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Johnson 90hp v4 cylinder wear

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fishhawk90

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Thought I show u guys cylinder 3 is 6 thou bigger than 4. The factory ring end gap is over the top end specs by 10 thou. I got oversized rings that seats perfect in the cylinder & can gap to book specs. My only concern is am I going to get blow by since their would be more of a space between the rings & piston? Or once the pressure push down on it would it seal just as a tight fitted bore?
 

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Oversize rings require oversize pistons! Not to mention I would never reuse a V4 crossflow piston! Before you do anything else get a factory manual and read it cover to cover.
 
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Piston rings fit is only part of the story on a two-stroke. Also important is the clearance between the piston skirt and cylinder wall. Think about it. The piston skirt is the only sealing between the exhaust ports and crankcase. Unfortunately, that won't show up in a compression test.
 
thanks for the response guys. spoke to a marine tech & just like flyingscott mention the piston must be a tight fit otherwise it would not put enough force on rings to seal against the bore which is more important that blow by though the ring end gap.
 
The piston does not put pressure on the ring! If you try to run an oversize ring on a smaller piston it will not end well for the engine. If the bore is to small for the ring when it heats up it will expand into the cylinder wall and cause damage. If the bore is to big the ring will not be supported by the piston and wil break the groove or or try to flip and break.
 
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