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Oil Pressure VS the Oil Filter on the L & F 134 Engines

This is extracted from a G503 post at: http://www.g503.com/forums/viewtopic.ph ... 4&start=15


Tony Norton
G-Colonel



Joined: 13 Dec 2002
Posts: 1250
Location: Dumfries VA
Posted: Thu Aug 19, 2004 9:40 pm Post subject:

Don't shoot me but I had to do this. I have seen a great many posts on the oil filter and oil pressure, or the lack of in the L-134. The latest is this post. There was some talk about the little hole in the oil canister standpipe. This hole plays a bigger part in the overall lubrication system than we give it credit for. If you guys think this is WIKI worthy, let me know and I will put it there.

All You Wanted to Know About Go-Devil L-134 Lubrication System But were Afraid to Ask.

Okay….First, let’s play the WWII jeep oil pressure game. It’s easy. Everyone open their mouth wide, and take a deep breath. With your mouth still open wide exhale forcefully. Do this a couple of times. Now, take a deep breath, but this time purse your lips and exhale forcefully. Did you notice that when you did this your cheeks puffed out? Now, remember this and continue reading.

Now let’s review the L-134 lubrication system. But before we do let’s define Pressure as “The action of a force against some obstacle or opposing force; a force in the nature of a thrust, distributed over a surface, often estimated with reference to a unit's area. “ and Flow as “The amount of fluid that flows in a given time”.

Oil Pump

Let’s start with the oil pump. Let’s clear up one sticky point before we go any further. The oil pump does not generate any “pressure” whatsoever. It only creates “flow.” “Restrictions” to flow create pressure.

The oil pump in the Go-Devil engine has a flow rate of one gallon per minute at 250 oil pump (OP) RPMs. The oil pump RPM is 1/2 engine RPM. So, if the engine is idling at 500 RPM, the OP RPM would be 250.

Now, if the engine RPM is raised to say… 2000 RPM, the OP RPM would be 1000, and the flow rate would be 8 gallons per minute.

Oil Galleries

Now let’s go back a look at the idle speed. At 250 OP RPM, pushing one gallon of oil a minute through an approximately 3/8” diameter main oil gallery with the plugs removed would be easy. So the oil flows unrestricted, so you have flow with no restriction, so no pressure. As the engine RPM is increased, in turn increasing the OP RPM and flow rate, the oil pump is trying to push a higher volume of oil through that 3/8” diameter oil gallery. Given the increased flow rate, the friction of the oil against the sides of the oil gallery will create a slight “restriction” to the flow of the oil and will create a little pressure.

Oil Pressure Gauge

Now, let’s plug all the openings to the main oil gallery and attach an oil pressure gauge into the main oil gallery on the left rear side of the engine. If we now turn the engine, and drive the oil pump, oil will fill the gauge line compressing some air into the line. Because air is more compressible than oil, slightly lower gauge readings will result than if this line were filled with oil and then attached to the gauge.

Oil will also now fill all the secondary oil galleries that supply oil to the cam shaft and crank shaft bearings. At this point we now have oil filling what we call a “Constant Volume.” This Constant Volume is made up of the main and secondary oil galleries, and the oil pressure gauge and line.

With the constant volume full of oil, the engine operating at 500 RPM, the OP RPM at 250 generating a flow rate of one gallon per minute being restricted by the oil gallery plugs and oil pressure gauge, the gauge will indicate the resultant restriction as “pressure”.

Crankshaft and Cam Bearings

Now we are taking the oil that was flowing through the 3/8” diameter main oil gallery and causing it to flow through several smaller galleries, and then around the crankshaft and camshaft journals. The clearance between the journals and the bearings can be considered as relief ports to the restriction built up in the constant volume of the oil galleries. As the bearings wear and the bearing clearances widen, it effectively makes the relief ports larger. Therefore, more oil can flow unrestricted through the oil galleries and around the journals. This has the effect of increasing the flow rate and reducing the pressure, which is reflected by the indication on the oil pressure gauge.

Oil Pump Relief Valve

We have been talking about flow rate, restrictions, and constant volume. Let’s remember that a resistance or restriction to flow can be measured as pressure. There is a relief valve in the oil pump body that is calibrated in PSI (pressure). It is a spring-loaded poppet valve that is forced off its seat at 50 PSI and is fully open at 75 PSI.

With the engine at idle (500 RPM) and the oil pump is running at 250 OP RPM the relief valve is closed, and at full pump flow rate should be generating 25 PSI at the output of the pump. Given that some of the oil is “flowing” past crankshaft and camshaft journals, the additional oil is not being forced into the constant volume of the oil galleries and oil gauge, so the gauge will indicate a pressure equal to the output of the pump (25 PSI.)

Now, as the engine RPM increases, the OP RPM will also increase as well as the flow rate. As the flow rate increases and more oil is being forced into the constant volume two things happen. (1.) The oil pressure gauge will indicate the increasing system pressure caused by the restriction to flow of the oil, and (2.) as the flow rate increases the restriction to flow will cause the relief valve to begin to open and shunt the excess oil that cannot be forced through the system directly back in to the oil sump. Since the working range of the relief valve is 25 to 75 PSI, on an unworn engine you should see a minimum oil pressure of 25 PSI at 500 RPM and a maximum oil pressure of 75 PSI at higher RPM. As the bearings in the engine wear, there is less restriction in the oil flow path, so even if the pump is putting out the full flow rate, the indicated pressure will be lower, based on how much the restriction has been reduced at the bearing clearances.

Oil Filter

The oil filter used on the Go-Devil L-134 engine is a “bypass” type oil filter. What this means is that not all the oil in passed through the filter 100% of the time. A “full flow” oil filter inlet is connected directly to the outlet of the oil pump. The outlet of the full flow filter is connected to the engine main oil gallery. In the bypass filter, the inlet of the filter is tapped into the main oil gallery.

In this lubrication system the oil enters the filter canister at the side at the top, fills, flows through the filter element, and then flows out through a small hole in the standpipe in the center of the filter. The outlet of the filter is connected to the engine timing cover, where the oil returning to the sump is used to lubricate the engine timing chain and gears.

There is some controversy that a bypass type oil filter is not as effective as a full flow filter. Remember that the oil pump is pumping 1 gallon a minute a 500 RPM and 8 gallons a minute at 2000 RPM. Since the filter is pulling the oil flow off the main oil gallery it is taking advantage of the full flow rate of the oil pump. So if your engine is operating at a constant 1500 RPM all the oil is being passed through the filter about two and half times in one minute.

Bypassing the Bypass Filter

There was statement in one of the popular jeep restoration books that advised to bypass the inefficient bypass oil filter. If you got anything out of the paragraphs above describing this oil filter you should now realize that it is very efficient, and the information presented in the book is WRONG.

However, let’s say you are not convinced. So what happens when you bypass the filter. There are two ways you might do this.

(1.) You could plug the oil gallery outlet tap just in front of the fuel pump and just stop the flow of oil to the filter. This method will result in depriving the engine timing chain and gears of all lubrication. That front crankshaft counterweight may be “going like a devil”, but it is not doing a cannonball, and the oil just does not splash that high. Oil pressure as seen at the oil pressure gauge will remain unaffected.

(2.) You could remove the oil line from the input to the oil filter canister and connect it directly to the port on the timing cover. Seems effective right? Timing chain and gear get lubed. Well…yes they do. But let’s look at what you’re missing.

First, you have no oil filtration at all. So hard little carbon deposits from the combustion process, plus tiny bits of abraded metal don’t get filtered out of the oil. These little guys get forced back into that tiny space between the crankshaft and camshaft bearings. This debris acts just like grinding medium and grinds away at both the bearings and the crankshaft and camshaft journals.

Second, the oil flow is going to take the path of least resistance, or should I say “restriction.” This would be the path provided by that flex oil line you connected to the timing cover. It’s as big as the main oil gallery. So guess where most of the oil is going to go? And since the flow is not as restricted as when going through the oil filter, the pressure you see on the oil pressure gauge will be less with the filter out of the circuit than with the filter in the circuit. As the engine bearings are quickly eroded away, you may think the timing chain and gears are thanking you, but they are being eaten up by the same debris that is circulating in the unfiltered oil.

Engineering the Bypass Oil Filter

Many folks have looked at the oil filter canister and wondered “How does this thing work?” You can see where the oil goes in. You can see where is comes out. You see the pipe in the middle that is plugged by the cover bolt, so how does the oil get into that pipe if the bolt is plugging it. Well, about an inch down the standpipe is a small hole that the oil passes through to the outlet fitting at the bottom of the canister. From here the oil flows through a flex line attached to the timing cover and flows onto the timing chain and gears.

Why didn’t they just make a screw on top to the oil filter and let the oil just run out the bottom you ask. Why didn’t they make that tiny hole bigger so more oil can get through it. Here’s why. That tiny hole in the standpipe that the oil must flow through to exit the oil filter is an “engineered” metering hole. The size is calculated based on the total bearing clearance of new bearings. This equals a hole about .055" in diameter.

The reason for this is if the hole was not there, or was any bigger, the oil flow would take the path of least resistance (here we go again, restriction). So, most of the oil would flow forward through the oil gallery, the flex line, into the oil canister, and back to the sump through this hole rather than flowing to the crankshaft and camshaft bearings. This would deprive these bearings of vital flow of oil they would need at the most critical time, which is the bearings half-life.

The hole is the same size as the combined new bearing clearances (about .055"), so oil flows through the main oil gallery, splits off and an equal amount is sent to the bearings and oil filter. As the bearings wear, there is less restriction, so more oil flows to the bearings, but the flow going to the oil filter remains constant because the metering hole never changes size.

How Do I Increase Low Oil Pressure (On the Gauge)?

There is talk about shimming the relief valve spring in the oil pump to increase the output pressure. What this does is to cause the relief valve operating range to move higher. Shims are install in a new pump. Each shim accounts for approximately 5 PSI in the pressure to unseat the relief valve. Shimming this spring is actually used in the manufacture of the pump to set the opening threshold of 25 PSI required to unseat the relief valve. Adjusting the output pressure by adding or removing shims is done at the final assembly pressure test to compensate for variances in the tolerances of the final machining of the pump rotors and body casing.

The end user may elect to attempt to raise the pumps output pressure by adding shims. However, if the pump is badly worn adding shims will not improve the pressure. In 98% of cases shimming the oil pump will not cause the oil pressure to increase because the bearing are worn to the point that there will still be “unrestricted flow” through the wide bearing clearances. Minimum specification oil pressure on the gauge is 10 PSI. Any less than this means that the engine requires that the crankshaft and cam bearings be replaced. And, if you are replacing these bearings you might as well overhaul the engine .
_________________
Tony Norton
Dumfries VA tonynorton@comcast.net







Alasdair Brass
G-Major General



Joined: 15 Dec 2002
Posts: 3102
Location: Christchurch New Zealand
Posted: Fri Aug 20, 2004 1:46 am Post subject:


________________________________________
Hi Tony,
Your article says it pretty much as it is but for the purpose of clarity I correct one point.

The timing chain sprockets get a quantity of lube from a drilling through the crankshaft from #1 main bearing journal. However, it seems the design engineers at WO felt insufficent quantity was being supplied and the oil filter return was directed at the chain. As earlier WO engines did not have a filter, both the addition of the filter and the return to the chain were likely to have been a measure to cope with extreme duty a jeep engine was likely to meet. It is therefore unlikely a failure will occur with the filter is blocked but it may cause a reduction in the service life of timing chain.

On a gear drive engine, the crankshaft is not drilled but an extra gallery is drilled from #1 cylinder block main bearing, through to a point midway between the two gears at the front of the engine. Here, a jet is fitted that directs oil to the mating point of the gears. In my opinion, a gear drive engine is less likely to be affected by the blocking of the filter oil return line as there is an improved flow compared to the chain drive design.

Thanks for laying it out,
Al
_________________
D. Alasdair Brass
New Zealand. al@southernviking.co.nz
MVPA 5676
GPW 53126
MB 290463
Bantam T3 36501
Part of the G since early '98

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