# Making cast iron piston rings



## nx06563 (Dec 11, 2014)

I know this subject has been hashed over a million times but I have a question that I haven't been able to find an answer to. 

Will making a cast iron piston ring to the relaxed size od and the proper thickness (size that will fit the cylinder bore and piston when compressed with proper gap), then heat treating while the ring is still unbroken, and then grinding the gap in the ring make a good ring.

I am building a .750 bore twin (Dale Diertich's design) and thinking of turning the rings to an OD of .812, heat treating, then cutting a gap of about .200 in the ring. When compressed the ring should fit the bore with a .005 gap.

The advantages I see in doing this is that the ring starts out perfectly round and the chance of warping when heat treating is greatly reduced.

What do the old pro's think- anyone ever done it this way?


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## Swifty (Dec 11, 2014)

For some unknown reason, my reply to the post below has jumped the queue and become the first post, I have deleted the content and answered below the original post.

Paul.


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## Swifty (Dec 11, 2014)

The purpose behind "heat treating" is to set the ring in the sprung open position, nothing about making it any harder. So heat treating the ring before splitting does nothing. (NOTE: I am assuming that you are making cast iron rings.)

If you turn the rings using your method, when compressed to fit in the cylinder, they will not seal as they will be distorted.

The general method is to machine the rings to the Dia. of the cylinder, split the ring, in the case of cast iron, it can be cracked, hold them open a set amount whilst heating them and they will then remain sprung open. When in the bore they will close down to suit the dia and seal all the way around (in theory)

Paul.


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## gus (Dec 11, 2014)

I am with Paul. He is my DIY C.I. Piston Ring Meister.th_wav:bow:
By now we have DIY many Piston Rings and all were good and gave us good compression.


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## nx06563 (Dec 11, 2014)

THANKS for the response.  I was afraid I would get the answer I got.  I was just looking for a quick and easy way to make rings.  As you can tell, I hate making rings as I have not had great luck in the past.

 Here we go again---- guess I better start out making about 10 to start with!


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## Piston_Broke (Dec 11, 2014)

I make my rings similarly, matching the ID of the cylinder. When I split them I have found a good way to go is to sandwich the ring between two pieces of thin hard board(pegboard material, 3/16" thick) and use a thin slitting saw to open them. I have not shattered any since I've been doing it this way. Good luck!


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## Swifty (Dec 11, 2014)

I cracked my piston rings by putting them one at a time on a morse taper of suitable size, and then tapping them down with a piece of tube. They then cracked at, what is in theory, the weakest point, this worked well. They were the first piston rings that I made, I only needed two, but made five, I still have not broken one yet. Once cracked, I held them open on a fixture where they were all clamped together, and then "heat treated " them. I then gently filed the opening to give me 0.10mm (.004") gap.

Paul.


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## tornitore45 (Dec 12, 2014)

> The general method is to machine the rings to the Dia. of the cylinder,  split the ring, in the case of cast iron, it can be cracked, hold them  open a set amount whilst heating them and they will then remain sprung  open. When in the bore they will close down to suit the dia and seal all  the way around (in theory)



That is the "classic" way but...
Notice the parenthetical quote: In theory

If we applied the theory to a 454 Chevy the resulting error from using the OP suggested method would be enough to burn oil and loose compression.

Scaled down to model engine size and considering all other irregularities is hard to say whether the error amounts to anything to worry about.

That said I was at the Cabin Fever show last year and met with a well known old craftsman exhibiting exquisite model engines and got to talk.

He told me add to the bore circumference the (relaxed gap - the working gap) divide by Pie an that is the OD for your ring.   Machine away the relaxed gap.  Done.

This is heresy, right?   Except it work just fine, after a short run in good compression no oil burn and on inspection the ring show axial wear marks all around indicating they contact with the cylinder.

Is the pressure constant all around? I do not know, and I doubt it make much difference.    On the other hand, the owner of that old Chevy engine may care about going 3000 mile before being down a 1/4 or the life between ring jobs.


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## Swifty (Dec 12, 2014)

Mauro, using the method that you have mentioned, if my bore is 20.00mm, my relaxed gap is 1.0mm, and my working gap is 0.10mm, I come up with a ring OD of 20.286mm. When compressed into the bore, there is no way it will seal all around, even if I could get the ring into the bore in the first place.

Perhaps the formula is more applicable to larger size bores in real engines. I'm not saying that there is anything wrong with using that formula, but we are making rings for model engines. There are other methods as well of making rings, as others have shown on other engine builds.


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## nx06563 (Dec 13, 2014)

I think I will try Mauro's method which is basically what I proposed without the heat treat and see how it goes.  I have found that as a rookie every additional step in the process adds to the FUF (foul up factor)..

 Next question..

 In my youth I raced methanol burning two cycle outboards (PRO).  Our engines used "L" shaped rings that fit at the very top of the piston with the L riding in a groove just below the top surface of the piston.  They had very little compression till you got ignition and cylinder pressure which forced the ring outward to seal.

 Has anyone tried this type of design?  If so what were the results in a model engine.

 Thanks for the great input.  

 HOgan


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## Brian Rupnow (Dec 13, 2014)

There are two or 3 ways to make cast iron rings, and they all are "correct". I have failed miserably at all of them.---Good Luck!!!.


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## tornitore45 (Dec 13, 2014)

Swifty, I believe you missed the step of machining away the working gap, in my explanation.Then your 20.286 ring will miss a 1mm of metal and compress into the 20mm bore an leave 0.1mm gap.


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## tornitore45 (Dec 13, 2014)

> I have failed miserably at all of them



Patience and practice, my friend.


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## Swifty (Dec 14, 2014)

tornitore45 said:


> Swifty, I believe you missed the step of machining away the working gap, in my explanation.Then your 20.286 ring will miss a 1mm of metal and compress into the 20mm bore an leave 0.1mm gap.



Hi Mauro, I will go back and check it out, thanks.

Paul.


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## Bentwings (Jul 26, 2020)

This is called a Dykes ring with the step. In the race car motors the pistons have the reverse of the step.  Combustion pressure seals the rings as you noted. There are variant that add a filler ring to the step too. Often these are chrome faced for wear. The fuel motors have very poor lubrication due the huge amount or fuel being pushed into the cylinder.as a rule they don5 wear the cylinder out before they are worn out.generally cast second rings with hard moly coating are used again these don’t wear out before they are burned by combustion temps. These are very brutal motors. Often a full set of pistons and rods are replaced per run. If a crank lasts 5 runs it’s tossed in the dumpster.8,000 bucks + for one.


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## WOB (Jul 27, 2020)

I have made about 50 cast iron rings for 1" cylinder bore using the George Trimble method as detailed in SIC Magazine.   The learning curve was a bit steep but once I  began to follow the instructions exactly as George wrote them, I had good success.   Shortcuts are bad.  Critical needs include good quality, homogeneous cast iron rod,  accurate machining with the final ring OD a mirror finish.  NO BURRS on the ring edges after slicing them off the finish machined tube.   Hand polished( 600 grit diamond bench stone) ring sides with ring thickness uniform and about .0005-.001" less than the ring groove width.  A temp controlled furnace is a helpful, but not essential.   The ultimate test is to insert a finished bare ring in your cylinder bore and hold up to a bright light.  Any light showing at the ring edge means you did something wrong.   A little light at the ring gap is proper since the test is at room temp.    Make at least 20% extra rings since even the best cast iron is not perfect and you will get an occasional broken ring on installation.    I break my rings with a small flush cut wire cutter with sharp jaws used on circuit boards.  The tiny distortion at the ring end is removed when polishing the ring sides and hand filing the correct ring gap.


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## johwen (Jul 28, 2020)

WOB said:


> I have made about 50 cast iron rings for 1" cylinder bore using the George Trimble method as detailed in SIC Magazine.   The learning curve was a bit steep but once I  began to follow the instructions exactly as George wrote them, I had good success.   Shortcuts are bad.  Critical needs include good quality, homogeneous cast iron rod,  accurate machining with the final ring OD a mirror finish.  NO BURRS on the ring edges after slicing them off the finish machined tube.   Hand polished( 600 grit diamond bench stone) ring sides with ring thickness uniform and about .0005-.001" less than the ring groove width.  A temp controlled furnace is a helpful, but not essential.   The ultimate test is to insert a finished bare ring in your cylinder bore and hold up to a bright light.  Any light showing at the ring edge means you did something wrong.   A little light at the ring gap is proper since the test is at room temp.    Make at least 20% extra rings since even the best cast iron is not perfect and you will get an occasional broken ring on installation.    I break my rings with a small flush cut wire cutter with sharp jaws used on circuit boards.  The tiny distortion at the ring end is removed when polishing the ring sides and hand filing the correct ring gap.


johwen from down under. I follow the George Trimble method exactly as this is very close to the way auto rings are made. The difference I apply is to halve the width of the ring and then place two rings in each groove with the ring gaps 180 degrees a part. This gives full compression once the rings have slid up and down the bore a couple of strokes. The important thing I found was the heat treatment process was to follow his recommendation closely and don't rush making them. The heat treatment jig is important as you get no oxidization on the sealing surface.


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## mrehmus (Jul 29, 2020)

The only problem the folks in our club (Bay Area Engine Modelers) with Trimble's method is that George set the heat treat oven at 1400 F. That causes the iron to change. We've found that a one hour heat treat at 1100 F to work well. Hundreds of hours on V-8s, straight 4's all the way down to single cylinders seems to prove the change is OK.


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## johwen (Jul 30, 2020)

I found that if I Kept the total heat treatment jig at red heat for around ten minutes I had very usable rings that last , scaling of the surfaces as the paper wrap around the rings before closure is important to cosume the oxygen and then there was no discoloration of the ring surface. Yes I de-bur the edges as I part the rings. The other important step is the ring groove as not to make the depth only a about 5 thou deeper the the ring and around about a thou wider than the ring or in my case two rings. The sides of the groove need to be as smooth as possible as the ring must seal on this surface as well as the bore of the cylinder I don't personally polish the ring surface as a good machined surface allows a quick settle in to the cylinder bore whereas a glazed surface can take a long time. You don't want blow bye to ruin an otherwise good job. Cheers.


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## WOB (Jul 30, 2020)

mrehmus said:


> The only problem the folks in our club (Bay Area Engine Modelers) with Trimble's method is that George set the heat treat oven at 1400 F. That causes the iron to change. We've found that a one hour heat treat at 1100 F to work well. Hundreds of hours on V-8s, straight 4's all the way down to single cylinders seems to prove the change is OK.


I agree.   1100deg works better.   I had less ring breakage on installation.    My first dozen or so rings were done using 1400 deg. as Trimble recommended.   Then I started on Lee Hodgson's 9 cylinder radial where he recommended 1100 deg.   Ring survival was better; even the very fragile oil rings were relatively easy to install.


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## josodl1953 (Jul 31, 2020)

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


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## WOB (Jul 31, 2020)

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.


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## stevehuckss396 (Jul 31, 2020)

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


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## peter smith (Aug 1, 2020)

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.


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## Skipper (Dec 21, 2020)

#7 above , what is the parting cap?
skipper


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## tornitore45 (Dec 21, 2020)

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.


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## Skipper (Dec 21, 2020)

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


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## SmithDoor (Dec 21, 2020)

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 



Skipper said:


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


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## Rocket Man (Dec 22, 2020)

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.


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## goldstar31 (Dec 22, 2020)

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


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## Rustkolector (Dec 22, 2020)

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


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## tornitore45 (Dec 22, 2020)

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.


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## Charles Lamont (Dec 22, 2020)

goldstar31 said:


> 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
> ...



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.


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## Andy Munns (Dec 23, 2020)

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.


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## goldstar31 (Dec 23, 2020)

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


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## Vietti (Dec 23, 2020)

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


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## lantain1982 (Dec 23, 2020)

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.


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## ajoeiam (Dec 24, 2020)

lantain1982 said:


> 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%20piston%20rings.html
		


I think this is the document being referred to in the quoted text. 
Please advise if it isn't!


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## a41capt (Dec 25, 2020)

ajoeiam said:


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


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


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## lantain1982 (Dec 25, 2020)

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.


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## abby (Dec 25, 2020)

As Norman says most small engines do not have rings or have labyrinth seals but with double acting steam engines the piston is very thin when compared to an IC engine and some form of ring or seal is necessary.
I am building Gauge 1 (1/32nd scale) British pattern locomotives with 1/2" bore steam cylinders.
I have used traditional graphited yarn and modern O'rings but am not completely happy with either.
The former is fiddly to apply and the latter suffers from stick-slip , ie. when stationary the O'rings grip the cylider walls rather tightly , often requiring a push to overcome this.
I have been experimenting with cast iron rings and have had some success even though the rings are so delicate that breakage is common.
 I am sure Norman and the older members will have come across Cords piston rings .
These were/are? made of spring steel and were very thin,  three rings would fit into a piston groove , the gaps being staggered at 120 deg to each other.
This configuration allowed a good seal to be restored to a bore that had worn oval.
So has anyone tried to make rings of this type ? I will try the idea out when I can find the time.
Dan.


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## goldstar31 (Dec 25, 2020)

Thank you Dan( Abby)) I as a stopgap solution to a worn ( out) 997cc Morris 1963 Mini Cooper, I did fit Cords Rings.  I was watching the over 50 year original and British version of the Italian Job where the best advertising of Mini can still be found.  Oddly, my son who is still into such things reminded me that Mini Coopers are changing hands at £20,000 whereas I paid a mere( now) £565 for mine.
As you say, Dan, Cords rings were fitted but am I correct in saying that the the worn ring channels in the pistons were re-cut and 'expanded?

I regret that it is such a long time ago that my memory may be confusing  a further 'modification' involved over boring +60 thous  scrap engine block- which cost me £10.
I can recall peening the conrods and worrying about the double springs on the re-worked 12G295 cylinder head( ex a later Mini Cooper of v998cc as opposed to my 997 version- with the long throw crankshaft.

You see I moved to dealing with my wife's Mk111 Triumph Spitfire which had SU carbs that were always going out of tune.
Really digressing, I recalled trying to buy a Seat600 which was a 'sort car version' with no roof or doors and black wickerwork seats.  It was in Menorca where I had a house( for £7500) and I was goingb to take it home as a 'Noddy Car' project for my son  and then my daughter. It would have gone home with a donor scrapper but sadly,  it is all buried in a local football field on the island.
The Best laid schemmes of mice and men gan aft tae glae. 

All that is left now is -- a model Min Cooper and a promise of van eye injection in the New Year.

I hope that the New Year brings something better for all of us


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