CREngines wrote:i just received my third (for the year) set of rings that were boxed wrong the other day. first it was SP with the wrong oil bands then HAST with the wrong oil bands now its SP with the wrong top rings.
As an update the rings are not boxed wrong. That is how they are selling them now as of a month ago.
As a warning for anybody using the basic sealed power E251K ring sets or any 4 inch bore 5/64 basic common ring set from any of the Mahle subsidiaries. They have changed the top ring in the set and instead of a ~.180 radial thickness for a .200 deep groove, they are now .140 radial thickness ring and when installed in a common piston the crevice volume is now .060-.070 deep. Sealed power informed me this was an engineering change to improve bore conform ability. In disbelief i called a well respected ring engineer at a competing company and asked him what he thought. It was just what i thought. as any one knows that is familiar with racing pistons this is exactly the opposite if what improves ring seal with the increased volume, lowering ring response time and sealing pressure. His theory was that they are consolidating part numbers to save money and are just going to use that ring to save money. so beware.
I figured this was sort of a big deal because anybody doing a basic 350 with the basic rings will suffer from this.
CREngines wrote:i just received my third (for the year) set of rings that were boxed wrong the other day. first it was SP with the wrong oil bands then HAST with the wrong oil bands now its SP with the wrong top rings.
As an update the rings are not boxed wrong. That is how they are selling them now as of a month ago.
As a warning for anybody using the basic sealed power E251K ring sets or any 4 inch bore 5/64 basic common ring set from any of the Mahle subsidiaries. They have changed the top ring in the set and instead of a ~.180 radial thickness for a .200 deep groove, they are now .140 radial thickness ring and when installed in a common piston the crevice volume is now .060-.070 deep.
I measured this also and thought no big deal on the engine we are running.
I am more worried about the land thickness.
I sent the first set we got in like this back also thinking they had been boxed wrong.
I had the sales person I deal with look through the boxes they had on the shelf until she found a set that was the .180.
Then a few weeks ago we got the bulletin. The next set I got in I went ahead and used them.
This was in an Econo class dirt track engine.
I noticed that the engine actually had a lot less vapor out the valve cover vents on break in.
It has always been normal for our engines to have a small amount of crank case pressure until the rings seat in.
This usually clears up after the break in runs and goes away after a few hard pulls.
This engine had almost none at all even when first started.
We build a bunch of these same engines and the only thing different on this one was the top rings.
So far the engine has several races on it and no sign of a problem.
Who Knows. Like the saying goes "Even a blind pig finds an acorn every once in a while".
CREngines wrote:i just received my third (for the year) set of rings that were boxed wrong the other day. first it was SP with the wrong oil bands then HAST with the wrong oil bands now its SP with the wrong top rings.
As an update the rings are not boxed wrong. That is how they are selling them now as of a month ago.
As a warning for anybody using the basic sealed power E251K ring sets or any 4 inch bore 5/64 basic common ring set from any of the Mahle subsidiaries. They have changed the top ring in the set and instead of a ~.180 radial thickness for a .200 deep groove, they are now .140 radial thickness ring and when installed in a common piston the crevice volume is now .060-.070 deep. Sealed power informed me this was an engineering change to improve bore conform ability. In disbelief i called a well respected ring engineer at a competing company and asked him what he thought. It was just what i thought. as any one knows that is familiar with racing pistons this is exactly the opposite if what improves ring seal with the increased volume, lowering ring response time and sealing pressure. His theory was that they are consolidating part numbers to save money and are just going to use that ring to save money. so beware.
I figured this was sort of a big deal because anybody doing a basic 350 with the basic rings will suffer from this.
Sealed Power maintains the same root diameter from std. to .060 over on pistons on ring grooves , and they no longer offer backspaqce wire. I wont use teir stuff. so if the radial thickness is now 140 you could have as much as .080-.090 backspace ?
TB from Mahle, they make SP/FM and PC rings along with thier own.
TB-7001 Issued: July 27, 2011
Steel Compression Rings with Reduced Radial Wall Thickness
MAHLE Clevite Inc. is transitioning its popular MAHLE Original ring sets from a grey cast iron top ring to a carbon steel top ring. The advantages include; 35% more strength, 30% less weight and double the resistance to side wear which is a common problem on late-model engines.
Since the steel is 35% stronger than cast iron, we can achieve the same ring tension with 35% less weight. That weight savings is made by reducing the radial wall thickness of the steel ring.
The net result is a ring that's lighter, so it has a higher effective RPM potential, stronger - so that it weathers the abuse of today's high output engines better, and actually seals better because the reduced radial wall allows it to conform to the cylinder wall better.
Having said all that, there's some additional explanation needed when it comes to back clearance - that area behind the ring which is calculated by subtracting the ring radial wall width from the root depth of the ring groove in the piston. For example; if I have a ring radial wall of .170” and a groove depth of .195” then my back clearance is .025”. Reducing the radial wall of the replacement carbon steel rings does increase the back clearance because they are going into piston grooves designed for the thicker radial wall of the cast iron rings.
It's been a well-accepted piston/ piston ring engineering design criteria, that for optimum performance, ring back clearance should be minimized. This comes from the fact that the top compression ring needs the pressure from the combustion gases to get in behind the ring and push out on the ring to maintain proper seal on the high pressure, or combustion stroke. The logic was that the smaller the area created by the back clearance, the quicker that pressure would build to push out on the ring, and the quicker the ring would react to its sealing requirements job. That logic is all good but what about the reality of the concept?
Since MAHLE makes both components in this equation - pistons and the rings, our MAHLE piston ring R&D lab did some testing in conjunction with one of our OE customers to see if engine testing could tell us what the right amount of back clearance should be. What the lab folks found surprised most all of us! The engine wasn't nearly as sensitive to ring back clearance as it was to ring side clearance.
The reason was the gases have to get past the top side of the ring in order to get around to the back of the ring to push out on it. When we tightened up the side clearance to less than .001", the ring went unstable even at normal operating RPMs. Blowby, which is gas leaking past the face of the ring, increased dramatically. Changing the back clearance didn't show us anything, negatively or positively either direction. We realized it was all about having enough side clearance to let the gases flow back to the back of the ring not how much back clearance we had!
We came to the realization that in any cylinder, you have hundreds of CC's of gases available to fill that relatively small volume behind the ring (0.4 cc's), Those gases are at a very high pressure, several hundred, or even thousand PSI, so they will fill the small space behind the ring very quickly if you give them enough room, a.k.a. side clearance, to get there.
Most OE and aftermarket side clearance specs are in the .0015" - .0025" range. For our regular, non-racing, customers; changing from a cast iron top ring to a steel top ring won’t cause any adverse effect at all from the increased back clearance because the side clearance is adequate to allow the gas movement. Remember, we have hundreds of cc’s of gas to fill the very small amount of space change.
The performance engine builders are a different story, but they take care of the issue with custom groove specs. The MAHLE Original performance ring catalog supplies radial wall specifications for every ring for just that reason. Many of the true high performance engine builders specify ring grooves with less than .001" side clearance, but they add gas ports, small channels drilled in the piston, either from the top or side of the piston, to give a direct path for those combustion gasses to get directly to the back side of the ring. The engine doesn't care how the gases get back behind the ring, it only cares that it does, and in enough volume and pressure to do the job.
In summary, you can replace cast iron top rings with carbon steel, get all the benefits we’ve talked about in this bulletin, and rest assured we’ve done our homework on the engineering side!
Ok, I'm bringing this thread back up, doing a basic freshing up on my Sbc 350. Got a new set of speed pro hyper H631 Cp piston .
Got a new set of E 251 K rings. Notice the top ring is .140 compared to the old one of .180 radial thickness. Put top ring in the block and gap is .032, 2nd ring is .022.
I know the old top rings were .016 gap and .020, question is should I use them or get a total seal ring?
If you are worried about the extra radial backspace clearance, you can buy back space shim stock # 003239 from total seal. While you have them on the phone ask them about some of their trick ring sets to lose some of that horrific parasitic drag from those antique tractor 5/64, 5/64,3/16 rings. I'm surprised that the piston people still use that ring package on anything other than vintage restoration stock replacement pistons.
BILL-C wrote: ↑Tue Jan 28, 2020 12:51 pm
If you are worried about the extra radial backspace clearance, you can buy back space shim stock # 003239 from total seal. While you have them on the phone ask them about some of their trick ring sets to lose some of that horrific parasitic drag from those antique tractor 5/64, 5/64,3/16 rings. I'm surprised that the piston people still use that ring package on anything other than vintage restoration stock replacement pistons.
Loads of pistons are still made with that ring package as standard unfortunately but I guess you know that.
Not sure why they don’t move to a more modern ring package .
