Author Topic: Steam engines - making cast iron piston rings, is it worth the effort?  (Read 610 times)

Online Gas_mantle

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I've just about finished building a smallish steam engine of at 1.5" bore x 1.25 stroke, in the past I've opted for piston rings made from oil soaked graphite yarn with pretty good results but have been wondering if cast iron rings may be worth a try?

I intend to run the engine on steam and it may end up doing light work powering a small pump so I'd like to make it fairly robust and low maintenance if possible. At the moment it is a cast iron cylinder with an aluminium piston (I can make a different piston if need be but not a cylinder)

So the question is, am I likely to notice any noticeable improvement over graphite and are they easyish to make?  From what I can see it looks fairly straightforward but may take a bit of trial and error getting the fit right and snapping a few during fitting  :facepalm:

Any thoughts?

Thanks  :)

Offline Jo

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Re: Steam engines - making cast iron piston rings, is it worth the effort?
« Reply #1 on: November 28, 2018, 08:28:15 PM »
Use the graphite yarn for the little one.

Try making CI rings for the No 4, they are not difficult: Make them to fit the bore, not too thick, easy moving in the slots, heat treat them to red with a gap (which will allow them to spring out and spring in a little). If you don't try you will never learn  ;)

Jo
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Online Gas_mantle

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Re: Steam engines - making cast iron piston rings, is it worth the effort?
« Reply #2 on: November 28, 2018, 08:34:21 PM »
Thanks Jo   :)

I kinda figured that with CI rings after a bit of trial end error I may get a better seal and ought to be able to fit 2 rings rather than the one graphite I had intended. Am I likely to run into problems with CI rings in a CI cylinder?

Offline john mills

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Re: Steam engines - making cast iron piston rings, is it worth the effort?
« Reply #3 on: November 28, 2018, 09:53:16 PM »
I have only used cast-iron rings on cast iron pistons in cast iron cylinders.
i have made  rings by turning an over size bush ,cutting the gap then holding in the chuck so the gap is closed
finish turning to size. when parted off the ring springs open .the gap needs be checked that there is a gap when
fitted in the bore.   

Offline sbwhart

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Re: Steam engines - making cast iron piston rings, is it worth the effort?
« Reply #4 on: November 29, 2018, 04:45:07 AM »
I use cast iron rings in my locos. Turn up the blank rings and split them with a very thin slitting saw them spring them by inserting a spacer and heating with a gas torch or putting them in very hot oven put them on a mandrel  closed up and turn to size. My locos have cast iron cylinders so far they have worked very well and show little signs of wear

So
A little bit of clearance never got in the way

Online gary.a.ayres

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Re: Steam engines - making cast iron piston rings, is it worth the effort?
« Reply #5 on: November 29, 2018, 06:24:48 AM »
Sounds like a worthwhile endeavour Peter. Good luck with it.

Offline Jim Nic

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Re: Steam engines - making cast iron piston rings, is it worth the effort?
« Reply #6 on: November 29, 2018, 11:27:32 AM »
Definitely worth a go.  I have a cast iron ring in my MEM Corliss and it is the smoothest turning engine I have.
I turned 4 blanks, broke 1 in the gap forming process, 1 in fitting to the piston and ended up with a good one in the engine and a spare (which is in a safe place currently unknown to me).
After breaking a ring in the very tense process of stretching it over the piston I made a 2 part piston with the top and bottom parts clamped together with the piston rod.

Jim
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Online Gas_mantle

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Re: Steam engines - making cast iron piston rings, is it worth the effort?
« Reply #7 on: November 29, 2018, 11:56:40 AM »
Thanks everyone  :)

What I'll do is get the engine running then when stripping it down to paint and fit gaskets etc I'll give it go at making CI rings, I guess even if I make a hash of it I haven't lost much.

I hadn't considered heating to get springiness, I just assumed they were made a few thou larger than the bore then squeezed together for fitting.

Offline gbritnell

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Re: Steam engines - making cast iron piston rings, is it worth the effort?
« Reply #8 on: November 29, 2018, 02:08:47 PM »
One thing I would suggest is making the piston from something other than aluminum. Aluminum is fine in an I.C. engine but as soon as you introduce water and iron into the mix you will get electrolysis and if the engine sits for awhile the piston will start to corrode.
gbritnell
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Online Gas_mantle

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Re: Steam engines - making cast iron piston rings, is it worth the effort?
« Reply #9 on: November 29, 2018, 06:03:29 PM »
Thanks, I guess I can experiment with the piston.

With a bit of luck I'll have the engine running in a day or 2  :pinkelephant:

Offline Mcgyver

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Re: Steam engines - making cast iron piston rings, is it worth the effort?
« Reply #10 on: November 29, 2018, 11:38:55 PM »
I just assumed they were made a few thou larger than the bore then squeezed together for fitting.

a better way is you make the ring and cut out a section at the split.  Then squeeze the ring closed  (held in a fixture) and turn the OD to fit the cylinder.  Released from the fixture there is outward spring at the cylinder bore, but also the OD of the ring is an undistorted perfect circle at that dia

Offline pgp001

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Re: Steam engines - making cast iron piston rings, is it worth the effort?
« Reply #11 on: November 30, 2018, 07:37:34 AM »
Peter

There is some useful information on making rings on this website.
http://www.modelenginenews.org/techniques/piston_rings.html

Phil

Offline john mills

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Re: Steam engines - making cast iron piston rings, is it worth the effort?
« Reply #12 on: November 30, 2018, 09:20:20 AM »
if you use the heating method to form the shape it is important to  heat evenly if you get part of the ring to hot
that can bend unevenly .I have only used the turning a bush first from continuos cast material cutting the gap
then holding in the 4 jaw chuck with the gap closed, face the end turn od bore the inside then part off face and part off each ring .the bush needs to be long enough to have a good length in the jaws.

Online Gas_mantle

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Re: Steam engines - making cast iron piston rings, is it worth the effort?
« Reply #13 on: November 30, 2018, 11:30:12 AM »
Thanks everyone, I'll give it a try one I have my engine running and experiment with a few different methods.

I'll take a few photos along the way to show how it goes  ;)

Online steamer

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Re: Steam engines - making cast iron piston rings, is it worth the effort?
« Reply #14 on: November 30, 2018, 02:47:26 PM »
Teflon rings work well if you dont have much superheat, or run on air only.
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