"Stuff the longest rod that can fit in the engine." - Smokey Yunick
Oiling Piston When Stopped
- Thread starter EMPIRE
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all I get is this, but in reply I can see it
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Dwell means this, the whole world knows it, so how long is this dwell time for the being being stopped? I did not bold the words, the definition was bolded.
dwell (plural dwells) (engineering) A period of time in which a system or component remains in a given state. (engineering) A brief pause in the motion of part of a mechanism to allow an operation to be completed.
Yeah ... dwell, when piston V=0 (ie, stopped) for a specific crankshaft angle.
That looks like BITOG website, not the one I linked to.
That's what I get when I clicked the attachment.
Dwell is a period of time, like 4sec, or 9min, or cooked in oven for 75min.
What's the period of time where the piston has paused motion? Is this question too hard, or you just not wanting to answer it?
Ok, where's the flat spot in the graph where piston motion is paused at v=0 for some some period of time (dwell)? There is no dwell where v=0.
Dwell can be one millionth of a microsecond too (a period of time) ... it's still dwell.
Guess you missed my post where I said you need way more graph resolution than the graphs being posted.
Take the piston velocity equation in that link and run a program (Excel would work) with super fine crank angle step resolution (like 0.00001 degree) and a very slow crank RPM.
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I did not miss it.
Yes, a time period is some time period, call it dwell or any other word if you like. What's the actual dwell time period the piston has paused it's motion? Math will tell us an exact #, but I can't seem to find what the # is, can you help find the actual time period? Is it "one millionth of a microsecond", or some other period?Dwell can be one millionth of a microsecond too (a period of time) ... it's still dwell.
And if the time period is that small does it make any diff whatsoever that the piston paused for that small time period? I would think the issue is only present when the pause is on same magnitude of, and bit longer than, the time it takes for the film layer to become useless (as explained by other people), so up front quick no-math analysis it seems the piston cannot stop for very very very small time period, otherwise the film layer would still be there and not be an issue.
A lot has changed (and been learned) since the hayday of Smokey Yunick. In reality, you pick the piston you need, the stroke you need, the block height you need, and the rod length ends up being whatever connects the piston to the crank. People spend far too much time chasing a mythical rod ratio. In many occasions, the longest rod you can fit means to piston is so thin that it flexes at higher pressure and rpm, screwing up the ring seal at best, and sending chunks of aluminum flying into the oil pan at worst.
A lot of the 4 cylinder engines that are lasting into the 500k mile range have a rod ratio in the toilet. NHRA Pro Stock is a good lesson as they typically have rod ratios in the 1.60-1.65 range. Going any longer on the rod means the piston is too thin to keep stable at 10,500 rpm. A taller block means a longer pushrod which means a less stable valvetrain. In the end, the rod length doesn't mean all much. While a short rod will create more side loading of the piston, rarely has this ever translated into more actual wear.
Contrary to popular belief, rod length has extremely minimal effect on dwell time. The degree of crank rotation for peak cylinder pressure is ~16 ATDC. On a 4" stroke engine the difference between a 1.6 and 1.8 rod ratio on piston position at 16 ATDC is thousandths of an inch with no appreciable difference in cylinder pressure.
Sorry, back to the subject. lol
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I'm not going to crunch numbers for you. The equation was shown, you do the crunching yourself.
Even if the piston stopped time period is a in Plank time realm, the fact is the piston and rings have to stop to make a linear 180 deg direction change. That also means the piston/rings need to slow way down before V=0 and speed up again on the 180 deg return trip. Rings going into the boundary lubrication mode (where the wear is greatest) happens before and after the speed goes to zero at TDC ... the piston just has to be at a very low speed to go into mix film lubrication (still some wear going on) and then into boundary lubrication closer to V=0. There is an area before and after TDC where the piston speed is very low (piston velocity equation shows that). That's why there can be more ring and cylinder wear at TDC if the oil is not fully up to the task (as the graph in the other thread showed that ring wear increases when the HTHS viscosity was <2.6 cP). Plus the heat of the combustion reeks havoc on the oil (thins it more and can coke the rings in the grooves) which doesn't help matters.
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You are now playing with delta t. t=10 min vs. t approaching 0.
speaking of speed of light, if you are sitting and watching TV ... at any given moment are you in past, present or the future? You are in the present but continuously transitioning ...
think of t0+t as t approaches 0 ...
if you select a bigger/longer t, you can argue during that delta t, you were in the past, present and the future at the same time.
In the other thread you said the math doesn't work or is not satisfied or support that the piston has stopped ... and I explained that it does.
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All this to remind the world of the point of tangency being a point. And to invent the directionless motion in TDC. One point cannot enable motion, motion cannot be without direction, why not accept that the world doesn't expect you to invent that much?
The world even knows there's problems with the concepts of time and still watches watches. The world goes through points to illustrate depressions, minima, whatever. The real piston comes to a full stop anyway, so the video was okay as it didn't deal with any more ambitious modelling and critique thereof.
What remains are problems of modelling and of persons messing up with it instead of enlightening the world. If you need "An Epistemological Use of Nonstandard Analysis to Answer Zeno's Objections against Motion" – go on with the nonstandard analysis first. The point of tangency ain't that impressive to lubricants, hot rodding, deep thought...
You don't think that modelling of piston ring lubrication up and down the bore needs to be modified at these two points of tangency on the crank circle, do you?
The world even knows there's problems with the concepts of time and still watches watches. The world goes through points to illustrate depressions, minima, whatever. The real piston comes to a full stop anyway, so the video was okay as it didn't deal with any more ambitious modelling and critique thereof.
What remains are problems of modelling and of persons messing up with it instead of enlightening the world. If you need "An Epistemological Use of Nonstandard Analysis to Answer Zeno's Objections against Motion" – go on with the nonstandard analysis first. The point of tangency ain't that impressive to lubricants, hot rodding, deep thought...
You don't think that modelling of piston ring lubrication up and down the bore needs to be modified at these two points of tangency on the crank circle, do you?
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The crank pin never stops. The piston pin is a different matter. At tdc and bdc the piston pin is not moving vertically it is just rotating within the piston bore.
After days of bickering (trolling), I found the perfect situation for the "ignore" option.
Plus you nor the OP will ever travel at the speed of light, someone with a degree in nucklear egineering would know that
In regards to how long something exists at a point it gets worse if you are massless and are traveling at the speed of light (at least from the perspective of the massless particle).
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