Sealed Bearings - question ?

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I can't say with certainty, but this passage on Sheldon Brown's site makes me suspect the answer is 'no.' At least...I wouldn't expect a drop-in replacement.

" There are two major types of one-piece crank sets, differentiated by their threading. The more common size uses 24 threads per inch, but some bikes, particularly older U.S. made Schwinn and Mongoose models, use 28 threads per inch. No part of the bearing assembly is interchangeable between threadings. "
 
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They will fit ‘American’ sized BB shells, I’m installing one on my 73 Schwinn Speedster
One of the sellers of the bearings got back to me and says that they will fit 51 mm frames. Schwinn frames are 2 inches so that's extremely close. Are you just using the bearing then using the original Schwinn hardware for the crank ?
 
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Another issue with these replacement bbs is related to how such frames are constructed. Electroforged Schwinns have wide open bb shells so usually no problem there. Some other brands have the frame tubes (seat tube, down tube, chain stays) protruding into the bb shell and those defintely get in the way. The standard bearing cup is curved on the inside but the sealed bearing units are more squared off and have to go in the shell farther.

You may need to clean out the shell a bit to get the bearing holder to fit all the way in. Grinding off some of the protruding stays may work but too much grinding may ruin the frame.

You can always swap those 28tpi cranks for 24 tpi cranks to work with the sealed bbs. They won't be authentic Schwinn but then a sealed bb isn't either. If you are looking to make your bike ride better, sealed bb and a cro-molly crank may help along with aluminum rims, good tires, etc.

I bought a supply of 5/16" caged bearings that have 12 balls instead of the fewer 9 or 10 ball versions that all bike companies use oem. More balls is better. Those get put in each of my cruisers as I service them.
 
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Another issue with these replacement bbs is related to how such frames are constructed. Electroforged Schwinns have wide open bb shells so usually no problem there. Some other brands have the frame tubes (seat tube, down tube, chain stays) protruding into the bb shell and those defintely get in the way. The standard bearing cup is curved on the inside but the sealed bearing units are more squared off and have to go in the shell farther.

You may need to clean out the shell a bit to get the bearing holder to fit all the way in. Grinding off some of the protruding stays may work but too much grinding may ruin the frame.

You can always swap those 28tpi cranks for 24 tpi cranks to work with the sealed bbs. They won't be authentic Schwinn but then a sealed bb isn't either. If you are looking to make your bike ride better, sealed bb and a cro-molly crank may help along with aluminum rims, good tires, etc.

I bought a supply of 5/16" caged bearings that have 12 balls instead of the fewer 9 or 10 ball versions that all bike companies use oem. More balls is better. Those get put in each of my cruisers as I service them.
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Thanks for all the info. I'll be building a 24 inch Typhoon (Stingray style). I really like original aesthetics but I'm open to customizing so long as it serves a purpose. The frame is pretty clean, there's a weld toward the bottom of the opening that could be safely cleaned up if needed.
 
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Here are two of my 24" wheel builds.
In general you can run a wider tire in a larger frame.

The white one was a 1971 Schwinn Racer. 26" wheel frame in the smallest frame size. The Racer came with 26 x 1 3/8" tires so I had to make more room in the chainstays for the wider tire. I added the 24" aluminum rims with 24 x 2.125" tires.

The green is a late 1980s Huffy mtb that came with standard 26" wheels. I changed it to a rigid fork. I built the wheels with 24" aluminum rims and 24 x 2.125" tires.

 

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I believe all Ashtabula cranks are 28tpi up to ~1980...after that (went out of business in 1982), they made cranks in 24 & 28tpi.
 

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