oil filter question

There are elements of understanding in some of the posts above, but also elements of misunderstanding. Full disclosure: I am a degreed hydraulic engineer, with a Masters degree in Engineering from the University of Kentucky in Lexington, KY. My day job for the last 20 years has been designing hydraulic systems for clients. While I do make mistakes sometimes because I am a human, I do have some knowledge of the engineering and feel I can clear up some of the misunderstandings. If you want to learn and follow along, grab a cup of coffee (or beer!) and keep reading. If you don’t want to learn, I can’t help you, sorry. 

I will attempt to explain the hydraulics of pressure systems as simply as possible. 

First, Confined vs Unconfined systems. In hydraulics the word “confined” has a special meaning, so we can’t apply the general English use of the word. “Confined” in hydraulic systems means there is no open inlets or outlets to the system. The hydraulic fluid is fully enclosed, and when pressure is applied somewhere, all of the pressure in the system increases because there is no release of pressure anywhere through fluid loss out of the system. This is Pascals Law. This is true of the braking system, and why (in theory) all of the brake cylinders work at the same time and with equal force when the MC is pressurised through foot pressure. When there is flow it is usually small, firstly in one direction, and then usually back again to get the system back in equilibrium. 

Unconfined systems have inlets and outlets, and they therefore have flow through the system in one direction only. The system pressure is determined by something providing the pressure (usually a pump) and where and how this pressure is lost on the way to the outlet/s. This can be through friction along the conduit to the outlet, or at bends, constrictions, or orifices along the way. So the hydraulic oiling system in the L134 engine is clearly unconfined as it has an unpressurised inlet (oil pickup drawing oil from the sump, acting as a reservoir), a device providing pressure (the oil pump) and multiple outlets returning unpressurised oil back to the sump. I count at least 16 outlets off the top of my head, but there may be more. These are at each crank bearing, the camshaft bearings, the rod bearings, each rod oil squirter, the timing gear oiler jet and the bypass oil filter system. I think there are more in the tappet bores. 

So, to summarise: one inlet, one source of pressure, multiple outlets. The system could be very simplistically drawn as follows:

Pressure added by the pump is lost along the length of each path to an outlet, firstly through friction in the conduit bore, but also at the bends, constrictions and tiny orifices along the way. In the L134, the length of the conduits are short, and proportionately large in diameter, so friction losses will be very, very small, and probably negligible. Almost ALL losses will be at the outlets of the system, where oil is forced through tiny holes or tight tolerances. Think how small the rod squirter holes are, or the 0.04” timing gear oil jet, or the hole in the centre column of the oil filter housing.

Now, hydraulic fluid, like most humans, will follow the easiest path from application of pressure to release of that pressure. If ALL branches of the system after the oil pump present equal pressure (think resistance) to the oil pump, then no path is any easier than any other path to follow and the oil will flow down all paths equally to an eventual outlet. In a lubrication system, this is obviously the goal. But if one path is noticeably easier than any other path, this pathway will receive most of the flow, and the others will receive proportionately less.

So the L134 designers goal would have been to ensure each branch after the oil pump would have the same resistance to flow, and therefore receive equal flow. Where this becomes difficult is that the diagram above is clearly an oversimplification. There are branches in the conduits after the oil pump that feed clusters of outlets, so that some outlets share common supply conduits. Maybe something like this:

Now the pressure presented to the pump by each clustered grouping of outlets has to be the same for each cluster to receive equal flows of oil. Lets assume this is achieved. So each cluster receives ¼ or 4/16 of the flow. And if outlets E, F, G  and H all present the same pressure at the point where they branch, they will receive equal flow. But lets say ONE outlet, D, presents an easier exit path than A, B and C do. Then within this cluster, D will receive most of that clusters flow, potentially starving A, B and C of flow within the cluster.

Note that does not necessarily mean that outlets E – P will also be starved of flow, as the clusters 1-4 could still present the same pressure to the pump as a whole, thus receiving equal flow into the cluster. The non-uniformity could be restricted to within a cluster, not necessarily between clusters.

I believe this is what happened with the 0.070” timing gear oil jet, and the reduction to 0.040”. 

0.070” was just too big an opening, presented too little pressure to the cluster and received disproportionately too much flow, in some engines starving the No 1 connecting rod bearing of oil and leading to failure. (For reference, a 0.070" diameter hole has 3 times the opening of a 0.040" hole!). This opening would have been enough to starve an adjacent component of oil within the cluster, but probably not enough to see reduced oil pressure within the whole system as measured at the gauge, for reasons as described above. However, consider in another scenario if all crank bearings are badly worn, and all rod bearings are equally badly worn…. 7 out-of-spec outlets out of maybe 16 outlets in total, especially if they are all fed off a common supply, could provide a strong preferred path within the overall system, resulting in observable low pressure at the gauge as the pump just can't keep up, and real oil starvation in other clusters that don’t get proportional flow. You’re on your way to engine failure.

That’s the best that I can explain it in an hour. I hope this helps.

Bruce, I can assure you that if you could drill and tap along the length of the oil galleries with an accurate enough gauge, you would find minor pressure drops along the way, due to friction loss along the length of the gallery. However this would be a negligible drop because of the short lengths involved, and the fact that the gallery bores are so much larger than the typical 0.04” outlets, which is where almost all the pressure in the system is lost on return to the oil pan. And I agree that you would not be able to read the difference with a normal Willys pressure gauge with a shaking needle. But, if you really want to bet, can we do it with money, and not your hat? That way I get something useful and you don’t destroy a good hat? 

Mike and others, technically yes, removal of the oil filter housing would reduce the number of system outlets by 1, say from 16 to 15. Other remaining outlets should theoretically share the additional flow equally ie each get an additional 1/15 of the 1/16 flow that would have gone to the housing, which would be 6.7% extra than the 1/16 they originally would have got on their own. It's debatable whether this 6.7% additional flow would prolong a failing bearings life by very long, but who knows? It might buy a few weeks...

Edit to correct the additional % flow 1/15 would give