explain 'valve lifter (tappet) gallery-intermittent oil flow at reduced pressure

[sdowney717]

Looking at an oil flow chart from the truck service manual
I dont see how the flow is intermittent on cam bearing number 5
oil flow enters between main bearing and cam number 5 to be equally distributed to both areas at the same pressure.
oil flows into cam number 5 bearing
the cam has a cut groove all round circumferentially
oil then enters drilled holes in cam and exits out the back cam holes and goes to the lifter galleries.
How is the flow reduced and intermittent at all?
It looks like it would be full pressure flow here.

[nctom]

Darn good question... Nothing is evident in the drawing that would cause it. Wonder if it just a mistake in the text?

[Jay Tabor]

its not intermittent to the #5 cam bearing,
its intermittent to the tappetts.
The oil hole in the cam rotates with the cam, and everytime the cross drilled hole aligns with the oil supply hole in the cam bearing, oil magically squirts into the cam oil hole, and then out the back of the cam to the tappetts.
so its a pulsating oil supply delivery..

go into the kitchen and turn your faucet- on-then- off, then- on -then- off-then- on-then- off.

[sdowney717]

ok, BUT, the groove cut into the cam shaft on the end means the oil hole does not have to line up, the groove carries the oil round the hole drilled in the cam continuously. IF there was no groove cut into the camshaft, then the oil would pulsate.

The only pulsating oil is the oil feed off number 2 and number 4 cam bearing. That oil feed goes up to the rocker shaft.

[Jay Tabor]

actually it does pulsate, [just like it says] because oil flows up and thru the cam shaft when the holes line up, just like them other two cam journals do.
the time interval until 180 degrees of rotation occurs- the oil bleeds off into the groove in the cam shaft, that lessens the pressure and flow to the lifterators.
and also supplies that cam journal with plenty of lube, which would be lost otherwise due to the huge loss of oil pressure when the oil spills out the back of the cam journals and goes on its merry way to the pushrod lifterators . .
them lifterators need a large volumne of oil, not so much pressure.
thats why the noisy lifters quiet down faster when the engine is idling , rather than at a higher speed.. more oil gets thru because the galleys are lined up longer duration.
no other cam bearing journals have that groovy groove.
neither does any main or rod journals or magazines or newspapers have a groove..
the lifters are groovy! and that annular groove around the lifter body is for good lubrication of the lifter as it slides up and down the lifter bore, a positive lube instead of splash lube, which isnt as good.
its groovy dude!!

[sdowney717]

seeing the groove exists, IMO any pressure fluctuations would be minimal.

It would be interesting to tap into the rear bolt on plate and measure the pressure to see how it compares.

The oil flow chart makes no mention of the pulsating flow to the rockers, why leave out that tidbit?

Perhaps whoever reviewed the document before publishing missed some things. I lean towards someone screwed up on the document and it never was corrected as it made little difference. Either the engine oil flow works or it does not, document has no effect on that, just our perceptions of how it works.

[ruderunner]

Jay's wording is a little more complicated than it needs to be and still incorrect.
Look at the diagram, #5 distribute oil to the lifters, full time as you noted. The grooved journal guarantees that.
#2 and #4 distribute to the rockers and is timed, oil only really flows when the cam holes line up with the passages in the block.
The important thing is the lifters and rockers get oil from different sources. This ain't no small block Chevy.

[Jay Tabor]

not in correct.
if the groove was necessary for oil passage- then there would be no need for a crossdrilled cam journal.
the cam bearings and journals for the rocker arms dont have that groove . . they still get oil.
it could flow on its merry way thru the cam journal center and out the back.
that large grooves dissipates the pressure increase volumne.
same as turning on that kitchen faucet and holding your finger over the bib, then letting go, big difference in pressure when flow is restricted.
the lifters/cam need a lot of oil, not high pressure.

[ruderunner]

OK think about pre lubing one of yhese engines. Spin the oil pump with a drill, do not rotate the engine. Do the lifter galleries fill up? You bet. Does oil get to the rockers? Not unless the cam passages are lined up right. Hence timed flow versus full flow

The cross drilling of the rear journal allows oil from the groove to reach the passage behind the rear cam bearing, not enough would flow out the sides of the bearing to properly feed the lifters. The groove allows oil to reach the cross drilled passages all the time, not just in certain alignments
IF the rear passage were drilled at a different angle so oil would flow to the rear of the rear cam bearing, the flow would be the same and the end of the cam wouldn't need to be cross drilled or grooved.

[nctom]