How To Shim The Oil Pressure Regulator

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There are several situations in which you would want higher oil pressure then the stock 64-78 PSI (at 3000 RPM and above). These include engines that are going to operate often at high RPMs, engines that will be producing significantly more power then stock, or engines that are going to otherwise operate in extreme conditions. High oil pressure means more oil flow through the engine, better cooling of internal parts, and stronger oil film between moving parts and their bearings. All of these generally lead to better lubrication and better reliability under stressful situations.

All of the major rotary vendors sell adjustable oil pressure regulators and they certainly have their place if you intend to "fine tune" your oil pressure. But in general a person will set the oil pressure at the time of the engine build and then forget about it for the life of the engine. Therefore, it is relatively easy to take a stock pressure regulator and modify it to produce higher pressures.

This document contains instructions on how to do just that. The procedure is easy and can generally be accomplished in under an hour assuming that the oil pressure regulator is already removed from the engine. Normally this is at the time of the initial engine build. The regulator can be removed from the engine while it is still in the car, but this can be a major pain in the butt due to limited access, high torque spec on the regulator and the use of Loctite on the threads. If you do wish to attempt pressure regulator removal with the engine in the car then the Haynes and Factory Service Manuals have instructions on how to do so. In summary you will need to pull the passenger side engine mount and pull the oil pan to gain access to the regulator. It will come out with a 28MM socket and you'll need either a breaker bar or ratchet with a very small head to have enough clearance to fit the socket over the end of the regulator.

Parts Required

• Oil Pressure Regulator (all 12A and 13B up to 1992)
• Several M5 Flat Washers
• 5/32 or 1/8" Roll Pin/Split Pin
• Access To A Welder

Instructions

Step 1 - Clean And Prep The Regulator

Clean up the regulator by removing all excess oil. A little bit of brake cleaner does the job easily, but of course a parts washer will work as well. The regulator is a lot easier to work on when it's not sopping wet with oil.

Step 2 - Drill Out The Roll Pin

To disassemble the regulator we must drill out the roll pin. If you turn the regulator so you can look through the threaded section you can see a pin across the piston that holds it in place. Once this pin is removed the piston will slide out and the regulator will come apart. A 3/16" drill bit is the perfect size. Drill into the indent below the discharge hole until you have drilled through the body of the regulator and as far into the roll pin as you can without damaging the piston. The farther you drill into the pin, the easier it will be to remove. Generally 1-2MM below the surface of the inside diameter of the regulator body is enough.

The roll pin is now ready to be removed.

Step 3 - Remove The Roll Pin

This next step is a bit tricky. With a screwdriver, push the piston down to relieve pressure on the roll pin then use a thin set of needle nose pliers to try and wiggle it out. If after a few attempts this doesn't work, you may find some success by rotating the pin to free it, then using a screwdriver to push on the piston while holding the regulator thread side down. Sometimes it just falls out. If you have drilled enough off the pin it may be possible to use a screwdriver to just pry it out. Thin Vice Grips are also great since you can lock them onto the pin and then use considerable force to bend it free from it's hole. At some point the pin should relent and come out. Pull it from the body of the regulator and discard it.

The pin has been removed from the regulator body and can now be discarded.

Step 4 - Remove The Piston and Spring

With the pin out of the way you can now remove the piston and spring. Using a drill bit or other appropriately shaped object, push on the back of the piston via the hole on the tapered end of the regulator. The piston will slide smoothly out of the threaded end of the regulator. Turn the regulator upside down to remove the spring.

With the regulator disassembled you can see how simple it is. The regulator is connected to the oil passage in the rear iron that comes from the oil cooler and leads up to the oil filter. Pressurized oil presses on the face of the piston through the threaded area of the regulator, compressing the spring. This spring is calibrated to determine oil pressure of the engine. As the spring starts to compress, the piston moves towards the tapered end of the regulator and starts to open up the bypass hole. This vents excess oil. As oil pressure lowers, the spring pushes the piston back towards the threaded area and closes the bypass hole. The regulator really only opens up above 3000 RPM or so because that's when the oil pump starts producing enough volume to create higher pressures.

Step 5 - Insert The Shim Washers

This is where the magic happens. Turn the piston upside down so you are looking inside it and insert your washers. Two washers increases oil pressure to around 90 PSI or so. Adding 3 or more will raise the pressure above 100 PSI. Be careful as too much oil pressure will cause the bypass in the front cover to open so unless you know what you are doing, use only two washers.

If you want to go past 100 PSI then you will need to shim the front cover regulator as well. The procedure for shimming is exactly the same but access is a whole different story. It is beyond the scope of this article to cover the front cover regulator. In a nutshell, you need to remove the nut from the bottom of the cover after the oil pan has been removed, use a magnet to get the piston from the top of the bore, insert washers and then reinsert the spring and tighten the bottom nut.

Step 6 - Reinsert The Piston and Spring

Place the spring into the piston, then lower the regulator body over the assembly. At this point you should be able to push the piston into the regulator body until the tension of the spring stops it.

Step 7 - Install The Split Pin

Now you can install the split pin. Push the piston into the regulator with a screwdriver until it has cleared the split pin hole, then push the pin down through the regulator body and into the matching hole on opposite inner wall of the regulator. This may take a few tries as the piston will want to fight you. Also you may need to shrink the inner end of the split pin a little with a pair of pliers to make it fit.

Using a hammer, pound the pin into the regulator until it seats. Be careful not to miss and hit the threads. The pin should seat solidly in the bottom of the regulator. Check the piston to make sure it still moves smoothly.

Step 8 - Weld In The Split Pin

The final step is to weld the split pin to the regulator body. Not only does this prevent the pin from coming loose, but it also seals the end of the pin and prevents oil loss through it. You can use virtually any welding process you want to do this but keep in mind that you want to minimize splatter and keep the threads of the regulator clean. If you are using a process that involves a lot of splatter (stick or flux core) then it's worthwhile to tape up the regulator body and threads with heavy duct tape. Grind the weld if necessary.

Step 9 - Clean Up

Finally, clean the regulator to make sure there aren't any left over metal shavings inside. A parts washer does this easily but brake cleaner works well too. Thoroughly clean the area between the piston and split pin because debris likes to get trapped there.

Notes

1. The 3rd Gen (FD) pressure regulator is already set up for 80 PSI and is a direct swap in to all 13Bs and 12As. It's available surprisingly cheaply (less then $50) at the dealer so it might be an option if you don't want to go through the trouble of shimming your own.

2. When reinstalling the regulator, be sure to torque it properly. The spec is 70 Ft-LBs. Also use some Loctite on the threads as the regulators have been known to work loose in high vibration applications.

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