The oil to the crank is restricted on both ironheads and evos.
Sidenote from chevelle http://xlforum.net/forums/showthread...=561553&page=3 :
Stock 76 and earlier pinion shaft hole is .1875" (3/16") the shaft has a reverse thread cut in it.
The threading in the shaft end alone is a restriction as well as friction and it's fed just like evos from the pinion bushing bore.
So they are all restricted, just a little more on Evos.
If you take a straight piece of 6" pipe, cap and tap the ends with the holes left open;
Then roll it down hill. As long as it stays horizontal, water splashes from both ends but there is no suction due to it rolling.
And the majority of water will stay inside the pipe.
Same same on the pinion shaft itself.
If it's just spinning, centrifugal force pushes the oil against the pinion shaft walls.
There is no force in that instance to make it move out to the crankpin.
The force that makes it move to the crankpin of course is oil pressure upstream (not just the presence of oil).
Let's forget about how much pressure for now.
Now oil (flow pressure) is carrying oil into the right wheel and out into the crankpin.
So now you have oil in the crankpin, good. But what happens next?
The motion of the wheels and the position of the crankpin as opposed to the hole position in the crankpin is important.
The crankpin is not spinning. It's locked into the wheels.
Wheel rotation throws oil in the crankpin against it's walls.
Every rotation, oil is pushed against the portion of wall away from the outlet hole then spins around where it pushes oil toward the hole and into the low end bearings.
Newtons law?, I believe, states that a body in motion will stay in a straight line until a force acts on it to change direction.
The oil wants to go out the hole but can't cause the crankpin is now in opposite rotation from the hole, then back into rotation direction the oil is traveling.
So if there were no bearings on the crankpin OD and with a window to the crankcase, you'd see oil would do the same as it does coming back to the tank.
Spurt out when rotation permits.
Now add the oil pressure back.
Oil flow pressure works in conjunction with centrifugal force.
Oil flow pressure will push oil out even though centrifugal force is in the opposite direction of the crankpin hole.
When the hole lines up with centrifugal force, that force is added to oil pressure as it is pushed out the hole.
Strictly nonsensical figures but, if you had 1/2 ounce of oil being pushed out by oil pressure alone when centrifugal force was out of rotation with the hole;
You might be looking at 1 ounce of oil being pushed out when centrifugal force is in rotation with the outlet hole.
If there were too much oil backing up into the crankpin, it would get slung out with more fervor by the time centrifugal force lined up with the hole.
Now we've got oil leaving the crankpin into the low end bearings. What happens next?
The wheels and crankpin spin twice the speed of the oil pump.
So there is plenty of time and speed to lower the static oil pressure in the pinion shaft before it gets to the crankpin.
When the wheels rotate and deplete the main body of oil of pressure in the crankpin, the only force we think of is oil pressure to replenish that.
But for every action, there is a reaction.
When the crankpin throws out oil, it leaves a lower pressure inside the crankpin (lower than incoming oil pressure).
Basically, it lessons the pressure in the crankpin and the oil pressure upstream doesn't have as much pressure to fight against to get into the crankpin.
So centrifugal force of the wheels/crankpin act to assist oil pressure.
The size of the crankpin hole was enlarged at one point and some have 2 holes instead of one.
So there has been some engineering done on that as well.
The restrictor in the pinion shaft on Evos was obviously not to lesson the amount of oil to the crankpin.
It was done to keep more static oil pressure at the lifter bores.
Ironheads feed the rocker boxes off oil pump (flow pressure).
They don't need a residual amount of oil, just constant flow.
So there is no need to build any oil pressure to keep up top.
Evos do not flow feed pressured oil to the rocker boxes. Oil from lifter action is the all they get.
Oil pressure to the rocker boxes stops at the lifter bores.
Since you're not keeping a constant flow up there, you have to keep a constant
oil reserve to the lifter bores.
Then when the lifters come down, they can pick up some of that "reserve" oil and send it to the boxes.
The stored oil up top for evos is called static oil pressure (oil that is resistant to flow).
This oil "reserve" just hovers there awaiting to be carried by the lifters.
In the meantime, oil is passing around there going to the piston squirters on 04-up models.
So there is slow moving oil up top that is fluent (still moving) and the reason it can do that is because of the restrictor in the pinion shaft.
Without the restrictor, more oil would go out the pinion shaft INSTEAD of hovering up top around the lifter bores.
From previous posts, I don't think I did that good at distinguishing between static and flow pressure.
But friction in the pinion shaft will slow oil down (deplete incoming pressure needed to push up to the crankpin).
As flow increases, so does friction,
Friction is the roughness of the passage walls (be it rubber hoses or drilled passages).
The more pressure you have, the higher the friction.
I had drawings and the whole thing on friction I lost with the power spike.
So this is more off the cuff than I had planned.
Due to friction, some of the passing oil basically sticks to the walls and the center of flow speeds up as the sides of the flow slows.
So if you can visualize a clear hose of oil with the sides flowing slowly and the center faster;
You'll see that what actually is able to flow does so in a smaller diameter thru the middle of flow, pressure drops like a restriction in the pipe.
As static pressure rises, so does the affects from friction.
So the lowered pressure in the crankpin from the affects of centrifugal force aide in lowering the affects of friction on the incoming oil.
Speeding up oil flow, lowering heat (higher the friction, higher the heat).
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