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[logoman]

I want to use graphite yarn to pack a piston ring. I've tried countless times now and it's driving me 

The piston (9mm) groove was packed with graphite yarn from the factory (Aster) so I can see that it is possible.

Two things:
1. how to begin the wind when the yarn just keeps slipping round in the groove.
2. how to stop the last 5mm from sticking out and preventing the cylinder going on.

if I try and avoid issue 1. by beginning the wrap with the piston in the center of the yarn and wrapping two ends around, issue 2. is twice as bad!

there MUST be a trick...

[kno3]

Never tried graphite yarn since Teflon is much easier to use for this application.

[mogogear]

Hi-temp o-rings an option Miles??

Having never done this though I will fancy a guess....

* With said yarn off the piston- tie an over hand loop



* Now pass the loose end through the loop again. (This will allow you to draw and tighten the loop in the ring groove and it should Stay snug
* once tightened use a pin to tuck the ends around the and under the yarn-loop.
* as the engine is used the yarn should absorb water and oil-Then expand some and assist with sealing the piston in the cylinder and provide a "wiping" action for lubrication

All a guess- but hopefully written understandably

[steamboatmodel]

I have never done it with model size pistons, but on full size you chamfer the ends, put a spot of grease in the grove, lay the end in the grease and wind it around. You then held that down with an elastic band and did the next one, most held three to five ropes, you had to make sure that the chamfers were all staggered, you did the same thing when packing glands, but did not need the elastic bands.
Regards,
Gerald.

[logoman]

of course! knot the two ends

The groove is fairly deep and takes about five winds of yarn, so I did four VERY tight winds and with the two free ends, used the simple knot pictured, tightened as much as i dare without snapping the yarn, and then very carefully cut the loose ends off as close as possible using a pair of Japanese rigging shears, though i expect a good quality pair of small nail scissors would do just as well. Then a little steam oil around the yarn before fitting in to the cylinder.

Cheers Greg.

[mogogear]

As my dear father would say, "A blind hog finds an acorn every now and then"   

Glad I was close enough to help!