Wiseco piston arrow Intake or exhaust.?

Question

XL500 Honda thumper piston ring installation going on here. The shop manual shows the honda piston has an arrow that reads "in" and points to the intake side. I pulled the head off and found a wiseco piston that points toward the exhaust or front of bike. Was the piston installed backwards ? Or just USA thinking compared to metric thinking.

Answer 1

Arrows on 2 stroke pistons face forward to the exhaust.

It's very critical with 2 stroke engines.

The rings on a 2 stroke are fixed (they don't rotate) so the ring end gap doesn't get caught in one of the cylinder ports.

4 stroke pistons have "in" stamped on them, so it will be very clear to install that marking towards the intake.

The top of 4 stroke pistons sometimes have cut-outs to give clearance for the valves.

The diameter of the intake valve face is always larger than the exhaust valve.

The cut-outs on the piston are 2 different sizes (sometimes there is only one cut-out, to compensate for the extra large intake valve).

It's critical that the larger (or the only) cut-out is matched up with the intake valve.

If there is no "in" stamped on the piston (as in the case with Wiseco) the arrow points forward to the exhaust.