Making Piston Rings

[MachineTom]

The plans I have show the piston rings CI at .045" over bore, then cut and a lap joint made, the inner dia is offset, resulting in a taper in wall thickness, from .032 to .062. My idea is to turn them .045 over, mount them in a fixture and and compress the ring, then turn to true bore size.

Any thoughts, experience on the choices.

 

[rklopp]

I use the George Trimble method with great success. It goes as follows: (1) machine a tube to net cylinder bore diameter & part off rings. (2) Grab rings with a shouldered internal expanding collet and finish to width and chamfer inside corners. (3) Crack rings and knock off the high spots on the fracture surfaces with abrasive paper or a needle file, but don't take out any more material than necessary. (4) Spread the rings with a rod in the gap and anneal to set the shape. (5) File the gaps, checking in a cylinder. (5) Install. Trimble's articles in Strictly IC give formulas for the gap rod diameter and plans for a guillotine for cracking the rings and a retort for minimizing scaling during the annealing step. I recommend you make a bunch of extras, because not all will crack nicely, and some might break during installation.

 

[MachineTom]

I neglected to state that the engine is a steamer, not IC. Real steamers used lap joints in the rings, and the plans call for the same.

Thanks for the info.

 

[stevehuckss396]

Any thoughts, experience on the choices.

I use the GT method also but I have a friend who does his rings the way you are proposing with much success. Just use care when installing the rings because they are soft and can loose there shape. I made some 5/8 rings and they bend very easy.

 

[Metal Butcher]

I'm machining my .750 rings .003 larger than the cylinder bore (.753). Then saw cut .010" wide, wedged open .112" and they will be annealed at 950 Fahrenheit.

-MB

 

[stevehuckss396]

I'm machining my .750 rings .003 larger than the cylinder bore (.753). Then saw cut .010" wide, wedged open .112" and they will be annealed at 950 Fahrenheit.

-MB

Just curious MB, why size the OD to +.003 and not right to size? When I anneal my rings, they clean up nicely with a soft rag. Does the size of the part change with the heating process?

 

[doc1955]

Here is the process I have used and have had excellent results it was featured in a HSM mag a long time back.

First off take your final cylinder bore size calculate and find the circumference 3.141x diameter +the width of your silting saw you use to split your ring then take that and divide it by 3.141 that will give you your diameter to start with.

Once you have your ring made to put some spring into it I split with a spacer block and lay it on a piece of steel for a backing plate. Now take a small torch and aim the flame at the center and slowly move closer to the backing plate and let the flame bounce off it and heat the ring up to a nice dull cherry red. Let the ring air cool and if you kept the torch close to center as you moved closer you will end up with a nice round ring once compressed. I have done this quite a few times and have never had any trouble with out of round rings.

I can look back and see which mag had the write up it was a long time back but I know I have it I have never goten rid of any of my back issues.

 

[Maryak]

Real steamers used lap joints in the rings, and the plans call for the same.

Some do some don't. One thing that is fairly common in steam engines is to use 2 Ramsbottom rings in 1 ring groove.

This is the method I use for making rings - no heat treatment, however the material must be spun cast iron.

http://www.homemodelenginemachinist.com/index.php?topic=5060.msg85208#msg85208

http://www.homemodelenginemachinist.com/index.php?topic=5060.msg86453#msg86453

http://www.homemodelenginemachinist.com/index.php?action=dlattach;topic=5060.0;attach=7698

Hope this helps

Best Regards
Bob

 

[Metal Butcher]

Just curious MB, why size the OD to +.003 and not right to size? When I anneal my rings, they clean up nicely with a soft rag. Does the size of the part change with the heating process?

In fact cast iron will grow when over heated (eye balled red color? 1400-F) using the torch method. Rings annealed with an uncontrolled method like a propane torch will grow in size, and this may be the factor behind the success rate using this method for making model rings. The cooling rate is impossible to control so any method out side a heat treating furnace adds to the ring-to-ring variances. I heard it said that some rings come out good, and some bad. Torch heating is the method used by most, and is considered to be a good method. By oven annealing just past the 750-F critical temp this growth won't happen and there is no scale to clean up, no hot spots that my be a contributing factor that causes rings to fracture, and all the rings will be uniform through out.

.003 over bore diameter is specified on my plans. The oversize will cover the outward pressure lacking at the split and the opposite end due to the way the ring is spread (wedged outward, but not outward at-and-opposite the split) This pressure will be lacking in a ring sized to exact bore dimension unless the critical temp is exceeded. However all of this is theoretical and needs proofing.

-MB

 

[b.lindsey]

Here's another possible method that worked very well for me. Nice perfectly round rings with no heat treating at all.
http://www.homemodelenginemachinist.com/index.php?topic=6014.msg103346#msg103346

Bill

 

[putputman]

Bill, that is the exact same process I use to make rings. I use the cast iron from McMaster Carr. Not sure it is the right iron to use but it works most of the time.

So far I have experienced about a 50% yield for good rings. I think all of the rings are machined true but when I install them on a piston, I suspect that they get slightly distorted on the surface opposite the gap. It only takes a very small distortion to prevent a good seal.

I saw a tool on another post that someone uses to install their rings. It looks like it should prevent some of the problems I am creating for myself.

I generally run the engines for about an hour driven by an electric motor to ware the rings in.

 

[MachineTom]

Thanks for the replies. Seems the compress and turn to size will be my plan. More when it happens.

 

[Ken I]

A trick tempering / annealing method for small parts.

Take a steel tray (an old tin can will do) filled with sand, heat it with a blow torch. Gauge the temperature from a piece of wire dipped into the sand until you get the colour you are looking for. Immerse the small parts in the hot sand and allow to cool.

If you need to go to high temperatures for annealing you can use carborundum instead of normal sand.

On a small scale (ie using a tin can or small metal pot) - you can introduce propane at the bottom and let it percolate through the sand and burn off at the top (this is not the heat source) where you must keep it lit (you don't want red hot propane leaking out) - you now have your own reduction atmosphere furnace.
Don't try this on anything bigger than a tin can or in an oven because of explosion risks. You start with the propane running - you can't add it to hot sand (POOF) and you have to keep the propane (reduction atmosphere) flowing and burning off at the top until the vessel has cooled to below ignition temperature.

A reduction atmosphere furnace uses a propane or cracked amonia atmosphere to burn off any oxygen and thereby prevent scaling. Reduction atmosphere furnaces are potential bombs - all entryways and leakage points are "gaurded" by pilot light flames to ensure leakage is burned off. I know this is kind of wierd but you prevent it from blowing up by lighting it.

Ken

 

[Lew Hartswick]

What ever happened to the old way of making a ring to the right size and fracturing
it "at one point". That is what I as always told was the way auto piston rings
were made.
...lew...

 

[doc1955]

What ever happened to the old way of making a ring to the right size and fracturing
it "at one point". That is what I as always told was the way auto piston rings
were made.
...lew...

Fractured expanded and the heat treated in a controlled atmosphere then during installation they need to be gaped. I have never tried to fracture one I just figure out the length on the circumference add in the slitting saw width expand and heat treat unfortunately the heat treat I do isn't a controlled atmosphere but it has worked for me many times without fail.