Autopsy Of A First-Generation RX7 Mazda Rotary Car Engine

November 8, 2025 by Maya Posch 13 Comments

The eccentric shaft and rotor of the Mazda 12A rotary engine. (Credit: Baked Beans Garage, YouTube)

In theory, Wankel-style rotary internal combustion engines have many advantages: they ditch the cumbersome crankcase and piston design, replacing it with a simple, single-chamber design and a thick, plectrum-shaped chunk of metal that spins around inside that chamber to create virtual combustion chambers. This saves weight and maximizes performance-to-weight. Unfortunately, these types of engines are also known for burning a lot of oil and endless seal troubles, especially with early rotary Mazda engines that easily died.

Yet even 1980 versions were not without issues, a case in point is the Mazda 1st gen RX7 with a 12A rotary engine that the [Baked Beans Garage] over at YouTube got their paws on. Starting with unsuccessful attempts to make the car start, the next step was to roll the car into the ~~morgue~~ garage for a full teardown of the clearly deceased engine.

About 35 minutes into the video, we get to the teardown of the engine, with its parts contrasted with those of a newer revision rotary engines alongside illustrations of their functioning, making it as much an autopsy as a detailed introduction to these rotary engines. Technically, they also aren’t the original DKM-style Wankel engines, but a KKM-style engine, as designed by [Hanns-Dieter Paschke]. [Wankel] didn’t like the eccentric KKM design, as he thought it’d put too much stress on the apex seals, but ultimately the more economical KKM design was further developed.

During the autopsy of the 12A revision Mazda engine, it becomes clear that it was likely overheating that killed the engine over the course of years of abuse, along with ‘chatter’ marks of the apex seals destroying the inner chrome coating. This would have compromised compression and with it any chance of the engine running, not unlike a piston engine with badly scored cylinder walls after ingesting some metal chunks.

While the Mazda 12B and subsequent designs addressed many of the issues with the early rotary engines, its use was limited to some sports models, ending in 2012 with the RX-8. The currently produced Mazda MX-30 does use a rotary engine again in its plug-in hybrid version, but it’s only as a range extender engine that drives a generator. Looking at the internals of those Mazda rotary engines, it’s easy to see how complex they are to keep running, but you cannot help but feel a little bit of sadness that these small-but-powerful engines didn’t make much more of a splash.

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There’s A Wrinkle In This 3D Printed Wankel

February 10, 2022 by Matthew Carlson 10 Comments

Rotary engines such as the Wankel have strange shapes that can be difficult to machine (as evidenced by the specialized production machines and patents in the 70s), which means it lends itself well to be 3D printed. The downside is that the tolerances, like most engines, are pretty tight, and it is difficult for a printer to match them. Not to be dissuaded, [3DprintedLife] designed and built a 3D printed liquid piston rotary engine. The liquid piston engine is not a Wankel and is more akin to an inside-out Wankel. The seals are on the housing, not the rotor itself, and there are three “chambers” instead of two.

The first of many iterations didn’t run. There was too much friction, but there were some positive signs as pressure was trapped in a chamber and released as it turned. The iterations continued, impressively not using any o-rings to seal, but instead sanding each part down using a 1-2-3 block as a flat reference, within 25 microns of the design. Despite his care and attention to detail, it still couldn’t self-sustain. He theorizes that it could be due to the resin being softer than other materials he has used in the past. Not to be left empty-handed, he built a dynamo to test his new engine out. It was a load cell and an encoder to measure speed and force. His encoder had trouble keeping up, so he ordered some optical limit switches.

This engine is a follow-on to an earlier 3D printed air-powered Wankel rotary engine, and we’re looking forward to part two of the liquid piston series. Video after the break.

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3D Printer Air Compressor Is A Wankel

March 11, 2021 by Al Williams 31 Comments

We wonder if mechanics are as annoyed when we say “engine” as we get when someone talks about a “computer” or a “radio.” Sure, you know what all three of those words mean, but there are many different kinds of radios, computers, and engines. In [3DprintedLife’s] case, he made a compressed air engine of the Wankel style.

The Wankel — a rotary engine — is most famous for its use in some Mazda cars. If you’ve done a lot of 3D printing, you know that creating an air-tight piston on a 3D printer is no mean feat. Of course, he didn’t do it right off the bat. It took what looks like a number of iterations to get it going, and he shares some of what he learned doing this project.

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The Rotary-X Engine Is A Revolution In Thermodynamics

February 15, 2021 by Kristina Panos 119 Comments

If you’re running an army, chances are good that you need a lot of portable power for everything from communications to weapons control systems. When it comes to your generators, every ounce counts. The smaller and lighter you can get them, the better.

Connecticut-based company LiquidPiston is developing a high-powered generator for the US Army that uses the company’s own rotary x-engine — a small, light, and powerful beast that sounds like a dream come true. It can run on gasoline, diesel, natural gas, kerosene, or jet fuel, and is scalable from 1 to 1,000 horsepower (PDF).

Co-founder and CEO Alex Schkolnik describes the design as a combination of the best parts of the Otto and Atkinson cycle engines, the Diesel, and the Wankel rotary while solving the big problems of the latter two. That sounds impressive, but it doesn’t mean much unless you understand how each of these engines work and what their various advantages and disadvantages are. So let’s take a look under the hood, shall we?

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Remanufacturing A Rotary Airplane Engine

April 13, 2019 by Jenny List 66 Comments

If someone tells you they have seen a rotary engine, the chances are that you will immediately think of a Wankel engine, as you might find in some of the more exotic Mazda sports cars. But there is another rotary engine that has a prior claim to the name, and it can be found as the power unit for many early-twentieth-century aircraft. In these rotary engines the cylinders are arranged radially around a stationary crankshaft, and it is the engine itself that rotates. They have the advantage of extreme simplicity, smooth power, and a low parts count, at the expense of total loss lubrication, a relatively large rotating mass, and some difficulty in controlling their power. These rotary engines were largely obsolete by the 1920s, but recent upsurge of interest in WW1-era aircraft has led to the creation of a small demand for them. New Zealand based Classic Aero Machining Service have stepped in to fill that gap and are remanufacturing the Gnome radial engine, the most numerous design of that era.

For anyone with an interest in internal combustion engines, the Gnome is a fascinating study. It’s a nine-cylinder design that runs a four-stroke Otto cycle, but instead of the two or more valves you might be familiar with from your motor vehicle it has only a single valve. The so-called Monosoupape design uses its valve for both fuel and exhaust, opening it on the inlet stroke as well as the exhaust stroke. The simplicity of a single valve and no carburetor is thus offset by a difficulty in varying its power , so rotary engines would frequently reduce the number of firing cylinders in lieu of throttling back.

The CAMS Gnome is a faithful copy of the original, but with modern metallurgy and the addition of an electronic ignition system. The original castor oil is still used — it seems classic aviation buffs like the smell — but becuase it is notorious for leaving sticky deposits in the engine they are evaluating modern alternatives. They have some technical details on their website, and there’s a good chance you my hear one of their engines one day at an air show near you.

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3D-Printing Wankel Engine From Mazda’s Beloved “Rotary Rocket”

December 30, 2018 by Al Williams 30 Comments

Although there was briefly a company called Rotary Rocket, the term is much better known as a nickname for the Mazda RX-7 — one of the few cars that used a Wankel, or rotary, engine. If you ever wondered how these worked, why not print a model? That’s what [Engineering Explained] did. They printed a 1/3 scale model and made a video explaining and demonstrating its operation. The model itself was from Thingiverse, created by [EricThePoolBoy].

One thing we really liked about the model was the use of lights to show the different stages of combustion. Cool air intake is a blue light, hot air is red, and so on. It really helps visualize what’s happening. You can watch the video below.

If you haven’t seen a Wankel before, it is a clever design. It has very few moving parts and offers very smooth power transfer and high power to weight ratio. The downside, though, is that the engine deliberately burns oil to lubricate and seal, so it is difficult to meet emission standards and requires a lot of oil. The fuel efficiency of current designs is not very good either, especially since manufacturers will often trade fuel efficiency for better emissions.

If you’d like to read more about the Wankel, check out our earlier post (and the 165 comments attached). We also looked at — or rather through — another Wankel earlier this year.

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See-Through Rotary Engine Reveals Wankel Magic

May 1, 2018 by Lewin Day 25 Comments

The Wankel rotary engine is known for its troubled life in the mainstream automotive industry, its high power-to-weight ratio, and the intoxicating buzz it makes at full tilt. Popular with die-hard enthusiasts and punishing to casual owners, it stands as perhaps the most popular alternative internal combustion design to see the light of day. There are myriad diagrams out there to explain its operation, but what if you could see inside?

The video comes courtesy of [Warped Perception], and features a small Wankel rotary engine intended for model aircraft. The engine’s end plate is removed and replaced with a transparent plate, making the combustion process visible. Add in a high-speed camera, and you’ve got a recipe for a great technical video.

It starts with a basic explanation of how the Wankel rotary power cycle operates, before cutting to the glorious slow-motion shots of the engine in operation. It also highlights several techniques useful for producing this type of video, such as painting surrounding components black to make it easier to image the parts of interest. The visuals are amazing and very clearly show the manner in which the intake, compression, power and exhaust strokes function in the engine.

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