I was resurrecting three 36 helicopter engines. On I was putting a new piston-sleeve assembly in. The cylinder & piston assembly is the AN0228. These assemblies are a little hard to come by.

The problem is that there is no cir-clip groove inside the larger hole for the gudgeon pin (wrist pin) of the piston.

Is this piston defective or was there no clip grooves on newer pistons, or was there an alternative method of pin retention?

I notice the present TT39H uses the clip.

Jim