I have a thunder tiger pro 21R, just got it off a guy, it didn't have a piston and sleeve so i picked one up today. Does anyone know the position of the piston. The piston itself has one cut out on it and it can be positioned either towards the intake or the exhaust. In the engine, the exaust port is higher than the intake port. Can someone please help me out?

Is the cut out you are referring to on the bottom of the piston skirt or on top of the piston?

If it's on the skirt, the cut out goes on the intake side.

Enjoy,

Jim

the cut out is on the bottom side of the piston itself, i guess that would be the skirt. I assumed it went on the intake side but wasnt 100% sure .

Hi!
Intake side ?!
On most engines the cut-out on the skirt on the piston goes forward.... towards the propeller......so it will not interfere with the large main ballbearing outersurface...

Regards!
Jan K
SWeden

I think we are all in agreement that it goes to the front which is opposite the rear facing exhaust.

There are two kinds of cut-outs.

If you are speaking of a circular cutout, it is intended, on longer stroke engines, to clear the rear bearing/crankshaft counterweight (The backplate usually has a level surface on top, to allow piston clearance.). The rectangular cutouts (with rounded corners), are to allow better passage for fuel/air mixture to a bypass.

In side exhaust engines, the boost port bypass if often masked by the piston skirt. Some engines with long skirted pistons, Irvine FE, have a rectangular hole in the piston and a "bulge" on the side of the crankcase, for "feeding" this intake port.

If you can send a photo of the piston, as well as the engine, it will be easier to tell you which way the piston should go.

Like the man said: the piston has ONE cutout that can be positioned towards the exhaust or the intake side

It should be directed towards the intake port...