If your an engineer then surely you understand that you CAN NOT build pressure to "float" the crank. To do this you would have to have a closed bearing with seals on each side to contain the oil (hydrostatic).
An engine with open sleeve bearing relies on hydrodynamic pressure. The speed and rotation of the crank/cam journal create a wedge of oil that the bearing "skates" on. The pressure in an automotive lubricating system is simply dead head pressure or reserve pressure. That pressure instantly goes away once it inters the journal. That wedge of oil however can have a hydrodynamic pressure of over a thousand PSI.

 

Yes, we are 100% in agreement.

 

Well, you don't see THAT too often around here.

 

I don't agree.

 

to the engineer - please explain how rod bearings survive without oil pressure floating them off the crankshaft.

 

Serves me right for replying after dinner and a few drinks. You are right, the bulk of the pressure is the hydrodynamic pressure resulting from the motion of the bearing itself, which is why the rod bearings survive. There are bearings in low speed machinery that do indeed use pure hydrostatic lubrication with pump pressure being the main thing, which is what I was thinking of... as I said engines aren't my specialty. (There are also automotive and aircraft engines that have "pre oilers", an additional oil pump to pressurize the bearings before the engine is started, to reduce wear on startup before the hydrodynamic lubrication can take over.) But... even relying on hydrodynamic lubrication, the bearings in an engine still require a continuous flow of oil to replenish what is lost out the edges, and that required replenishment flow is directly proportional to the bearing clearance. Worn bearing = more clearance = more oil volume required. Whether the standard pump is now giving me enough flow to supply my worn bearings, I don't know. But a high volume pump certainly can't hurt in this situation.

Hah! Maybe we should just fill our radiators with motor oil, then a coolant leak won't dilute the oil and fry our engines (just kidding).

 

Another in agreement in general on all these quotes on engines on a whole. But even more so for the OP's 4.0 no need for a HV or HP oil pump and have saw then cause problems with stock engines in the past (no experience with 4.0's) but they should be no different same principle.


The additive decals you see at the racetrack on a lot of cars, they do not use any of them. But if you race in a series and they are a sponsor you have to run one of them and where they tell you to place them even. That entitles you to part of the contingency money with how you place.

 

4.0/2.5 distributors are weak and cannot handle the additional stress of HV or HP pumps.

You will notice wear/stress on the drive pins, also, gear failure and shaft wear are common, as your will read on Jeep sites quite often.


Also, no mention here of the fact that lifters fail, or begin to fail, at 6lbs of pressure.




Since I'm a 'snake oil' salesman.............just waiting on all the over educated engineers to point this out.


Edit to add- thinner oils are 'wet' and bleed out easily. Lucas is 100% pure petroleum, not an 'additive' in the snake oil sense, it does force the oil to cling to the metals longer, slowing the bleed of worn bearing for a time......not a fix but may gain you time.

 

Yes. That's traditionally been one of Lucas' biggest customers...shady used car dealers trying to foist cars with noisy motors off on the public. There is no real purpose for the "stabilizer" other than to quiet a worn engine. Modern motor oil is incredibly stable as-is.

 

But the "additional stress" is offset by the reduced back pressure on the pump, reducing the torque it takes to drive it...

 

I don't follow your logic.......


Case in point.......posted just minutes ago.......

https://www.cherokeeforum.com/f2/new...y-4-0l-222659/

 

The input torque on the pump drive shaft is equal to the output torque produced by the back pressure (i.e. oil pressure) on the pump gears. Less back pressure, less input torque, less load on the distributor shaft.

The fact that Mopar offers a high volume pump says they believe the distributor drive shaft is strong enough to drive it, even at the maximum pressure, which I'm not achieving.

What does that have to do with oil pump drive torque?

 

The distributor drives the pump. Has everything to do with it.


The gears are larger on the HV pump, cogs of the gears are longer to move more oil.
It does cause more stress.

You are seeking HV at idle, the HV pump may offer you that at idle but your engine spends little time at idle.......thus the trade off.........solving one problem and creating another.


I studied this some time ago, every article I read was against the HV pump in most cases, specifically in the 4.0/2.5

 

The distributor driveshaft drives the pump, but nothing in the linked topic suggests that the bearing failure was related to the oil pump.

In a healthy engine with good oil pressure already, I agree that a HV pump is unnecessary and possibly harmful. But in an engine that has 20psi oil pressure at highway speed when hot, that's a different matter... and if it increases that 20psi to 30psi, that's still less stress on the distributor shaft than a stock pump at the 75psi relief pressure.

 

Well...I hope you folks are wrong about the HP pumps....I've installed 4 of them, 3 in 4.0L XJ's and one in my Comanche. No problem whatsoever. The only one of those 4 vehicles with an oil pressure gauge was my '87 Waggy, it bumped the oil pressure 15lbs. No problems yes, but if the distributor TAS, I guess I will know why.