Gas ported piston rings

[cjshaker]

Power improvements aside, which material is best for longevity and minimum cylinder wear? Something to consider on these old blocks that have likely been bored at least once or twice in their lifespan.

[gt350hr]

  IMPE ductile iron/plasma moly/barrel face is the easiest on the bore. There are still some "economy" moly faced rings out there that can be tough on cylinder walls. Barrel faced steel rings are slightly tougher on walls than moly faced ductile iron and getting better all the time.
  Randy

[My427stang]

Here's a question, I understand the barrel faced steel requires a moly coating for an iron block, is that sacrificial and the cylinder burnishes allowing it to live?, or does the moly survive on the little oil the top ring sees?

[gt350hr]

    Ross,
      A steel ring does not "require" a moly face. There are barrel face steel rings ( T/S "AP" rings and NPR rings are made without moly , but do have a "PVD" ( plasma vapor deposition) coating on the face. The PVD is considered a break in coating. There are also steel rings with plasma moly face material. The industry is moving away from ductile iron for top ring material to steel. As this continues to happen attention must be paid to top ring back clearance. If a steel ring is .020 less in radial width as an example , "I" have seen a change in top ring seal numbers. IIRC Sealed Power ( Scott Gabrielson ) did some testing and didn't see a difference . Barry could shed light on this as he was there and I was not. Correct information is key here , and "I" could be wrong.

         Randy

[Barry_R]

As I get further away from my years at F-M my information on parts becomes more "observational" and less "factual based on engineering data".... so I am just going to list some bullet points and take them as you wish.

Top rings whether cast, ductile, or steel do not require a moly facing to function - but you probably really want one in the vast majority of applications.

I personally would not run a plain cast iron, non-moly top ring in anything this side of a lawn mower.

Moly on rings is not really a sacrificial material, but it is the material that "sees" the cylinder and thus is the material that accumulates the most wear.

Moly is hard, sort of functionally porous and wear resistant, and functions as something of a sponge for lubricant.  A moly faced ring will last longer than a non-moly faced ring in most cases.  In those cases where the base material of the ring is harder and stronger than the cylinder wall the cylinders run with moly rings will last longer.

Basic cast iron rings use moly that is applied by comparatively inexpensive wire feed.  As ring materials get stronger, more temperature resistant and more comformable the moly must be applied by plasma arc to keep it attached to the base ring material, hence most race quality rings will feature "plasma-moly" facings.

Really extreme applications can reach the point where even the plasma-arc moly application is not sufficient, and can kick the moly off the rings.  These would include high loads of nitrous or lots and lots of boost.  In these cases you have no choice but to run a non-faced, non-moly ring.  Its not that you "want" to run without the moly - it's that you can't run with it.  In these cases they are actively trying alternate face coatings in an effort to reduce ring and cylinder wall wear.  Running a uncoated ring in these high load applications will definitely show increased wear.  These are the places where you see use of PVD and titanium dioxide coatings.

The coating and alloy development is apparently coming down from diesel engine OEM technology, where extremely high cylinder pressures are the norm.  At F-M I was shown a pretty wide variety of polymer, oxide, and PVD coating samples by the engineering folks - and that was well over a dozen years ago.  This stuff is "new to us" but has been around for quite a while.

The top ring is probably lubricated by fuel as much as by oil.  I do know that alternate fuels required different ring materials or facings.  Dry fuels such as alcohol, CNG or propane required a specific approach.

Ring back clearance is the distance between the inner diameter of the piston ring and the inner diameter of the corresponding ring groove.  At one time, all manufacturer's rings and pistons used "inside to outside" dimensions per an agreed upon number based on SAE standards - the sometimes referenced "SAE D-wall".  As performance improvements and cost savings were found in reducing radial wall thickness, the standards were either ignored or abandoned and things got a bit freewheeling.  We used to work on minimizing back clearance to improve pressure loading on the top ring.  Then someone claimed it did not matter (probably a claim driven by economics).  Now I think it 's been decided that it still matters on top rings and we're back to where we were. 

Mahle led the move to steel top rings in high volume aftermarket stuff, but it was a bit bumpy on the way in.  At first they just swapped ductile for steel (cost savings and a potentially better part), but found out that the steel rings in the same dimensions as iron were comparatively stiff and unforgiving.  Then they went to a reduced radial wall steel ring to get the tension sorted out, and told folks not to worry about the back clearance.  Eventually they figured out that was not ideal either, went to smaller cross sections yet with a thin metric ring with a tightened up back clearance - and everything gets "happy" again.  Except for the poor custom piston guys (Hi Randy...) who need to sort through a million ring variables when grooving pistons.

Scott G remains one of the nicest and smartest guys I ever had the pleasure of working with.   The Lord of the Rings was on speed dial from every Pro Stock and NASCAR team in the country for decades.  He lives about a mile away from the shop and visits once in a while.  He is retired, look 20 years younger than his actual age, raises bees in his backyard, has about a million grandchildren, and drives a Buick station wagon.

[My427stang]

Barry, thanks for taking the time on the moly discussion, and I agree with it, but I believe steel specifically needs treatment for iron blocks.  I am not even sure where I learned it, as I understand it doesn't apply to any iron ring, cast or ductile, and as Randy pointed out, it likely doesn't have to be moly specifically, but I do think something needs to be done to make the ring work with cast iron

That being said the material discusion, it's all academic, because the "wire" rings DO work, and I like a 1mm Mahle (not moly) LOL very much.  I also have used Total Seal, Hastings and Mahle in the 1.5mm packs and have to say from an assembly and drag "feeling", I like the Hastings and Total Seal better in that ring size.  I am not sure what Mahle does in their manufacturing process with the 1.5mm ductile, but can leave a light track on the bore and you can find small areas that you can feel that the others don't. It could be psychological, but I like the way the old guard U.S. rings feel as you assemble too.  Those of course are ductile iron though in 1.5mm for all three

Where I am a bit fascinated is what got us talking about this, 1/16, 3/16 pack versus 1.5 mm, 3.0 mm pack, standard tension, very different in drag but not materials.  Maybe the 1/16 ring is made to the old material dimensions?  Maybe it's a sum of the slight drag difference?  Maybe as Brent said it's in the oil ring, but it's surely different. I can wrap my head around the 1/16 vs 1mm because of material differences, but not as much with the others.   My gut tells me the 1/16 ring must be made to old dimensions, I have a 1/16 build coming and will see how much different they are in shape from a 1.5 mm

Regardless, I am a big proponent of thin rings, I came around slowly, but if even just for speed of assembly, never mind all the performance benefits, they are a big win

[Joe-JDC]

One question about thin rings that I have that was not answered above is how is the block prep different?  I have an engine that I tore down after a head gasket blew, and when looking at the rings and bores, there seemed to be chatter marks laterally as if the rings were digging into the bore instead of sliding up and down.  Made me think the cross hatch was too narrow, and not ~45* or so.  If the cross hatch finish is not moved up and down fast enough, does the 1mm ring dig in?  Anyone?   Joe-JDC

[Barry_R]

Lateral as in "up and down" or on the diameter?

You see a lot of "up and down" scratches on bores when running Hastings oil rings.  Many of the ring brands use a Hastings oil ring now no matter who's name is on the box.  They do this because the Hastings oil ring is CHEAP, not because it's better.  Hastings uses a chrome faced oil rail, just like most manufacturers have for decades.  But at Sealed Power back in the day, we used to brush the chrome rails after plating to remove surface artifacts from the plating process.  Hastings skips this step - in large part because their original customer base was large scale rebuilders who valued price above all else.  They used to sell Jasper rings sets for a dollar per cylinder, packaged in brown paper lunch bags.  To make that work you need to save every penny possible in manufacturing...it ain't easy to change that sort of culture in a company.

You will not find these scratches when running a Mahle or Japanese sourced oil rail....

[Joe-JDC]

Laterally as in diameter.  I know what causes scratches up and down.  This was a first for me, using 1mm rings, and I am wondering if the block had the wrong crosshatch for thin rings.  Joe-JDC

[gt350hr]

   Joe ,
       Ring companies are suggesting the use of a profilometer now days for the actual surface finish. They suggest specific values for the different ring materials. Cross hatch angle ( IMPE) should change as the ring gets a thinner cross section ( axial height) to slow down ring rotation a bit. I have used the NPR steel top rings with the same bore prep as a moly faced ring without issue. Others will have different opinions.
  Randy
   

[Joe-JDC]

I have two engines with similar prep, similar ring packages, different compression, and one runs great, and one has a little blow-by.  The one with blow-by blew the head gasket, and that is when I found the chatter gouges laterally.  I don't really think it was detonation, but I am considering it a real possibility.  Joe-JDC

[gt350hr]

    "Lifting the head" could certainly be a result of detonation , especially with modern gaskets. If it was that bad , you should see some evidence on the piston or in the pin bore of the piston. Plus make sure the rings weren't butting.   
    Randy

[pbf777]

    "Lifting the head" could certainly be a result of detonation..................................make sure the rings weren't butting.   
    Randy

      +1       

      Scott.

[Gaugster]

   Joe ,
       Ring companies are suggesting the use of a profilometer now days for the actual surface finish. They suggest specific values for the different ring materials. Cross hatch angle ( IMPE) should change as the ring gets a thinner cross section ( axial height) to slow down ring rotation a bit. I have used the NPR steel top rings with the same bore prep as a moly faced ring without issue. Others will have different opinions.
  Randy
   

+1 Thank you. I was curious about the surface treatment as well.

[70tp]

I remember ,once, that plasma ceramic rings were offered as the new hot item.   What ever became of those?   How did they fare in usage?     Also when I first tore down my tunnelport when I first got it - it had slight “chatter marks” in the cyls.  It had led a hard life in a nitrous mud truck before I got it. I just chalked it up to “ring flutter” and never really gave it anymore thought, but I never saw that pattern in any of the other engines that I went through.