--- title: Part 2 12A Engine Rebuild before it tears itself up description: 12A Rotary Engine Rebuilds with quality and performance for Colorado's altitude and dry hot air. REspeedshop in Frederick, CO image: https://www.respeedshop.com/hubfs/IMG_0434.jpeg --- # Rotary Engine build Blog Building the Rotary Engine is all in the right tools, experience and knowhow. Get it right [12A](https://www.respeedshop.com/blog/tag/12a), [Colorado Rotary Engine shop](https://www.respeedshop.com/blog/tag/colorado-rotary-engine-shop), [Rotary Engine REbuild](https://www.respeedshop.com/blog/tag/rotary-engine-rebuild), [SA Rx7](https://www.respeedshop.com/blog/tag/sa-rx7)   |   8 Min Read # Part 2 12A Engine Rebuild before it tears itself up ![Picture of MazdaDoug](https://www.respeedshop.com/hubfs/respeed%20rotor%20logo-2.png) [ Written by MazdaDoug ](https://www.respeedshop.com/blog/author/mazdadoug) ## [![Rx7 Performance street porting 12A](https://www.respeedshop.com/hs-fs/hubfs/IMG_0434.jpeg?width=312&height=234&name=IMG_0434.jpeg)](https://www.respeedshop.com/services)Part 2 Rebuilding the Rx7 12A with performance gains and reliability Once we got the motor apart, remember this motor was running fine, drove nice and started hot and cold. The fact that I did not get to drive this car, I didn't notice it was low on power, it sound right, pulled to redline and didn't smoke. My assumptions were not all accurate as once we got it apart, I thought a seal kit, some replacement of a few worn parts (oil pump / chain, the usual) and a few upgrades. Not so fast. Like I tell everyone, we do not know what the motor needs until we get it apart, measured and ultrasonic cleaned. The big tell was looking at the lower compression area of the rotor housings, both of them had coolant leaking into them over time (inner seal giving way) and the chrome was flaking, reducing compression. When we rebuild a motor, it has to be done correctly, I do not take shortcuts to save a few dollars. And, as I tell every customer, I do not want to see the inside of that motor for a long time. - ![Engine Coolant Seal Failure](https://www.respeedshop.com/hs-fs/hubfs/IMG_0406.jpeg?width=5712&height=4284&name=IMG_0406.jpeg) Engine out, ready for disassembly - ![12A engine rebuild](https://www.respeedshop.com/hs-fs/hubfs/IMG_0301.jpeg?width=5712&height=4284&name=IMG_0301.jpeg) Pretty typical intake manifold, ready for the Ultrasonic - ![Bad 12a rotor housings](https://www.respeedshop.com/hs-fs/hubfs/IMG_0417.jpeg?width=4032&height=3024&name=IMG_0417.jpeg) Chrome flaking off, time for new ones - ![12A engine runout](https://www.respeedshop.com/hs-fs/hubfs/IMG_0438.jpeg?width=4032&height=3024&name=IMG_0438.jpeg) Always check the end play, right on up to 10,000 of an inch. - ![12A engine porting](https://www.respeedshop.com/hs-fs/hubfs/IMG_0424.jpeg?width=5712&height=4284&name=IMG_0424.jpeg) Street porting for drivability at 5000 ft. - ![Colorado Rotary Engine Shop](https://www.respeedshop.com/hs-fs/hubfs/IMG_0470.jpeg?width=5712&height=4284&name=IMG_0470.jpeg) Rotor housings sanded, prepped w/ exhaust porting. Ready to assemble. - ![12A engine rebuild shop](https://www.respeedshop.com/hs-fs/hubfs/IMG_0472.jpeg?width=5712&height=4284&name=IMG_0472.jpeg) Motor being assembled 12A rotary engine rebuilds - ![Rotary Engine REbuild 12A](https://www.respeedshop.com/hs-fs/hubfs/IMG_0474.jpeg?width=5712&height=4284&name=IMG_0474.jpeg) All assembled, pressure tested.....pass. - ![Side seal tolerances 12A rebuild](https://www.respeedshop.com/hs-fs/hubfs/IMG_0467.jpeg?width=4032&height=3024&name=IMG_0467.jpeg) side seals ground to exact tolerances. Do it right. As you can see by the pictures, the combustion chambers were both corroded. This is from coolant leaking into the chambers (because it was sitting for long periods of time and the seals just drying out over time) and the chrome becoming weak and flaking off. Notice that all of the corrosion happened at the bottom of the rotor housings.   We needed new housings, with that we went further and called up Atkins Rotary about their new cut down 13B GSL-SE housings. Excellent option for improved reliability and performance gains. I called the customer and stated that it would be a shame to just put it together without adding in some needed porting. Based on his expectations, we did a mild street port on the primaries and larger on the secondaries. The goal is solid horsepower gains without sacrificing drivability. Big ports are not always the answer, it is all about flow. Our experience with altitude and street performance means we get it right. Our engine build program has many years experience & knowledge, we build quality motors. [![Ask questions, knowledge & experience matter to make good decisions](https://hubspot-no-cache-na2-prod.s3.amazonaws.com/cta/default/85804/0ade32cd-7cca-4de0-82c1-091aaa7cf2c8.png)](https://hubspot-cta-redirect-na2-prod.s3.amazonaws.com/cta/redirect/85804/0ade32cd-7cca-4de0-82c1-091aaa7cf2c8) Topics:   [12A](https://www.respeedshop.com/blog/tag/12a), [Colorado Rotary Engine shop](https://www.respeedshop.com/blog/tag/colorado-rotary-engine-shop), [Rotary Engine REbuild](https://www.respeedshop.com/blog/tag/rotary-engine-rebuild), [SA Rx7](https://www.respeedshop.com/blog/tag/sa-rx7) - [** ](https://www.facebook.com/sharer/sharer.php?u=https://www.respeedshop.com/blog/part-2-12a-engine-rebuild-before-it-tears-itself-up&title=Part%202%2012A%20Engine%20Rebuild%20before%20it%20tears%20itself%20up&picture=https://85804.fs1.hubspotusercontent-na1.net/hubfs/85804/IMG_0434.jpeg&description=12A%20Rotary%20Engine%20Rebuilds%20with%20quality%20and%20performance%20for%20Colorado's%20altitude%20and%20dry%20hot%20air.%20REspeedshop%20in%20Frederick,%20CO) - [** ](https://twitter.com/intent/tweet?source=https://www.respeedshop.com/blog/part-2-12a-engine-rebuild-before-it-tears-itself-up&text=Part%202%2012A%20Engine%20Rebuild%20before%20it%20tears%20itself%20up) - [** ](http://www.linkedin.com/shareArticle?mini=true&url=https://www.respeedshop.com/blog/part-2-12a-engine-rebuild-before-it-tears-itself-up&title=Part%202%2012A%20Engine%20Rebuild%20before%20it%20tears%20itself%20up&summary=12A%20Rotary%20Engine%20Rebuilds%20with%20quality%20and%20performance%20for%20Colorado's%20altitude%20and%20dry%20hot%20air.%20REspeedshop%20in%20Frederick,%20CO) - [** ](mailto:?subject=Part%202%2012A%20Engine%20Rebuild%20before%20it%20tears%20itself%20up&body=Part%202%2012A%20Engine%20Rebuild%20before%20it%20tears%20itself%20up%20https://www.respeedshop.com/blog/part-2-12a-engine-rebuild-before-it-tears-itself-up) ## Related Articles [12A](https://www.respeedshop.com/blog/tag/12a) [vintage racing 12A](https://www.respeedshop.com/blog/tag/vintage-racing-12a) ### [20-Year Sleeping 12A: Bringing a 1971 Rotary-Powered T-bird Back to Life](https://www.respeedshop.com/blog/20-year-sleeping-12a-bringing-a-1971-rotary-powered-t-bird-back-to-life) Rebuilding a First-Generation Mazda Rotary Engine The Mazda rotary engine has been around since the late 1960s, and a few of those early engines are still out there powering cars that mean a great ... 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[![Picture of MazdaDoug](https://www.respeedshop.com/hubfs/respeed%20rotor%20logo-2.png) MazdaDoug ](https://www.respeedshop.com/blog/author/mazdadoug) google-site-verification: google66f53be324ef579e.html ```json { "@context" : "https://schema.org", "@type" : "BlogPosting", "author" : { "@type" : "Person", "name" : "MazdaDoug", "url" : "https://www.respeedshop.com/blog/author/mazdadoug" }, "dateModified" : "2025-02-24T02:04:57.160Z", "datePublished" : "2025-02-23T14:30:01.000Z", "headline" : "Part 2 12A Engine Rebuild before it tears itself up", "image" : [ "https://www.respeedshop.com/hubfs/IMG_0434.jpeg" ], "mainEntityOfPage" : { "@id" : "https://www.respeedshop.com/blog/part-2-12a-engine-rebuild-before-it-tears-itself-up", "@type" : "WebPage" }, "publisher" : { "@type" : "Organization", "logo" : { "@type" : "ImageObject", "url" : "https://www.respeedshop.com/hubfs/respeed%20rotor%20logo-1.png" }, "name" : "REspeed LLC" } } ```