Clupet Piston Rings

[chris vine]

Last year, I had a lot of fun making a set of 8 clupet rings for the valves for Bongo.

I filmed most of the work and have just put it together into a youtube video.

The video from the Steam Workshop on making clupets was what got me started, but I felt that more could be added. Hence the video.
Some of it is a bit shaky, but hopefully it will be useful...

The direct link to the video is here youtu.be/pquXx5JBFfM

Other videos are on our channel here www.youtube.com/@petersrailway/videos

All best
Chris.

[simon6200]

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?

[chris vine]

Hi Simon,

Yes, there was a bit of work to make up the tooling/fixtures etc.

The reason that I decided to replace the rings with the same, clupet, type was that the valve liners (bores) were not perfect in the first place. There was a tiny bit of porosity in the castings. What I should have done, of course, is to remake the liners from continuous cast iron bar. However, there is a lot of machining in them and I didn't want to scrap them. In truth, they worked fine for many years.

When I started to get a significant amount of blow by, I decided to ream them out with a large expanding reamer. I didn't want to remove the cylinders and machine out the old liners etc. The clupets seemed like a good way to give a bit of belt and braces.

To start with they were immediately better than before, but not perfect. Now the bores and rings have bedded in, it is lovely again...

I would never have been able to make my set without the steam workshop video to get me started!
Chris.

[simon6200]

My liners are made from CCI bar. I made two sets before I was completely happy, even though there was really nothing wrong with the rejects. It is beautiful stuff to machine.

[chris vine]

That is exactly what I should have done.
Older and wiser etc!!

C

[steamer5]

Hi Chris,
Great how to video! Many thanks for taking the time to put it together. Other than the expansion of the diameter for heat treating what other ring width, ring thickness dimensions based I guess on diameter would you suggest?

Cheers Kerrin

[chris vine]

Hi Kerrin,

That is a good question, which means that I have no idea!

There are quite a few references for ring dimensions. For us, Tubal Cain's Model Engineers Handbook would be a good start.
For these particular rings, I just copied the dimensions of the commercial ones which I had fitted 18 years previously.

Have a go and see how you get on...

All best
Chris.

[Roger]

It would be interesting to attempt to make these in PTFE. I suppose you could even 3D print them in PEEK, although the finish on the OD may not be good enough. You could put them on a mandrel for finishing though.

[Roger]

Just to ask a stupid question. How do you make sure that the joggle in the outer edge of the ring doesn't coincide with the valve slot? Surely that would have to be pegged? I can see how these are ok of Piston rings, but I'm not sure how that would work for Piston Valves.

Am I missing something? Maybe the fit of the piston is so close and that diameter is so near to the end of the piston valve that it doesn't matter?

[SteveW]

Jun 14, 2023 9:05:05 GMT Roger said:

Just to ask a stupid question. How do you make sure that the joggle in the outer edge of the ring doesn't coincide with the valve slot? Surely that would have to be pegged? I can see how these are ok of Piston rings, but I'm not sure how that would work for Piston Valves.

Am I missing something? Maybe the fit of the piston is so close and that diameter is so near to the end of the piston valve that it doesn't matter?

Seems to work OK on two stroke petrol engines and that's with simple rings. Don't recall my MZ engine using pegged rings but could be wrong.

[chris vine]

Hi Roger,
They just seem to work ok. No pegs etc.
I think that if they and bore are truly round, the amount a loose end will stick out into a port will be very small.
Chris

[chris vine]

Ps. The video has now had over 55,000 views!
Some things cannot be predicted…
C

[Roger]

Jun 14, 2023 12:26:11 GMT chris vine said:

Hi Roger,
They just seem to work ok. No pegs etc.
I think that if they and bore are truly found, the amount a loose end will stick out into a port will be very small.
Chris

Hi Chris,
That's not the issue I was referring to, it was the moment of port opening. If you use the ring to determine the port opening, then you've got a piece missing. I presume you keep the piston diameter outboard of the ring to be a tight enough fit to determine the port opening?

[SteveW]

Jun 14, 2023 17:56:19 GMT Roger said:

Jun 14, 2023 12:26:11 GMT chris vine said:

Hi Roger,
They just seem to work ok. No pegs etc.
I think that if they and bore are truly found, the amount a loose end will stick out into a port will be very small.
Chris

Hi Chris,
That's not the issue I was referring to, it was the moment of port opening. If you use the ring to determine the port opening, then you've got a piece missing. I presume you keep the piston diameter outboard of the ring to be a tight enough fit to determine the port opening?

Is it simply the ports are longitudinally narrower than the Clupet ring is. wide (or long or high) thereby preventing leakage around the ring via the port slot. Perhaps the valve bobbin end go a long way to minimising anyway.

[steamer5]

Hi Roger,
By piece missing are you referring to the the gap in the piston ring? I can see what you mean for a normal ring, ie the gap is from one side to the other, but not so…. well that’s what I figure in the clupet ring. Being one of the 55000, ok I have watched it more than once, the gap at the end of the ring when installed is going to very small, assuming that Chris’s excellent video is followed, but unlike a standard ring it’s not directly open to the other side, the gap as such requires the steam to make a 355 degree circuit around the ring, there by causing any bypass to take the long way round and I would think with the speed of the piston reciprocating would be fast enough not to cause an issue.

Or am I wrong entirely & you are referring to something else?

Cheers Kerrin

[Roger]

Jun 14, 2023 22:35:00 GMT steamer5 said:

Hi Roger,
By piece missing are you referring to the the gap in the piston ring? I can see what you mean for a normal ring, ie the gap is from one side to the other, but not so…. well that’s what I figure in the clupet ring. Being one of the 55000, ok I have watched it more than once, the gap at the end of the ring when installed is going to very small, assuming that Chris’s excellent video is followed, but unlike a standard ring it’s not directly open to the other side, the gap as such requires the steam to make a 355 degree circuit around the ring, there by causing any bypass to take the long way round and I would think with the speed of the piston reciprocating would be fast enough not to cause an issue.

Or am I wrong entirely & you are referring to something else?

Cheers Kerrin

Hi Kerrin,
I'm referring to something else. I'm probably not explaining it very well.
The piston valve uncovers a steam port to allow steam to pass. If edge that does this is the piston ring, the ring couldn't have a joggle in it. My locomotive uses the edge of the piston ring to set the timing because the covering cap is smaller than the piston bore. I peg the ring to make sure the gap never coincides with the port, but instead passes over a place where the port has a bridge.
I presume that for a Clupet ring to be used here, there must be a close fitting part of the piston valve outboard of the rings, else the joggle in the ring will come into play.
None of this matters much with conventional rings if the gap is really small.

[chris vine]

Hi Roger,

One of us is misunderstanding the other, but I don't know who!!

On my valve heads, the ring edge is the timing part. The outside end of the valve head is slightly smaller to expose the edge of the ring.

The ring, when compressed into its working size/bore, doesn't really have a joggle at all. There is a tiny gap, just like any other ring, but it doesn't go through to the other side. I think the best way to see this is in the video at or just before 23.50. In fact the viewing angle isn't perfect, but you can't really see the gap when compressed. Also, you can see that there isn't an apparent joggle.

Does his help??

People do think there is no leakage path in a clupet ring. However there is one, which took me a while to realise. If the diameter of the underside of the groove gives a large clearance, and the ring is worn a little, so the end gaps get large, then there is a leakage path in one gap on one side, under the ring and out of the gap on the other side. Maybe an O ring could be placed underneath to cure this future defect?...

Chris.

[uuu]

Butting in here: I think Roger's issue is that for the ring to leak into the port, steam does not have to pass all the way to the other side. If the ring is only just closing the port, much of the ring width is oversailing the port opening, with only a sliver fully surrounded by the bore. But there's a gap in the ring, the steam only has to enter the gap and away into the port. It doesn't even have to cross as far as the middle, or into the area under the ring.

Wilf

[Roger]

Jun 15, 2023 13:07:30 GMT chris vine said:

Hi Roger,

One of us is misunderstanding the other, but I don't know who!!

On my valve heads, the ring edge is the timing part. The outside end of the valve head is slightly smaller to expose the edge of the ring.

The ring, when compressed into its working size/bore, doesn't really have a joggle at all. There is a tiny gap, just like any other ring, but it doesn't go through to the other side. I think the best way to see this is in the video at or just before 23.50. In fact the viewing angle isn't perfect, but you can't really see the gap when compressed. Also, you can see that there isn't an apparent joggle.

Does his help??

People do think there is no leakage path in a clupet ring. However there is one, which took me a while to realise. If the diameter of the underside of the groove gives a large clearance, and the ring is worn a little, so the end gaps get large, then there is a leakage path in one gap on one side, under the ring and out of the gap on the other side. Maybe an O ring could be placed underneath to cure this future defect?...

Chris.

Hi Chris,
That makes sense. I didn't realise that the gap at the edge was almost closed.
Yes, an O-ring under it would certainly help. That wouldn't work on my PTFE ring design, because the gap has to be big. I do have an O-ring, but that's under a second ring that's smaller in diameter and sits under the outer ring. Unfortunately, you have to peg that design, else it's going to leak badly.

[chris vine]

Hi Roger,

Now I see what you mean! Yes, I guess that there is a route in though a gap and then backwards into the rings and into a port. However, it isn't much different from a normal ring and the gap is pretty tiny in any case.

When I first finished them, they were immediately much better than previously. How much that was the new rings (the old ones were clupets too), and how much was the fact that I had reamed the valve liners to get rid of some corrosion/porosity, I don't know. However, now that they have run a few miles, the exhaust is really crisp again. Phew!!

Chris.