Making cast iron piston rings

[nx06563]

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?

 

[Swifty]

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.

 

[Swifty]

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.

 

[gus]

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.

 

[nx06563]

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!

 

[Piston_Broke]

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!

 

[Swifty]

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.

 

[tornitore45]

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.

 

[Swifty]

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.

 

[nx06563]

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

 

[Brian Rupnow]

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!!!.

 

[tornitore45]

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.

 

[tornitore45]

I have failed miserably at all of them

Patience and practice, my friend.

 

[Swifty]

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.

 

[Bentwings]

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.

 

[WOB]

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]

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.

 

[mrehmus]

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.

 

[johwen]

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.

 

[WOB]

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.