94 Miata Engine Rebuild - Part 4

Time to finish up the story of my engine rebuild in the 1994 Miata. The first part of this is here, here is part two and part three. The images that follow are roughly in chronological order, but not exactly. I'll just briefly explain each photo so you'll know sort of what's going on. My purpose here is just to let you know what you're in for if you're doing this, not explain exactly how to do it.

Once the pistons were all assembled and installed, and the rod bearings installed and torqued down, it was time to build the motor up. Here you can see the tops of the '01+ pistons. If you were to compare to the '94 pistons you'd see these are a bit more domed on the top, which is what provides the additional compression. You can also see where they are marked as oversize with the 0.50 stamp (upside-down in this image).

The next step is to plop the cylinder head back on the short block. I didn't get a photo of the head gasket installed but there's nothing tricky about it other than to make sure you don't block the oil feed to the head. There's only one correct orientation for the head gasket. I didn't disassemble the head for this rebuild since it was just refreshed about 25k miles ago.

Next the intake manifold goes back on.

This photo shows the VICS butterflies in the '99 intake manifold. You can see by default they are open. I don't have a way to control these yet so for now I opted to wire them shut. Even though I don't get the (admittedly miniscule) benefit of VICS, the '99 head still flows tons better than the '94 head and also has the solid valve lifters that are much less problematic than the HLAs of the '94.

Next I assembled the crank nose with the timing belt cog and a new key. You can also see the new oil pump I installed and some of the sealant spooging out from the front of the oil pan. I had to trim away this excess sealant as it interfered with the pulley boss a bit later.

This photo shows the orientation of the fuel pressure regulator and the new fuel hose connector to mate the '94 fuel system with the '99 fuel rail. This is discussed in great detail in an earlier blog post but since I got this better photo I wanted to include it.

Keep building. Here the timing belt and water pump is installed, also the throttle body, thermostat, some coolant hoses, and the A/C belt idler (my car has no power steering pump).

Close-up of the belt idler for the A/C belt. Cars with power steering will have a power steering pump here.

The front of the engine is pretty much fully dressed. The alternator is in place, the water pump pulley, and crank pulley.

Motor mounts are next. I went back to the standard mount after having Mazda Competition motor mounts for a few years. I didn't like the extra harshness I felt while driving with the competition mounts. If this was a track car it would be different.

Next I bolted on the flywheel, clutch, and pressure plate. I didn't get any photos of it! I used my trusty Flyin' Miata crank nose tool to lock everything in place while torquing things down. You can see I substituted some grade 10.9 cap head bolts for the original bolts here. No reason to do that if your old bolts are in fine shape.

Next is to mate the engine and transmission. This is much easier to do on the floor of the shop than under the car. I used the crane and the transmission jack to maneuver them in place, then just let the bolts do the work. Now it's time to fly the engine into the car.

This part was a lot harder than it looks. A helper would be very..uh...helpful right here. I was wishing for a bigger crane because this one couldn't quite reach far enough. Note I have a leveler. This is crucial for getting the whole assembly oriented and dropped in place. You have to work in fractions of inches while constantly making adjustments to the attitude of the assembly. Once the motor mounts engage with the holes in the subframe you are home free. Don't forget to reengage the driveshaft with the tail of the transmission as you move it back or you will have to do like I did and unbolt the driveshaft from the differential so you can plug the nose back into the transmission. No big deal but an unnecessary step if you think ahead.

Finally when the engine is bolted in you can start hooking everything back up. The exhaust manifold, hoses, wiring harness, radiator, A/C compressor. Everything you had to unhook before. Refill the transmission with gear lube. You'll probably forget something and wonder why the car won't start. Just be methodical and it will work out. Don't take shortcuts and don't skimp on parts or tools.

Now that this is done I'm very happy with the engine. It definitely has a lot more power than before, and runs smooth as butter. Now I have to bring the rest of the car up to the standards of this motor. It never ends. Hope you enjoyed this series of posts. Sorry they were so far between.

Engine install details

I found the issue with my transmission not wanting to mate to the engine. It was my fault. Using the transmission jack, I got the transmission perfectly lined up with the engine block, threaded all the bellhousing bolts in by hand and proceeded to tighten them down thinking that would just pull things together easily. It would have worked if the splines on the clutch disk and the transmission input shaft happened to be lined up or at least pretty close to lined up. Unfortunately, they were exactly NOT lined up and the slow compression by the bolts drawing things together just crushed the splines and made it impossible for them to engage the input shaft. I can probably clean up the splines with a file and salvage this clutch disk but I didn't have time to do that now. I threw the old clutch disk in since it showed very little wear anyway. It's got a good 80-100k miles in it still.

 

A quick clean up of the starter. Wire brushed it and hit it with some chassis black. I replaced the mounting bolts with new ones.

The Power Plant Frame was nasty dirty from the oil leak so I pulled it out and cleaned it up. Having it out made maneuvering the transmission back into place a bit easier, too.

I had sort of underestimated the amount of work involved in getting the engine fully dressed and everything hooked back up. I spent a whole day and a half doing just that. I installed the starter, A/C compressor, PCV hoses, belts, brake booster lines, clutch slave, Power Plant Frame, exhaust header, O2 sensor, and fuel pressure reference sensor. I still have to install the radiator (ordered a new all-aluminum KOYO 37mm radiator) and associated hoses, plus the heater hoses but I'll do that when the radiator gets here.

Using the '99 head and intake manifold leaves nowhere to mount the PRC solenoid valve, so I relocated it to where the carbon canister was. It has to be within reach of the wiring harness and it has two vacuum connections so it has to be in this general neighborhood. Hopefully it won't matter that it's vertical instead of horizontal. This valve helps the engine start under hot-restart conditions and doesn't do anything most of the time.

Finally, I filled the transmission with Amsoil MTG 75W-90 gear oil. It's very easy with a proper pump.

Installing the Miata Engine.

Today I installed the flywheel and clutch and dropped the engine in the car. But first...

Here's my method for getting seals out. First I drill a small hole in the middle of the seal. The top of the seal is metal underneath the rubber so it's quite hard.

Then I screw a screw into the hole, being careful not to drive it too deep. It just needs to thread in a couple turns.

Then grab the screw with pliers or vise-grips and pull.

Viola! This one was really easy. Smaller seals like the cam seals can be more stubborn and sometimes you have to put in two screws so you can pull from two sides.

Here's the F1 Racing chromoly flywheel just before being bolted down. It weighs about 11 pounds so should be a nice performance enhancer.

The holes for the pressure plate bolts were threaded wrong! The factory bolts are M8x1.0 while the flywheel is threaded for M8x1.25. Of course they don't tell you that so when I started to bolt on the pressure plate I was met with resistance. I got all six screws about halfway in before I decided something was not right and pulled them out. I went to the hardware store and bought new bolts.

I was going to plan a tech day with some friends to help me install the engine, but my time has been so limited lately I had to just forge ahead whenever I could and ended up doing it by myself. Flying the engine on the crane into the engine bay was not too hard. It just took me about 15 minutes to maneuver it into place. I wasn't able to finish bolting up the transmission due to a complication. Usually the engine and transmission will mate up and go together pretty easily. Sometimes they fight a little bit but with some finessing, they will eventually pop together and from there it's easy to bolt them down. Today though they never got friendly with each other. I got the bellhousing bolts about halfway in and was met with extreme resistance. The transmission and engine are still a good 3/4 of an inch apart and the bolts just don't want to go any farther. I'm afraid I'm going to bend the transmission input shaft so I desisted for today and will start over next weekend. Something isn't mating up right and I'm not sure why. I've seen this before, though, and I'm confident I can sort it out next weekend.

I'm glad it's back in its place!

All put up for the night.