Motor first, Datto later. Izzo Jr at it again.

[Janksun]

Took some more accurate measurements.

 

Skirt of the piston 88.9

 

 

Top of the piston 88.08

 

 

Is this normal?

[datzenmike]

Yup, even more so for a forged piston. They are almost pure aluminum and will expand with heat. The top will be the hottest so it has to have to loosest fit. Forged pistons make a racket on cold start up and until warmed up. Hyper-eutectic pistons have a high silicon content with very little heat expansion. Besides being cheaper they are quiet on cold start up and owners like that.

 

Not saying you can't. The cylinder wall to piston clearance is usually between 1 and 1.8 thousandth of an inch for stock pistons. Not much but if too worn the rings won't seal as well and although it may not burn oil it will be 'tired' like a high mileage motor. However on forged pistons the aluminum alloy is purer and the clearance is much wider to allow for heat expansion. This is likely why you measured over 87mm on the pistons. Again if too worn the same thing applies.