It really depends on the motor builder.. Generally .006 thousands per inch of bore.
This is kind of a standard for these motors…racing motors are a whole different ballgame.
Too much gap, you get blow by, too little and the ring ends may hit at temp..
About .0174 should be ok in your motor…2.9 *.006 = .0174 thousands of an inch.
http://www.richardsoutboardtools.com
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