Explained: Why Diesel engines need a throttle body & throttle plate
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Your post is very well written and explains the basic differences on older engines in a way that would give a student a good picture of the basics...
But...what you are explaining in detail is air movement up to the intake valve and not in the cylinder... and I am referring to air movement after the intake valve on a NA older diesel.
I am not saying that there is any significant vacuum in the intake manifold other than what you pointed out from air filter restriction.
Thanks for the detail about Detroit engines...I did not know that and it was another thing to investigate when I feel inspired to look into it and learn about them.
On my point...
Since the swept volume of a diesel cylinder is...lets say 'X'...when the piston is at the bottom of its stroke...and the speed of the piston is 'X' when it is moving in the downward direction...and the intake valve opening is many times smaller than the swept volume of the whole cylinder...I am talking NA here...not forced induction...then the only way the cylinder can fill is by the piston creating a vacuum in the cylinder.
I believe you are talking about MANIFOLD vacuum...and I am talking about the dynamics of CYLINDER filling...
Which...by the way...there is an overlap period in the cycle where the intake and exhaust valve are open at the same time...although very short in this instance...but I would bet that would explain at least some portion of the oil getting past the exhaust valve past 'loose' valve guides and into the cylinder to create the...
It will just smoke on initial startup.
I believe you are basing your rationale of the unlikelihood of oil being drawn into the cylinders by vacuum from thinking that the intake and exhaust events are seperated to the point that they do not coincide at any given point in the cycle...we would have to take a diesel cam and set up a pair of dial indicators on the lobes and turn the cam one turn and observe the events...
I would be interested in seeing that...and as soon as I get my hands on a cam...I am going to try it...better yet...I need a block, cam, lifters and cam gear...then I will know for myself if any overlap occurs...
Or...we could ask one of the guys that builds the engines or grinds the cams...
The original question was seals on the exhaust valves. As far as pulling oil past an exhaust valve with vacuum how can that even happen? Think about it, when the piston is on the intake cycle moving down the exhaust valve is closed so the stem should not even be exposed to vacuum. When the exhaust valve is open the piston is on an up stroke expelling the cylinder at that point in time the exhaust valve is under pressure.
You have a good question and a good point here...
I want to know, too...and then we can put this to bed and move on...
This reminds me of when Morpheus is trying to introduce Neo to the concept of everything he believed to be true was a lie and created to keep him in a tub...plugged in and generating energy for the Machines...
This also is reminding me of something my Dad told me about him having an argument with a science teacher...he said that...when you draw water through a straw out of a glass...the water moved through the straw by creating a partial vacuum...the science teacher said that the water moved by atmospheric pressure.
Sounds like two ways to explain the same concept...
Waiting to see what come next...this is thought-provoking...