Hazen

Hello,

Rennovating an '81 Schwinn World Tourist for my girlfriend. Serial number confirms it is Taiwan/Giant in origin. It has the three piece front freewheeling crank. I need to get a new bottom bracket but am at a loss as to exactly what I need to replace the old one with. After doing some cursory research I ordered a Sunlite 28 TPI bottom bracket off eBay only to find I should have done some more research because it is the wrong part.

Any help is appreciated.

duffer1960

Firstly, a disclaimer. I'm only an 'intermediate' mechanic and I don't have any direct knowledge of this bike.

What are the symptoms? Are you sure you need to replace the BB? Maybe try disassembling & inspection first:

I examined the photos at T.R. Findley's catalog site: https://www.trfindley.com/flschwinn_1...0/1981_13.html .
Is it a standard 'English/ISO' bottom bracket shell? Given that it's a Giant, my bet is that it is, and I bet it contains a standard (for the era) cup-and-cone bottom bracket. Is it a garden-variety standard, square-taper cotterless crank design under that flashy front freewheel? Pretty typical 3-piece crankset if so.

You will probably need a 'puller' to get the crank arms off the spindle. The catalog image says it's a 'cotterless'. Sheldon's link ( https://www.sheldonbrown.com/tooltips/cotterless.html ) shows a puller tool for cotterless cranks. Don't know if it will work with this odd one. If this is the only time you'll use it, maybe having a bike shop do it for you would be cost-effective.

Then, a device to break loose the lockring that immobilizes the adjustable (non-drive-side) cup. Lockring spanner. https://www.sheldonbrown.com/tooltips/bbcups.html . And something to back out the adjustable cup, possibly a pin spanner.

At this point, you can inspect & re-evaluate whether you want to replace the bottom bracket. Unless the bike has 'a million miles', the spindle and cups may be in good shape. May just need a clean and repack, maybe in addition new bearing balls.

Don't need to remove the fixed cup if not replacing the bottom bracket.

Lots of online resources for reassembly, so I'll be brief. Important to get the cone adjustment 'just so' so it isn't loose and isn't too tight. Trial and error as necessary. Also very important to torque the cranks to about 30 ft-lbs; a torque wrench is really necessary here. Make sure the spindle & taper holes are clean and well seated before wrenching down. Do not retighten aluminum cranks later after putting them on properly the first time. Let us know how it goes.

sailorbenjamin

I'm gonna guess 24 tpi. Is the BB shell 68mm wide? Are you keeping the FFS system? Those had a sort of unique set of bearings and axle and you'd need FFS specific replacement parts. I believe they fit into a standard shell, though and will accept a standard set of cranks/axle/bearings.

mplotkin

The front freewheel system may need to be rebuilt with new bearings ect. If I recall the back is a five speed fixed cog set with no freewheel. So a regular crank may not work. Or it will make the bike a track bike with speeds...?

Hazen

The front freewheel and and bottom bracket have already been pulled so no problem there. I plan on keeping the original front freewheel and rear five speed cog w/ derailleurs which all work fine. The whole bike came with the Shimano Positron system which I'm trying to keep. Although it was a PIA to find replacement cables and I'm not looking forward to actually installing them. I have the original bottom bracket still but wanted to replace it with something newer. I'm going by the LBS today. One of the guys I spoke with yesterday thought it would accept a more modern BB since it is 68mm/English.

treebound 

Do you really want to keep the semi-fixed rear hub and the freewheeling crank?
Seriously if you're not doing a proper restoration and are just building it up as a "rider" then I'd look at converting the crankset to standard and finding a donor bike for the rear. But that's just me, I just prefer the chain to stop moving when I stop pedaling, seems safer somehow, but again that's just me.

A decent bike shop with experienced mechanics should be able to get you set up regardless of which direction you go with it.

Hazen

Yes, that's what I want to do. ;-) I want to update the components (not top end, but newer), spread the rear dropouts for a newer IGH, and convert to 650B but girlfriend thinks she wants it with vintage components. Its her bike so not my call.

Onions

I'm actually jealous. I wish my '80 World Tourist (also made by Giant) had the FFS.

Hazen

Well after dropping by the LBS on my lunch and talking with the mechanic I made a judgement call. Left the frame there to have the new headset installed but was told that the bike would require new cranks if I had a new BB installed. He said the old one would probably work ok if I replaced the bearings, but frankly I'm already sick of the Shimano Positron drivetrain and I haven't even gotten to the installation part (not to mention it will be a HUGE PIA to fix in the future due to non-availability of parts).

I'm going to go ahead and convert it to 650B or 700C and update the components. Having the rear drops spread to 135mm and going to put a 3 speed IGH back there. I think my fiancee will much happier with this functionally, and I will be much happier mechanically.

With that said I will have a complete Positron Drivetrain up on eBay within the next week.