Full Flow Oil Filter
As published in

Street Rodder Magazine

July 1988

Pages 64 - 67

Oil filters on Flathead Fords were the old by-pass type which shunted off a small portion of the oil supply to the filter. If there was dirt or grit in the oil which could get past the screen on the oil pump pick-up, chances are it would circulate through the engine a few times before it found its way to the filter. Modern engines use full flow oil filters which filter all the oil before it is circulated through the engine, trapping any particles before they can get to your bearings. This article will show you how to adapt a full flow filter to your flathead.

What we must do is modify the oil pump so it pumps out through the pump cover, through tubing out the side of the oil pan, through another tube to the filter, and then through a third tube back into the engine.

The pump is modified by plugging the outlet port by brazing a steel plug in the slotted outlet hole and making a new outlet in the pump cover plate. A new cover plate was fabricated out of 3/8" steel plate with an outlet hole tapped for a 3/8" pipe thread. The side of the plate that the pump gears run against should be dressed flat and smooth with a surface grinder and then case hardened. A short steel hex pipe nipple like a Weatherhead No. 3069 x 6 is screwed into the new outlet port. Make sure the nipple does not protrude past the inside surface of the plate where it could contact the pump gears. On the other side of the pipe nipple a Weatherhead No. 452 x 8 female elbow is installed which has 3/8" pipe threads on one side and a 1/2" inverted flare tube fitting on the other side to accept the flared 1/2" OD tubing.

 Modified pump on left with outlet port plugged and new cover plate added; stock oil pump on right.  

A bulkhead fitting must be built to provide pipe thread fittings where the tubing can attach to the oil pan. I made mine out of a piece of 1/4" steel plate and two steel 1/2" pipe half-couplings which were shortened to 1/2" long before welding to the plate. A length of 1/2" O.D., .035" wall steel hydraulic tubing is bent up to fit between the oil pump and the bulkhead fitting. The tube goes from the pump across the engine, then forward till it clears the pump pick up screen, back across the engine again and then back a short distance where it will screw into a Weatherhead No. 402 x 8x8 male elbow. The elbow screws into the bulkhead fitting which will mount in a 1-3/8" hole in the flat area on the side of the pan. You will want to make lots of measurements before punching the hole in the oil pan or bending the steel tubing. I used copper tubing for trial fits on all the tubing runs, as it was easy to find and a lot cheaper than the steel tube. Don't be tempted to use the copper tubing in place of the steel, besides being weaker than steel, according to my Weatherhead catalog, copper acts as an oil-oxidation catalyst, causing sludge.

 Pump and tubing installed on engine, ready for oil pan.

On the outside of the pan a heavy 3" O.D. washer with a 1-3/8" 1.D. was drilled to match the mounting holes in the bulkhead adapter, with a gasket between the pan and the flange. The oil filter adapter is a J.C. Whitney No. 84GK0625T with two more No. 402 x 8x8 male elbows and mounted to the side of the oil pan with an "L" shaped bracket. The bracket is fastened with two 1/4-20 bolts which screw into nuts brazed to the inside of the pan. Check for clearance here between the bolts and the crankshaft counterweights and rods.

 Tubes used on outside of engine


One more 402 x 8x8 male elbow is used to screw into the bulkhead adapter and a tube runs from it to the inlet port of the filter. Another tube goes from the outlet port of the filter to the boss at the left rear of the engine. A 45° street elbow Weatherhead number 3350 x 4 and a 1/4" pipe to 1/2 " tube adapter Weatherhead number 202 x 8 x 4 connects the tube to the 1/4 " pipe threads in the block. The tube nuts used on all the tubing runs are Weatherhead number 100 x 8. The filter is a Fram PH-8 which has a built-in bypass valve and anti-drain back valve. I should add a note here that the elbow and the tube adapter have an inside diameter hole size of 5/16". This is the narrowest portion of the tubing run from the oil pump to the filter and on to the block. This seemed to be sufficient as the oil pressure looked good when the engine was running but when I had the outside tubes off the engine later I decided to enlarge them by drilling them out to 3/8" for a little added flow and peace of mind. Be careful when you drill out these brass fittings as the drill bits tend to grab if not ground specifically for drilling brass.

I'm listing the tubing bending details here that I ended up with on my engine, they may not fit another situation exactly because of minor differences in the fabricated brackets and adapters but at least will give a starting point. All dimensions are to the center line of the tubing and all bends have a 1-1/2" radius. Also note that bending steel tubing requires a good tube bender, spring type benders won't do. I used a Rigid No. 398 for this project.
The inside tube from the pump to the pan measures 3" from the end of the tube farthest from the pump to the center of the tube at the first bend, then 6-9/16" between centers to the second bend, then 7-1/8" to the third bend, and 7" from the third bend to the end of the tube at the pump. All bends in this piece are made in the same plane, without rotating the tube as it is advanced in the bender.

The tube from the pan to the inlet of the filter should be marked at 4" and 7-3/8". The first bend at 4" is about 30°, then the tube is advanced in the bender to the 7-3/8" mark and rotated 90° clockwise looking at the end of the bender. Now bend the tube 90°. The length from this bend to the end is about 9-7/16." Allow some extra length here so the other tube from the filter outlet to the block can be made up and both trimmed to the same length.

The last tube is 3" from the block end to the first 90° bend. The second bend is made 4-1/4" from the first bend. Advance the tube in the bender to the mark for the second bend and rotate the tube 90° clockwise, then bend the tube about 42°. From this bend to the end of the tube is about 10-1/2", match it up to the end of the other tube before cutting.

When I finally had the tubing inside the oil pan correctly positioned to line up with the hole in the pan, and all the fittings were tight, I soldered the brass tubing nuts to the brass elbows to lock them in place.

A late model oil pump should be used, which has the oil pressure relief valve built into the pump. I believe these were used from 1949 to 1953. When using this pump in the 1948 and earlier blocks, the oil pressure relief valve in the front of the valley chamber should be disabled by replacing the spring with one that is stiffer than the one in the pump. This puts the pressure relief valve in the correct part of the circuit, protecting the filter from unregulated oil pressure.

I am pleased with the way this project turned out, aside from modifying the pump and cutting the hole in the pan, the rest of the pieces just bolt on. My exhaust headers are home made, so I can't say that every engine will have clearance for the filter. My car hasn't been driven on the street yet, but the engine has been run in the garage and the oil pressure looks fine. The oil pressure and volume may be slightly increased with this modification because that portion of the flow that would have been diverted to the by-pass filter is now going to the engine.

There are certainly other methods one could use to block off the original output of the oil pump. I would think it would be possible to epoxy a sheet metal patch wrapped with wire over the opening as there shouldn't be very much pressure against the patch after the filter and oil gallery is full and up to pressure. At that point the pressure would be essentially the same inside and outside of the pump.
Also other materials could be used for the new pump cover. Brass, or cast iron would be good. Maybe one could drill a hole in the original cover and sandwich a thicker plate on top to hold the fitting. Gasketed, of course.

Maybe this will help to keep some of that old iron running a little longer.

Bill Mumaw

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