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.
For more specifcs on the reconstruction of Princess go to the following pages:
OUR "LOCAL7" COMMUNITY | THE WORLD OF THE RX-7
This page last updated March 19, 2009