Piston Diameter

[ronin_ae86]

The bore is the diameter of the cylinder.
Allways the pistons are some 0.01mm smaller than the cylinder diameter.
Each piston has a different diameter on each surface of.
The smalest diameter of a piston placed at the side surface of the piston head.That happend because the piston head exposed on the hightest temperatures and has largest sweeling.

We measure the pistons at their skirt on the height where placed the pin holes but vertical of that holes.

That measures must be done with micrometer which can measure 0.01mm.

Most engine should have piston to cylindere clearance 0.010 to 0.050 mm.

In some extreme applications the clearance maybe exceeds the 0.050mm then when the engine is cold sounds the pistons .

The piston skirt has the bigest diameter because it lead and dont let the pistons to depart.
Thats why many racing pistons has coating on the skirt.

So first you should carrefully messure the pistons and after that you calculate how to boring and honing the cylinders.

Be carrefull if you talk about a 4AGE engine dont look the TOYOTA 4AGE engine repair manual about the piston to cylinder clearance they write about the axial clearance of the pistons not about the trust clearance.

The axial clearance is about the head of the pistons.