Making Piston Rings

Hi all,

I have made piston rings for a sweet pea as per the website below

http://users.tpg.com.au/agnet/make%20piston%20rings.html

Making them and snapping them seems to be the easy bit. After heating them up as per these instructions.

http://users.tpg.com.au/agnet/make%20piston%20rings2.html

I cannot seem to get them on the piston without breaking them, I have been trying to fit them as below.

http://www.youtube.com/watch?v=Abi6CGVTmbE

Can anyone help me out as to how to make and fit them correctly. I am using normal grey iron, does this matter?

Also I am expanding them between 10 and 15% of the bore.

Thanks in advnaced for your replies

Think we need slow motion on that video to see how he is doing it, I usually just spread the ends apart until they slip over the piston.

I use a decent Meehanite iton Grade 17 (250) yours may be a bit coarse grained and that may be a reason for the failures

How might I determine the quality of the iron?

Hi, there is an artical in ME 4450 about piston rings a how to make them. Should be in the shops next Friday.

Regards Nick.

P.S. 4450 is in the digital issues already.

Edited By Nicholas Farr on 16/02/2013 20:37:22

> Hi, there is an artical in ME 4450 about piston rings a how to make them. Should be in the shops next Friday.

In my sweaty palms today!

Neil

Yes if you are making piston rings well worth a good read

Bob

I'v resently made half a dozen piston rings, the first four were for a petrol engine with a 2" bore, made of Meehanite, the same as one of the pistons, the other piston (have not tryed it yet) is aluminium), I cut the gap with a thinned junior hacksaw blade. The other two were made for a Stuart Turner S6 with a bore of 1.5", they were made from an old brake disk, to machine the outside diameter, I first bored the inner diameter, then glued it on a mandrel, the ring broke (in one place), on removal from the mandrel. All the rings were heat treated by wedging the gap open (1/4" I think),eating to red, and holding for a few miniutes, The Meehanite ones went on just like any small engine rings. The Stuart ones are fairly shallow, 1/8" wide x about 1/16" deep, and they are both in the one 1/4" ring groove, the rings being / seeming rather delicate, thought I'd have trouble, but no, they just popped on. They are all working OK, I only wish the petrol engine would work as well as its bits and piecesaybe one day! Ian S C

Thanks for the replies. I will look into alternate sources of iron. Mine after heat treating were not very springy. Could push the gap together and it would pop back but more and deformation occurred.

Yes they are square in section but this is what the plans require so many others must have had some success.

I do not have that article, as I do not have a large collection of ME's can you point to online resources?

Edited By Dave Bond 1 on 18/02/2013 08:52:19

At our little museum we have an old Continental industrial engine, I think its about 3 1/2" bore, twin cylinder. when we got it, it had a broken piston ring, so I made one using the rim of a V pully, not much wall pressure, but it seems to work.

I made a small ring using window weight iron, even that didn't break, but I can't remember what it got used for. Ian S C

Ok sounds like material is though important not critical as V pulleys are not going to be amazing. So maybe I should be asking why I had so little spring to my rings.

They are 1.5" diameter and 1/8" square as per the sweet pea plans. This was made from a bit of drawn grey iron from black gates.

They had enough spring to put the gap in the groove and then draw up and over the piston. Though there was not enough flex to bring it round over the piston so the deflection would be another 1/8" beyond its relaxed state. Just as I believe Graham suggested.

Iron should be OK if it came from Blackgates.

Thats quite a thick section ring for 1.5" bore, not really a loco man but is the 1/8x1/8 groove definately for rings and not packing, my similar bore traction engine uses 1/16x1/16 rings.

J

That is interesting, I put the grooves in as per what I could see on the drawings. Can anyone else advise as to their Sweet Pea? I assumed it was specified for rings not packing.

Dave, I am building a Sweet Pea, about 12 months behind you by the sound of it. I have experienced exactly the same problem as you posted. Very frustrating. How did you resolve the problem. Different material? different thickness. Very interested to find out.

Regards Les Brown

I seem to recall one of Professor Chaddocks articles on rings commenting that if they would not spring on over the piston without breaking they were too thick. That would be radial thickness. Rings don't need to be very thick, the spring tension in the ring is just to help hold them against the cylinder wall and the actual sealing comes from the pressure getting behind the ring and forcing it out against the wall. With the piston speed and the pressures being quite low in a steam engine, not a lot of wall pressure is needed.

I've used the ordinary continuous cast iron bar to make rings, in sizes from about 5/8" to five inches with no problems so far.

Don't overdo the heat treatment, I believe that too long and too hot can cause the grain size to grow although I stand to be corrected on that.

John

Tubal Cain did some experiments and calculations, he found ring pressures for rings specified for steam engines were almost universally excessive, greatly so.

Bear in mind that he was an authority on diesel engines, so he knew a thing or three about piston rings.

Neil

Hi Dave,

I am not a steam specialist but have made many piston rings for IC engines. I Always use the Trimble formula. The thicknes of the ring should be between .040 and .045 of the bore diameter. For a bore of 38 mm the ring should be 1.67 mm thick. This is rather critical! To thin and there is not enough wall pressure, to thick and you have to much installation stress (broken ring). The gap should be .15 times the bore, that is about 5.3 mm in your case. The hight of the ring is not inportant. I should go for 1.5 a 2 times the thickness. in your case `2.5 a 3.5 mm. for a steam cylinder. I Always use continous cast iron bar.

I wish you succes with the make of new pistons and rings.

Kind regards, Johan.

I have had mixed success with rings. Big ones no problem, small ones break. Easy solution is don't use metal rings, use graphite square section. I was sceptical about this but the results have been brilliant. Other option is find something that fits on ebay. You wont find them that thick but putting multiples together gives good results.

What about Delrin or some of the other modern plastics ? They would be less likely to break upon fitting.

Edited By Brian John on 11/09/2014 18:12:53

Rings must be expanded by the absolute minimum. To do this, cut three narrow strips of tinplate and make a right angled bend near one end of a short length. Arrange the strips aroung the piston then slide the ring down over them. When the ring is over the groove, remove the strips and the ring will spring into the groove.