Hot-rodding the Nash/Rambler 195.6 overhead valve six

Conversion to full-flow oil filtration

the 195.6 OHV has partial flow/bypass filtration as an option". i modified the pump for full-flow filtration by fabricating a new pump top cover with pressurized oil outlet and blocking the outlet on the bottom of the pump body with a steel gasket that blocked the factory oil outlet hole that fed the main gallery. with this mod oil is pumped out the cover, through a PTFE 6AN line to the rather large oil cooler mounted in the front valance, from there into the oil filter, the filter outlet feeding the main gallery.

In 1964 AMC did add a full-flow filtration oil pump to this engine, but it won't fit into the pre-1964 small (01) chassis, the filter doesn't clear the suspension. I got a rusted 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. The oil pump is external to the block, and sits very close to the lower A-arm pivots. 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.

System overview

Here are some pictures of the completed system with the engine out of the car. The chosen oil filter location is very convenient for many reasons, including under-car access, hose length and mounting point stiffness.

(the initial build in 2010 was with the rubber hoses shown, which were replaced within a couple months with the 6AN braided stainless steel, PTFE lined hose shown above. the "red" engine is the current 2017 build, the green engine is the 2010 build of the same engine. i didn't trust the hose barb system.)

the oil cooler is not yet shown here; see the main page for the reasoning on the engine oil cooler.

The pump, of the common gear type, (green assembly with three cover bolts, lower left in the first picture) sucks oil from the pan and in this modified system, pushes it out the pump cover through the brass fitting and lower-most hose, into the filter inlet. Oil flows through the filter and out the top-most hose (arches up and over) and 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.

Pump body modifications

The trick was to interrupt this circuit to insert the filter. This turned out to be very easy. My first version involved drilling and tapping the pump body outlet for a plug but my final version was vastly simpler -- leave the pump untouched and replace the paper gasket with a 20-gauge steel plate "gasket" the exact size and shape as the pump-to-block gasket that didn't have the outlet hole cut. I used Permatex Right Stuff as sealant. There's a lot of leeway in pump to block insertion depth (gear mesh depth) and during normal operation there's no or little pressure difference on each side, so it can be thin.

I then fabricated a new cover for the pump with an outlet directly opposite the original outlet in the pump body; oil under pressure now exists through the cover. The cover is fabricated from two pieces of 1/4" steel stock, the small piece add stiffness in the center, builds up enough height for sufficient threads in the fitting, 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 exactly matches the factory configuration.

The location of the new pump 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. The fitting has to be removed for access to that bolt. The hole seems large but the effective diameter is actually the ID of the brass 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 really 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.

Note also that internally, the fitting must be flush or below cover plate flush; I pre-assembled the cover plate and fitting, then filed the fitting (not while installed in the cover!) such that it was 10 or so thousandths below flush when assembled.

The top pump hex bolt head interferes with the new oil outlet; I replaced all the bolts with hex 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; the pressure relief bypass is downstream of the filter. This is fine as long as the upstream flow restrictions are low, which they are. I chose a filter (initially Wix 1374, recently switched to Wix 51088) that has both anti-drainback and a 10psi internal bypass; when the filter inlet pressure exceeds filter outlet pressure by that much, it lifts off it's seat and bypasses the filter. The stock oil pressure relief valve remains in the stock block location and does it's job from there.

since the filter is mounted upside down, the anti-drainback feature isn't needed.

I was wary of putting flow restrictions into the main oiling system. The factory passage from pump to main gallery is only 5/16" diameter, but it's only one inch long! Here I am adding nearly 24" (60" with the cooler) of additional path and filter. The fitting out of the pump is necessarily a 90-degree bend but all of the others are be straight.

Ever wary of reliability problems, this new system leaves increased exposure for potential failure: hose-related failures and problems with the filter. a plugged filter isn't a problem on a car well maintained.

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 oil pump failed. Live and learn.

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 welded itself to the cover, shearing teeth off the drive gear. (I shut the engine down immediately, it seems no further harm done.)

I now have a dead-stock oil pump in place, with the blocking plate and custom cover and full flow filtration. Pressures are a more normal 20+ psi at idle, 40 - 60 psi hot 1500 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.

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. here are photos of it apart, before cleaning and reassembly. there is some minor scuffing of the cover by the gears. i neglected to photograph the steel blocking gasket.

Parts list


Drawings and dimensions

oil pump pressure relief valve spring

oil pump cover gasket

one of of the failure-contributors was the oil pump pressure relief valve spring, which i had purchased new from Kanter in 2010. some time during the 2016 LeMons Hell on Wheels Rally it collapsed, and fairly suddenly. new replacements are scarce; i bought one at a dear cost from Blaser's AMC. it's dimensions are below, which should be sufficient to source a replacement frmo industrial sources. (the shorter spring in the pic is the dead one.) in my experimentation before this new spring arrived, i experimented with shimming the old spring. this actually worked well, and since it can be done from outside the engine, is easy to do. shimming would be acceptable to get a new generic replacement to the right output pressure. it's likely not OK for a used spring that's lost it's temper, except in an emergency.

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.

Paths not followed

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.