13BREW Engine Rebuild - Building a Better Heart


I think the answer is obvious in this case. My engine "done blown up!" So why not slap a simple simple remanufactured engine into my FD? As of this webpage writing factory remanufactured engines are running about $2650. Not bad really. Many of the remanufactured engines are coming with a lot of new parts, such as new rotor housings, which total in value more than the cost of the remanufactured engine itself. A deal. Why not have a performance shop rebuild my blown engine? A few simple reasons; 1) I could build a new (and better) engine for less - provided I didn't make any mistakes of course, 2) I have trust issues...I don't think I've found anyone who I believe can satisfy my OCD nature, 3) I wanted to learn more and have a better understanding of my car, and 4) I believe I could make it better, more powerful, more reliable, and do it for minimal cost. Ok...on with the show.

By April of 2007 I had begun the process of ressurrecting my FD, "Princess." The engine had been pulled and the long-block disassembled. Followed by the short-block. See here for more on the chronology of the 2 year process. After the teardown, being careful with every part to avoid denting a flange or critical mating surface, as suspected the rear rotor was the problem with one chipped apex seal tip and one other cracked seal. Only the tip of the one seal was missing. I removed the turbine housing to look at the turbo to see if it had gotten damaged by munching an apex seal tip. No damage to the turbo – clean as a whistle.

Turbine looks good...thank goodness. Even after passing the broken apex seal fragment.

Unfortunately, the rotor housing was not reusable...at least not by me :-( The rest of the teardown showed everything else to be in good shape. The front housing had some minor flaking along the edge of the housing. It's still a good housing for a general street motor but my standards are high and go a little beyond "general street." And with it all apart it was time to start the nasty and time consuming cleaning process BLECH! Lots of carb cleaner, lots of brake cleaner, lots of gasket remover, Navel Jelly (phosphoric acid), brass wire brushes, tooth brushes, various dental picks, used seals for cleaning grooves (the only way to effectively clean the side seal and apex seal grooves of excess carbon is with a used seal), several boxes of rubber gloves, etc. etc. A Dremel tool with the small wire wheels are also very effective at removing carbon from hard to reach places and are gentle enough to not damage sensitive and critical seal edges) I found most useful the deep stainless steel trays from food steam tables as good cleaning vessels. They are durable, sturdy (try carrying a dirty “iron” in a plastic dish washing basin!), do not corrode from the nasty chemicals used, and come in a variety of sizes for housing/soaking parts. They can be found relatively cheap off eBay if you can’t get them from someone who works in a restaurant. The time spent prepping parts for cleaning compared to motor assembly is easily 4:1. Each part as it was cleaned was coated with a light coat of WD-40 and sealed in a ziplock baggie until it was ready to be used. On to the rebuild!!!

Cutting Metal - Porting and Portmatching

I’ve always said that I wouldn’t touch the engine in my car unless I had to. Well with a blown motor now was the opportunity to make some performance “improvements.” What can you do to improve the performance of a rotary? It pretty much boils down to porting of the intake and exhaust ports. Yeah you can lighten rotors and mill the housings but this was a little bit extreme for my “street” engine and beyond my ability...for now at least. Balancing the rotating assembly will also allow a higher RPM limit and more Hp. Porting involves not only changing the size and shape of the port itself but also, for the intake ports, the shape of the port “bowl” and shape of the runner that feeds the “bowl.” The port shape dictates the “timing” of the engine and also the emissions output, the fuel efficiency, and of course the power curve and output. For example, bridge ports yield BIG power due to their immense size but only at extreme RPM levels while barely being able to run at anything below 3000rpm and are far from really being “streetable,” at least not in my daily commute to work! Likewise the stock port shape and configuration yield a wide and smooth power-band and are emissions friendly but are so small they become simply too restrictive to flow anything decent above 9000rpm and start choking power at anything above 6000rpm. To learn more about porting…READ! There is a ton of info out there, in books and on the web. Rotary porting is a skill and an art, and in my opinion, learned through practice and lots of trial and error to reveal the true potential of your engine. I estimate I spent several weeks reading nothing but porting techniques and trying to find everything I could on the internet. Some scary things (things only a moron would think would be beneficial) and some good things are to be found. And some techniques consistently espoused by several of the more respected rotary builders in the US, Australia, New Zealand, and Europe and others. In the end I bought medium street porting templates from Pineapple Racing. The laser cut stainless steel templates were very well done and yielded consistent results. The key is that the templates give you the port shape and location but the “bowl” is all up to the person behind the grinder.

Pineapple Racing Medium Street Port template

The actual porting I did with a straight cut and round tip carbide cutting bits in an adjustable speed Dremel tool. I also used various grit sanding wheels in the Dremel. This is a slow but precise method. I transferred the port shape from the template to the iron by first coloring the iron with a Sharpie marker then scoring the port outline with an awl or pick. Then I removed the template and cut the port shape with the carbide cutting tip. The hard part was then shaping the bowl. Not much I can share other than to be sure to not remove too much material and cut into the water jacket and try to make sure the “bowls” in each runner are the same shape/depth/ contour, etc. Next I removed all the excess casting “flash” and rough sand finish in each of the intake runners…smoothed them out and in the process made them a bit larger. I opted not for perfectly polished intake ports and runners but a semi-polished finish to optimize fuel atomization. On the exhaust side I enlarged the ports by going slightly wider and I cleaned up the discharge runner outside of the port to smooth flow. The exhaust port is of lesser consequence than the intake ports on turbocharged engines. With this all said a picture tells a thousand words. What I can say is that I practiced on several engines and ported at least a dozen irons before I felt comfortable porting the irons for the engine to go into Princess. Below are images of the porting work I did for my FD.

Pineapple template port shape and enlarged area of secondary port shown by scored line in Sharpie marking.

Pineapple template port shape and enlarged area of primary port and final enlarged port and "bowl."

Cut primary port and bowl. Finished secondary port and bowl - note how the inner edge follows the arc of the oil control ring.

Finished secondary port and bowl - note how the outer edge follows the arc of the rotor corner seal. Image to show the gently radiused "upper" side of the port runner.

Images to show smoothed, but not polished, port runner. All the rough sandcast finish removed.

Comparison of the very mild exhaust porting. Completed exaust ports.

In the same vein as porting of the irons’ intake and exhaust ports I also port matched the LIM and irons. Using the LIM metal gasket I traced the runner port shape onto both the LIM and respective iron and opened up the port shape on both so that they matched. Cutting of the aluminum LIM was harder as the aluminum is softer and requires a slower cutting speed and different bit. It was amazing how uneven and different the port shapes were on the irons and as compared to the LIM.

Portmatching using metal LIM gasket. Note the uneven shape of the runner in the center iron - original compared to finished. LIM gasket overlayed on LIM. Note amount of the runner that is filled.

original LIM port shape relative to the gasket port shape. Final ported LIM.

Less of a performance improvement and more of a reliability improvement were a few modifications in the oiling system. I didn’t go so far as to drill and tap the front iron to deliver oil directly to the rear rotor (front iron oil plug is drilled and tapped and a dedicated oil hose is then plumbed directly from this location to the rear iron to equalize oil pressure – no room to run the line on my “street” car but a great mod for a high RPM race motor) but I did “teardrop” the oil ports on the eccentric shaft (better oil distribution of oil to the rotor bearings and stationary gear bearings) and hog out and smooth the oil pump housing and passages. Some suggest replacing the oil jets in the eccentric shaft with carb jets to increase oil flow but the side effect of unstable oil pressure did not appeal to me for a street engine so I passed on this mod. I stuffed a small wad of paper towel into the eccentric shaft oil port to stop the machined metal particles from entering the oil port and shaft interiro. After careful removal of the plugs the eshaft was thoroughly cleaned. The last thing you want is a small and hard eshaft chip in your oiling system and royally buggering up a bearing face.

Oil pump ports - Before and After.

Teardropped eccentric shaft oil ports. (ports are plugged to minimize metal chips from entering the port passage)

Next page for engine assembly

For more specifcs on other aspects of the reconstruction of Princess go to the following pages:

Custom baffled deep well aluminum oil pan.
Installation of dedicated 2 stroke oil feed system.
Replacement of all the fuel system lines with SS braided hose and AN fittings – tank to engine.
Installation of a dual fuel pump arrangement with fuel tank baffle box cover.
Replacement of all turbo hoses with SS braided hose and AN fittings.
Relocation of the ignition coil packs to the drivers’ side fender wall.
Simplification and rebuild of the engine wiring harness and removal of all un-used control solenoids.
Porting and polishing of the throttle body and removal of the double throttle control assembly.
Turbo “improvements” to fix lower grade hardware and potential trouble areas.
Installation of 3 Bar MAP sensor and tuning for higher boost applications.

And for review:
Rebuild Overview Part 1
Rebuild Overview Part 2
Rebuild Overview Part 3
Rebuild Overview Part 4



If you would like to contact me and converse about my experiences with my RX-7's:
please feel free to send an e-mail to crispyrx7@yahoo.com

This page last updated March 19, 2009

Disclaimer: All images contained on this page are the sole property of C. Regan.