Making cast iron piston rings

[josodl1953]

I wonder if anyone could tell me more about the kind of cast iron that is generally used. There is grey cast iron with graphite in flakes and nodular cast iron , also known as Meehanite, with spherical graphite. Now it seems to me that one should use material with the highest possible yield strength. I used GGG 60 nodular cast iron for my Edwards, I do not know the U.S. equivalent but this was the strongest CI I could purchase. The Edwards drawings specify machining the rings in a cold pre- stressed condition, without heat treating. I had to make quite a lot of rings to get the required amount so maybe I should adopt the heat method but the question remains: does the tensile/yield strength matter?

Jos

 

[WOB]

According to this site, it seems nodular iron would be the obvious choice : Difference of gray cast iron and ductile cast iron
Tensile strength is important when spreading the ring over the piston crown before it drops into the groove. If a ring survives that, I don't think it matters what it is made of in our little engines. I think your will find that heat treating will improve your production yield.

 

[stevehuckss396]

you want to use fine grain gray iron. Do not use ductile

 

[peter smith]

1 have just finished the Kinner 5 cylinder radial the pistons are just over 1" dia there are 3 rings on each piston, I used the turn to size part off then break them in the vice with a piece of tool steel, gap them then heat them to cherry red while holding them open to give them tension. I fitted all 15 with this method using fine grain cast iron without any breakages.

 

[Skipper]

#7 above , what is the parting cap?
skipper

 

[tornitore45]

josodl1953 I made the Edwards 5 and followed the process indicated. Used Gray cast Iron without much stressing about because it was my only choice.

There is a religion about making piston rings, and each believer will not entertain to sin by crossing into other faiths.

I have no doubt that on a full size engine the ring must be round when compressed. The geometry and metallurgy dictates that it must not be round when free from stress.

I also have no doubt that on a model engine one can cheat a little. I have built a dozen engines and found no difference between the annealed process and the no anneal method. After a break in compression is good and that is all a ring is there to do.
In the end the theoretical differences are probably of the same order of the tolerances and what the wear in can accommodate.

I turn the ring to an OD = Bore + GAP/pie GAP = (Open Gap - Working Gap) In other words the Gapped ring length is equal to the Bore circumference, so when it is closed it fits with no Working Gap. File the Working Gap later or include it in the formula above.

Some people may be offended by this blasphemous thinking.

 

[Skipper]

How much clearance is required between the bottom of piston ring groove.? Thickness of ring?

 

[SmithDoor]

You a gap of 0.002" to 0.005"
The best way make the piston rings first and fit the piston.

Some old automotive books before 1950 will give more details. At time auto repair shop would get blank piston and auto mechanics would machine to fit.

Dave

How much clearance is required between the bottom of piston ring groove.? Thickness of ring?

 

[Rocket Man]

Hasting piston ring company makes 100,000s of different, size, shape, diameter, thickness, width, designs, you can order rings directly from their sales department for about $3 per set of rings. I needed 6 sets of rings best price I could find was $15 per set then I called Hasting I got 6 sets of rings plus shipping for $9 package arrived in 3 days. Hasting does not sell rings my engine name or model number. They need, bore diameter, piston groove width, ring design, piston groove depth, number of rings per piston, type of ring for each piston groove, etc. There are several types of compression rings, several types of oil rings & other types of rings. You can by over lapping ends with no gap for improved compression. Use your machinist micrometer to check all dimensions before you call Hasting.

 

[goldstar31]

Thinking of the 'real' Rocket man- George Stephenson, I recall in my lectures billions of years ago that the sealin th pistons was achieved by the judicious use of the foreman's felt hat. This leads me on to mention the regular use in model railway circles of using graphited yarn.

Perhaps someone would care to enlighten me of the confusing disparity in the two well established systems.
Thank you

norman

 

[Rustkolector]

Mauro,
Using your method how is the relaxed gap dimension determined, or did I miss something?
Jeff

 

[tornitore45]

The relaxed gap is a given data, from the plans.
I am no theorist, all I can say is that plans I have seen have a relaxed gap length of about 1/10 of the bore.
The gap length does not depend from the method, but the way is achieved does.
In the annealing method the ring is made to OD = Bore so the Gap is achieve by bending the ring open and keeping that way during the annealing which sets the gap to stay open
With the method I described the ring is machined to be larger then Bore so the gap needs to be cut out for the ring to be compressed into the bore. Cutting the ring needs to be sandwiched because is a bit delicate.

 

[Charles Lamont]

Thinking of the 'real' Rocket man- George Stephenson, I recall in my lectures billions of years ago that the sealin th pistons was achieved by the judicious use of the foreman's felt hat. This leads me on to mention the regular use in model railway circles of using graphited yarn.

Perhaps someone would care to enlighten me of the confusing disparity in the two well established systems.
Thank you

norman

Pistons were packed with hemp until John Ramsbottom of the LNWR invented metalic piston rings around 1850 - therby greatly reducing the frictional resistance of the engine.

 

[Andy Munns]

We have turned rings oversize and then cut a bit out - Works for steam/display engines, but gives irregular wear. For essential applications like main engines or boiler feed pumps we use Harringtons in Melbourne - They premachine close to size, then cut + expand in clamp, then heat to set. Then compress in a clamp and finish grind to exact bore. Harringtons require a poker gauge to be mailed to them to avoid errors in micrometer reading. Our machinists can do this work, but we still buy these critical components in.

Also, many of our steam pistons have built-up pistons and the traditional term 'junk ring' is still used.

 

[goldstar31]

Good Morning Charles. Thank you for your observations but I was 'in vacant or in pensive mood' Nothing moreI On my bookshelf is a copy of LBSC's book 'Mabel' a 3.5" and she had/has graphited cylinders both in cast iron and gunmetal. Again, my long gone Gauge 1 Flying Scotsman had no rings and further back in my childhood, I had several little oscillating engines running- some professionally made and others brought in in brass by my father- again with no rings.
Into a more adult phase, I seem to recall that compression ignition engines made by Mills Bros, ED and so on were 'ringless'
Howver, I did build A Series engines and had them over-bored +60 thous and worn standard ones with pistons re- machined to increase the land size to take up the wear.

Merely a glimpse in old age before 'secomd childhood and mere oblivion'

Thank you and my Best Wishes for Christnas and hopefully a Better New Year to All

Norman

 

[Vietti]

Interesting thread. I have made lots of rings with variable levels of success.

I was curious if anyone can comment on the Edwards slotted oil ring detailed above. I wonder if it really helps with stopping oil getting by the rings? Clearly used in many full size engines. I built B. R. Tite's Hermes and broke one of the slotted oil rings he provided. I remade one sans the oil grooves and really cannot see any difference in the oil coming out the exhaust. Finally I reduced the oil pressure at the pump and that worked well.

On a different engine I have oiling issues and Paul Knapp suggested either 60 or 70 weight oil and that seemed to help. Apparently this is what they used in old Harleys.

Thanks, John

 

[lantain1982]

Andy Munns has hit the nail on the head. The only way to end up with a round ring is to machine the ring over size in the first instance, split, heat treat. compress in a sliding sleeve to the original turned size and then machine/grind to your exact bore size.
Gap to suit. The process involves some extra tooling but the end result is a "round ring" Following Prof. Chaddocks writings will ensure success.

 

[ajoeiam]

Andy Munns has hit the nail on the head. The only way to end up with a round ring is to machine the ring over size in the first instance, split, heat treat. compress in a sliding sleeve to the original turned size and then machine/grind to your exact bore size.
Gap to suit. The process involves some extra tooling but the end result is a "round ring" Following Prof. Chaddocks writings will ensure success.

http://users.tpg.com.au/agnet/make piston rings.html
I think this is the document being referred to in the quoted text.
Please advise if it isn't!

 

[a41capt]

http://users.tpg.com.au/agnet/make piston rings.html
I think this is the document being referred to in the quoted text.
Please advise if it isn't!

I use this method with great success, including the use of a small die grinder in my tool post during the cutoff phase of the work. Tensioning the rings with the rod and torch method works very well, but caution must be used to ensure even heat application. A standard plumbing type torch head doesn’t provide a wide enough flame to cover the entire ring and gives uneven heating causing egg shaped rings when they drop free. Found that out the hard way! I now use a “weed burner” head purchased at a local hardware store, and/or a rosebud head with my oxy/acetylene torch.

After that egg shaped event, I always cut at least 2 times as many rings as I will need!

John W

 

[lantain1982]

The article quoted by ajoeiam is not the Prof. Chaddocks edict. It seems to deal with larger size rings and in my experience not necessarily appropriate to rings of 0.040 x 0.060" sections which we may be dealing with. The article is an good read.

May I suggest Google :- Prof.Chaddock/TomWalshaw/piston rings for IC engines. There you will find a comprehensive section on these two gentlemen`s thinking and concepts. A second article can be found in the Model Engine Maker forum by
Steamer5 on January 22, 2014 titled Making Piston Rings. This is a lengthy document which covers a wide range of the piston ring subject. There has been many forum entries on the piston ring subject, all have something to offer and we can always learn from such explanations and experience.
In my case I found the Chaddock concepts, although requiring tooling for varying bore sizes depending on the model one is making, has given me a "round" ring with good initial sealing properties leading to an anticipated engine performance.
For others do what suits you best. Open discussion always a good thing.