X-Mozilla-Keys:                                                                                 
Bob Darrah wrote:

  >>Don Sherman wrote:
snip
   why do virtually all

rotaries [radials] (piston type) have an odd number of cylinders in each bank?

To make them fire evenly.  They fire every other cylinder around the bank. (4 cycle).  > In 2 revs, all cylinders fire in an even order of every other cylinder. 
If you have an even number of cylinders, you can't do that, 2 adjacent
cylinders will have to fire somewhere.  You could have an even number 
with a 2 cycle, firing  all adjacent cylinders in order.

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