195.6 OHV lubrication

updated 21 mar 2020

Lubrication system overview

The lubrication system in this engine has proven to be adequate to the task. However, this engine was built before the Interstate highway system was designed; it was never intended for extended high-speed operation and this engine's weakest point is engine oil cooling. i found this out the hard way on an admittedly challenging drive. But my measurements show that engine oil gets very hot on even modest highway driving, and because the modifications for adding oil cooling are fairly invasive, i strongly suggest installing an engine oil temperature gauge (details below), and don't allow temperature to go over 250F -- the oil might be OK over that but the bearings won't like the reduced thickness oil film.

If you plan on prolonged highway driving some way to limit, or at lease see, oil temperature is required.

Oil selection

Lubricants are so good today that any good quaity 10W-30 or 10W-40 is more than adequate. the problem with this engine is heat in the oil. Read below for my measurements and experiences. The bottom line here is that oil viscosity depends on temperature; hot oil is thin oil, and a too-thin oil film will lead to destruction. since this engine does not have full-flow filtration there is no easy way to add oil cooling. If i were to run this engine in daily use without an oil cooler i would at least install an engine oil temperature gauge and drive to keep temperatures under 250F.

I strongly suggest high quality oil, preferably synthetic. I'm not convinced by any claims of synth oil causing any problems in engines that have been run on non-synthetic oils and have never experienced such problems. (I recently switched to synthetic oil on my '68 American, a single-owner car with a documented maintenance history, with zero problems.)

Except as noted below, I recommend Mobil 1 "High Mileage" 10W-30 full synthetic. List price is high but O'Reilly's Auto Parts, at least, sells it for about a buck a quart more than a competitive non-synthetic. Oil is cheaper than motors.

The oil pump

the stock oil pump (Melling M-61) is an external but typical gear pump. the pump inserts into the lower side of the block, pulls oil from the pan and pushes directly into the main gallery. top end (rocker shaft, etc) is lubricated by an external line that carries oil from a tap on the block up to the head casting where it flows upward through a rocker shaft support, into the hollow shaft and from there to each rocker. on earlier engines the top-end source is the main gallery, eg. full engine oil supply. on later engines the top end is fed by an intermittent source generated by a flat on the camshaft's front journal that pulses the main gallery feed, to limit oil flow to the top end.

(The oil pump can be removed fairly easily. Remove one of the two bolts attatching the idler arm to the chassis, loosen the other (I forget which is which), and swing the idler arm out of the way. The pump will come out and just clear everything. On my modified pump I take the hose off, leaving the 90-degree elbow in place.)

Crankshaft main journals (4) are fed directly from the main gallery as is each cam bearing. connecting rod bearings receive oil via drilled crank. The connecting rod big end has a squirt hole that lubricates the cam lobe journals. the cam is also splash lubricated. some years have piston squirt lubrication via conn rod squirt hole. the specifics of the oiling system make it very easy to modify.

Oil pump pressure relief valve spring

Oil volume and pressure increases with engine RPM since the pump is geared to the camshaft. Additionally, when oil is cold it is thick. For these reasons there is an oil pump ressure relief valve, a plunger and a spring. Excess oil pressure lifts the plunger off it's seat, dumping main gallery oil into the sump. Simple. On this engine the spring and plunger are under a plug screwed into the block outside, aft of the oil pump.

Here is more information than you ever wanted to know about this spring. It features a little more heavily into this story further below. This information (should) have no meaning in ordinary circumstances...

AMC oil pump pressure relief valve spring, part 3112400
length 2-5/8"
diameter 7/16"
wire diameter 0.058"
turns 22.3

Note that i have found used springs with different number of turns. i did not measure overall length beause they were all 50 years old and i didn't trust that dimension.

Leakage at the rear of the valve cover

The valve cover design is pretty good but engine oil flows along the rocker shaft and pours steadily right onto the spot where the cover gasket meets the head, and they often develop a minor seep there, even with a new gasket. any tendency to leak is made worse by the oil pouring off the rocker shaft onto the seal.

A simple twist of steel wire around the far end of the rocker shaft provides a path for oil to return to the cavity in the head casting. there is now no oil leak or mess even when running with the valve cover off. the same wire twist has been in place for nine years. it is tight enough to have a shape, but loose enough that it can't wedge itself between the rocker and washer. Even if it wears into two pieces they'll lay harmlessly on top of the head. here's a brief movie (AVI format) of it in operation.


The bypass oil filtration system on eat least the earlier models was an extra-cost option. Many 195.6's have no oil filtration at all. This is not good. If your engine does not have a filter (mounted adjacent to the radiator, it's fairly obvious) you should find one and install it. It's quit easy to do.

I originally assumed without doing research that the bypass filtration system was inadequate, and engineerd a full-flow system, below. An AMC forum member's research found that given in operation the volume of oil is such that all of the oil is passed through the filter in a surprisingly short period of time. Full-flow filtration is preferable (a given particle will be stopped the first time through the pump) but given adequate oil changes and today's high quality oil, is not a reason to worry.

So my original impetus for working out full-flow filtration wasn't as critical as I'd imagined, but full-flow filtration made oil cooling possible.

Modification for full-flow oil filtration

I modified the pump for full-flow filtration by fabricating a new pump top cover with pressurized oil outlet and fabricating a steel gasket that blocked the pump's main gallery output. With this modification oil is pumped out the cover, through a 90-degree (clearance) 6AN line to the cooler and filter, then into the main gallery. details follow.

the pump is Melling M61. buy a new not remanufactured one. the old ones always "look good". there is subtlety in this crude lump; bodies wear, pump volume drops, new gears don't fix cavity wear. you were warned.

Prototype installation

below are photos of the original 2010 installation. the rubber hose/nipple system shown here was swapped out for proper stainless steel braided, PTFE lined, crimped 6-AN fittings a few months after these photos were taken. these photos however show component location well. the oil filter mount is from a remote oil filter kit. it's mounted via bracket bolted to the timing chain cover bolts.

Pump body modifications

The pump (green assembly with three cover bolts, lower left in the first picture) sucks oil from the pan and as modified, pushes oil out the cover through the lower hose. Oil flows through cooler, filter then into the center of the main gallery where the AMC factory conveniently put a 1/4" NPT tapped hole, directly above the original pump feed location.

sadly i don't have a single photo of the steel shim "gasket" that blocks the pump-to-gallery outlet, but it was easy to fabricate -- i simply traced out the oil pump base gasket onto .025" sheet steel and drilled all of the holes except pump outlet.

The new pump top has an outlet directly opposite the original outlet in the pump body; oil under pressure now exits up not down. The cover is fabricated from two pieces of 1/4" steel stock, the small piece stiffens and builds up height for sufficient threads in the tapped NPT hole, and allowed the driven-gear lubrication well to be a simple through hole in the larger plate. The small milled groove feeds pump inlet oil (not outlet pressure) to the top of the driven gear and matches the factory configuration.

The location of the outlet hole was fairly touchy; note that it is not centered in the gear output cavity, but slightly to one side. This is due to interference with the top pump bolt. socket-head bolts are required. The hole seems large but the effective diameter is actually the ID of the fitting, about 3/8".

After welding, the plate warps; I milled it more or less flat then ground it flat flat with 80-grit wet-or-dry on a ground cast iron plate. Flatness matters here, this is the mating/sealing surface for the pump gears as well as the pump body gasket surface. The gasket is dimensionally thin, hard, and subject to full pump pressure, and this is a core mission-critical part. It's worth the extra effort to get this perfect. Note also that the gasket is trimmed around the new outlet hole.

To the cover I added a 90-degree 3/8" pipe to 1/2" flare tubing adapter. I used a stainless steel part instead of plumbing store brass. i needed to shave about 1/16" off one side of the flare adapter to clear the hex socket bolt head. I assembled the adapter and plate on the bench and was able to get it very tight. It should be left pointing towards the front of the car, up 45 degrees or so from horizontal; this gives maximum clearance under the car and allows for easy wrench access.

(a hardware store type brass 90 degree hose nipple is shown here; when i switched out the rubber hoses i installed much larger bore and higher quality stainless steel AN flare elbow.)

Note also that internally, the fitting must be flush or below cover plate flush. i removed metal from the fitting so that it was 0.010" or so below flush when assembled.

the hex head bolts shown in this early photo interefered with the line fitting; I replaced all the bolts with socket head bolts. The top bolt also needs to be 3" long rather than the stock 2.5" given the additional thickness.

Plumbing, oil filter, sizing and flow

This system puts full un-bypassed pump pressure into the inlet of the filter, which only matters for OEMs making millions of cars where owners do no maintenance. The stock oil pressure relief valve remains in the stock location. The filter (initially Wix 1374, now taller Wix 51088) has both anti-drainback and a 10psi internal bypass. The filter is mounted upside down so the anti-drainback feature isn't needed.

The devil is in the details. The critical hoses that appear to stick up exposed are carefully placed to fit into recesses in the hood and aren't as exposed to harm as the appear to be here. It's tight in there, it's a small car.

There's a lot of hose in there, and it's "only" 6AN. Bends are all large radius, two 45-degree fittings and one 90, necessary for clearance out of the pump, but it was bored and smoothed out. Also see the smoothing and debugging done to the pump.

But this isn't a big modern V8 oiling system. here, the pump feeds the main gallery through a 5/16" hole. With the admittedly weak test of blowing through the hose, there's little restriction. by 1600 rpm the relief valve is open, limiting pressure to 60 psi, so volume is adequate for that to happen. In any case it's been running for years with good effect.

With cold 20W-50 oil pressure at idle has the relief valve open; even 2000 rpm pushes cold (60F) pressure past 75 psi, hence the switch of oils.

As of March 2020 this system has three years and over 25,000 miles of fairly demanding use.

2010's modded pump disassembled in 2017

When the engine was again overhauled in 2016/2017 this modded pump had been in use for six years and some 50,000 miles. There is some minor scuffing of the cover by the gears. I neglected again to photograph the steel blocking gasket.

i did not re-use this pump body and gears; it was a used part when i started, and i found a brand-new pump to replace it. it received the same modifications and fabricated top cover and is now in service. gear to body clearance is tighter too.

Pump cover gasket

it's .009" thick, hard paper. it's photographed here on 1" grid paper, 10 lines per inch.

Another modified system

A friend of mine recently bought a '63 hardtop as an imcompleted project. The engine was nicely built, and the builder also modified the oiling system for full-flow filtration.

In this case the builder drilled and tapped the stock, factory cover for the 90-degree elbow. I didn't do that because I thought there would not be enough threads, but it seems adequate here. (I do have a tendency to overbuild.)

Pushing my luck: lubrication system failure

Some time after 2008 I started treating my little '63 American as a sport(y) car, and pushing the engine harder and harder. In 2010 I rebuilt it, using a local shop for the machine work, what I thought at the time was good work.

In 2016 I burned that engine up, melting all the rod big-end and main bearings in an admittedly stressful situation: 24 Hours of LeMons Hell On Wheels Rally (rally, not race); wide-open-throttle in top gear, climbing a 20% grade in Death Valley in August 2015, 115F air temperature.

I managed to limp home with an increasingly loud bearing rap. before the teardown for the current (2017) build i did some tests and experiments to determine the source of the failure. Suspecting hot oil, i inserted a Stewart Warner temperature sensor into the rear-most main gallery port (1/8" NPT) and drove up the local freeway -- within 10 miles and at modest speeds (60-ish mph) the temperature rose to nearly 230F. Now 230F is fine -- but this was a brief test drive in cool weather. Wide open throttle desert highway 115F ambient is quite another thing.

That only partially explained the low operating oil pressure. I pulled the engine out, and examined the oil pump pressure relief valve spring, and found that it had collapsed.

The failed spring was fairly easy to find; there was little tension on it when i removed it from the block. Shimming it (ultimately with a 3/8" spacer) brought oil pressure up to normal.

Conclusion: failure was caused by two factors: severe engine oil overheating and a collapsed oil pump pressure relief valve spring. Oil viscosity is directly relate to temperature, so the oil film was thin. The failed (soft) spring lowered oil pressure from it's typical 55..60 psi to 45, then 40, then 35... psi, at highway speeds.

Upon disassembly, all of the connecting rod big end bearings had melted in place. the 2017 build included a substantial oil cooler. now, under similar load conditions, oil temperature stays under 220F, and on modest highway use 190F (engine coolant temperature).

High performance lubrication

In 2017 I saved up a lot of pennies and had a professional builder, Pete Fleming in the San Fernando Valley, build my next engine. Many pennies. Nearly all of the hefty expense went into top-notch machine work, such as very careful clearancing of crank and rod bearings and journals.

Pete clearanced this engine to run 20W-50 Valvoline VR1 racing oil (available in Los Angeles). This oil is thick when cold; during warmup i keep RPMs down so that oil pressure stays under 75 psi. One cold morning spiked oil pressure high enough to poop out the oil filter gasket. Road side repair, limped home, did more research, and switched to Mobil1 15W-50, one of the few full synthetics to have sufficient zinc and phosphorous for the (highly stressed) flat tappets because it has beter viscosity index.

Oil choice and selection

Here are the documents I ended up with after my oil research, above the ones given earlier.

High-performance system components

I'll allow my squirrel helper here to show you the oil cooling and filtration system installed on this engine. Her right hand is on the cooler feed line. She doesn't actually accomplish much around here but ensures that no peanuts are left lying about.

The current system consists of the stock pump modified for full flow oil filtration, a fairly large stacked-plate cooler with fan, and an Accusump accumulator system from Canton Racing Products. how and why i got here is described below. The full oiling system is visible, other than the oil filter hiding beneath the alternator. The photo below shows the oil pump (red, protruding from the block), the line running to the alternator forward, and the line from the Accusump feeding the main gallery, top and center. Lines are PTFE lined stainless steel braid, crimped 6 AN fittings.

Oil cooling

Given that I had already made the full-flow filtration modifications back in 2016, adding an oil cooler was relatively easy. Oil cooling is flatly necessary for anything more than casual Sunday drives. However without the substantial mod to the oil pump described below there is no way to get at the oil flow.

Oil temperature sensor

For the 2017 rebuild I installed a 1/8" NPT bung for a Stewart Warner temperature sensor down low in the pan.

A note on oil cooler mounting: i originally had the oil cooler mounted down in the valance, a big screened hole below the right headlight. In Death Valley (or equiv.) this was great -- however in cool/cold weather it took over 30 minutes to warm up. It's since been moved to it's current location under the hood.

Here it is mounted on a bracket bent to fit the cooler onto the curved inner fender and to provide about an inch of clearance for air flow. I'm not totally happy with it circulating under-hood air, but it seems adequate. (If i 'hole' the inner fender the fan will then draw cooler air from the wheel well area, should i need it.)

Oil cooler fan operation

In my installation I have a fairly elaborate all-electronic closed-loop cooling system controlling the oil cooler fan. However, the inline thermoswitch built into the cooler is more than adequate.

These modifications allow me to run this engine at more or less full output for extended periods and have engine oil temperature stay below 200F. On a 6000 mile drive across the country (Los Angeles to the southeast, for the 2016 HOT ROD Power Tour) peak oil temperature was 220F.

oil pressure loss in hard turns: Accusump

Yet another serious oiling system problem appears only when the car it's in is driven hard and fast on mountain/canyon roads like we have here in California. i do planned/routed "tours" with a vintage sports car crowd and the roadster is now fast enough to cause severe loss of oil pressure in turns due to sloshing in the pan. i neglected to take the time to baffle the pan when the engine was built. the sump only holds four quarts, though i often drive with five, but then i get oil misting issues and increased oil consumption.

Someone on the 2018 California Melee suggested i look into an Accusump; after research and email discussion with Jeff at Canton Racing Products i bought and installed one.

Briefly, the Accusump accumulator is a cylinder with a sliding piston inside, oil on one side and pressuried air on the other. the oil side is connected to the engine's main gallery through two separate and distinct valves: a small, low flow orfice with checkvalve and a larger, electrically controlled dump valve.

The small orfice and check valve allows high-pressure engine oil to fill the accumulator relatively slowly, the piston compressing the air side until equilibrium. (Here, the accumulator has two quarts of oil at something over 70 psi, which is the cold-engine-oil startup pressure). The slow-fill assures that an empty accumulator won't starve the engine while it fills.

The second valve on the Accusump is large and electrically controlled. its purpose is to allow the pressurized oil in the accumulator to feed the engine when the oil pressure form the main pump temporarily plummets; in my typical case, in severe turns at speed in mountain roads (or panic-type stops) when enough oil has sloshed to one side or the other, allowing the oil pump to suck air. it typcically takes 2 to 10 seconds to recover from this during which oil pressure is zero. plain bearings don't like this especially under load.

Canton has different manual and electric solenoid valves, and different range pressure switches to control the electric solenoid valve. the switch closes (applying power to the solenoid, opening the valve) at a fixed pressure, and opens (powers off) at a somewhat higher fixed pressure. the trick is to pick a pressure switch that remains closed during typical idle (lowest speed/lowest normal oil pressure).

My engine idles at 600 rpm where oil pressure is typically 35 - 40 psi and i selected a switch that closes (turns on) at 35 psi and off at 40 psi. This would mean that when i throttled back the accumulator would dump oil until it equalized to idle pressure (eg. 35 psi). In my case i added a computer output that is "off" below 800 rpm and drive the switch from that. any aftermarket ignitions (eg. MegaJolt Lite Jr, Megasquirt, etc) have outputs for this. or simply set the idle up, or put up with it as-is; in my case at speed the thing would be full anyway under load/speed when i needed it.


The second thing that sold me on the Accusump is that it provides full-pressure engine pre-oiling. at ignition-on the switch is closed (0 psi), solenoid open and the accumulator pushes oil into the engine until it reaches the "off" pressure (40 psi here). takes about two seconds.

Slightly complicated oil changes

the Accusump makes oil changes slightly more complicated. before draining the oil the accumulator must be emptied; simply power the solenoid on until the air pressure gauge reads minimum. after draining and refilling, pull a wire off the switch/solenoid to ensure that the big valve does not open and starve the engine. post-oil-change is the one time when the accumulator is empty and there is no oil in the gallery.

Paths not followed

Oil pump "blueprinting"

This oil pump is very old technology. Huge clearances, rough castings, heavy, cheap to make, and reliable. Note the rough casting in the pump outlet! There's a lot of room for improvement here...

My first modified oil pump failed.

Stock gear-end clearances on the stock pump run about .008 - .009". Hoping to improve oiling, I carefully ground the pump body down so that total gear-to-cover clearance was about .002". Oil volume and pressure went way way up -- 40+ psi at idle, 60 - 80 psi above 1500 rpm. In fact I had problems with the bypass valve not able to dump enough oil back into the pan to keep cold-engine pressures under control. 2000 miles later, the driven gear nicked the cover, and momentarily locked, shearing teeth off the drive gear. (I shut the engine down immediately, it seems no further harm done.)

At that time, 2010 or 2011, I replaced it with a factury pump, with the blocking plate and custom cover and full flow filtration. Pressures are a more normal 25+ psi at idle, 50 - 60 psi hot 1600 rpm and up. Somewhere between these two extremes, .002" excessively tight, .009" factory loose, is probably a happy compromise. Without a specific reason I'm reluctant to do the experiments. Probably dropping clearances to .005 - .006" would make for a healthy increase without any reliabity threat. (the pump needs explicit end-play control, such as a ball.)

note the pump packed with vaseline for initial startup -- this is required. it is not possible to prime the pump externally. it is geared directly to the camshaft, not via the distributor drive gear. it's a slight pain to pack but keep the gasket surface grease-free so that sealer will seal, but this is a critical feature.

The 1964-up factory full-flow-filtration oil pump assembly

The aluminum engine (used only in the 10 series (Classic) chassis) had a pump that incorporated full-flow filtration; in 1964 that pump was installed in iron 195.6 OHV engines in the new-for-1964 01 series (American). the filter on this pump will not clear the suspension or chassis of the pre-1964 01/American.

i got a rusted '64 pump from a friend, it was too far gone to use but it served as a model for cogitating on a solution. The fundamental limitation in the pre-1964 American chassis is clearance. i believe that if i had a decent Classic pump i could have modified it for my own ends, but i couldn't find one, and the non-filter pump is common enough so i based my hack on that.

Below are some pics of the 1965 full-flow filtration pump I got from Joe. Though the casting was too pitted to be used, I did make mods to it that would have solved the problem.

This casting is based upon the venerable old pump, but has a complicated cover that incorporates the overpressure bypass that dumps oil back to the pump inlet; therefore the filter will never get unregulated pressure. That's a required choice for an OEM environment, but not a much of a worry in mine.

Worse, this pump does not fit the earlier blocks; the block casting is wider at the pump mounting face, because there is a passageway in the pump outlet that requires the block face to seal it. The old blocks have air where the new block has cast iron.

However, I needed to block that outlet anyways, so I fabricated a steel button that would clamp under the pump body and block the main gallery passageway. Additionally, the pump outlet would be drilled and tapped as is the other pump. This made the button dimensions critical (note the paint marks I used to verify alignment and contact area) and in the end I abandoned this path; the other pump is far easier to mod, far more common and is in fact lower-profile than the 1965 pump.

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