13BREW Engine Rebuild - Assembly

Stacking the Engine

Parts ready for final assembly.

A rotary engine is merely a sandwiched assembly of parts. So finding the “best” parts was my challenge. I had my original 40k engine to start with. This gave me three good irons, one good rotor housing and rotor, and a spotless eccentric shaft. I had two other low mileage “blown” motors from which to gather parts; one low mileage new “blown” engine and the other a low mileage “blown” Mazda remanufactured engine. Both of these were completely disassembled and inspected. Both had one good rotor and housing. The eccentric shafts in both were in lesser condition than my own original and both had decent irons. I will say I was rather disappointed with the condition of the parts used in the remanufactured engine. Although all were within spec, they were obviously “used” and surprisingly in poorer condition than those good parts out of my 40k engine.

After finding suitable useable parts to make a complete engine, each respective part was spec’d out following the acceptance criteria in the FSM. The engine was going to be pretty tight with particular attention to rotor seal grooves. See my page on engine building for tools and measurements HERE. Each part was thoroughly cleaned and in the case of the rotor housings and front cover they were each polished and the rotor irons each coated in a ceramic based high temperature paint. I invested in a small ultrasonic cleaner for the nuts and bolts but it is still big enough to clean parts like the fuel rails, etc. It is a very good tool for breaking loose dirt in places that cannot be seen or reached by any other means. A lot of effort but I like my work to look as good as it works. Polishing and painting was probably 12-16 hours worth of time. The rotors, after cleaning, looked and measured out as good as brand new rotors. Perfect! The irons were all well within spec with no evidence of wear or damage. During the rebuilt I decided to stick with OEM coolant and gas seals. They are good for motors that can last 150k miles so I feel confident they are quite suitable for my purposes. I have not seen conclusive evidence that there is any benefit to the “upgrade” aftermarket Teflon seals. In fact the condition of the aftermarket Teflon seals I pulled from both of the low mileage engines disassembled for parts was less than stellar. OEM seals will do fine…thank you very much. I opted for OEM oil control ring seals also but did choose to upgrade to the Mazda competition oil control ring springs. The oil control rings used were out of the low mileage “new” engine and were near perfect, essentially as new. For the rotors I re-used low wear side seals, ground to the lower end of the tolerance spec with new side seals springs. Solid corner seals (the smooth side is facing down with the dished side facing out) from Atkins with FD side seal springs of course, and finally I decided to go with OEM 2 piece apex seals with stock apex seal springs. After much research I weighed the pros and cons of each aftermarket seal and decided the OEM seals best suited my needs. What I can say, and that I found most impressive, was that in one of the blown engines I disassembled, the damaged Hurley 2-piece apex seals had left NO housing damage at all. One of the Hurley seals had broken and disintegrated. What was astonishing was the rotor housing had remained completely undamaged…not a trace of the seal fragments. The same engines with the damaged OEM seals had resulted in severely scored housings that had rendered them unusable. What this told me was the Hurley seals were made of a softer material...good or bad? Engine builders indicate the aftermarket seals are typically made of a softer but more abrasive material leading to worn rotor housings and uneven apex seal wear. I can confirm the uneven seal wear. After cleaning the low mileage (13k) Hurley seals, they look really worn. They were visibly worn in the center and were not as smooth and polished on the contact edge as broken-in OEM seals. The Hurley springs on the other hand look REALLY beefy compared to the OEM springs. As for the rotor housing wear, that is best left to internet lore…good or bad? In the end I stuck with the decades of Mazda testing and development of their OEM 2 pieces seals.

With all the new seals provided in the OEM rebuild kit, I slapped it all together. Well actually I had built a few engines previously as practice and watched both a the DIY-RE Productions series of “DIY-RE 13B” Do it yourself Rotary Engine rebuild DVD set and the rebuild tape by Bruce Turrentine several times…multiple times. I also watched the on-line videos at rebuildingrotaryengines.com I was sure to mark each part, as assembled, to be sure they were assembled correctly. I used Vaseline on all the seals to aid assembly, assembly lube on all the bearings, and proper Hylomar sealant where appropriate. Assembling the center iron was a PITA as the e-shaft was so well lubricated it kept sliding back into the front iron. I made sure the fuel diffusers in the center irons were seated correctly and pointed in the right direction. I installed an oil bypass pellet instead of the failure prone thermostatically controlled oil plug when rebuilding the short-block. I chose to keep using the FD thrust roller bearings vs. the Renesis thrust bearings provided with all the rebuild kits these days. Why? I just thought the FD bearings looked more durable. I had a scare when assembling the thrust bearing stack as my torque wrench crapped out on me and I snapped an assembly bolt due to over-tightening that set me back an hour or so but I had another set of bolts to reinstall with the proper torque spec. Dowels were in near new condition and all the tension bolts had threads in perfect condition. New front and rear main oil seals were installed in the front cover and rear iron. I changed the spacer (E thickness spec) to provide the correct end float. And finally, torqued the tension bolts in 10 increments…it took me forever! Shortblock DONE.

Preassembled Rotors - side and corner seals and oil control rings installed. Front housing seated.

Installing the apex seals: tricky but once you figure it out fairly straight forward. Please ignore the goof! Stacking the rear housing after eccentric shaft installation.

A new set of tension bolts. Rear iron installed w/tension bolts numbered for torque sequence. New rear main seal.

Front thrust bearings installed. What a jammed torque wrench can do - 4 overtorqued bolts. One needed extraction after snapping off. Note the necking of one severely stretched bolt! Stupid torque wrench!

Front cover installed after installing the guts of the oilpump drive, correct spacer, pulley boss, etc. Installed SR Motorsports flywheel on the back side.

Next page for Aluminum oil pan installation

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

Rebuild and porting of the 13B short-block to include port matching the intake side.
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.