Rebuilding a Rotary Engine for the First Time

They say a rotary engine only has seven moving parts.  It all depends on your definition of moving.  In bulk, I only count three: each rotor and the crankshaft.  Not sure what the other four are?  But, once you start taking this thing apart, you find tons of moving parts.  For example, each rotor has 30 separate parts that make up the sealing system.  These ride up and down on springs, so are technically moving parts.  It's quite a job to put one of these together.  If you work at Mazda in Japan, you have at your disposal a selection of side seals of various lengths.  Hang on, maybe I should first describe what I've learned about rotor seals.

In a piston engine, you generally have 3 seals: a compression ring, a wiper ring, and an oil control ring.

A rotary engine is similar but everything is turned on its side.  Since the rotor, ummm rotates, one needs the same seal arrangement but across the face of the rotor.

The amazingly simple geometry of the rotary engine belies the complexity needed to seal it.  The corner seal, side seal, and apex seal together make up the compression ring in a piston engine.  To be honest, I'm not sure what the cut-off seal does or how it survives so far from an oil supply.  Returning to the side seals, they have to be filed to length.  The Mazda master mechanic in paragraph one has bins of various lengths available.  Most of us buy extra long ones and file them down.  Pineapple Racing sent me a fixture to give the right angle but I disagreed with them.  It was a handy way to support the seal while filing the angle of my choice though.  Sadly, they failed to ship me $600 worth of parts and have now ghosted me but Key Bank is on it!

They go in the outer slot in the pictures above.

The inner and outer oil seals are the equivalent of the wiper and oil rings.  As amazing as a piston engine, the only way this whole thing survives is by spraying a gout of oil at the piston or rotor.  I guess enough of this spray migrates across the seals to keep them alive.  That's years of engineers trying things out.  Now, I can drink a beer and put that together in my garage and it WANTS to work!

So, my brother and I did the initial assembly.  That went quickly!

We couldn't find any left over parts so I guess we did OK.

Along the way, I decided to improve on my fast and crude method of sealing off unneeded cooling lines of which there are several.  This was my "the new engine is almost, what's quickest?" method:

I failed to recognize that screw threads present a passage for coolant.  And struggled for two years with coolant leaks.  I read about the simple solution below on a racing forum.  A little RTV and a set screw.  After all, I do have a machine shop, right!

Next, I did the flywheel and clutch.

In previous posts, I showed that this clutch is still healthy!  The new disc will improve things!

I then flipped the engine over and started on the front.

Here you can see the oil pump installation.  Amusingly, I put the pump in place, installed and torqued down the front cover, and found the oil pump bolts.  So I un-torqued, installed the oil pump, and retorqued.  

The front bolt needs something like 200Nm of torque so that has to sit on the floor!

The intake and exhaust manifolds get attached next.  A few drops of fuel dripped out of one of the fuel injectors upon disassembly.  Therefore, I decided to change the seals.  I have a recurring nightmare where fuel drips down onto the exhaust manifold (which is directly below the intake in a rotary) and I burn BB to the ground!  So new seals.  

Here's the collection.  There is one O-ring and two rubber collars.  This set-up is very elegant.  The fuel rail clamps the injector into the manifold, compressing the collars.  Here are the collars installed in the intake.  

The O-ring seals to the fuel rail.  I decided to change the filter baskets although I guess they didn't need it.  It turns out one needs a clever tool for that:

It's just a wood screw in a puller.  You screw the wood screw into the filter basket as seen above.  Then you turn the knob on the end and it retracts the screw.  The filter pops right out.  I then popped in the new filter.  There are two more injectors in the block and they were similarly updated.

Now to assemble the intake and exhaust.  It went fairly well although I discovered that one can flip the gasket and the bolt holes don't line up.  A moment of panic that I had bought the wrong one but quickly figured it out.  

Here you can see it in place on the block.  The short block is getting dressed!  I missed a picture of the exhaust manifold bolted up.  That's because it was a moment of frustration.  For whatever reason, the holes in the manifold that I fabricated, wouldn't line up anymore!  I finally had to drill them out bigger.  That worked and I started the delicate work of sliding the engine down and into the transmission.

If you look up a picture of an RX8 engine compartment, it may look tight to you.  Like it might be difficult to lever an engine in and out.  But, I assure you, squeezing one into and MGB is far tougher.  You have to change angle several times as you move then engine down and back.  You have to make sure you're not pinching a brake line or a wiring harness.  Then, you have to engage the input shaft.  I've done this many times but I always find that getting the input shaft started requires some level of violence.  In this case, it worked and I got the engine remarried to the transmission!

Now starts the slow slog of tightening hidden bolts.  Over the years, I've developed skills at turning bolts so hidden they should not be accessible but this is ridiculous!  Three of the bellhousing bolts are under the tunnel.  I documented the amazing wrench I found to disassemble them in an earlier post.  It went together faster but just barely.  I had literal hand cramps, where my fingers curled up for a half hour after struggling with these.

Here, I've got the oil lines connected (which caused all this trouble to begin with!).  Also the oil galley and alternator.  Most of the wires were connected at that point.  Sadly, I discovered this guy:

That goes under the oil filter housing which had led to some finger cramps and now had to come out.  Not only that, but it needed to be installed before the engine went in.  There is no clearance to the tunnel to plug that in.  However, this engine is never coming out again!  Finally, my neighbor got it plugged in after I ground away quite a lot of plastic on both ends!

You can just barely see it deep in the tunnel.

I thought I was then on easy street.  All that remained was bolting up the intake and cranking her over!  Hahaha.  For one thing, I had decided that I needed the Metering Oil Pump that lubricates the apex seals, even though I premix my gas with oil.  I mean this is $4000 and a hundred hours in this rebuild!  I'm not doing this again (unless I decide to do a Bridgeport but that will be another winter!).  So I decided I had to get my oil injector working.  I was very proud of the manifold I machined to avoid having to make a hole in the frame rail to fit it.  But somehow the thing had never worked.  It sucked up 3000 miles of oil in 10 minutes.  So it needed fixed.  My 10 year old neighbor Gabe, is taking it apart in the picture below.  

At first, I was thrilled with how easy it went.  I discovered the problem immediately.  I set it up in my vice and filled it with oil and the oil promptly ran out the bottom.  Upon disassembly, I noted that the pump is sealed with an O-ring around the manifold connections.  There is, however, no seal around the pump inside diameter.  Naturally, because it's designed to bolt to the engine, where the oil just runs back into the sump.  In my set up it runs right into the driveway!  A little RTV fixed that but then the trouble began.

The electric motor wouldn't start and I wasn't totally sure which way it should turn even if it did.  I actually ran the pump with a drill and tried both directions and confirmed oil injection.  I then shimmed the motor until it ran consistently and in the correct direction!  That was two days of troubleshooting alone!

Then I started on the heater lines.  Ironically, I had developed a slow drip from this heater valve and had ordered a replacement before the major cooling melt down!  But it still needs changed out.  Along the way, I found that this big booger of RTV was not helping the drive home from my Mom's on cold fall nights!

I then installed the oil pan and tried to fill her with oil.  Sadly, one needs to remember to put the oil plug back in the pan for that to work!

During that process, I realized I had forgotten to eliminate the abrasion that started all this trouble!

I guess that should be OK but I'll be checking!  I also lined the radiator mounts with rubber bumpers (yes, those are what is on your office door at work!).  I was further pleased to fill in the slot in right mount.  That was also part of the hurry on installing the new engine before summer faded.  I got that filled in and painted them black.  Matte, not shiny, BB is a road and track car, not a Concourse car!

I then installed intake and air filter and cranked her over.  No joy.

Hmmm.  Lots of forum posts suggest that a rebuilt rotary will have low compression until the seals bed in.  A little oil in the intake raises compression.  So it did, and with a bit of starting fluid, she was running!  However, very roughly and would stall at idle.  Strange readings on the ECU for Manifold Absolute Pressure.  Vacuum leak?  Maybe.  I changed ignition coils and she started without oil.  A hopeful sign!  But something was still up so I pulled the upper intake manifold.  The intake manifold on an RX8 is roughly the size of the engine but she does breathe well!

I went in looking for vacuum leaks but found an electrical connector which I had failed to plug in.  Another hmmmm.  I was very thorough.  Here are the markers I removed as I reinstalled all the connectors.

However, I missed one:

Checking the wiring diagram revealed that I had plugged a temperature sensor into a fuel injector.  That will never work.  I swapped them and she started immediately and idled fine!  I made a video of the victory drive:

The lesson of all this is: basic physics works!  If your engine overheats, stop and call a tow!  If you're too foolish to do that, well then everything can be fixed!  Keep on having #funwithcars!