PTFE piston rings

[duncan webster 1Participant @duncanwebster1]

Just bored the cylinders for my latest loco (gunmetal). There are some pinholes at one end of both castings. Can't send them back as I bought them second hand, anyway I'm not sure it's that bad. I'd like to try PTFE rings, backed up with an O-ring to give the out spring. I'm sure this has been done, but I can't find any reference in previous threads. Anyone got actual experience?

[duncan webster 1Participant @duncanwebster1]

[nigel jones 5Participant @nigeljones5]

I tried this a few years back with bad results. The rings expand after machining and even more so when they get hot . Piston siezed in bore, engine thrown under bench…still there somewhere!

[ruston165Participant @ruston165]

Ive recently had ptfe rings fitted to a 5 inch black 5 i have. And ive gotta say they are superb. No problems at all. They were done by Ben Pavier at BP Loco works, can pass on contact details if needed.

Lee

[julian atkinsParticipant @julianatkins58923]

Hi Duncan,

I am very old fashioned so would fit graphite square asbestos packing to your gunmetal cylinders properly fitted – which few appear to know how to do properly.

However a friend of mine has recently done extensive experiments with PTFE on piston valves and pistons. I will email you a few links. They take things a bit beyond current thinking.

Cheers,

Julian

[John BaguleyParticipant @johnbaguley78655]

I've used them on several 2½" gauge locos with excellent results. Also used PTFE on piston valve heads with equally good results. With these smaller bores though I haven't used backing O rings and just relied on the plain PTFE rings on their own. I fit two thin rings side by side with the gaps 180° apart to prevent leakage. It is essential to allow clearance for expansion when the rings get hot.

I haven't done it yet but I've thought of using graphite filled PTFE for the rings as this material is harder and springier than virgin PTFE and may not need the backing O rings in the larger sizes.

John

[Brian OldfordParticipant @brianoldford70365]

Is the shared wisdom to include a bell-mouth at the end of the cylinder to assist with insertion of the rings à la full size practice?

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