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B21 Crank in a B20 120-130

posted by  122_Canadian on  Thu Aug 14 06:44 CST 2008
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last visit: Tue Oct 20 07:51 CST 2009
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It was easier for me in this case to go with a B21 crank as there was one 3 blocks from my house...a B20 crank was also found, but it was a few hundered kilometers away. I also have a '75 B20 (metric bottom end).


As far as the numbers go, here's the difference.





















































B18B B18D/B20(early) B21
Journals
Main 2.4977-2.4982 2.4977-2.4982 2.500-2.5005
Rod 2.1295-2.1300 2.1295-2.1300 2.1271-2.1276
Shells
Main 0.0779-0.0781 0.0781-0.0784 Not listed - same part number
Rod 0.0722-0.0725 0.0722-0.0725 Different part number







I couldn't find the bearing shell thicknesses for the B21, but the mains are the same part number as the B20, the rods are lised as a different part number (B20 = 271052 B21 = 271063).

So the mains are slightly different sizes, but use the same part, and the rod journals are different sizes and use different parts. This means that you can use the crank from a B21 but the rods have to be B21 rods to have the right clearances. My rods are B21 rods (custom H-Beams) as I had an 8 bolt crank (metric = same as B21).





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New B21 Crank in a B20 [120-130]
posted by  122_Canadian  on Tue Aug 12 13:47 CST 2008 >


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