Opinions of Low Tension Thin Piston Rings

[Don D]

Looking for opinions on the newest rings we are seeing in the piston kits for our motors. .043 top and second and 3mm oil pack are common from several manufacturers. I have my own thoughts but would like to hear from others. On a related note.

Just had an M8 failure, S&S kit with CP pistons. Presented with scratch lines in the cylinders and dark splotches where obviously the rings were not sealing. Pistons were in perfect condition and no signs of a dirty install. Had 50 dyno miles from a well known and respected tuner. The cylinders were not measured just installed by the shop out of the box. After the fact they present pinched on the pushrod sides, -.0008 to -.0012" and very open at the bottom. Last 1.5" are +.008 nominal on the thrust side. Thrust side bore are from 0 to +.0017 except in the bottom. A lot of words for all screwed up! So wondering if others have had similar issues and wondering about opinions of root cause and prevention.

Thanks in advance

[SP33DY]

I have been using thin rings for some time now. Some of the sprint car and midget engines I build use even thinner rings, 1mm (0.0394") top and second rings. Those guys really hammer on their engines and they hold up good. The key is round straight bores and proper finish. I check the bores with a profilometer. Shoot for Rpk in the mid teens. I got my profilometer from Total Seal, they're good people to talk to if you're having ring problems.

When I finish Harley cylinders, I get to within a half thou and let them sit for an hour or two before I bring them to final size. Then I leave them sit in the torque plates overnight and recheck them the next morning. Often they need a little bit more attention.

Cylinders out of the box, no measuring? That's brave.

[wfolarry]

Ball hone.
I read a lot of negative comments on ball honing so I usually stay out of it but with thin rings I do it every time. It will save you a lot of aggravation. Some guys use a brush hone [have that too] but if the cylinders were finished with stones or diamonds a few strokes of the ball hone gets rid of the torn metal left from the stones. Thicker rings would knock it off but the thin rings have a hard time with it. It works for me.
Also ring gaps. Different companies give different specs but with thin rings err on the high side. A tight gap will kill it fast.

[SP33DY]

I agree, 320 ball hone or Sunnen PHT-731

[Don D]

Great information.  I have sunnen brushes. I also have a good assortment of ball hones.
So are you guys taking new kits and putting the cylinders on the machine if they aren't straight and true or rejecting them?

[Don D]

Here are a few photos of the cylinders I mentioned.

[Don D]

One more

[jsachs1]

I try to stay away from Harley pistons with 2mm oil rings. IMO, oil control with them, in the common sizes gets to be iffy in short time.
John

[SP33DY]

Great information.  I have sunnen brushes. I also have a good assortment of ball hones.
So are you guys taking new kits and putting the cylinders on the machine if they aren't straight and true or rejecting them?

I always check them. If they need a little bit of touch up, I'll take a minute and fix them. The S&S cylinders rarely need anything but I feel better by making sure. Harley cylinders are another story.

[mike jesse]

George Bryce has been discussing piston and ring design on his facebook page.
Lots of good info from one of the best out there.

Worth a look.

[1workinman]

George Bryce has been discussing piston and ring design on his facebook page.
Lots of good info from one of the best out there.

Worth a look.

I been working a lot of over time and I think I missed that one I have to watch that one for sure . I was wondering if there was a way to go ahead and season the cylinders in some manner then bore hone to final size

[Don D]

I do that, seasoning. I heat then to 250° for an hour then just turn the oven off to let them cool naturally. I don't do it however when the cylinders are already to size.

[kd]

Bare or in torque plates Don

[Don D]

No torque plates.

[machinist]

Guy across the street rebuilds Subaru engines exclusively. Worked at dealer many years. Said those motors really lasted, until they went to low tension, thin rings. Done for MPG.

[Don D]

Lower tension is the oil ring pack. The compression and oil scraper are what they will be. They are lower friction which "in theory" is more horsepower and MPG. But remember the HD Vtwin is air cooled and the rings are the conduit to carry heat out to the cylinder and then the fins. Less surface area means less heat removed. Now lets assume these cylinders start out perfectly true and sized. With air cooling there are hotter and cooler spots, uneven temperature removal. How can such a thin ring such as .043" conform and remove the heat? Could this be contributing to the problem? The cylinders I measured, which probably started out from S&S near perfect, are now all over the place.

[Geezer_Glider]

Wonder if those cylinders have casting voids up against the liner? You know others have had that problem sometimes. Could saw them or X-ray.
R Meyer

[Don D]

Guy across the street rebuilds Subaru engines exclusively. Worked at dealer many years. Said those motors really lasted, until they went to low tension, thin rings. Done for MPG.

Very hard to hone them right, can't overstroke

[1workinman]

Lower tension is the oil ring pack. The compression and oil scraper are what they will be. They are lower friction which "in theory" is more horsepower and MPG. But remember the HD Vtwin is air cooled and the rings are the conduit to carry heat out to the cylinder and then the fins. Less surface area means less heat removed. Now lets assume these cylinders start out perfectly true and sized. With air cooling there are hotter and cooler spots, uneven temperature removal. How can such a thin ring such as .043" conform and remove the heat? Could this be contributing to the problem? The cylinders I measured, which probably started out from S&S near perfect, are now all over the place.

That's a good point I never thought about it that way . I experienced a new LC SS 124 motor that from the time I picked up a  Harley Dealer , long story , dripped oil out of the TB with not breathers attached to it after I shutting of motor every time . That version is long since gone as so is the problem. I like the idea of seasoned cylinders bored and honed with a torque plate with premiums pistons , I prefer diamond or cp and the best rings that can be had. I give up a couple of HP for long life and oil control 

[Don D]

My preference is Mahle or KB Forged. Most of the KB pistons ignore the thin ring trends and use standard size and tension rings, like 1.5 x 1.5 x 3mm from Hastings and Nippon.

[1workinman]

My preference is Mahle or KB Forged. Most of the KB pistons ignore the thin ring trends and use standard size and tension rings, like 1.5 x 1.5 x 3mm from Hastings and Nippon.

[1workinman]

My preference is Mahle or KB Forged. Most of the KB pistons ignore the thin ring trends and use standard size and tension rings, like 1.5 x 1.5 x 3mm from Hastings and Nippon.

On a hot rod street motor what do you think about gas ported pistons to aid in ring seal . 

[Don D]

I have no issue with horizontal gas ports for a street motor. Can't hurt may help ring seal.

[dave brode]

All,

Fwiw, Years ago, I had the 2nd rings converted to gapless for a 2.2 S-10 engine of mine.
[no, I'm not trying to open that can of worms LOL]

The fellow at Total Seal said that he did not like the low tension rings that were normally supplied for that engine. It was std bore. He suggested using a +.020" oil ring groove tensioner. Not the scrapers, obviously.

I wonder if a +.005" or +.010" tensioner would help the 2mm Harley ring engines? I also wonder if that's what you would get if you asked TS for a std tension oil ring set.
Dave

[mike jesse]

George specs his street pistons with vertical gas ports from what I can see.

I've done a few SBF's with the vertical gas ports and they sealed up nice and ran extremely well.

Round and straight cylinders are a must to start with.