dougo83

Ok...I have an older (probably mid-90's) Scott Arapahoe that I have been riding. I like the bike for hitting trails around my house. I need to replace the crank bearings before I can do any more riding and I can't find a bike shop with a reasonable, to me, price. I contacted Scott and they don't have any tech specs for bikes that far back.

Does anyone know what size bearings this bike has?

Thanks!

jimc101

Depending on the year, you are most likely looking at having to replace the cartridge bottom bracket, this is a sealed unit, rather than replacing bearing, If this is a on off, would look carefully at the cost of tools vs the cost of getting a LBS to do it, as the tools will probably cost far more than the shop charges.

For tools, check out the Park Tool repair guides https://www.parktool.com/blog/repair-...et-service-bbt you will also need the tools to remove the crank https://www.parktool.com/blog/repair-...e-spindle-type a ruler / calipers to measure the BB shell (will be 68 or 73mm) and to measure the spindle length. (this info should be printed / stamped on the BB when removed)

FBinNY 

I don' know the spec or what kind of BB hat bike has, but let's define terms here.

A bearing is the entire assembly that allows the crank or whatever to turn. Meaning the inner and outer races and the balls. When you replace a so-called sealed or cartridge bearing you buy a bearing. When rebuilding a classic field serviceable bicycle BB with cups and spindle, you're only replacing the balls.

In that case 99% of BBs use 1/4" balls, and you can find them cheap on the net if you search bearing balls. Though they're much better than you need, Grade 25 balls are only slightly costlier than lower precision balls, so go ahead and splurge.

joejack951

You have to buy the right kit, but one of those fairly cheap mechanics kits from Nashbar will have all of the necessary tools to swap a cartridge bottom bracket. If it is a cup and cone BB, those kits won't have the lockring tool necessary for R&R and adjustment.

This $45 kit will swap a cartridge BB though a torque wrench would be a nice addition: https://www.nashbar.com/bikes/Product...2_524452_-1___

You really only need the splined bottom bracket tool and crank puller but the cassette lockring tool, chain tool, chain whip, and pedal wrench and will come in handy eventually. Those cone wrenches will do the job in a pinch but you are better off with a nice set of Park Tool ones if you plan on servicing a number of wheels.


The bottom bracket is most certainly 68mm in diameter. Length is probably 113mm but you can easily measure with a tape measure to confirm after pulling the crank arms.

Don't forget to grease all threads and any other metal-to-metal contact area to avoid creaking. And don't skimp on the crank arm bolt torque. 30 ft. lbs. seems like a lot for an 8mm bolt but you'll destroy them quickly if that bolt ever comes loose.

joejack951

I did a quick Google search and found this page: https://www.bikepedia.com/quickbike/B...e#.Ui9DST_By1k

Similar year and and same model. 68mm diameter, 113mm spindle. Doesn't specify cartridge or cup and cone but if you could upload a picture of that area it would be easy to tell which style it is. If you want to keep this as cheap as possible and it is a cup and cone BB, just swap the ball bearings, add new grease, and adjust. If you want a better sealed unit, you can swap in a cartridge style for $20: https://www.amazon.com/Shimano-Square.../dp/B0068FVOEM

Bill Kapaun

Trusting bikepedia.com is pretty risky. I've found too may errors.
The bike assemblers can also change components mid stream.
My 2008 Globe had a different low end Shimano crank than what bikepedia.com listed.

joejack951

Point taken, Bill, but it's always been accurate for me.

jimc101

Would avoid greasing the BB spindle to crankarm surfaces, this is an interface fit, and doesn't need any grease, here's an old thread on the subject, plenty more if you google https://www.bikeforums.net/archive/in.../t-726551.html

HillRider

It's a semantic point but the bottom bracket shell will be 68 mm in length, not diameter. Assuming it's English threaded the thread diameter will be 1.37" or about 35 mm.

joejack951

Not a semantic point at all, just me typing without thinking. Thanks for the correction.

FBinNY 

You're right that cylinder are generally described by length and diameter. But, as long as we're dealing with fine points, we usually refer to diameter and width rather than length because the BB is crosswise to the bicycle.

Phil_gretz

What exactly did your LBS tell you they could do, and for how much? I would think that a replacement, bottom-end Shimano cartridge BB installed would be reasonable at $50 for you, since you lack the tools and experience. Was the quote more than that?

Alternatively, if you can identify a local bike coop, you can learn to do it yourself while supervised for a nominal fee. You can identify and buy your own BB, or can simply replace the bearings and grease (if it's a loose bearing style) as previously suggested. It's not a difficult job...

joejack951

I was in that camp for a while but the reality is that aluminum will gall on steel without lubrication and will also corrode especially if the bike is used in the winter months with salt on the roads. A little grease goes a long way to preventing both. Typically with an interference fit between aluminum and steel (common for bearings) the aluminum would be heated to allow interference-free assembly of the parts to avoid the galling. Since no one is heating crank arms and the fit is on a taper anyway (allowing accurate alignment prior to the press fit occurring), grease makes sense, at least to me after giving it probably too much thought.

HillRider

I agree with joejack951. I also lightly grease square taper bottom bracket spindles for corrosion protection and to prevent galling. I do tend to torque them to the low end of the spec. If the recommend range is 300 - 400 inch-pounds, I use just over 300. In 28 years and way over 100,000 miles on square taper spindles, using cup-and-cone, Shimano cartridges and Campy cartridges I have never had a crank arm come loose or split from over tightening.

Also, when I remove the crank arms for bb service and reinstall them (with grease) they go back to exactly the same place and I never have to readjust the fd's limit screws so, obviously, I'm not distorting the crank arm's square socket.

dougo83

They wanted $100 to replace the whole mess. I am going to take it apart when I get home, so I will get pictures later. I wouldn't say I have no experience, either. I have been a mechanic for about 10 years now, so I imagine if I can pull and swap bearings on cars, trucks, and buses that a bike should be a breeze. A stupid broken micrometer is making it a little tough to find bearing size though haha

As far as bikes coops, I don't see any in the Houston, TX area.

dougo83

Haha...I'm in Texas. We don't have winter...or any other reason to salt roads, so that won't be an issue.

joejack951

Galling between the aluminum and steel is just as important of a reason as corrosion, if not more, for greasing the spindle.

bikemig 

If you have an almost 20 year old BB that has not been serviced, I wouldn't be surprised if a lot more is going on that just the ball bearings going bad. This is a good time to put in a cartridge system (assuming you have a cup and cone and a square taper crank which is likely given the age of the bike). If you have access to shop tools, you should be able to get the old BB out even without specialized tools. Once you post some pics, people here will give you some ideas on how to proceed.

reptilezs

that is high, really high, costs 55 here to get new shimano cartridge bb and labor. 25 labor and 28 for the part

dougo83

I haven't been able to take it apart yet. I will post pictures as soon as I can. I am probably going to invest in the tools because I plan on doing my own work as I ride more and purchase more, or hopefully newer, bikes.