We've had a number of piston failures due to the top ring land breaking. It's been noted that stock, we have a rather narrow top ring land (.10") coupled with a rather narrow ring gap. Heat causes the ring to expand, the gap closes and the ring presses up on the top ring land breaking it. Why does the ring press on the top land? Because it continues to expand after the gap closes and it either bows (most likely?) or it "wedges" itself against the cylinder wall and binds -- piston keeps going up and down with the ring applying a lot more pressure on the lands due to the friction agains the cylinder walls. In either event the ring is applying more pressure against both lands and the top land ends up being the weak link and breaks off. I get the impression that a lot of people think the narrow top land is a flaw and/or under designed. If we just had pistons with a .50" top land or if we just had pistons made of stronger metal this wouldn't be a problem. Is that really the case? If your ring gap closes you have a failure. Maybe if the top ring land holds together it's not as catastrophic an instant failure but still a failure. Maybe you don't need a tow truck right when it happens but you're going to need major work to fix it. I think best case you end up with scored cylinder walls, then it burns oil, loss of compression, major acceleration of wear, etc. Or busted rings which end up doing the same thing a lot faster. It's kind of like getting shot with a bullet or getting fatal cancer. Either way it's a failure. The piston and rings form the bottom of the combustion chamber. When you touch off the charge it expands and exerts pressure. This is going to be a downward force on the piston and ring and will be forcing the ring against the bottom land. That doesn't change when you add power. Pretty much, the top land is simply a retainer for the ring and shouldn't be subject to any additional force, possibly negative, due to combustion. Stock, blown, heads, cam, nitrous, shouldn't make any difference to the top land. It's the ring gap closing (due to expansion from heat) that is the failure. At some point you need stronger pistons to withstand the pressures and maybe heat if you can't control it but it's not the top ring land that's the problem. It's just a symptom of the root cause failure. Just wanted to clear that up (am I right here?)
"root cause failure"......... very nice dave!!! for guys like me that deal with lean manufacturing, "root cause problem solving" is a term often used!! i will take it one step further..... Problem - Failed Motor....... Causes - Rings, Piston, Heat, F/I, Nitrous, etc. etc...... don't mean to overly simplify, but all this talk about pistons, rings, ring lands, etc being problems..... they are not...... the problem is a failed motor, the causes are all/some of the above. i am really interested in what cam finds out after his "experiment". the fact we have a very good idea of the CAUSES, hopefully we can now adress these causes and find a solution to the PROBLEM of blown motors. what i find more interesting is the fact that there are no pistons made for direct OEM replacement that are forged???? at least that i know of..... some one correct me if i am wrong. all i know, is that when i see boost and 14.xx a/f on the gauges...... my foot comes off the pedal or goes on deeper to get to open loop!!! lol boosted cars are becoming much more informed drivers that should help people from staying away from the inevitable result boost on stock internals! lol
^^^ That will keep your motor living. Good thread and my first thought is yes and no. During normal operation, the ring floats in the groove in the piston. During the intake and power stroke, the piston is forced down and the top ring land pulls the ring down with it. During the exhaust and compression strokes, the ring is on the bottom of its groove as the piston is moving upward. Heat expands the ring until it goes solid, then it binds and doesn't float anymore. The expanding and binding puts pressure on the thin top ring land and pops it off. So yes, a bigger ring gap would stop the ring from going solid. Yes, a thicker and/or forged ring land would be harder for a solid ring to pop off. Damn...gotto go back to work. More later.
Ok... this thread is addressing the perception that we have "weak" top ring lands and this is what I'm getting at. Why are you interested in forged pistons? Let's say EVERYTHING was EXACTLY the same except the piston was forged. Do you think that would alleviate the problem?
if the piston was forged (imo) the ring would just break, not the piston. but this is still broke. the ring land needs to be moved down and they need more ring gap (or rings made of better matteral that does not expand so much).
yes, but this is still what I'm talking about. It's NOT the ring land that needs fixed. I'm thinking there isn't anything wrong with the ring land we have. It's not like it needs to be beefed up for power adders. It's all in the ring gap closing (which happens to be from heat).
Its not ALL in the ring gap closing. As an example...say the top ring in a blown hemi gains 30 thousandths of length with heat, the ring gap is 20 thousandths. So that extra 10 thousandths of length exerts 10 pounds of force against the ring land (which is only rated for 5 pounds due to the thin land and material). The ring land pops, dead cylinder. Now its a thick forged ring land that can withstand 20 pounds of force...everything cools down and life goes on without a problem. The bottom line is that you should have them both. Rings and pistons that are both designed for their intended usage.
first is to adam..... adam, no offense, but you obviously have not studied true problem solving concepts. i never said the 6.1 was not a good motor, or touched on the fact that we are asking it to do things outside of the parameters it was designed...... instead i am simply stating the ACTUAL PROBLEM..... if the motors had not failed (often due to the ringland/piston/ring/etc...), we would not be having this discussion on ringlands problem identification is actually very easy....... it is the root cause problem solving that is more diffcult and time consuming...... would eliminate motor failure........ maybe, maybe not. might push to the next weakest link, if any exists. my thoughts were more on pistons with larger ring lands and forged. do these exist or is it even possible to make such a swap without addressing rods, etc. good point ralph..... is this possible while still keeping the rest of the rotating assembly in place???? i am thinking it must be an issue or we would see/hear more on oem piston replacement..... so you simply want a bigger ring gap????? i am with you on this one adam!!!
Actually, I have, it was part of my doctorate training. If we weren't using them for something they weren't designed for, they wouldn't have failed and we wouldn't be discussing ring lands. That's what I was getting at.
you too!!! lol the designation of something does not detract from the bottom line of what is present. Problem - Motor broke Why (cause) - ringland broke due to boost rod snapped due to over rev motor siezed due to mouse crawling into tb dealer ship lacky decides to hot rod your car when moving it (sorry momo) etc, etc, etc........ again problem identification is simple....... does there exist some kind of issue, if yes then why???? it is the why part that is time consuming and tricky at times. that is why there are people that get paid big bucks to do just this....... find the causes!!!! lol i am definately with you on the thicker ringland & forged piston thoughts!!!!
No, I don't think that's likely to be the case. That 10 pounds of force in your example has to go somewhere. It's not just going to be against the ring lands. If the ring lands don't give it's most likely going to be against the cylinder walls or the ring breaks. When the gap closes and it keeps expanding the ring is going to get wavy or the diameter will continue to increase. It only bows because it's being contained from getting longer by the cylinder walls. If you stop it from getting longer it has to go somewhere. That's probably going to damage the cylinder walls if the ring and ring lands hold. NO. That's not the point. (The rings are there to seal for compression. too big of a gap and they don't work). The cause here is heat. Sure, the ideal would be if everything was exactly matched... piston strength, rings, ring gap, resistance to heat, etc. And if everything was just perfect and you exceeded the parameters everything would fail at the same time (it'd be just like when the anti matter containment field fails). The whole point of this thread is that people tend to think of the top ring land as being a weak point that's way out of line with everything else. My point (unless convinced otherwise) is that it wouldn't make any difference if we had a .5" top ring land instead of a .1" top ring land.
i understand where you are going dave, but i still think if the rings and pistons were addressed, then the problem of failed motors due to ringland breakage, would decrease. thick ringland would discourage failure of top of piston. i would suspect heat treatment of the piston/rings would also go a long way in helping decrease the chances of ring over expansion. soooooo, maybe a piston that is forged, thicker ring land, AND heat treated..... what do you think dave???? more of where you are going????
You're right, but that would be wear on the cylinder and ring. To the observer, there is no piston failure but the engine will wear faster. When the ring gets hot, it goes from this -------- to this ~~~~~~~~~~ (lovely drawing huh). The highs and lows of the sine curve are where the force is exerted on the piston. There is also the heat in the piston itself. I don't know if you've noticed, but every blown ring land I have seen on a HEMI is on the thrust side where friction is the highest. That's why it all needs to work together like you're saying. So yes, a thicker top ring land will stop ring lands from breaking - but if you don't address the ring too you'll see other problems (premature wear).
No... I actually wasn't going anywhere, just trying to change people's perspective on the problem. I did not mean to discuss any solutions. Just get an understanding that the ring lands are not to blame. For example, you keep mentioning thicker/stronger top ring land. I don't think there is anything wrong with the current ring land. The top ring land is only there as a retainer for the ring. On the intake stroke there will be a vacuum in the chamber so there would be a little bit of upward pressure pressing the ring against the top land but not much to speak of. So again... it's not the top ring land. It's the gap closing. Basically when your gap closes you have a failure. Sure you might get away with it depending on other stuff but it's like saying you need stronger piston heads because the valves keep punching holes in them.
So there is not diffeence in presuure on the ring with an increase in boost or power? It seeems the more boost the more force. Am I wrong in thinking that more power comes from a more powerful combustion stroke? If you open the gap on the first ring you will force more pressure to in between the first and second ring potentially causing another problem. Maybe more pressure between the rings is a related problem. Is our second ring gapless design or is it gapped? Here is a read... Quoted fromhttp://www.carcraft.com/techarticles/piston_ring_technology/index.html "Thinking on piston ring gaps has also changed. In the old days, second ring gap specs were tighter than those for top rings because they didn’t see as much heat. But this didn’t account for inter-ring gas-pressure buildup between the top and second rings. If the pressure between these rings equals or exceeds the pressure above the top ring, it can cause the top ring to lift off the bottom of the piston ring groove and lose contact with the sealing surfaces. It also inhibits the ring’s ability to transfer heat from the piston. To keep inter-ring pressure from becoming a problem, the current trend is to create an easy escape path for the built-up pressure by gapping the second ring larger than the top ring. Another benefit is that because gas pressure is now directed downward towards the sump, any oil that has collected in the ring pack areas will go with it. Of course, normal ring wear causes the gaps to open up, allowing more combustion gases to escape. At least one ring manufacturer—Total Seal—offers gapless rings. Traditionally, these gapless rings went in the second groove along with a conventional top ring, but ring technology refinements plus the new thinking on ring sealing has led Total Seal to revise this installation scheme and introduce a new line of gapless top rings that achieve significantly less blow-by under real-world running conditions."
Exactly right. BUT that's forcing the ring down onto the bottom ring land... Still nothing wrong with the top ring land. The inter-ring pressure problem lifts the top ring off the bottom land and it loses seal resulting in a loss of compression. It's not ramming the ring up against the top land. It's probably just barely getting it off the bottom land. Still nothing wrong with the top ring land.
Do I undrstand PSI wrong? In simple terms downforce is applied by the PSI generated during compression. The pounds per square inch is greater on the piston surface than the top ring surface area therefore the top ring actually rises during the compression down stroke, because the piston leaves it behind, due to more force. Plus the top ring is carrying the friction from contact with the side wall assisting in making it rise during down stroke. ..
That's a pretty big leap in logic... You left out a few things like the rod holding the piston up and the ring free floating and maybe their relative mass and probably a few other things.
Hmmm good point.....but there is still considerable amout of force on the piston top compared to the ring. I thikk it still lifts....imo Does anyone have picture of a broken land and the psiton still in the block? I am curious if the break occurs near the gap. ..
Ummm, you posted/quoted this above In fact I believe you will find the bottom land to be beveled and the bottom side of the ring to match. As the pressure pushes the ring onto the bottom land this will spread it to make a seal between the ring and the cylinder wall.
