Bicycle Mechanics - One-Piece Crank Parts?

My mom has an exercise bike from the early 80's or so (no "Made in China" logo). The one-piece crank seemed to be very loose. When I took it out of the bottom bracket, I saw that one of the bearing cups (the thing that is pressed into the bottom bracket and holds the bearing cage) is broken (part of it missing). As a consequence of riding the thing like this, both bearing assemblies are also ruined, and the bottom bracket was full of loose ball bearings. It will need new bearing cups and bearing cage assemblies. My guess is that the thing was damaged in transit years ago, because it's hard to believe that my mom (now age 82) could have done this by herself with the infrequent use she gave it, but that's water under the bridge at this point. A couple of questions:

1) Where do I get parts? Local bike shop? Since it is a brand of bike that I have never heard of, I assume that I will need to punch out the existing bearing cups and bring them to make sure that the parts I get are the right ones. I doubt that they have a book where they can look up parts specs for obscure brands of exercise bikes.

2) Are parts from all one-piece cranks interchangeable? I have some bearing cage assemblies from a one-piece crank that look like they would fit. Are all bearing cups and bearing cage asssemblies the same size, or are there a multitude of sizes?

there's two one-piece crank standards, schwinn and some mongoose (28 tpi) and everything else (24 tpi). trial and error should tell you which cones will work. retainers for 28 tpi BBs have 9 balls, 24 tpi have 10.

My mom has an exercise bike from the early 80's or so (no "Made in China" logo). The one-piece crank seemed to be very loose. When I took it out of the bottom bracket, I saw that one of the bearing cups (the thing that is pressed into the bottom bracket and holds the bearing cage) is broken (part of it missing). As a consequence of riding the thing like this, both bearing assemblies are also ruined, and the bottom bracket was full of loose ball bearings. It will need new bearing cups and bearing cage assemblies. My guess is that the thing was damaged in transit years ago, because it's hard to believe that my mom (now age 82) could have done this by herself with the infrequent use she gave it, but that's water under the bridge at this point.

Back in the '80s. "Made in China" meant absolute crap. Quality of Chinese products has greatly improved since then. Generally stuff used in stationary exercisers is lower quality than parts used in real bicycles anyway.



A couple of questions:

1) Where do I get parts? Local bike shop? Since it is a brand of bike that I have never heard of, I assume that I will need to punch out the existing bearing cups and bring them to make sure that the parts I get are the right ones. I doubt that they have a book where they can look up parts specs for obscure brands of exercise bikes.

2) Are parts from all one-piece cranks interchangeable? I have some bearing cage assemblies from a one-piece crank that look like they would fit. Are all bearing cups and bearing cage asssemblies the same size, or are there a multitude of sizes?

There are basically only two sizes, the 28 tpi style used by Schwinn and Mongoose and the 24 tpi style used by everybody else, including the manufacturer of your mom's unit.

For more details on this see: http://sheldonbrown.com/opc

Rather than get mired in interchangeability issues, it's probably better to just drop $10-15 on a complete bearing set (cups, cones, retainers, washers) which you should be able to find in any decent bike shop that deals in kids' bikes.

If you strike out locally, we can help you: http://harriscyclery.com/opc

Sheldon "OPC" Brown

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| The difference between science and the fuzzy subjects |
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Thanks, guys! This unit preceded the "Made in China" boom of the 90's. Very heavy and solid - makes my 1960's Schwinn single-speed look flimsy by comparison. I will go ahead and get the complete kit, assuming my LBS has it in stock.