Briggs & Stratton piston to bore clearance - Page 3
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  1. #41
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    Dec 2012
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    Just about every small motor now has a nickasil bore,and wear is not an issue....They can be bored out,and a liner substituted ,if there is enough metal in the cylinder.....A friend of mine used to do that to install overbore kits in modern Triumph motorbikes......Seemd silly to me to wreck a nickasil bore to get a few extra cc s.......You can also get nickasil redone,but its not cheap.

  2. #42
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    May 2007
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    A forged piston will have more clearance than a cast piston, but they will both fit in the same hole. The reason is the clearance is built into the piston.

    Pistons are cam ground on the skirt as they warm up the skirt grows in the direction of the wrist pin. The skirt is also tapered the diameter at the tip of the skirt will be larger than up near the oil ring. The proper way to measure a piston diameter is 90 degrees to the wrist pin at a height equal to the center of the wrist pin.

    Skirt taper, clearance, and cam grind will vary by piston design so it's best not to second guess the manufacturer. A .020" piston will fit a bore .020" over standard. Also make sure you have the correct standard diameter, A sales brochure may say it's a 3" bore but the service manual may say 3.001" bore so make sure you have the proper standard size before sizing the hole.


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