Rebuilding Mac .21

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MarkScott

Well-Known Member
Joined
Oct 5, 2014
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Putting new bearings in one of my Mac .21 OB. Ran into a concern with the large crank bearing. The bearing that was to be used was in a packaged marked as a 6901. Is this the correct bearing to use? The new bearing has the proper O.D. but the I.D. is to small.
 
Mark, According to my notes the 6901 should be the right bearing. The dimensions should be 13-24-6mm. This is the same size as the K&B .21 with the 13mm crank. Hope this helps.

Chris
 
It is the wrong bearing as it won't fit the K&B 13mm crank either. Appears to be the 12mm ID. Guess that's what I get for buying "clearance price" bearings.
 
Its been a long time since I let my bearing business go but if I remember correctly you need a 2413 which is 24 mm od 13 mm id and 6 mm wide.
 
Ron, thanks for the info. Think I found the bearing number via Boca. They list the 6901 as 13x24x6...
 
Yes they have what they call a 6901 at 24x12x6 and a 6901/13 which is 24x13x6. The better bearings list them as 2413.
 
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