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

ask your question [link=http://www.rcuniverse.com/forum/m_6587349/tm.htm]here[/link]

If it doesn't use circlips, it must use the teflon retainers like a K&B.

FBD.

On the 36 . . . .

The piston has a shoulder in the front to retain the piston. In the rear, there is just a straight hole. You can not use a nylon pad because the wrist pin hole comes half way across the rear Schnurle port.

I have pads, that would be easy.

....hmmmm, you wouldn't think the wristpin would extend into the port without a circlip. [sm=stupid.gif]

FBD. []

The old piston did have a circlip and there was a groove in the wrist pin hole but the new ABN piston has a smooth bore.

....maybe it is defective....missed that manufacturing step. If it is over a port,
it must have a circlip to keep the pin out of the port.

FBD.

I think it is a defective part?

But with Thunder Tiger's personality, with regards to parts, (the USA Thunder Tiger and the way Thunder Tiger of Taiwan treats them), I'm probably going to have to figure out how to use it as it is?

I think your first suggestion is worth a try? I've got to OK it with the owner of the engine first.

The button may be rubbed off if it extends into the port. [X(]

I think only about 1/4 of the button comes across the very radius end of the rear Schnurle port

I've been trying to get the owner on the phone.

Do you have the circlip from the old set-up ? Make a tool, and cut a groove
in the new piston for the old circlip.

I have the old circlip. To cut a groove would be difficult without a jig to hold the piston on center and a lathe?

I contacted the owner and I'm going to go the nylon pad route

OK. I would cut a groove by hand. Grind an old small screwdriver, and leave
a *** on the edge. Use the pin in the piston as a guide, and run your small cutting
edge around in a circle, pressed up against the pin. Cut a groove around, about
.008 to .010 and you have a groove for the circlip.

I guess the aluminum being soft that it would be possible?

The trick is to sharpen the leading adge of the tool so it will cut. A cut-off wheel
for the Dremel tool would do nicely. You have to shape it like a lathe cut-off tool.

The Dremel cut off wheel could make all the cuts for the tool.