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How do I fit a rope piston ring to a beam engine condenser?

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AndyB: Hi all. here's one for you. I help out at a local industrial steam museum and, among other things (it is a constant work in progress), we are renovating the self-contained condenser on an 1879 Gimson & Co beam engine. We have got to fit a new piston ring which is made of rope wound 3 or 4 times round the piston and which is secured by the ends in two holes in the ring groove held by pegs hammered in. My question is; how do you/I trim the ends of the rope so that the outer strands are retained by the peg while making the rope thin enough to go in the hole and be held by the peg? My thoughts are to 'paint' the outer strands (to identify them when winding it all back up) and then undo the whipping, then use scissors to trim out the inner strands. I feel that the inner should be cut to a taper, cutting a cone into the rope about 1 inch long, ending up at a point in the middle in order to keep the profile of the rope to as close to the hole as possible while giving the peg a chance at fitting the hole to give a start. Having thought this out, is it then possible to 'drill' out the centre using a cone cutter that I could make? The whipping on the ends of the rope could, maybe, hold the outer strands in place while this is being done. The rope looks and feels like sisal (the original was) although it is a man-made fibre. Just to let you know, PTFE rope to do the job is nearly £2000! :jaw: Does anyone have any experience or ideas please? Just something to get the grey cells working. Many thanks Andy

Fergus OMore: I'd remember however that you could tease all the strands out and put them back at random. George Stephenson apparently packed the cylinders of Rocket with the felt from---- the foreman's hat!  :doh: On a more serious thread( :hammer:), model loco builders used to use graphited yarn( or so the story goes)

DMIOM: --- Quote from: AndyB on February 05, 2012, 08:32:48 AM ---.........Having thought this out, is it then possible to 'drill' out the centre using a cone cutter that I could make? The whipping on the ends of the rope could, maybe, hold the outer strands in place while this is being done.... --- End quote --- Andy, Never had experience in this context, but have worked with rope quite a bit, so a few thoughts: The only way you would stand any chance of rotationally coring the end would be if you had fused it solid - otherwise I'm sure the fibres would just turn away from the pressure of any edge tool, rather than staying still long enough to be actually cut. You might manage to 'scoop' a little of the core out if you made a wire U tool to use with the likes of a Weller heat gun (as in heavy duty pistol-style soldering iron) - however you then run the risk of being left with a hollow fused cylinder which you would impede you compressing the tapered end. You could try completely fusing the end and then thermoforming the taper; but you're likely to be left with a less-flexible transition which would be awkward to turn into the securing hole and might be a weak point. All of these of course depend on what stock the rope is made from - polypropylene, polyamide, etc. - some melt, some just char. I suspect the most practical way to tackle this is, as you outlined, to remove the whipping and then progressively trim the strands. In terms of what to trim: without seeing the actual rope in question, and how it is laid, the issue seems to be that you wanted to keep the outer 'strands' in place.  Typically the yarn and the strands are twisted in opposite directions - the yarn to form strands may be right-hand laid and the strands twisted together left-handed to form the rope - this balanced twisting (hawser laid) is to stop a rope un-twisting in service. Becuse of these twists, what is the outer yarn at the end may be well inside the rope an inch or two further back. So (from a detached perspective) I would suggest that trying to keep all the fibres that are on the outside surface may be a challenge not worth pursuing! To achieve a taper like this, the first thing I would do is to confirm that the end is suitable - its not unknown for the end of a rope to be fused and then whipped, so you may have to go back up an inch or two to get workable material. I would place a stop whipping on the body of the rope going back up the rope from where the taper is to start, to stop it unravelling beyond the head of the taper.  I would then remove any current whipping and trim the rope just a little longer than the final taper length (the reason for this is that when you re-twist the trimmed strands they won't lie as tightly as when the rope was machine twisted, and may leave you short). I would then un-pick / comb out the strands and trim the taper (allowing for the diameter of any whipping that'll be re-applied)- either tapering it by eye, or push a fid up the centre and trim back to a cylinder. The yarns can then be twisted to give a bit more structure - but as its such a short taper you may not be able to achieve that great a structure - and it may not be practical to achieve the same number of strands as in the original rope. Keeping a permanent whipping on such a steeply tapered tail can be a challenge - the original whipping won't be much help, and (unlike normal whipping) you'll probably need to use a needle and take periodic stitches all the way through try to keep it in place.  Depending on the final destination, you may even find that applying a few bands of thin-walled heatshrink, or something like Copydex, may be sufficient to hold the taper together until the pin is driven in. Dave

Fergus OMore: Is it worth mentioning something called--- a piston ring compressor? OK, it's no more than caulking which is putting oakum in between deck planks. Or if you want me to be rude-- it is the basis of the  expression-- money for old rope. see BBC I Player-- Cutty Sark-National Treasure. Only 3 days or so ago. And of course, Stuffing Boxes using greased flax. ( never thought that I'd have to get me arse to the marste again, and put me helm hard over. Gybe ho, Choc le foc and other such heave ho me hearties)

AndyB: Thank you chaps, We didn't go to the museum today because of the weather but I will take some measurements and photos next week. The holes are about 3/8 diameter and the rope about 1/2 or 5/8 inch. DMIOM: I had not thought of Copydex to hold it and that is a great idea. If I fuse the end it will not crush to secure (haven't tried heat on it). I didnt take the plugs out but the original sisal had all but disappeared so not a lot to go on. I will ask whoever took out the plugs how the rope lay (there are only 5 of us). Fergus: a piston ring compressor is no good; I have to reduce the rope end enough to be able to secure it in the hole with the plug without the outer unravelling otherwise it will just all come undone in use. I have to reduce the end by at least half to secure it. Please keep any and all ideas coming, it all helps enormously. Thanks Andy

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