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  337 ROTAX
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   Author  Topic: 337 ROTAX  (Read 519 times)
1970TNT
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337 ROTAX
« on: February 15, 2017, 11:34:05 AM »
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I AM REBUILDING A 337 ROTAX AND SEE THE RING GAP SPECS ARE .008-.063. I HAVE A RING GAP OF .048. IS THIS GOOD FOR THE LONG HALL OR SHOULD I USE A 1ST OVER PISTON???
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Green and Gold
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Re:337 ROTAX
« Reply #1 on: February 15, 2017, 04:43:49 PM »
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What's the piston to cylinder wall clearance at?  I personally would let that (and the presents of any excessive grooving/taper/out of round) drive the decision to go oversize or not. 
As long as your ring gap is within spec, I'd certainly run it on a rider.  Unless you're headed out on a Polar expedition.... A good bore/hone around here is $80, plus piston, plus gaskets, plus a new tube of goo. 
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Re:337 ROTAX
« Reply #2 on: February 15, 2017, 05:30:58 PM »
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Is this new piston and ring or reusing. It is in spec but with a new ring it will wear down more to seat to the bore. What do you mean by long haul. I personally would go next size if you are making it a rider.
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69 Olympic370,71  Elan250,1980 Blizzard9500plus,2000 MXZ440F,2002 MXZ600
1970TNT
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Re:337 ROTAX
« Reply #3 on: February 15, 2017, 06:50:39 PM »
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THAT WAS THE GAP AFTER HONING. PISTON CLEARENCE IS .006. RINGS ARE NEW AND SO IS THE AFTERMARKET PISTON. WANT A GOOD RIDER MOTOR
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Re:337 ROTAX
« Reply #4 on: February 15, 2017, 07:35:02 PM »
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71 Shop manual says for a 337 piston to cylinder clearance max is .0035 to .004.  Also says  std bore should be 3.070 with a max wear of .004 (3.074) measured 1/2 inch below the top of the cylinder.  Piston dia measured 5/16 inch above the bottom of the skirt. 

If  you got good measuring equipment, good technique, and everything at the same temp sound like a visit to the machine shop is in order.

And what I intended to say in the first post was as long as your piston to cylinder clearance, taper, scratches, etc were all within spec, I'd run a ring that was in the middle of the wear limit.  i.e. like if a tad too much was filed from the ring when fitting.  Unfortunately not the case.         
« Last Edit: February 15, 2017, 07:42:32 PM by Green and Gold » Report to moderator Logged
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