Piston Rings

HI. I'm having problems with CI piston rings! I am currently building Martin Evans Highlander design. Having finished the piston valve as the drawing, I then made the rings. I followed the methods as set out by Tubal Cain and others, after machining I carried out the full annealing process as recommended. So far, so good. I made six spares, but have now broken seven rings in attempting to fit them! The valve has three ring grooves, I can get the first one in ok by "screwing" it into the groove, but then that prevents fitting the others in the same way.. Trying to expand the rings far enough to ease them over the piston head simply breaks them. I should really apreciate any suggestions before I run out of Mehanite bar, or my patience Tom.

Tom,

I don't know the Highlander engine, but standard fitting procedures should apply.

Assuming that you don't have a special tool for holding the rings open ... try the method shown in he bottom-right picture of the second post here.  --- Three little shims.

But; before you next try fitting ... Do check the diameters very carefully.

If you still break rings; I would suspect the quality of the material.

Good Luck

MichaelG.

Edited By Michael Gilligan on 24/05/2013 08:40:35

There is a very useful description of various piston ring materials here.

MichaelG.

Tom
A little trick I used to use well my bruv and me while working on Austin 7s a large hose clamp, a bit of leather or rubber tighten up gently then push into bore, there are lots on fleabay for sale still.
for the bikers, and by the way they scream around they need to change regular...(that is the bike pistons)
Bob
Oh make sure there is oil on the inside. I am sure that some comedy act could put a lot of connentations on this advice.

Good luck
Bob

Is this the valve size?

I am not experienced on steam loco's but the rings are a similar size to my flash steamer apart from mine being dykes rings.

When making a ring I expand the ring with a shim in the gap then heat to a red heat and let them cool then clamp to a mandrel and finish to size.

I just expand them with my fingers and have very few problems fitting them.

Not sure but think Professor Chaddock did an article on this way for ic engines?

Paul

Edited By Windy on 24/05/2013 10:29:16

When I rebuilt a Stuart S9 earlier in the year, I made my own rings, using the cast iron from a brake disc, on compleation I wedged the rings open about 1/4", heated them to red heat for about 5 min, then let them cool slowly. On that engine the rings both fit in the one 1/4" wide groove, I was a bit worried about breaking them, but they slipped on no trouble, I have since made and fitted rings on a IC engine with a 2" bore, they required the three shims method. When I heat treated those ones I opened them about 3/8". Ian S C

Thomas,

Your problem lies in your post!

When you get your first ring in the first groove you need to then move it to the next groove and then the next. You will only ever get a ring across the small gap between the ring grooves. If you try to have all the ring on the full diameter of the valve or piston or try to take it over another ring it will break as you have discovered, something I found out years ago when I first started using rings on pistons and valves.

Eddie

Quite so, Eddie

That's what the three bits of shim, that I mentioned this morning, are for.

MichaelG.

Hi all. Thanks for your advice and assistance. The valve in question is as the drawing shown in Paul's comment. As regards the making of the rings, I followed the information in Prof. Chaddocks article to the letter, including the heat treatment, for which he specifies a temperature of not more than 560'C followed by slow cooling. I am using continuous cast Mehanite bar of stated good quality.

Whilst I can easily "screw" the first ring into its grove, it has proved quite impossible to move it on to the next one, it always breaks when I have tried. Also, having made a tool for expanding the rings, they break before opening sufficiently to slip them over the piston head...I can only assume that; 1, the annealing process is not working or, 2, the material is not all it's supposed to be! I will try the heat treatment again, holding at the temperature for longer than the recommended 10 minutes and see what happens... Thanks to you all, I'll let you know what happens!!. Regards, Tom.

I have made 8 rings fior the two grooves on my suffolk. They are only 0.040" wide by 0.030" thick. I as surprised how flexible they are.

Neil

I've made a couple of IC engines with tripple rings and not had any problems fitting them, I usually make a few spares but they were not needed.

Your 560oC sounds a bit low I usually get them upto red heat, 560o would be barely glowing.

Thomas,

I've never ever heat treated a ring and I've built a number of locos over the years with pistons of similar dimensions to your PVs and one loco with piston valves just 0.550" diameter and three rings on each head. My current loco is now in its 11th year and the pistons are a tight as you could want and never been opened up in all that running.

When you say you are 'screwing' the rings on I'm not sure what you mean. The technique is to get one end into the groove by twisting the ring and then gradually feeding the rest of it into the groove by pushing it sideways a little at a time until it is all in. If you can get it into the groove this way then the stress on it is no greater when you lift one end over into the next groove and gradually feed the rest round.You might need to help it out of the first groove with a bit of shim. 'Screwing' it on suggests to me that you are trying not to twist the ring and getting it all over the full diameter at once whilst turning it, a bit like someone might get a wedding ring off a fat finger!

If you are using the right technique and the rings are still breaking then the iron you are using is too coarse in the grain and its tensile strength is too low. You need a mehanite that has been proof turned to show the fine grain and consitency. It would be difficult for the amateur to heat treat a coarse grained iron to change the grain structure.

Eddie

Just a thought if you have some broken rings use them as bridging piece for the piston grooves and see if you can feed the ring over them to the far groove.

Having made many rings some out of unknown cast iron and very few problems with them you might have a bad batch of iron.

Paul

I made a ring for an old Continental industrial engine (3.5" bore), out of the rim of an old cast iron V pully, I think its still OK, although we have not had it going for a couple of years. Ian S C