Japanese Bottom Bracket
 

I have a mid-80's Takara made with Tange Champion tubing in excellent shape. The cranks are long and I'd like to change them out to a shorter length compact from the 42/53 that's on the bike. Is there any kind of standard BB size from that time period for Japanese manufacturers? Do I just need to take the bike to the LBS and have them take it apart and measure it? I'm watching several auctions on ebay and many come with BB's included, wondering if there's a uniform bb size I can look for.

BB has 2 match 2 specs
1. Your frame - yours is English 1.37x24 threading
2. Your crank - each crank is specific, so you have to match the BB to the crank. There's not a "standard".

More than likely your current BB will not match any compact you could buy, but I am just making an educated guess here.

If you buy a crank w/BB included, just make sure the BB is English threaded.

I could not have said it better

I am a bit confused... do you want to change the length of the crank arms to shorter ones? or you want to change the chainrings to smaller ones? Both are doable without changing the bottom bracket:

If you want smaller chainrings keep the crankarms and change the chain rings (possibly you might need a different RD)
If you want shorter arms, look for a crank just like yours (or compatible with your BB, i.e. same make and same time frame ) and just get shorter arms to use. (most Dura Ace/600/and 105 bb work with all 3 kinds of cranks and the reverse - with some exceptions 7410- if made around the same time)

Here is Sheldon Brown's BB size database

Yeah, sorry about the confusion! I want to do both - shorter arms and smaller cranks, at least the 42. Just figured if I were going to that trouble, it would be easier to get an entire compact assembly.

Thanks to you all for the great info!