nebben123

I would like to replace the BB and crankset on a stock 88 Centurion Ironman Dave Scott. The BB size is 68-113, the crank is 52/39, and the cassette is 7-speed. All components are Shimano 105. I took the BB apart and it is completely worn with pitting and scarring on the spindle. I'm guessing the hubs probably need replacement too.

Since it seems all components these days are 9 or 10 speed, will they work with my bike? For instance, I was looking at replacing the crank with a Shimano FC-5700-S paired with an appropriate BB, however it says it requires a 10 speed chain. Will it still work with a 7 or 8 speed chain?

I am replacing the rims with Velocity "Deep V" rims, so I figure it's a good time to swap out the hubs. Will any 126mm modern hub work with the 7-speed cassette? I would like to keep it so I don't have to replace the shifters too. Plus I don't ever need more than that. I barely shift as it is since it's so flat where I live.

I'm trying to keep my budget under $400. I have done some bike maintenance before but this is the first time I have replaced parts and it is confusing since bike components have changed so much in the last 20+ years. Please give me any recommendations you have that will allow me to upgrade the aforementioned parts (bb, crank, hubs), without getting stuff that is too "cheap" -- I would like to stay with replacements that are at least as good as the original 105 gear.

Thanks,
Ben

joejack951

Are you interested in upgrading or do you just want a working bike? Square taper bottom brackets are easy to find and cheap. You could be back on the road for under $20 using the same crank.

Probably. I've had issues with 9 speed triple chainrings but I've heard that doubles aren't nearly as picky. Worst case, you just use a 9 speed chain keeping everything else the same.

"126mm modern hub" is an oxymoron. All modern road hubs are 130mm these days. Fitting one in your 126mm frame will likely not be an issue at all though. Rear triangles stretch surprisingly easily. Or you could have the hub respaced to 128mm (typically easily done) which would make it even easier to fit. The freehub body will be too long for a 7 speed cassette but spacers are readily available to make things work. I think the necessary spacer thickness is 5mm. Link: https://www.amazon.com/Wheels-Manufac.../dp/B000C17KV4

More than likely, your hubs are salvageable which will save you a bunch of money. Likely worst case, you need new cones and ball bearings. Put them together will new grease and properly adjust them and they'll feel like new. If you want new wheels, there are a lot of off-the-shelf options for ~$200 that will do the trick. Try to save your current hubs first though (I would).

Loose Chain

Just get on eBay and buy the same stuff already on the bike. Tons of new, used, NOS and in between show up constantly. I have several 126mm bikes and the conversion to modern is a PITA getting everything lined up and then there is the thing of these so called 20 speed 10 speeds and index shifting and brifters and all of that. The "many" speed bikes just don't seem to friction shift very cleanly like the six speed cluster do/did.

nebben123

Is a replacement BB like this any good? I can't imagine quality for only $8 but maybe I'm wrong?

https://cgi.ebay.com/Shimano-BB-LP28-...item5888484bae


It also seems like some of these newer BBs have plastic cups (is this the right term?) on one side. Is this an issue? I'd rather pay for metal. Hell, I'll pay $40-70 for a BB if it's gonna last.

nebben123

This one looks better, no? And likely what I need?

https://cgi.ebay.com/IRD-QB-55-JIS-Sq...3#ht_500wt_928

dedhed

Throw a un-54 in there, replace $5 worth of bearings in the hubs, $10 worth of cones if needed - good to go

https://bicyclewarehouse.com/product/...te=google_base

joejack951

The plastic cup square taper bottom brackets are fine. I've used them for a lot of miles on my own bikes and seen them last just as long on others' bikes. All you do differently is use a lower torque on the plastic cup side. There are better square taper bottom brackets out there if you want to spend more:

https://www.universalcycles.com/shopp...8&category=268

You need a JIS taper (not Campy) for your cranks.

Either of the bottom brackets you linked to will work fine too.