Gapless compression rings and oil...

Pennzoil motor oil
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SonofJoe

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Okay, so it was like this...

I was lying in the bath, thinking about pistons going up and down (like you do) and how it be a great idea if someone could just invent a better piston ring...

And then it came to me in a flash! Why not have TWO compression rings, one sitting on top of the other but fixed in such a way that their gaps didn't overlap. You would at a stroke eliminate the single biggest source of blow-by gas. Not only would you make the engine more efficient, you would get rid of the thing that does most to degrade engine oil. You would also get less carry-over of oil into the air intake so less oil consumption and less inlet valve deposits. The more I thought about this, the more ideas I had. You could have two rings of two different materials and tensions; maybe one optimised for suck and the other for blow. I was half way to writing the patent!

So imagine my disappointment when I got out of the bath only to find out on Google that gapless compression rings had already been invented. Bah!

But here's the thing. The only people that seem to be remotely interested in gapless rings are the racing fraternity looking to squeeze the last ounce of HP from an engine block. Given the automotive industry's obsession with fuel efficiency and reducing emissions, why aren't all engines built with gapless rings? Specifically why aren't GDI engines, with their various blow-by gas/engine oil related problems built with gapless compression rings?

I'm not a spanners and screw driver kinda guy so if anyone knows the answer, could you please enlighten me?
 
Yep, I used them 20 years ago in a high performance kohler I built for garden tractor pulling. Also seemed like a good idea to me, so if they aren't using them in auto engines now there must be some reason.
 
The thing that struck me as odd is that a properly designed gapless compression ring, provided it was suitably mass produced, must be one of the cheapest add-ons you could tag onto a pre-existing engine design which would/should deliver tangible benefits to power, emissions, fuel economy and oil life. Why as an OEM wouldn't you do this?
 
Oem's don't use them because they must be hand fit and that takes a bit of time.

I've heard above 6K zero gaps can induce flutter but in a marine app I didn't need to worry about 6K+.

Ran Childs and Albert zero gap secondaries, on my 500HP/500Ft lb 406 for decades.

Ran like a scalded dog and didn't use any oil.

UD
 
Originally Posted By: rooflessVW
Gapless Piston Rings.

A link for the uninitiated. Most engine with gapless rings installed are oil-burners, if I'm not mistaken. Not a daily-driver friendly part.

Gapless rings are used as compression rings, why would they cause oil burning?
 
Originally Posted By: UncleDave
Oem's don't use them because they must be hand fit and that takes a bit of time.

I've heard above 6K zero gaps can induce flutter but in a marine app I didn't need to worry about 6K+.

Ran Childs and Albert zero gap secondaries, on my 500HP/500Ft lb 406 for decades.

Ran like a scalded dog and didn't use any oil.

UD


Thanks for the info. It confirms what I thought, that these rings have the potential to eliminate oil loss. I really do wonder what would happen if you ran a cheap, all Group II 20% Noack oil on an engine fitted with these rings?
 
Oldmoparguy asks:"Gapless rings are used as compression rings, why would they cause oil burning?" The Gapless rings most of the time include Low Tension Oil control rings (not gapless) along with the top and second gapless rings. Low tension oil control rings should only be used on race type engines. NOT even for Endurance race events (12/24 hour races) They WILL let enough oil by to be a oil burning/useage issue for a long term useage.
 
Originally Posted By: ShotGun429
Oldmoparguy asks:"Gapless rings are used as compression rings, why would they cause oil burning?" The Gapless rings most of the time include Low Tension Oil control rings (not gapless) along with the top and second gapless rings. Low tension oil control rings should only be used on race type engines. NOT even for Endurance race events (12/24 hour races) They WILL let enough oil by to be a oil burning/useage issue for a long term useage.


I found a racing forum that said exactly that.

Just a thought, but why don't we have a couple of drain holes either in the second groove to dispose of oil that the scraper ring had scraped off or even a couple directly in the piston face of the third land so that if the oil control ring starts letting oil past (or even worse, sticks flush in it's groove), then accumulated oil would have a pathway to get out of harm's way?
 
but with sufficient flow by the oil control ring, that wouldn't stick as contaminants get flushed constantly? so make the drain holes in the oil control ring groove bigger?
 
I can't figure how the rings are going to compress without the ring gap. They need to be compressed to get the piston into the cylinder. After they're in the cylinder, they need to be able to expand to create the seal.
 
Gap less rings seem to be used only in all out high output engines like pro drag racing.
Don't last long IIRC. But the 3-5% horsepower increase is worth it to some builders.

there are, or were, rings that overlap at the gap, not sure if they stayed around long though.

My 2¢
 
Originally Posted By: Merkava_4
I can't figure how the rings are going to compress without the ring gap. They need to be compressed to get the piston into the cylinder. After they're in the cylinder, they need to be able to expand to create the seal.


I've never seen the real thing but in the bath I imagined two normal (but somewhat thinner) compression rings sitting one on top of the another in the same first groove. Both rings had normal gaps but the two gaps would be diametrically opposed to each other. When the mixture fires around TDC, the gas pressure gets behind both rings spaying them both against the cylinder wall but the upper ring gap would be sealed from underneath by the lower ring, blocking the usual path for blow-by escape. I sort of envisioned that with a short ridge and long trough, the two rings both be free to rotate independently of each other but only though 330 degrees because what you would want to avoid is the two gaps aligning with each other. I also had in mind that one ring might be very slightly elliptical so that as the bores distorted one ring would align itself better and provide better wall to ring sealing. Having two rings with different tensions I figured would ensure the bottom of the top ring and the top of the bottom ring would flex relative to each other (a) to pull oil in to the gap to prevent wear and (b) prevent deposit build up.

I like baths. They are the perfect place to think thoughts!
 
Originally Posted By: Merkava_4
I can't figure how the rings are going to compress without the ring gap. They need to be compressed to get the piston into the cylinder. After they're in the cylinder, they need to be able to expand to create the seal.


Its an overlapping "L" on its side It still compresses but there is no real overlap.

Its better to think of as a pressure path that takes longer to leak VS "sealed" thereby giving a % or 2 cylinder pressure

http://www.hotrod.com/articles/childs-alberts-zero-gap-second-ring-test/

My rig running them make absolutely ridiculous power and torque. Big block level power.

UD
 
Last edited:
Originally Posted By: SonofJoe
I've never seen the real thing but in the bath I imagined two normal (but somewhat thinner) compression rings sitting one on top of the another in the same first groove. Both rings had normal gaps but the two gaps would be diametrically opposed to each other. When the mixture fires around TDC, the gas pressure gets behind both rings spaying them both against the cylinder wall but the upper ring gap would be sealed from underneath by the lower ring, blocking the usual path for blow-by escape. I sort of envisioned that with a short ridge and long trough, the two rings both be free to rotate independently of each other but only though 330 degrees because what you would want to avoid is the two gaps aligning with each other. I also had in mind that one ring might be very slightly elliptical so that as the bores distorted one ring would align itself better and provide better wall to ring sealing. Having two rings with different tensions I figured would ensure the bottom of the top ring and the top of the bottom ring would flex relative to each other (a) to pull oil in to the gap to prevent wear and (b) prevent deposit build up.

I like baths. They are the perfect place to think thoughts!


The typical gapless rings have an overlapping "lap joint" where the gap would be...means that there's a cantilever off each end of the ring a little weaker than the main ring, and the lap joint adds friction as it tries to expand and contract to the vagaies of the bore.

That which you invented in the bath has been done in a couple of configurations.

Simply two narrow rings has been used.

Another was an "L" shaped ring (the base of the L against the bore), with a smaller "filler" ring that fills in the void of the L.
 
They make them for lots of applications. Local shop I know of used Total Seal rings in a high compression BMW M20 with ITB's and it makes plenty of power.
 
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