cylinder identification

[beano]

Hi Guys
I have 2 cylinders which are slightly different from each other, one is marked ez71/2r and the other is ez71/5r could anybody tell me does the last number mean the year ( or is that being to simplistic ) and which would be the better one to put on a 74 mx.
 Many thanks

[wildman]

The last number and r is revision level. You have a revision 2 and revision 5 cylinder. The revision 5 is probably better design porting as far as power is concerned. A nice article on this very subject in a recent "Still Keeping Track".Wildman

1975 250 Cross Country, 1974 175 Jackpiner, 1975 125