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Piston rings?

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doby303uk

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A quick question my old (must be 12 yearsish ) irvine .21 ABC engine used piston rings, never seen a mention of piston rings anywhere over the last couple weeks of returning to the scene?

would be cheaper than replacing piston and liner
 
strange not one reply, a piston ring would good me thinks, could help increase the life of the engine and also help keep the compression of the engine more constant at all temps, also cheaper to replace
 
I think you haven't gotten a reply b/c many of us aren't familiar with piston rings. Maybe you could post a pic and then someone may be able to help you.
 
Weird... even my decade old Magnum ABC .21 engine doesn't use piston rings..

Thomas
 
sorry guys no pics ill try to discribe, a piston ring a a thin springy circlip like piece of metal that sits in a groove near the top of the piston, this springy circlip expands to make the seal between the piston and liner, all parts will wear but the piston ring will take the most, i think this would help prelong the engines compression and performance also making it more constand.

piston rings are used in most engines today i think :)

anyway i think a ring would be a good idea, and me wonders why they no use anymore?
 
I follow now. I didnt realize they used the same piston rings as are in a 350 big block. But now I understand fully your concept. I think the main reason would be because of how high of a tolerance these parts are machined with today. Not to mention, most ABC constructed piston/sleeves are made out of those materials for a reason. Primarily for expansion and longevity. The entire piston is machine so tight that they are extremely difficult to break in and the brass sleeves are made to expand when hot. The avg. running temp being around 200 and moving tep 250-300. Just enough to expand it for awesome compression. With the excessive RPM's added is where the wear and tear come in to play (some times excessive heat causes over expansion as well but thats usually poor tuning). With the addition of a piston ring combined with those RPM's I would expect the same wearing result. I could be wrong, but thats just my opinion. The ring would only be 1/2 a mm at most and the piston itself it 10-15 mm??? Know what I mean or am I way off base?
 
thats about right, i and a m8 came to 2 conclusions as to why they not use any more,

1. like u said materials used, would the thin fragileish piston ring be able to take the beattings given from a top race spec engine of today? but they did then, no sure about my old irvine specs, RPM?

2. to help keep the maintence of the engine more expensive, making more money on the fly for the engine companies etc.

i may have to agree with the first option the materials, me thinks a little more research is need on the history of the nitro engine. i give that a try tomorrow, i have limited acces via my local library at the moment? spaent all me money on that blasted car :D fooking buggy shaped doorstop for the moment :(
 
Originally posted by doby303uk

piston rings are used in most engines today i think :)

anyway i think a ring would be a good idea, and me wonders why they no use anymore?
Click to expand...

That is correct... every engine in a full sized car uses piston rings today. And not only one, but mostly 2 or 3. While the top ring is for compression, the lower rings are there to keep the oil out of the combustion chamber.

Thomas
 
I don't think a piston ring would last long in todays' race engines. At 30K+ RPM that ring would probably unseat/disintigrate fairly quickly.
Piston rings are fairly common in the RC airplane world though. Almost all four strokes have a ring. But the airplane four stroke engines are designed with about a 10K RPM limit. There are some ringed two strokes. But they top out at around 16K RPM. That's not even close to the stress of our car engines. The only ringed car engines I know of that are in production are the OS four strokes. With a top of 18K-20K RPM I think they are about pushing the limit for a ringed piston.

Tex
 
The most detailed info I have seen is in the Ultimate Nitro Tuning Guide book by Airage media. According to that, ABC (aluminum, brass, chrome) engines can rev much higher than a ringed engine, 2-3 times higher. The rpm limit has something to do with the ring moving back and forth through the required clearances in the piston groove. Ringed engines are still common for model aircraft engines, which are limited to about 15,000 rpm by the propellers. So ABC is an advantage for making power in a car, the drawback is more critical break-in.

This book also describes what it calls the ultimate break-in procedure: Mount the engine to the bench with a small airplane prop, (7"x4"). Warm the cylinder to 200F with a heat gun. Start and run wide open at a rich, but not 4-cycling mixture for 1 minute, checking mixture to maintain 210-230F. Then stop and wait for it to cool completely down. Repeat 5 times then go to 2 minute runs, then 3 until 45 minutes total run time. Te secret is to keep the engine hot.

I know it sounds shocking, but it makes sense, even though it is the complete opposite of what we have thought was right for the last 15 years. The book says it is a mistake to run a new engine cold, because the cylinder will not expand enough, causing excess wear on the parts, and leading to low compression too soon. Another mistake is running too rich, to where the engine "4-strokes".

You know how hard it is to pull start a new engine? That is because of the cold cylinder and too little clearance. Try warming a tiught engine up with a hair dryer or heat gun, and you will be amazed. I have tried this breakin, and it does work (I did it to my boss's Picco .26 first, rather than risk my own engine!). The Picco has 1/2 gal of 30% through it, and has awesome compression and is insanely fast. If that technique was a mistake, that new engine would already be toast. Give me a minute and I will post a photo.

OK, here is a photo of my breakin setup. The tape around the head is there to help maintain a run temp of at least 210F.

https://www.rcnitrotalk.com/gallery/showphoto.php?photo=2789&papass=&sort=1&thecat=500
 
I don't know if any of you are aware of this, but the new HPI .25 engine uses an oil ring on the piston...

746044hpiengine.jpg
 
Hey Scott, that setup looks really nice. Never thought of breaking in an engine like that. It sounds so interessting, I'm gonna go out and look for that book. I just finished breaking in an engine, but I did it byt the book. THe book that OS included in the box :ha:
 
NCnitro, I think that is a groove, rather than a separate ring. I just looked in the .21 on a new AE monster GT and it has a groove in the same place.
 
Scott, read what it says right next to the pic of the piston.

" Aluminum Piston with oil ring"

If I am not mistaken I believe that the four stroke model engines also use rings, but I am not 100% sure on that.
 
Originally posted by NCNitro
I don't know if any of you are aware of this, but the new HPI .25 engine uses an oil ring on the piston...

746044hpiengine.jpg
Click to expand...

That looks exactly like my old Magnum .21 where there is a groove at the top of the piston. I don't know, but i can't see a ring anywhere in this picture.

Thomas
 
The airplane four strokes use a real ring. Not just a oil groove like in the S-25 picture. The piston is machined with a groove like this . And the groove has a ring like this .

Tex
 
Originally posted by scottm
NCnitro, I think that is a groove, rather than a separate ring. I just looked in the .21 on a new AE monster GT and it has a groove in the same place.
Click to expand...

Your right, it's a groove, there is a misprint on the picture or something.... A few years ago, someone did a project on their beater engines and came up with something interesting. He grooved his piston and was able to get longer life out of it. I forgot everything aready, since it's not a everyday thing(ringed rc pistons). Someone said it ACTS as a ring, but it's not.... The Thunder Tiger .70 engine on their truck also use rings, and RCCA/RCnitro did a article on it, I think it was somewhere in 02, when the truck was barely releasesd, I'm too lazy to look for it....:egad:
 

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