Piston rings?

[GreenTwin]

It looks like the price of gray cast iron bars is way up; like many things.

I would price out the same piece at McMaster, Speedy Metals, and Online Metals, and be sure to include shipping, and find out which is the cheapest.
Some places will nail you on shipping.

May be worthwhile to check on ebay too.

.

 

[peterl95124]

While on the topic of material, how's the gray cast iron from McMaster Carr found here?

McMaster says "conforms to ASTM A247" but that standard covers everything from flake graphite to nodular graphite and everything in between, since they aren't being specific I would not touch the stuff, flake graphite is desired in our applications for its gall-resistance and self-lubricating properties.

 

[NapierDeltic]

One question:
Controlled mechanical permanent deformation cannot replace heat treatment for obtaining constant pressure ring-liner all-around?
I know that there is no procedure for such equivalence and no one would waste time for it.
Cast iron has a reduced degree of malleability - which is there anyway.
At the lower end there would be axial punches with variable force on the inner rim of ring.
On the higher end would be integration so continuous axial compression on inner side of ring with variable compression, higher at the ring edges. Deformation should be tapered -like a steel ball pressing the ring -but slightly off-center towards the ring cut . Pressing could be done before ring cut -just to prevent additional stress and unwanted behavior. It should affect only less than 30% from ring's height, on the inside piston groove. Compressed material should induce side tensions - ring opening.

 

[peterl95124]

One question:
Controlled mechanical permanent deformation cannot replace heat treatment for obtaining constant pressure ring-liner all-around?
I know that there is no procedure for such equivalence and no one would waste time for it.
Cast iron has a reduced degree of malleability - which is there anyway.
At the lower end there would be axial punches with variable force on the inner rim of ring.
On the higher end would be integration so continuous axial compression on inner side of ring with variable compression, higher at the ring edges. Deformation should be tapered -like a steel ball pressing the ring -but slightly off-center towards the ring cut . Pressing could be done before ring cut -just to prevent additional stress and unwanted behavior. It should affect only less than 30% from ring's height, on the inside piston groove. Compressed material should induce side tensions - ring opening.

grey cast iron is not malleable, it does not deform, it breaks.

There's only two ways I know of to make a grey cast iron ring, either the "hot" method of Trimble where a ring is machined to fit exactly in the bore and then spread and heated to set that new shape, or the "cold" method where you calculate what the diameter and spread gap are for the fully formed Trimble ring and machine to that, I've tried the latter but it requires so much lapping to pass the "light test" that the ring depth isn't even around the circumference (the lapping takes away a lot of material near the gap), and I've even tried to compensate for that but haven't been very successful at that either (I have made a set that way for my Duesenberg, we'll see if or how well they work eventually and I'll let you know...)

 

[Nerd1000]

McMaster says "conforms to ASTM A247" but that standard covers everything from flake graphite to nodular graphite and everything in between, since they aren't being specific I would not touch the stuff, flake graphite is desired in our applications for its gall-resistance and self-lubricating properties.

I have had plenty of success with a ductile iron cylinder and grey iron rings. I suspect the reverse configuration (ductile rings, grey liner) would also work, and grey iron for both rings and cylinder certainly does as demonstrated by automotive practice. I don't think ductile iron rings would work against a ductile iron cylinder or a steel cylinder... Not without some sort of anti friction coating like they use on modern automotive rings anyway.

 

[peterl95124]

I have had plenty of success with a ductile iron cylinder and grey iron rings. I suspect the reverse configuration (ductile rings, grey liner) would also work, and grey iron for both rings and cylinder certainly does as demonstrated by automotive practice. I don't think ductile iron rings would work against a ductile iron cylinder or a steel cylinder... Not without some sort of anti friction coating like they use on modern automotive rings anyway.

I agree, IIUC automotive is mostly steel and steel, these things obviously can be made to work, so I think the reason we hobbyists tend to use grey-cast-iron when we can is that its more forgiving, CI is the only known metal that doesn't gall with itself and is somewhat self-lubricating, for us its maximizing success in spite of things like less-than-perfect oil pumps, and like you said no access to high tech coatings.

I'm sure you're right about ductile iron against grey iron, probably work fine, just be sure they're adequately lubricated. In deed most of my IC engines to date have steel liners rather than CI because they're scale models and there's not enough room for an adequately thick CI liner so I use thin 4130 steel, and as a consequence use pre-mix 2-cycle fuel in my 4-cycle engines to keep the CI rings lubricated against the steel liners just in case (at least one of them has chronic low oil pump pressure) !!!

 

[petertha]

On the Durabar site, they reference G2 as 'built around ASTM A48 Class 40 gray iron'. Now how exactly that compares to other grades of Class-40 gray iron with even less information is rather cloudy. The ductile irons are a different group designated by prefix 60,65,80,100 series.

But I wanted to draw your attention to their heat treating section, link below. They show 2 modes; annealing & hardening. My interpretation (maybe wrong) is you can do either from the same reference temperature. The difference is what you do AFTER it has reached temperature. According to their definitions, if you allowed it to cool naturally inside the oven, that would equate to annealing or stress relieving mode. OTOH if you accelerated the cooling rate by quenching, that hardens the material to the corresponding hardness values. But only if heated above 1100F just eyeballing the graph.

Trimble never mentions hardening, he said ANNEALING and referenced 1475F. He said 'they don't have to soak at that temperature but they have to get that hot'. This temperature level on Durabar G2 would put it into the subcritical anneal temperature. 1100F corresponds to what they call stress relieving zone. But of course, without knowing his particular material reference specs, its relative guesswork. Maybe this type of graph exists for some of the gray iron varieties we have discussed. Once upon a time I went looking but did not find anything quite as simple. If you have anything, it would be interesting to compare.

Durabar references an (annealing) soak temp of 1300-1400F for 1 hour/in2 of cross section, then furnace cool to 650F. That temperature kind of goes round with Trimble (but again maybe just coincidental without more material data). Just to put numbers to a single model ring for a 1" bore: (0.043" radial thickness x 0.023" axial thickness) = 0.00097 in2 cross section area. Even a stack of 10 in a heat set fixture would be less than 1% of 1 square inch section area. I'm not sure if or how this scales to a shorter allowable soak duration, its probably not that simple. BTW I'm not challenging the wisdom of others, just mentioning FWIW.

https://www.dura-bar.com/getmedia/5cf7c409-fdce-4861-b2b7-770c942368b1/heat-treat-guide-0719.pdf

 

[peterl95124]

Petertha, great research !!!, Trimble is *correct* in saying you want to *stress relieve* the ring to its new shape, but he is *incorrect* about the temperature, 1100-F is the correct temperature, if you go up to even 1200 you risk annealing the ring and it will be too soft. as Mike Rehmus, myself, and others can attest to by experience. your research seems to confirm this. (ps, AFAIK no one quenches their rings, they are either sealed inside stainless foil to avoid surface oxidation, or sealed inside a fixture for the same reason). HTH, IMHO, YMMV, VWPBL, yada, yada, yada...

 

[Nerd1000]

On the Durabar site, they reference G2 as 'built around ASTM A48 Class 40 gray iron'. Now how exactly that compares to other grades of Class-40 gray iron with even less information is rather cloudy. The ductile irons are a different group designated by prefix 60,65,80,100 series.

View attachment 158660

But I wanted to draw your attention to their heat treating section, link below. They show 2 modes; annealing & hardening. My interpretation (maybe wrong) is you can do either from the same reference temperature. The difference is what you do AFTER it has reached temperature. According to their definitions, if you allowed it to cool naturally inside the oven, that would equate to annealing or stress relieving mode. OTOH if you accelerated the cooling rate by quenching, that hardens the material to the corresponding hardness values. But only if heated above 1100F just eyeballing the graph.

Trimble never mentions hardening, he said ANNEALING and referenced 1475F. He said 'they don't have to soak at that temperature but they have to get that hot'. This temperature level on Durabar G2 would put it into the subcritical anneal temperature. 1100F corresponds to what they call stress relieving zone. But of course, without knowing his particular material reference specs, its relative guesswork. Maybe this type of graph exists for some of the gray iron varieties we have discussed. Once upon a time I went looking but did not find anything quite as simple. If you have anything, it would be interesting to compare.

Durabar references an (annealing) soak temp of 1300-1400F for 1 hour/in2 of cross section, then furnace cool to 650F. That temperature kind of goes round with Trimble (but again maybe just coincidental without more material data). Just to put numbers to a single model ring for a 1" bore: (0.043" radial thickness x 0.023" axial thickness) = 0.00097 in2 cross section area. Even a stack of 10 in a heat set fixture would be less than 1% of 1 square inch section area. I'm not sure if or how this scales to a shorter allowable soak duration, its probably not that simple. BTW I'm not challenging the wisdom of others, just mentioning FWIW.

https://www.dura-bar.com/getmedia/5cf7c409-fdce-4861-b2b7-770c942368b1/heat-treat-guide-0719.pdf

View attachment 158661

The iron I use is Chinese made, grade FC250 which I understand to be a Japanese standard about the same as class 40. So it should be quite like dura-bar.

I just flame mine with a torch to red heat briefly, then allow to air cool. In fact I don't even use a fixture, I just spread the ring over an appropriate sized pin held in a vise.

Seems to work so far, though I do have a fair % of rejects. Usually make 2x as many rings as needed and end up with a few spares.

 

[Aerostar55]

Hi everyone,

I've been planning on building an IC engine for a while now. I've done some pretty extensive research, but I can't seem to find any of the specifics of doing the Trimble method. I know I need to cut them on the lathe, polish, and cut them (I know there was a tool that could be made for better consistency, but I can't find any info on it) and then place them into some sort of fixture to hold them open and not allow oxygen in. I can't find anything about this fixture either. Then, they need to be heated to 1100°F and air cooled.

If I'm missing anything else, please let me know. This is the only step in the build that would hold me up. All info is appreciated.

Thanks!

Jason

Jason:
Don't get too hung up on piston rings. Every time someone mentions them in a thread it blows up. I've built engines and skipped the piston rings just to see if it would run> (it did). Making the rings is not magic. The Trimble method is excellent, but you can make them
and heat treat them one by one. The Atkinson Cycle engine book by Vincent Gingery takes the reader through a step-by-step method of making piston rings for a 1 1/4" bore aluminum piston. The book is still available from Gingery publications.

 

[Lloyd-ss]

@pyro I think you can see that the subject of making piston rings is quite provocative, with more chance of failure than success (IMHO).

Figure out what size ring you need before you start building your engine and do a google search for the rings. You might not find exactly the size you need, but at that early stage you can adjust your design to fit something that is readily available. And you can find them pretty cheap. Seriously, no problem.
Buy the rings and save all your blood, sweat and tears for making the camshaft.
Lloyd

 

[Aerostar55]

@pyro I think you can see that the subject of making piston rings is quite provocative, with more chance of failure than success (IMHO).

Figure out what size ring you need before you start building your engine and do a google search for the rings. You might not find exactly the size you need, but at that early stage you can adjust your design to fit something that is readily available. And you can find them pretty cheap. Seriously, no problem.
Buy the rings and save all your blood, sweat and tears for making the camshaft.
Lloyd

DeBolt machine has model engine piston rings for sale on Ebay, I have used them and they are pretty good.