spindle ISIS type, which are a different animal entirely than the square taper type. As mentioned above, the square taper is unlikely to break, but a Shimano replacement is likely a $15 part, so replace if it makes you feel better. The bike shop will charge labor, of course. If you want to do it yourself, you'll need a crank extractor, the proper splined BB tool, and a torque wrench to install the new one to the proper torque.

I wouldn't worry so much about the BB, but I have worked on some cheap cranks that are simply too crude and badly made to bother with. Incredibly soft metal, easily stripped threads, etc. I can imagine your "Lasco" crank might fit into that category.

For $20 you can get a quality (albeit cheap) Shimano compact square taper crank, brand new: http://www.ebay.com/itm/NEW-SHIMANO-...item35eaa126bc

A new Shimano bottom bracket should run you another $10-15.

Simple. Lasco FR670