It is a good discussion. However, there's one factor that has not been mentioned yet... pressure-viscosity coefficient.
Interesting observation using Castrol Edge Full Syn 0W-16
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The blowby pressure behind the ring won't be uniform. There will be a larger pressure (ring pushed in more) on the thrust side and a smaller pressure (the ring pushed out more) on the antithrust side. When I made the calculation in post # 96, I neglected this, but to get the lateral force, you need to find the difference between the pressures on the thrust and antithrust sides. This will result in a lateral con-rod force smaller than the 2,600 N I calculated—perhaps about half that large.
I think it would actually depend on how large the ring gap is, and where the ring gap is located with respect to the thrust direction of the piston. Rings can and do rotated some in their groove. It would also depend on the clearance between the top of the ring and the top surface of the ring groove. I'll use this figure again which shows the blow-by going down through the ring gap, and through the top gap in the ring groove around the ring circumference.
But in any respect, the ring is always in contact with the bore wall regardless if there is zero or 1000s of PSI behind the ring. The rings never loses contact with the bore wall, it's just the force at which the ring face contacts the wall that changes based on the gas pressure behind them. So think of the rings as always in contact with the bore wall throughout the piston strokes, and depending on the piston design, piston to bore clearance (ie, piston tilt capability), and how much piston acceleration side inertia force there is (ie, effected by power level and RPM), that will determine just how much the piston tilts and is able to contact the bore wall in the ring pack area. The rings don't move with respect to the bore wall in the ring's radial plane - they float in the grooves - but the piston can tilt in the thrust direction around the rings. Imagine the rings are stationary in the radial plane, and the piston can move fore/aft from thrust in the bore while the rings never move in the radial plane.
Not sure how you're seeing the statement in bold. Even if the pressure distribution behind the top ring is not uniform, the ring never loses contact with the bore wall. There might be an uneven ring radial force distribution which causes the force of the ring face to be different around the circumference of the ring, but it's not causing the ring to push out more in any direction. Look at the figure above - they have shown that with the different colors on the top ring. There is less pressure and force at the ring gap because gas is leaking past that area and trying to pressurize the backside of the 2nd compression ring.
The only thing that "pushes the ring in more" with respect to the piston circumference is the piston tilting fore/aft in the bore as the rings float. If the piston tilts all the way towards the bore, then the ring face on that side is pushed into the ring groove more, and the ring 180 deg from there is poking out little more (it has too) because the ring is always in contact with the bore around its entire circumference.
Again, the ring will always be in contact with the bore wall around it's whole circumference (assuming of course everything is perfectly round and true), so if the piston tilts and contacts the bore wall on one side, then there will be larger gap between the piston surface above the ring pack and the bore wall on the opposite side.
Have you ever put a piston on TDC and take your hand and rock the piston fore and aft in the bore? Example video below. The piston moves as much as the piston to bore clearance allows, and the rings never lose contact with the bore ... they float. That's the whole key to understanding how the piston and rings are not locked together and act independently as the piston goes through the strokes in the bore. Lots of videos showing this. If the piston to bore clearance isn't excessive, and depending on the piston design, that will determine if the top area of the piston can make contact or not at full tilt in the bore.
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Right, I never disputed that the ring never lost contact with the bore—albeit, the actual clearance will be different on the thrust and antithrust sides, depending on how much the oil film is being squeezed at either side.
What I meant by the ring being pushed in was only in the relative sense. Of course, if you consider the engine block as the stationary reference frame, then the piston is being pushed out on the thrust side, but if you consider the piston as the stationary reference frame, then the ring is being pushed in (with respect to the piston) on the thrust side.
I have to disagree. My last change of “warren” synthetic blend 5w30 made my daily drivers old 302 Ford pickup loud and rough instantly and it’s still noticeable weeks later. I actually considered changing it out it’s so annoying.
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I would write to warren they may offer you a refund or something for your troubles. 
I think I see what you're saying. Yes, if there is an uneven force distribution on the ring face (as seen in Figure 1 above) due to uneven gas pressure, and the film thickness is smaller where the ring face force is smaller, then the ring will be moved inward in it's groove a few micrometers more. Dang, I know we like spitting hairs on BITOG, but this ranks up there pretty high.
Thing is, the radius of the ring face and the radius of the bore over the piston's stroke distance is probably way beyond a few microns from perfect round. Once it all breaks in, the fit variance would be a little better, but probably still not perfect. So assuming the ring face force was exactly the same around the entire ring circumference, if you could measure the oil film thickness at every square micrometer between the ring face and bore surface over the entire swept area of the ring, it would most likely vary by quite a few microns.
That oil runs fine in lots of other things I use it in. Just seems that my warn out truck doesn’t like it.I would write to warren they may offer you a refund or something for your troubles.
This is very complicated stuff, probably beyond the expertise of anyone except those doing research specifically in this field. That said, I will conclude with a reference to an MIT master's thesis, in case someone wants to dig deeper into the rings, blowby, oil, and lubrication:I think I see what you're saying. Yes, if there is an uneven force distribution on the ring face (as seen in Figure 1 above) due to uneven gas pressure, and the film thickness is smaller where the ring face force is smaller, then the ring will be moved inward in it's groove a few micrometers more. Dang, I know we like spitting hairs on BITOG, but this ranks up there pretty high.
Thing is, the radius of the ring face and the radius of the bore over the piston's stroke distance is probably way beyond a few microns from perfect round. Once it all breaks in, the fit variance would be a little better, but probably still not perfect. So assuming the ring face force was exactly the same around the entire ring circumference, if you could measure the oil film thickness at every square micrometer between the ring face and bore surface over the entire swept area of the ring, it would most likely vary by quite a few microns.
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Warn out engine calls for formula shell
The A25A in our Toyota does appear to be a little “quieter” with Valvoline and Pennzoil (* on the Pennzoil cause it was done at an oil change place so I’m not sure what is actually in it) than with TGMO.
All that said the MPG did not change at all and the engine runs well on all three brands. Also, the high pressure DI system still clacks like a diesel so there is that.
All that said the MPG did not change at all and the engine runs well on all three brands. Also, the high pressure DI system still clacks like a diesel so there is that.
That paper looks to be modeling everything but the oil film on the ring face, and instead the gas and oil dynamics going on between the rings and ring grooves ... but it's sill interesting, and a whole other part of what's going on in the ring pack.
Yes, what goes on in the ring pack is certainly complicated when you really start digging in to it all. It's amazing that rings even survive as long as they do when you look at the environment they live in. A good mechanical design and precise manufacturing, use of proper materials and proper lubrication (including a good motor oil and maintenance schedule) are definitely all important factors to make rings last as long as they do.
Now let's throw in the factor of pressure-viscosity coefficient. PAO has ~9% greater film thickness @ 100°C compared to group I-III and close to the same at 80°C. Down at 50°C though, the mineral oil is upwards of 20% greater film thickness than PAO.
So, throw all of that in the mix. Oh, and don't forget the POE and AN having their own effects.
So, throw all of that in the mix. Oh, and don't forget the POE and AN having their own effects.
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Another good study ... similar findings.
PDF download: https://www.researchgate.net/publication/258047957_Advances_in_Piston_Rings_Modelling_and_Design
Snip its ...
"The first consequence of piston/liner relative velocity decreasing when the piston is approaching one of the dead centres is the reduction of the oil film thickness. The asperity contact can occur if the oil film becomes thin enough. In order to numerically describe these effects, the computer simulations of ring performance generally include mixed regime of lubrication models. The oil film boundary value for the mixed lubrication model can be determined in many ways, but it always depends on surface roughness. Boundary lubrication occurs when the surface contact becomes continuous. The oil film thickness has decreased to such a low level that the oil film only provides lubrication between the asperities: the load is carried by the surface peaks and not by the oil film. Mixed lubrication of piston rings was effectively investigated by applying the simplified average Reynolds equation presented in the work of Wu et al. [24]. The inter-ring gas pressures, as well as the pressure on the inner rim of each ring, are normally computed from the experimental cylinder pressure data and assumptions on the blow-by and rings sealing effect [25]. The hydrodynamic lubrication simulation algorithms normally include an iterative scheme on the oil film pressure in order to find equilibrium of the force acting on the ring in radial plane, see Fig. (3)."
"THE EFFECT OF TEMPERATURE IN THE OIL WEDGE
The analysis of the oil film thickness can be performed by using Reynolds equation coupled with the two dimensional energy equation, in order to take into account the oil temperature increasing due to the heat generated from the viscous dissipation [29]. In fact, using the energy equation, temperature distributions in the oil film as well as the average value can be calculated; then, the oil viscosity is estimated by using the mean oil film temperature.
Since the oil film temperature between the ring and the liner varies from the liner to the ring as well as from the inlet to outlet, it is necessary to be cautious about the prediction of oil film thickness using the original Reynolds equation in which viscosity is assumed to be a constant in the vertical direction of oil film. Under the hypothesis of incompressible oil film with Newtonian behaviour, uniform viscosity along the whole ring surface, laminar flow, uniform properties as specific heat, heat conductivity, in a engine cycle while the oil viscosity is a function of temperature, fully flooded inlet and Reynolds boundary conditions, the one-dimensional unsteady Reynolds equation can be coupled with the energy equation [29]. The temperature distribution along the cylinder liner has a higher slope near the top dead centre and a lower slope near the bottom dead centre, as observed through experimental analysis. An interesting approach to the liner temperature is to use the measured temperatures at the top dead centre, mid-stroke point and bottom dead centre, and to adopt an approximate expression to evaluate the liner temperature distribution. One of the results obtained by the Authors in [29] is the graph of the oil film thickness as effect of the ring temperature at 1600 rpm and engine no-load conditions, Fig. (4)."
PDF download: https://www.researchgate.net/publication/258047957_Advances_in_Piston_Rings_Modelling_and_Design
Snip its ...
"The first consequence of piston/liner relative velocity decreasing when the piston is approaching one of the dead centres is the reduction of the oil film thickness. The asperity contact can occur if the oil film becomes thin enough. In order to numerically describe these effects, the computer simulations of ring performance generally include mixed regime of lubrication models. The oil film boundary value for the mixed lubrication model can be determined in many ways, but it always depends on surface roughness. Boundary lubrication occurs when the surface contact becomes continuous. The oil film thickness has decreased to such a low level that the oil film only provides lubrication between the asperities: the load is carried by the surface peaks and not by the oil film. Mixed lubrication of piston rings was effectively investigated by applying the simplified average Reynolds equation presented in the work of Wu et al. [24]. The inter-ring gas pressures, as well as the pressure on the inner rim of each ring, are normally computed from the experimental cylinder pressure data and assumptions on the blow-by and rings sealing effect [25]. The hydrodynamic lubrication simulation algorithms normally include an iterative scheme on the oil film pressure in order to find equilibrium of the force acting on the ring in radial plane, see Fig. (3)."
"THE EFFECT OF TEMPERATURE IN THE OIL WEDGE
The analysis of the oil film thickness can be performed by using Reynolds equation coupled with the two dimensional energy equation, in order to take into account the oil temperature increasing due to the heat generated from the viscous dissipation [29]. In fact, using the energy equation, temperature distributions in the oil film as well as the average value can be calculated; then, the oil viscosity is estimated by using the mean oil film temperature.
Since the oil film temperature between the ring and the liner varies from the liner to the ring as well as from the inlet to outlet, it is necessary to be cautious about the prediction of oil film thickness using the original Reynolds equation in which viscosity is assumed to be a constant in the vertical direction of oil film. Under the hypothesis of incompressible oil film with Newtonian behaviour, uniform viscosity along the whole ring surface, laminar flow, uniform properties as specific heat, heat conductivity, in a engine cycle while the oil viscosity is a function of temperature, fully flooded inlet and Reynolds boundary conditions, the one-dimensional unsteady Reynolds equation can be coupled with the energy equation [29]. The temperature distribution along the cylinder liner has a higher slope near the top dead centre and a lower slope near the bottom dead centre, as observed through experimental analysis. An interesting approach to the liner temperature is to use the measured temperatures at the top dead centre, mid-stroke point and bottom dead centre, and to adopt an approximate expression to evaluate the liner temperature distribution. One of the results obtained by the Authors in [29] is the graph of the oil film thickness as effect of the ring temperature at 1600 rpm and engine no-load conditions, Fig. (4)."
Since we are focused on oil film thickness (OFT) in engine components, and cam components came up earlier, found this paper which addresses cam to flat tappet OFT. PDF download link available.
koreascience.or.kr
Oil Film Thickness Measurement of Engine Bearing and Cam/tappet Contact in an Automotive Engine -Tribology and Lubricants | Korea Science
The capacitance technique was used to measure the minimum oil film thickness in engine bearing and the central oil film thickness between cam and tappet. This method is based on the measurement of total capacitance of oil film. For the measurement of the oil film thickness between cam and...
koreascience.or.kr
Are there any other factors that effect the pressure-viscosity coefficient besides the base oil and oil temperature?
What about PAO and the comparitive pressure-viscosity coefficient at temperatures well above 100C, like seen in track use?
Oil temperature on the top compression ring will be well above 100C on the daily driver. Not trying to make an argument here.
Yes, Figure 4 in post #114 above shows the OFT on the top ring as a function of oil temperature in the cylinder.Oil temperature on the top compression ring will be well above 100C on the daily driver. Not trying to make an argument here.
The temperature distribution along the cylinder liner has a higher slope near the top dead centre and a lower slope near the bottom dead centre, as observed through experimental analysis. An interesting approach to the liner temperature is to use the measured temperatures at the top dead centre, mid-stroke point and bottom dead centre, and to adopt an approximate expression to evaluate the liner temperature distribution. One of the results obtained by the Authors in [29] is the graph of the oil film thickness as effect of the ring temperature at 1600 rpm and engine no-load conditions, Fig. (4)."
Hermann, to your point. my Pontiac 'dealer' put 15W40 Quarker State in everything! i questioned the service manager once('90's) and he said the engines 'run' quieter. #2 my BMW 'dealer' put 20W50 Valvoline Racing in everything. i questioned the service manager('90's) and he said 'they had better experiences with the 20W50 racing(castrol 10W60 in M's). i had a pont. GP 3.4L '91. i decided to try an off brand of oil , AGIP SINT 10W40. and i was surprised by how much quieter the engine ran. at some point manufacturers required their dealers to utilize 'their' Branded motor oil IF dealers want warranty support...i don't know what my BMW dealer has in their over head lube lines these days. i bring my oil(5w40 pennz) and have them to install it(have it noted on work order)'10BMW X5M..note; REDLINE ESTER AND MOTUL 300V OILS run quieter vs most others.
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