Wankel Engine Essay

The Wankel rotary engine named after the designer, Felix Wankel, was engineered in the early 1930’s. The rotary engine was unlike the conventional four stroke internal combustion engines and lacked the need for pistons, valves and camshafts. With only three moving parts involved in the design, this engine showed great promise in reliability and efficiency. The first Wankel rotary model was shown in 1960, not as an engine, but as a pump drive. Instead of the very complicated system involved in a conventional reciprocating piston engine, the wankel engine incorporated triangular “rotors” (see figure 1) that rotate within an epitrochoidal chamber around an eccentric shaft. Not only is this engine much more simple (only 3 moving parts rather

than about 25 minimum in a piston engine), it is also much smoother and delivers a more efficient power band. Instead of a piston, which comes all the way up to its peak point, where an explosion then pushes it back down, a rotary engine is constantly spinning, which allows it to keeps it momentum therefore making it high revving and move more fluidly.
The first company to produce a rotary engine for a consumer vehicle was Mazda, with the release of the 1969 Mazda Cosmo, a two seater sports car which used the first release model 10A engine. The US missed out on this refreshing styling and new alternative to the standard clunky piston engine because the Cosmo was a Japanese release only vehicle. Mazda’s engineers were able to solve most of the engines problems and actually created a very successful range of vehicles throughout the RX-series, the most recent ending in 2012 with the RX-8. The rotary engine model started with a very basic non- release 2-rotor L8A model, which made very little power and was really bad on fuel efficiency. Later, the 10A and 12A models were created to replace this engine, and were much more successful.
A major problem with these engines, however, is that because they have no “cooling stroke”, or time between two explosions for the engine cools down, the engines are known for getting very hot.

This requires the engine to have a state-of-the-art coolant system. Big tunnels through the perimeter of the engine allows coolant to flow all around the motor at all times and keep the engine cool. The radiator is also much thicker from the factory, and is angled at 45 degrees in the engine bay to maximize air flow. The number one reason why these engines stop functioning is due to a problem with the coolant system.

My focus on this project is how one of these engines is “rebuilt”, and how can they be changed (from stock) to create more power or be more efficient, through what is called “porting”. I chose this topic because when I was introduced to the rotary engine last year when I bought my second car, I immediately fell in love with the idea. My cars engine was “blown”

meaning it no longer functioned due to major engine problems. This required me to bring it to a shop to have it fixed, where I found out just how rare these cars are. Not only did the shop tech not know what the engine was, he had no instructions in his system on how to work on it. After being turned away from three different shops, I decided to learn how to do it

myself.
Rebuilding a rotary engine, as I found out, is no easy task. First, the engine must be pulled out of the car, which is about a ten hour job with help. Once the engine has been removed, all the accessory parts must be removed from it, for example all emissions parts,belts and pulleys, etc. At this point, the engine is taken apart through the removal of the front cover p-bolt, flywheel nut, and then all 19 tension bolts. Once all of these have been removed, the engine is taken apart in sections from the rear to the front (see figure 2). Once the inside has been exposed, all the parts must be delicately placed onto a clean cloth, sprayed with WD40 to prevent rust, then covered with a towel to prevent dust from settling on them. Once you have isolated the problem with the engine, in my case I needed a new rear iron (see figure 3), and I bought a new one craigslist.
The most important part of engine building is in the cleaning and preparation. If the rotors are not perfectly clean, they will not seal against the housings, and the engine will not run at all. Therefore, The cleaning phase usually takes anywhere from 8-12 hours depending on how dirty the parts were after removal. All carbon buildup must be scraped away carefully with a pic, and brake-cleaner or carburetor-cleaner is used to break down excess particles. I used a toothbrush to clean out the passages that the coolant flows through, but I have heard of people using a isopropyl alcohol to break down any dried up coolant. The slots that the coolant seals sit in (figure 4) must also be scraped out and cleaned very well, or the coolant seals will not seat right and the engine will leak coolant into the area where the combustion process occurs and lead to a major engine failure. This process must be completed on all 3 Irons, and on both sides of the middle iron, as well as on both housings.
The process for cleaning the actual rotors is entirely different. First, the bearings must be pressed out of the center to protect them, and then the rotor is set into a tub of chemical solvent for 4 hours. The solvent is a mixture of some very corrosive chemicals that reach into all the small grooves and slots on the rotors and break down any grime or carbon that is hard to get with tools. They are then blown dry with compressed air, and covered in a good coat of WD-40. Using an old side seal and some brake clean, you can clean out all the passages that the seals sit in to insure the seals will seal properly. After sliding the old seal back and forth through all the slots, the dirt should be completely removed from them, and the rest of the rotor is scrubbed with a PLASTIC brush, because a metal one would leave metal particulates behind that would scrape the inside of the housings and leave you with a “blown” motor.
Lastly, all the old seals must be replaced, and the new ones must be cleaned with brake clean so that no residual dust will get into the engine. The seal kit can be found on Atkins Rotary, where they sell all sorts of different kits for different rebuilds or model engines, I got mine for about 700$ after tax. It comes with new side seals and springs, corner seals and springs, and apex seals and springs, along with a ton of other small miscellaneous o-ring seals. The metal seals are very thin and brittle, so they must be handled very gently. Once everything is 100% clean, and you have inspected all parts to make sure there is no rust anywhere, the block rebuild can begin.
The first step is to bolt the front iron up to the engine stand, with the seal side face-up (see figure 5). The last step in preparation is going over the iron one final time with a microfiber cloth and squirt some assembly oil to give the parts a coat of protective lubricant, and a layer of silicone sealant on the legs of the iron (figure 6) to create a seal for the oil pan. The first housing is placed over the iron, and aligned with the front iron through the use of two “dowel pins” that keep everything straight. Next, the first rotor face must be prepared. Each rotor is numbered 1 for front and 2 for rear, and the rotor faces are labeled 1A, 1B, 2A, and 2B. Press the bearings back into the rotors, now that we are ready to build, and cover them with a layer of assembly oil. There are two oil sealing rings on each rotor face, as well as three corner seals. The oil seals are very important, and can only work properly if put in a certain way. There is a spring that is placed underneath them that holds them out, and this spring must be set so that when the engine is rotating, the seal locks in place and does not allow the seal to rotate independently of the rotors.
Next, there are three corner seals for each rotor face, each with their own spring underneath. The corner seals just slide in, and then the side seal springs can be placed in, followed by the side seals themselves. Once they have all been inserted, you must make sure that all of the seals are able to push back out when pushed in. If they become jammed when you push them down, you must remove them and trim them with a sanding wheel then re-clean them. After they all are able to slide in and out smoothly, That rotor face is done. Once this has been completed, the first rotor can be set down into the housing (see figure 7) around the stationary gear. The oil seals and springs can now be placed onto this rotor face 1B, and the eccentric shaft placed through the center. Once the rotor is placed down and set firmly (it only goes in one way), the apex seals and springs can be set in. Originally, apex seals are three separate pieces that are very difficult to insert. The atkins rebuild kit comes with improved two-piece apex seals that are much easier to insert. There are two springs that must go in with the main apex seal piece, and slid down very carefully. The second piece of the apex seal with fit down in the slot left once the main seal is down. This is done for all three apexes, or corners, of each rotor, so six in total. This process is repeated after the middle iron is placed down over the first rotor. Housing, Rotor seals on face 2A, put the rotor down, complete rotor 2B, place down the front iron, and then everything is sandwiched together using the tension bolts. The tension bolts get some new o-rings to help seal the engine together, which should come in any rebuild kit. They are torqued down in a 3 step process in a very specific order (see figure 8). The first round is to 15 foot pounds, then 25, then a final torque of 35 foot pounds. After this has been completed, the front cover must be put together, which involves inserting your oil pump and drive gear around the eccentric shaft (see figure 9). This is what pumps oil through the engine while it is spinning. Then, the area where the front cover is bolted down is covered with a layer of silicone sealer, and then it is bolted down to 20 foot-pounds. With this, the engine short block rebuild has been completed, and all that is left is to put all the accessories back on.

Now, porting is not necessarily a mandatory part of the engine rebuild, but it is recommended if you want to make the engine more powerful. From the factory, there are 6 holes that are used to bring air into the engine. These holes come together in each iron through the “port” and then used to create combustion. “Porting” is the process of altering that intake port in certain ways in order change the power output of the engine. There are many different types of ports to choose from, starting from the mild port all the way to what is called the “J port” (see figure 10 for port diagram). The alteration of these ports can allow air to flow easier, allow more air to be pulled in, or to direct the air a certain way to create what is called turbulence, which uses the flow of air to help increase engine efficiency. On my engine, I chose to leave the ports stock so that I could have a better chance at passing smog. The most common port is actually the street port, which is just a larger version of the stock port and allows for a small but noticeable gain in horsepower, without sacrificing fuel economy.
From the factory, a 13B rotary has what is called a “6-port” intake, which has four small holes for air to flow through during the low to mid-range rpm, and two more larger ports that open up for more top end power. This was an attempt by mazda to increase idle engine efficiency, but actually causes the engine to run rich (more fuel than units air), and therefore be less efficient. With a “mild” port, the engine is able to reach a more level Air/Fuel ratio (specifically 14.6-14.8 units air per unit fuel) which increases fuel efficiency at idle. This means traffic, stop lights, parked, any time the engine is idling you will be getting better fuel efficiency. This is just one benefit to aftermarket porting.
On the other hand, porting can be used to drastically improve power. Ports used in racing, bridge ports and peripheral ports, were developed for high RPM use but are in no way suitable for street use due to emissions regulations and drivability. A bridge port is a port that is added above the original ports that opens earlier in the cycle to allow airflow overlap. However, torque is lost in the lower rev range but horsepower is gained in the higher RPM band. Bridge ports have rough idle characteristics and tend to be very loud. A peripheral port is the pinnacle of rotary porting is is the ultimate port for power. To achieve this port the stock ports are plugged up with a metal or resilient plastic filler and a new port is created on the rotor housing to allow maximum air flow. This port is banned from many racing series because of its amazing efficiency. In 1991, Mazda won the 24 hours of LeMans with a four rotor “26b” peripheral port engine finishing 63 laps before the second place car. Lemans banned the use of the Wankel engine in 1992. Porting is a great tool but Mazda kept fuel efficiency and emissions in mind when the design was released.
Mazda has an amazing racing heritage and even today mazda has the most cars on racetracks on any given day but many forgot how Mazda reached its success in racing. For years the early Mazda RX series cars dominated the road racing scene. In the 70s the RX2 and RX3 won countless amount of races but were still not given the respect the deserved from the racing community.
Rotary engines have many pros and cons, but when it comes down to it, it’s really the drivers choice as to which engines are better. Rotarys are high maintenance, high budget, powerful and sophisticated motors and obviously have their faults, which has contributed to their slow decline in popularity since the early 1990’s. This fact only further interested me in choosing my topic, because I knew I wanted something unique that likely hasn’t been done before.