Which bottom bracket do I need?
 

My latest project is a Schwinn 754. I'm wanting to take the Tiagra 3x10 group (FC-4603 crank) I replaced on my Trek and put it on this bike. Currently has a square taper Suntour crank & BB. I have no idea what I need to put the Tiagra crank on the bike. Can anyone help me find an answer?

You need a Shimano Hollowtech II bottom bracket like this one for your Tiagra crankset.

You'll also need some bike-specific tools for the job:

• A crank puller like a Park Tool CWP-7 to remove your old crank arms.
• The appropriate bottom bracket tool(s) to remove your square taper bottom bracket. Exactly which tools you need will depend on your particular bottom bracket.
• A bottom bracket tool like a Park Tool BBT-19 to install your new bottom bracket.

I actually have that one but it won't screw into the BB shell. It was on another crank I got from a friend. I just assumed it was threaded different than the Schwinn. Will check again.

The Schwinn 754 is a standard English threaded bottom bracket size the same as your Trek. Roger

Is it possible you've got the left and right cups mixed up? They're threaded in opposite directions.

The trek is a press fit, not threaded. The BB I've got didn't come from the Trek (that one is in a box). This is one that was on a different crank a friend gave me.

We've already removed the old BB & crank (the frame is getting cleaned & new clear coat applied so everything is coming off.

I know the cups are side specific but it was 11:00 when I was messing with it & thought I had them on the correct sides. I'll try it again. Worst case, I'll take it back to the LBS and have them look at it. They had a little trouble getting the old BB loose. Hope they didn't screw up the threads ut I doubt that's the case. I may be wrong in thinking the BB recommended in this thread is the same one I have. I'll look at it when I'm home for lunch.

If the one you have is labeled like the one I linked, you should be able to confirm the threading. If it's marked "1.37 x 24", it's English threaded and you should be good to go.

You should get your BB threads chased and BB faced (one <5 minute operation with the Park tool). Facing is critical for BB30 systems.

I checked it again and feel like a dumb azz... What you had linked is the same BB as what I have. I had the sides reversed. Screws in fine, we're good to go. Actually, I need to check and see if I have the fork upside down... lol (sigh)

Sometimes it's good to be wrong! It might be a little embarrassing, but in this case, you'd need to buy another bottom bracket if it really didn't fit!

Glad you got it installed and here's hoping the rest of the work goes smoothly!

The fork isn't installed upside down but it is backwards (where does the spoon go?). Guess I'll need a special tool for that.

Seriously though, I'll be putting the bike back together this weekend hopefully. Goal right now as stated above is to clean the frame, touch it up and give it a nice layer of clear coat. Anyone have any recommendations for that? Once I start the rebuild I'll start up a thread on it. Thanks for the help.

I have a 1989 Schwinn 754 that I bought as a new leftover in about 1992 or 1993 from a small, older, Schwinn Dealer. It was partially converted to Shimano components from the original Suntour when I bought it. I have upgraded other components over the years since then.

One of the first things I did is upgrade the front fork from the original steel fork to a Specialized aluminum fork, saving weight and eliminating the "lawyer lugs" from the front wheel dropouts. I usually carry my bikes on a Thule roof rack, and the original Schwinn fork required me to remove the quick release completely to remove and replace the front wheel.

Bottom bracket threading is English.

I replaced the bottom bracket with a Shimano BB-UN70 square taper sealed cartridge bottom bracket. It surprised me when I found out that I needed a wider than expected bottom bracket to get adequate clearance from the chainstay to the small ring (double RX100) on the crankset. When I initially installed a Shimano sealed bottom bracket, the small ring was too close to the chainstay (less than 1mm). If I remember correctly, I had to get a longer 118 length, instead of the expected 113. The chainline and shifting work fine with the wider bottom bracket.