The Great Engine Rebuild Adventure


It went a little something like this....

October, 1997: Started up the car to go running some errands. Noticed the stock boost gauge didn't seem to be working; oh well, I'll get to that later. Ran a few errands, then decided to go cruising around. Did a nice 1-2 boost run, heard a little detonation at the top of 2nd. Let off, and came up to a light and stopped. Suddenly, I noticed the car wasn't idling right...instead of a smooth idle, I got "tah-tah-tah-tah-tah-tah". Oh Crap! Drove it back home REAL easy and began flipping out. Did I blow the motor? Once my roommate John got in we did a compression test - sure enough, blew an apex seal on the #2 rotor. The car was grounded for fear of doing further damage to engine internals.

It wasn't until after the rebuild that I realized what really killed the engine - THE VACUUM TUBE TO THE BOOST SENSOR HAD POPPED OFF. The ECU had NO idea how much boost the car was running, and the mixture was DEAD lean. The stock boost gauge is there for a reason! If it doesn't work, make sure it does! The vacuum line in question has been replaced with a silicon tube that holds on VERY snugly.

Anyhow, back to the story. I called up Ted Koseki in Hawaii. I was in somewhat of a panic - what do I do? Ted gave me some good advice and pointers on what it would take (parts-wise and cost-wise) to rebuild the engine. By the end of the weekend, I decided I would go ahead and do it.

Money became the next problem - I didn't exactly have a pot of it laying around. So, it was time to sell the computer...kind of a bummer, but also a transition from one hobby to the new one. Got $800 for it (man, did I make out like a bandit!) and socked it away.

Now it was time to get to work. First things first - pulled the hood off and put it up in my room (didn't want it to get banged up, dirty, fall over, etc.). MUCH easier to work on the car with the hood off! I started unbolting everything and getting the motor ready to pull out. Took about 3 evenings of work to strip the motor down. One thing to keep in mind - the engine wiring harness is usually kind of brittle. Be VERY gentle with it! Treat it like GOLD - a new one is about $1200! You don't want a wire to snap in the harness somewhere!

We got the ol' engine hoist ready and pulled it right out. I needed tools to remove the world-famous flywheel nut and an engine stand adapter - Dean Colver let me borrow his. He shipped them over from Jacksonville, and when they came in the flywheel and front pulley was removed, and the engine was mounted on the stand.

We then pulled the motor apart. Undid the tension bolts one by one, slowly, in the correct pattern, to decompress the housings properly. Pulled off the rear cover, and got to see the damage. A corner of one of the apex seals had broken off, scored the rotor housing, and embedded itself in the rotor. The rest of the motor was fine, thankfully.

After getting it all apart, and assessing the damage, it was time to get the stuff I would need to rebuild it. From Mazdacomp, I ordered:

  • 6 new apex seals
  • new corner seals
  • new corner seal springs (the 93-95 springs; MUCH better than the '86-91 springs)
  • new side seal springs
  • new oil seal o-rings
  • engine gasket set
  • new motor mounts (stock; they also have competition mounts)
  • new front and rear seals
  • new oil metering pump lines

Now, I had to deal with the bad rotor and housing. Brian Cain, who had just swapped in a new motor, gave me the good rotor and housing from his bad motor (thanks!).

While I was waiting for everything to get in, I cleaned all the parts up. For the internals (rotors, housings, etc.) I used Purple. You can get it at a big hardware store (Lowe's, Home Depot); it's an industrial cleaner. Works GREAT - make sure to use gloves when working with it - it's VERY hard on your hands. I used Purple and a brass scouring pad to clean all the caked-up carbon off the rotors. It took at least a day to clean both rotors. I also cleaned all the external engine parts (manifolds, etc.). I decided to paint everything, so I got some Plasti-Kote high-temp engine enamel. The rotor housings were painted white, the intake manifolds black, the water pump housing and front cover white, the water pump red, alternator pulley red, etc. Looks GREAT!

OK, finally it was time to build the motor. On a Saturday morning in December, my roommate John and I cleaned up the garage and went to work. We went real slow and easy, and had both the Hayes manual and the factory shop manual on hand. We read each one, and did it step-by-step. 5 hours later, we had a complete motor! I spent the remainder of the day bolting stuff onto the motor. One of the exhaust studs snapped, which signalled the end of that day.

Next day (Sunday) we went to his dad's house and borrowed some EZ-Outs and his drill. The EZ-Outs got the broken stud out in NO time. Pep Boys actually had a stud in stock that fit the bill; so we luckily were able to replace it. I then continued bolting everything back on; exhaust manifold, turbo, lower intake manifold, front cover, oil pan, motor mounts, oil injector lines, clutch, etc. That night, we dropped the motor into the car. Took QUITE a while - the motor mounts are a BEAR to line up. Lining up with the transmission was actually pretty easy! Looking back, it might have been easier to bolt the motor mounts into the car, then line up the engine onto the mounts.

Monday night, I came home from work and started bolting things back in. I worked like a DEMON and by about 10 or 11 o'clock, I had the whole thing back together ready to go. I used all new fuel line (good metric line that fits FANTASTIC), silicon vacuum tubing, new gaskets, etc. About 11:30, we opened the garage, hooked up the battery, and crossed our fingers. IT STARTED ON THE FIRST TRY! Hallelujah! We had the motor running for a while, then it died. It flooded out pretty good, so it didn't want to start up again. No biggie - that's for the next night.

Tuesday night I went to work debugging things. Turned out I had a big vacuum leak - I forgot to tighten down the air control valve block-off plate! After geting it sealed up, I saw that sweet 750 RPM idle...awww yeah! Time for the customary drive around the block without the hood on! I bolted the hood on that night, and drove the car to work the next morning.

The break-in didn't go as I would have liked it...I was rushing to get the car together so I could go to San Antonio for Christmas. I had to take it on the long trip there, which I don't recommend. I stopped frequently and let the motor cool down, as well as staying off boost and varying the RPM. It's a much better idea to break it in for about 1000 miles - 500 of under 4000 RPM, no boost driving, and 500 of higher RPMs and low boost.

During the rebuild, I got a chance to do a lot of extras. I had the fuel injectors cleaned, balanced, and blueprinted. I pulled out the seats and cleaned them, as well as applying leather dye to darken the wear spots on the seats. Worked out well - I stored all the pieces inside the car, where they were out of the way.

Rebuilding a rotary engine is MUCH easier than you would think! If you're pretty handy with tools, can follow directions, and have the patience to take your time and double-check things, YOU CAN DO IT! Read the instructions through 3 times, visualize doing it, ask questions. A blown engine is not the end of the world!

A lot of guys make the error of bolting on a full turbo-back exhaust, fuel cut defender, and a cone intake and start hauling ass. You will have a very fast TIME BOMB on your hands. WITHOUT EXTRA FUEL, YOU WILL BLOW YOUR MOTOR. Maybe not today, maybe not tomorrow, but it WILL happen. Too many guys on the FC3S list have had to learn this. That's why my next upgrade is a fuel computer - not an exhaust system. Lay the foundation, then build up the car from there. Unfortunately, I blew my motor with a popped-off vacuum line. At that point (and now) I have a 2.5" downpipe and presilencer, and it's running about 8.5 pounds of boost. Once you get into the 10s and 11s, you're going WAY past the fuel cut defender (fuel cut is at about 8 pounds) and there isn't any additional fuel going to the motor.

So, how much time and money are we talking about? Took me 3 months (a LOT of waiting in there that could have been avoided) and I spent around $800 for all the parts necessary and all the extras. Not too bad - about half the cost of a rebuilt motor. Swapping in a motor is MUCH easier - I could probably swap in a motor in a week, maybe a long weekend. The more experience you are with how the car fits together, the faster you can do it.


OK, here's what you REALLY want: Pictures! There's more of 'em to come!

Everything laid out ready to start building. Notice the engine stand.

Another shot of all the pieces. You can see the housings, rotors, gasket kit

Another shot - notice the front cover, eccentric shaft. The yellow packets are apex seals

Getting ready to start - that's me in the doorway

This is the front housing with the water seals in place. The tube on the side is Hylomar - dope up the seals with it.

Front rotor in place

Eccentric shaft in place for a test fit

My roommate John and I installing the apex seal springs. Like my jeans? :)

Almost done - Moutain Dew, the drink of champions!

Here's a comparision of the old (bottom) and new (top) apex seals. You can really see the wear!

Installing the engine tension bolts

Installing the rear seal. We used a metal bar and a roll of Duct Tape to drive it in!

Oil pump installed

Applying RTV for the front cover

Installing the oil pan

John torqueing on the flywheel nut. That's why we call him Big Torque!

John extracting the broken exhaust stud. Notice the tape - didn't want anything getting in!

John got it!

Cleaning up the turbo assembly some. It's going together nicely!

Turbo and manifold, from the rear. Painting the heat shields didn't work - the paint ended up burning off! :)

Installing the front pulley

John tightening the front pulley, with me stopping the engine from the other side

The lug wrench John bent removing the front pulley. It was ON there!

Ready to go in the car! You can see the Centerforce DF pressure plate


Time to start the car....

The car backed out, ready for a try.

SUCCESS! Started first try!

John enjoying the smoke

Smoke coming from the tailpipes - all the assembly oil burning off. Takes a while to burn off!

Jumping the car - the battery was pretty spent from using it in a Fiat while I built the motor

Me bolting in the driver's seat

Getting in for a ride!

Jumping it AGAIN - yes, Fiats have the battery in the trunk :)

Setting the timing

Finally! An empty garage!

Driving down the street with no hood!

Bolting on the hood so I can drive to work in the morning

All done - me and my trusty sidekick :)


Last updated - 7/13/1998