Electra Piston clearance

Might this help?

Sounds perfect to me (never having owned a lightweight) . These short stroke motors seem prone to piston troubles if ignition not spot on . I would not go with less , They are not quiet motors anyway so a little rattle when cold wont be noticed!.

I wonder how old that Hepolite data sheet is.

I'd call those piston skirt clearances and ring gaps a bit tight for some old bikes.

... err on the side of slightly generous piston clearances as I have better things to do than spend my life running in...... I would go for .004" - .005"

Hi Nick,

   No need to over-think this, the size stamped on the piston crown is the size the rebore should be. The makers cam-grind the pistons to the correct clearance to match the stamped bore size so the piston will be smaller if you measure it. The piston skirts are very slightly oval with a bigger clearance at the gudgeon pin faces and this is why you have to measure either the front OR back face for the correct gap. Pistons are also tapered from top to bottom and the measurement should be taken at the bottom. All this is due to heat expansion and thrust forces. If you feel the bore is a little tight you can get this honed slightly bigger by your engineer.