oldnorton
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5" gauge LMS enthusiast
Posts: 693
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Post by oldnorton on Jun 29, 2023 10:09:50 GMT
That's a good video Chris, just seen it, thank you. As you say, it builds on the story from Steam Workshop.
It is a good technique as the inside out heat treatment pulls the two halves together, and sets it to a larger diameter to create the spring out, but then the cold machining of the OD is what ensures they are true to the bore. That's the bit I like.
Cold machining of conventional rings, using the same clamping tool, has been published by others in ME, as SteveW describes above. I would use this method if not going to a full Clupet.
Two things come to mind: will a Clupet ring pass better over a valve's transfer ports than a conventional ring? It seem possible as there are not two opposite points pressing out. You have made those rings for a 7 1/4" set of valves but I just wonder what the smallest diameter might be and whether a set could be made for 5" valves? If all the dimensions of depth and width are scaled then there is no reason why not perhaps.
Norm
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Post by chris vine on Jun 29, 2023 18:09:24 GMT
Hi Norm,
I think to go smaller you would want to make the section of the metal rather less. IE scaled down, but probably thickness even more so. I reckon it was touch and go with them not breaking!
There have now been over 800 comments on the video with many of them asking how much better they are than standard rings. Also, many people have suggested that they would improve car engine efficiency. I don't think, that on a perfect cylinder, there would be much difference if any. If they were a big improvement in modern car engines, the makers would have found a way to mass produce them, or fitted more standard style rings...
Enjoy the challange... Chris.
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oldnorton
Statesman
5" gauge LMS enthusiast
Posts: 693
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Post by oldnorton on Jun 29, 2023 19:00:24 GMT
I don't think, that on a perfect cylinder, there would be much difference if any. If they were a big improvement in modern car engines, the makers would have found a way to mass produce them, or fitted more standard style rings... Yes I agree. IC engine designers will know exactly what the leakage is past conventional ring gaps. The IC engine problem was oil control, hence the complex scraper ring. And conventional rings were good enough for 'modern 1950s steam'. At our much lower pressures in model steam I doubt that the ring gap leakage is an issue. Norm
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Post by jinks82 on Nov 30, 2023 10:23:18 GMT
I saw your video earlier today. Very good. I made one just as an exercise a couple of years ago, from the Steam Workshop video. All the holding fixtures must be a fair bit of work before you start. They have a lot of appeal but I can’t believe conventional rings leak significantly through the gap. My Springbok valves have Clip-Lok rings that used to be used in truck transmissions before plastics took over. They have an overlapping section so no continuous gap. Pistons have them too. Any idea how many miles/ hours It took to wear out Bongo’s original set? Aha! A post about Clupet rings! I bought these for my 5" B1 from a clupet manufacturer. I have fitted them as per his instructions but I am very concerned about the friction in the bore. The rings were tailor made to my cylinder dimensions but I cannot believe that there should be so much effort required to operate the piston. Any ideas?
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uuu
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Post by uuu on Nov 30, 2023 14:23:45 GMT
There should not be a huge effort required to move the piston - some effort, obviously, but not huge. Since Clupet rings are used in I.C. engines as well as steam, there may be different requirements - did your manufacturer know they were for a steam model? There's an interesting reference within this web page ( www.jerry-howell.com/PistonRings.html), to work by Prof Chaddock and Tom Walshaw (Tubal Cain) on the excessive wall pressures found in many models. Chaddock suggests 13lbf/sq.in to be appropriate for rail models. Not that it's easy to work out what wall pressure you've got. Wilf
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Post by chris vine on Nov 30, 2023 17:20:37 GMT
There will be some friction but I think you should be able to push the piston in out with fingers. If there are tight spots that tells you something isn’t right. If modest friction then they will run in quite quickly. Just make sure the gap isn’t being nipped by the bore… Chris
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Post by simon6200 on Nov 30, 2023 20:22:54 GMT
There have been articles in ME about pressure exerted by different rings. From memory radial thickness was the main variable determining wall pressure.
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Post by chris vine on Nov 30, 2023 20:28:24 GMT
I would add to that by saying that the two determinants of wall pressure are radial thickness and the size of the gap, IE by how much it is sprung open when free.
Back to the original question by jinks82, If you feel there is too much friction and nothing is binding/jammed, then it is either too much wall pressure or spring. However, maybe you can work it back and forth by hand with plenty of oil and see if it frees up. My belief is that with our machining, there is quite a bit of initial wear and bedding in.
Chris.
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Post by jinks82 on Dec 5, 2023 11:51:32 GMT
Many thanks for all of your replies. It is currently an effort to move the piston up and down the bore. I was wondering whether I should scrap the whole clupet idea and either find "traditional" rings to suite my bore and piston or use PTFE. I have spent some time honing the bore but the friction seems way too high. If I were to re-order suitable rings how should I calculate dimensions? I agree with the above re wall pressure. Getting the piston with clupet rings into the bore is quite difficult as there is quite a lot of compression required to close the rings.
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Post by ettingtonliam on Dec 5, 2023 15:18:12 GMT
Have you spoken to Clupet (or whoever made your rings) about this?
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Post by suctionhose on Dec 6, 2023 7:14:24 GMT
Many thanks for all of your replies. It is currently an effort to move the piston up and down the bore. I was wondering whether I should scrap the whole clupet idea and either find "traditional" rings to suite my bore and piston or use PTFE. I have spent some time honing the bore but the friction seems way too high. If I were to re-order suitable rings how should I calculate dimensions? I agree with the above re wall pressure. Getting the piston with clupet rings into the bore is quite difficult as there is quite a lot of compression required to close the rings. Firstly, Clupets are an attractive curiosity. They were devised as a solution to worn bores in early motor vehicles because they could tolerate out of parallel bored. Put some Clupets in and oil consumption was reduced in a worn motor. I think they found their way to preserved steam for similar reasons. In a new model, I don't know what case exists in their favour beyond the curiosity value of making them: a mystery to most of us before the steam workshop YouTube video. The conventional rings in my loco have seen 35 years of really hard work. I haven't even looked at them. They might be on their last legs, I don't know, but they still seal well enough to pull 2 ton trains with a 2" bore. So your choices are simply to analyse what you see as unsatisfactory and do something about it: thinner ring section / revert to conventional rings / anything else that, by your own judgement, is taking you in the desired direction. That is model engineering in a nutshell!
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Post by jinks82 on Dec 6, 2023 11:19:03 GMT
Have you spoken to Clupet (or whoever made your rings) about this? Sadly he has now retired. I did discuss this with him and he assured me that the rings were correct
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Post by jinks82 on Dec 6, 2023 11:31:17 GMT
Would someone be kind enough to advise me on the use and sizing of conventional piston rings? I have been rebuilding an old Triumph twin and there are three rings per piston (one being the oil ring). What arrangement do I need for this application? How do I size these? Do I need to make a new piston or can rings be made to suit the existing ring machining. As this is my first build any friendly advice would be gratefully received (after all, isn't this what this forum is for?)
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uuu
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Post by uuu on Dec 6, 2023 14:45:30 GMT
For an old motorcycle, I'd be looking for a spares supplier, like here: montysclassicmotorcyclesshop.co.uk/pistons-and-piston-rings-30-c.asp. They'll likely do them for standard sized pistons, and in increments getting larger to suit a re-bored cylinder. They'll also likely have the specialist knowledge to guide you if you're unsure of what you've got. Wilf
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oldnorton
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Post by oldnorton on Dec 6, 2023 19:08:57 GMT
Jinks, you buy pistons and matched rings from an old Triumph supplier. If you are very lucky you might get NOS rings to suit your existing pistons, if they can be identified. And the bores have to be in the right condition. Normally, if there is anything wrong in the bore/piston/rings then it is a rebore and new pistons + rings. You can't mix and match or attempt any DIY guesswork.
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Post by jinks82 on Dec 7, 2023 10:45:23 GMT
Sorry chaps, you have missed my point! The Triumph engine is all sorted. I was merely using it as an example of how rings are used in that application as opposed to what may be required in my B1 piston. What I am trying to understand is which rings I need and how they are spec'd
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uuu
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Post by uuu on Dec 7, 2023 11:31:22 GMT
I don't expect the designer went through much heavy thinking:
How many rings shall I fit? One would be too few, three seems like overkill - two it is then.
How big? Well, the makers will have a Myford, and a ruler. So 1/8" wide ought to be do-able. Nice round number. And, say, 1/16" thick.
Does this work in practice - it seems to - so Tada!
Then it takes a more cerebral person to come along (Prof. Chaddock) to add a bit more analysis, and conclude that in most designs the rings are too stiff.
Wilf
Most of us don't even trouble to think at all - we just make it according to the drawings. A few brave souls experiment with alternative materials. And Roger ploughs his own furrow, of course.
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Post by chris vine on Dec 7, 2023 13:06:55 GMT
How stiff is too stiff? Even quite high wall pressure rings should move fairly easily. So, back to original question: is there something which is blocking their correct fitting? Eg ends with no gap, rounded corner at bottom of groove in piston causing interference with a sharper corner on inner edge of rings??? Chris
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Post by timjenkins31 on Dec 7, 2023 18:18:05 GMT
I make these and other piston rings for a living. Sounds to me like the bore size you gave to Alan may not of been so accurate. If they are finished to a diameter even a thou over your actual bore size, the rings will be too compressed meaning there is less than no ring gap, causing excess wall pressure. Clupet rings are difficult to gap if your not practised in manipulating them. I usually stress the importance of giving a accurate bore diameters for this very reason. A 0.001" difference in bore is equal to over 0.003" at the ring gap, or a difference of pie. I usually machine the final diameter of rings to give a small ring gap, depending on how confident I am of the customers measurement!
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Post by racinjason on Dec 8, 2023 10:11:15 GMT
Why not get a brake hone and run that through the cylinder until the ring has the feel you want, you will also have a nice surface for the new rings. regards Jason.
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