Introduction

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This writeup walks you through the process of modifying a stock oil metering pump to pump oil from an external tank instead of motor oil. Here's a quick review from the detailed [The Metering Oil Pump and Choice of Oil] for why this might be a good idea:

1. Crankcase oil is not designed to burn.
2. The stock MOP prohibits use of synthetic oils for the entire engine.
3. Contaminanation builds up between oil changes, worsening the above problems, and further decreases lubrication and sealing efficiency within the combustion chamber.

It seems the original system isn't the best solution. Fortunately, there is a simple modification that can fix the stock setup and solve all of these problems. The answer lies in replacing the oil supply from the crankcase with a source of clean, dedicated TC-W3 2-cycle oil.

How 2-Stroke Oil Works in its Original Setting

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2-cycle engines do not have a crankcase lubrication system at all; instead, the lubricating oil is mixed with the fuel and fed into the combustion chamber through the intake path, which on a 2-cycle includes the crank bearings and rods. As the fuel heats, expands, and combusts, some of the oil falls out of the solution and adheres to the cool(er) metal parts of the engine, while the rest burns almost completely. The part that sticks to the engine lubricates it until the next cycle, when it is scraped off and burnt in the combustion process. Note that there are some 2-cycle engines that use an injection system to supply this oil just like Mazda does, and it is in fact likely that this is where Mazda got the idea, as some of the motorcycles and things that have this setup use a nearly identical Mikuni injection pump, and date back much earlier than at least the RX-7, if not all production rotaries.

Advantages of 2-stroke Oil

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• It is designed to be burnt. As described above, the application that 2 cycle oil is designed for involves burning every bit of it, so it is designed to burn as completely as possible and leave very little ash or other deposits.
• It has a high lubricity. This means that it is very slippery, and lubricates surfaces very well. Information on the lubricity of specific oils is very hard to find, but it is a safe assumption that the TC-W3 is at least as good a lubricant as standard motor oil, and probably much better.
• It does not lower the octane rating of fuel as much. Regular motor oil really lowers the octane rating quite a bit, where the 2-stroke still does some, but not to nearly the same extent.
• It is relatively cheap and easy to obtain. The price is about $8/gallon for Wal-Mart brand, and a gallon is enough for about 5 tanks of gas.

Adaptating the Mazda System to use TC-W3 Oil

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There are two ways to adapt a rotary powered car to use 2-cycle oil instead of motor oil. The most common way is to just disable the stock system and add oil manually to the fuel, in the same way as you would for a 2-cycle lawn mower or dirt bike. This is known as "premixing", and works, but has several problems:

Problems with Premixing:

1. It is a pain in the ass: There is no more subtle way to put it, it is really not much fun to have to carry a jug of oil and a funnel around with you anytime you drive your car. The oil smells bad, and is relatively corrosive, and the containers often leak right out of the store. The funnel must be cleaned all the time, and the oil is fairly viscous so it takes a while to pour it into the gas cap. Plus, the mixture must be fairly accurate, so the oil has to be measured in proportion to how much fuel you add. All this is not to mention the funny looks you get from anyone who sees you dumping oil into your fuel tank.
2. The oil isn't good for your fuel system: No, it isn't horrible either, but it has been known to prematurely kill filters, pumps, and injectors. It is also possible for it to separate if the car sits for too long, meaning you will get either too much or too little for the first few minutes when starting until you slosh it around enough to mix it.
3. Premixing adds too much oil: When you premix, you have to add enough oil for the worst case scenario, ie high RPM WOT acceleration. The rest of the time the premixed fuel has way more oil in it than is really necessary.
4. It is easy to forget: Every once in a while, you may not remember to add the oil if you have something else on your mind. Not to mention that not all gas stations carry it so if you don't have some in the car you may not be able to fill up. Although one unmixed tank probably wont kill your engine, it certainly isn't good for it.

The Other Option:
The second way is the main focus of this article. This involves adding a reservoir under the hood that is filled with 2-cycle oil, and adapting the stock MOP to feed from this container instead of the oil pan. The modifications required to set up this system will be outlined below.

The DIY 2-Cycle MOP System

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Here is the step by step process to modify the stock MOP to pump 2-cycle oil from a reservoir. Before we start it should be mentioned that if this seems like too big a chore, there is an adapter available which performs the same function, and can be purchased for $80-$90 at [»http://rotaryaviation.com/oil_injector_pump_adaptors.htm»]. However, if you would like to try the mod on your own, and without the extra parts, read on.



Tools Required

• FSM (available here: [»http://teamfc3s.org/main/factory_service_manual»])
• 10mm wrench, socket
• 1/4" drive socket set
• electric drill
• drill bit set
• dremel
• screw drivers
• A tap and die set is also nice, but not necessarily required
• Some grease solvent (I like either brake cleaner or Purple Power)

Parts Required

• Enough oil for an oil change (You can use synthetic now, yay!)
• Oil filter (My personal favorite is NAPA store brand, but whatever)
• At least a quart of TC-W3 oil, preferably a gallon.
• 3 ft 7/32 vac hose (Braided stainless or brake line is MUCH better)
• 1/4" brake bleeder screw, or other very small hose nipple with one threaded end
• Small (~1-3 quart) tank capable of holding 2-stroke oil
• Level sensor (a spare stock RX7 oil pan sensor works great!)
• Cheap hole-mount LED
• 16-20 gauge wire
• Some thin flat sheet metal (I used the bottom of a coffee can)
• Tube of RTV or other oil resistant sealant

Procedure

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1. Remove the metering oil pump. If you don't know where it is, see picture below, and check out page 2-2 of the 86-88 FSM. To remove the pump, take off the 4 10mm bolts on the front that hold the lines on. Make sure you get the 4 copper washers, and one big 4 hole copper gasket and set them aside. Remove the small cotter pin that holds the linkage in place, and pull the linkage out of the pump arm. Make sure to get the washers that are on it. Remove the 2 10mm bolts that hold the pump to the front cover and pull it off.


2. The first thing to do is to reroute the oil feed line for the MOP. (NOTE: This step may not be necessary, and to do it right, the front cover should be removed, so keep these things in mind and decide for yourself whether or not to do it.) If you look at the front cover where the MOP mounts, you can see the feed line (right next to the shaft) and the vent line (hole about 1/8" away) Here is a picture of what I'm talking about:



The idea here is to connect these two holes to vent any oil pressure that might be present, since our pump will not use the oil anymore. Use your dremel with a cutoff disk to grind a small channel to connect these two holes. Try to keep as much of the aluminum dust you produce out of the hole as possible. As mentioned above, if desired you can skip this step, and if you do perform it, it is recommended to remove the front cover so it can be cleaned afterwards.

3. Now we must separate the MOP from the crankcase oil supply so that we can feed our own oil into it. To do this, we will make a metal block off gasket out of the thin sheet metal. The MOP receives oil in the intake chamber shown here:



so this is what we need to block. Take your sheet metal and using some old scissors or the dremel, make a plate like this:



Make sure the holes are big enough to put the bolts thru, and try to get the center hole as tight as possible around the pump drive.

4. Once the block off plate/gasket is made, we can think about how to feed the pump from the new oil source. Note that this article does not include a section on the oil supply tank, as there are a wide variety of options. Here are a few guidelines however:

• If possible, a metal tank should be used, as 2 cycle oil will eat many plastics. Try to find a tank that can be easily adapted to use a level sensor, as knowing when the tank is empty is a very important part of this modification. I personally welded together a tank out of aluminum treadplate, but that may be beyond the means of many. There are lots of options available though.
• The tank may be mounted anywhere, but must be at least 4 inches above the OMP, and should be as close as possible to allow the oil a direct flow path.

5. The next thing is modifying the MOP to accept oil from an external source. The idea here is to add a nipple to the pump that allows it to feed from the line connecting it to the oil reservoir. To do this, start by drilling a hole in the pump that will enter the inlet area shown above. The size of the hole depends on the fitting being used. Note that to do this step correctly, a tap should really be used to thread the hole. It is possible to do it without one, but it isn't easy. A cheap tap and die set is a good investment for any garage, and can be picked up at Harbor Freight or Biglots or similar for around $20. A nicer set from Craftsman will be about $50, and they go up from there. You can also buy individual taps at Sears or Lowes, but they are much more expensive individually. If you choose not to use a tap, just pick a drill bit that is 1-2 32nds smaller than the outside of the threads on the fitting. Here is a picture of my pump with the hole drilled:



Once the hole is drilled, tap it and thread the fitting in with some sealant on the threads. check to make sure that it does not stick so far through as to interfere with mounting the pump. If you elected not to use a tap, this is the hard part. Find a socket that fits the fitting and bottoms out with some threads still exposed. Carefully start the fitting in the hole you drilled, then slowly thread it in while pushing down very hard. Once you get it threaded far enough that it at least pokes out the other side, stop messing with it, and definitely do not try to take it back out. If you bought a steel nipple, this should work out fine. If you bought brass, you may end up buying another one and a tap and doing it right.

Once the fitting is installed, it should look something like this:



6. Now it is time to put it all together. Make sure to clean all the parts very well to get rid of any dirt or metal shavings first. Then coat the metal gasket you made with a liberal amount of RTV, especially on the engine side, and install it and the pump back on the engine. It should look something like this:



If you are wondering what a liberal amount of RTV is, here is a reference:



Note that this is the most RTV I have EVER used on ANYTHING. It is slightly off topic, but most people use WAY too much RTV most of the time, and the excess squeezes out, dries, fall off, then clogs the hell out of oil pumps, filters, strainers, and all sorts of other things. Just a little tip, when applying the stuff, keep in mind that any excess will squeeze out, and have to go somewhere.

Install the rear two oil metering lines, but leave the front two off.

7. Now it is time to do a little cleanup. Change your oil in the usual manner. You can now use synthetic engine oil if you so desire, so keep that in mind. ADD 2-CYCLE OIL TO YOUR GAS TANK. Use 1-2 ounces per gallon of fuel. This is to lubricate everything during testing, and for the first few miles should your system fail for some reason. Mount your tank and fill it with at least some oil. It might be a good idea not to fill it all the way in case there are any problems it can be more easily removed. Connect the tank to the pump using a small diameter rubber or -AN line. Braided stainless is recommended, as the TC-W3 will eventually soften most rubber lines, causing them to swell.

8. Time to test the system. Leave the bottom (MOP) end of the vac hose unhooked until it drips oil. hook it back up, and put a (~1quart)container under the MOP. Did you remember to premix?

start the car, let it warm for a second, and then run it at 2k rpm for 5 minutes, with the MOP actuator rod pulled all the way up. you should get a steady drip of oil from the MOP into the container, and when done, the bottom should be covered. Don't panic if you don't get any oil at first, it took mine a little bit to start pumping.This test is per the FSM, and if you check in there there is an actual volume number for the amount metered in this test, but for our purposes, as long as it is dripping, it should be working fine.

Shut off the car and hook the other 2 metering lines up.

Here is a pic of my test:



9. Hook up your level sensor. Note that this may be different if a different type of sensor is used, but will work if using the stock oil pan level sensor. Hook a switched 12v wire (ignition on) to one of the wires from the level sensor. From the other, run a wire into the car, to a light of your choice, and ground the other side of the light. To test your sensor, drain the tank and turn the key on. The light should be on. Fill the tank up and it should go off.

Here's my light:



10. You're done! Go enjoy it. It is a good idea to premix the next couple of tanks of fuel, and watch the level in your oil tank. It should drop at a ratio of 1:100 oil:fuel, so that's a quart for every 25 gallons of gas. This is just a ballpark figure and depends on driving style, so a bit more or less is fine. If it doesn't drop a significant amount, your system is not working, and needs to be fixed asap. If it drops too much, it probably has a leak. Assuming it seems to be working, you can quit premixing after a couple of tanks.

Final Notes

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The pictures included with this article are very poor quality, which I apologize for. If anyone does this modification and has a decent camera, please submit better pics.

I am willing to answer questions about this setup on a limited basis, I can be contacted through this system here [patman] or by the same name on rx7club.com. I may also be willing to perform this modification or fabricate tanks for people for a small fee, but that is not relevant to this article.