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.

94 Miata - Engine Rebuild, Part 2

Since my last post I've removed the engine from the car and disassembled it. I was hoping to be able to simply hone the cylinders and put the engine back together with new rings and bearings, but I found there was too much wear for that. I didn't even make any measurements. There's obviously a lot of scuffing on the piston skirts and there are enough scratches on the crank journals that I figured I'd better have it polished and maybe even ground down one size if necessary. So off to the machine shop it will go this week. I'm taking them the block, rods, new pistons, and the crank from a spare 2002 engine I previously tore down. Here are a few pics of the pieces.

In this photo you can see quite a bit of scuffing on the piston skirt. The oil control rings on all these pistons did not appear to be stuck, so I believe my oil consumption issue was simply due to wear in the bores.  

This is one of the main crank bearings. It's probably the worst one but they all looked similar. It's not the worst I've seen, but you can tell this is an engine with 175,000 miles on it. It's worse than I expected it to be. This engine has always had synthetic oil in it, and although I've pushed the change intervals pretty long a few times, it's had regular oil changes. I chalk up the increased wear to several factors, though. 1) I had a very crappy cold air induction system for several years that didn't filter the intake air very well. It was an oiled foam filter and several times I found actual grit in the airbox. Most of the bearings showed deep scratches indicating large particles in the oil. This is usually due to ingested silicon grains. 2) I had a supercharger on this engine for about 10000 miles, and 3) this engine saw some track mileage where it was at very high rpm for extended periods of time.  

On the left is a rod from the '94 engine and on the right is a rod from the 2002 engine I previously tore down. I didn't weigh them but to me the 94 rod looks like it might weigh a little less. The webbing on the I-beam portion of the rod is definitely thicker on the 02 rod. Maybe they beefed them up in later years to compensate for the higher compression the NB engines run. At any rate, I decided to stick with the '94 rods for my rebuild. I'm sure they're still strong enough and I just thought the construction looked a little better. If I was going with forced induction I'd probably use the '02 rods.  

I bought some new pistons in 0.5mm oversize (83.5mm) because I figure it's safer to oversize rather than just hone this block, based on the amount of wear I'm seeing. The bores in the block look pretty good, but the amount of scuffing on the old pistons tells me there's gotta be some wear. So just to be safe we're going to overbore.  

This pic just shows the crank still assembled to the block. The main bearing caps are stamped with numbers 1 through 5 and there are cast arrows indicating the direction to the front. The numbers are hard to see but they are there. I elected not to use this crank and will instead use the one from the 2002 engine I took apart because that one looks brand new and this one shows some wear on the bearing journals and seal surfaces.  

Here's the bare block in all its glory. Not much to it when it really comes down to it. Part three of this series is here.

94 Miata - Engine Rebuild, Part 1

Going back about 3 years on this blog you'll find a long series of posts about how I went through my Miata and refreshed a bunch of stuff. Highlights of the project included installing a '99 cylinder head on my '94 motor and painting the entire car myself in my garage. What I didn't do back then was rebuild the bottom end of the engine. Since then it's been burning oil pretty rapidly and showing some rather poor compression when cold. So, I decided it's time to pull the engine again and do a complete rebuild on the bottom end.

I'm picking this project up sort of in the middle here, because I've already got the engine out and on a stand. When I last had the engine out in 2012, the cylinder bores looked very good, so I think I can get away with a simple hone and re-ring job, with new crank and rod bearings. I plan to use a Flex-Hone rotary brush type honing tool. These are inexpensive, can be done by hand with a drill, and provides a high-quality finish with the proper cross-hatch angle to ensure a good seal by the rings. I've torn down a spare 2002 engine block we had at the Gorilla Garage and I plan to use it to practice my honing technique. I also plan to use the pistons from that engine to take advantage of the 10:1 compression ratio enjoyed by the 2002 Miata engine. This will be a true budget-build, because if the block looks and measures ok, I'm going to get by without doing any machine work. We'll see if that pans out! The head only has maybe 35k miles on it, so I'm hoping to leave it alone at this time.

To sum up part 1 of this series, here are my goals for this project:

• Rebuild engine bottom end
• Inspect head and correct any issues (don't expect any)
• Refresh suspension
• Install soft top
• Install Flyin' Miata frame-rail braces
• Detail engine compartment
• Repaint hardtop

This list is subject to change and I probably won't get to all of it before I put the car back into service as a daily driver, but it's all the stuff I'd like to get done, so I can drive this car for another three years. Stay tuned for part 2 of the series as I get into the engine over the next few weeks.

Randall Cowl Intake Installation on '94 Miata

Time for a little more work on the '94. Since I got the fuel issues sorted, it's been running great. So today I installed the Randall cowl intake. It's just a carbon fiber tube that connects the factory airbox to a hole in the firewall that ingests air from the cowl area where the air is nice and cool. I bought it from Flyin' Miata and it's one of the few aftermarket intakes that actually shows a horsepower gain on the dyno. I didn't get it for the horsepower, exactly. Mainly it was just because my stock intake tube was cracked and I figured while I was replacing a part I might as well get something that could somehow be considered an upgrade. In other words, because racecar.

 

The tube.

The intake comes with a template, because you have to cut a hole in the firewall. You also have to bend the clutch hard line a little bit to get it out of the way.

Possibly the most imprecise cutting tool on earth, but it got the job done.

Two holes. Sorry for fingers in photo!

With Dremel tool, make one hole.

Touch up with paint.

Cram carbon fiber tube into place.

I found it best to loosen the airbox from its mounts to make it easier to snap the Randall onto the flange.

Driving impression: so far so good. There's a little more intake noise and my highly calibrated butt can detect a little more responsive throttle. Nothing dramatic, obviously. It's a tube.

Update to '99 Miata Head on '94 Engine - Fuel Rail Issues

I've been waiting to post this until I had a definitive solution, but if you look a couple blog posts back you'll see my car on the back of a flat bed. The issue that cropped up was the fuel lines simply let go from the fittings on the fuel rail and I couldn't get them to hold on no matter what I tried. This led me down a path of learning more than I ever wanted to know about high pressure fuel injection hose and what type of hose is proper for this installation. Maybe this was obvious to everyone else who has done the '99 head swap but in all my reading about the subject I never saw it mentioned and I did find a few posts from people who were having trouble with leaking fuel hoses.

In this photo you can see the fuel pressure regulator. When installing the '99 Miata head on the '94 block, it's necessary to use the '99 fuel rail with the '94 fuel pressure regulator (FPR) because the '99 is a returnless system, while the '94 uses a return to the fuel tank from the FPR. The '94 FPR can only be oriented one way, due to a vacuum port that has to face out. That's no problem, but it dictates the routing of the fuel hoses. You can see this one sticking straight up, and the other one sticks straight down. The '94 fuel rail has an input that has a flared end on it so the fuel hose with a clamp on it will be nice and tight. The '99 uses the newer style fittings that click into place and require a special tool to remove, so the input to the rail has NO FLARE. The '94 FPR has an output on it that is flared, and so must be a clamped connection. Being ignorant when I embarked on this project, I blithely bought the first spool of high pressure fuel hose I found online and simply clamped the hoses to the fuel rail connections and on the other end to the fuel hardlines from the tank. It worked for 2000 miles.

Here's a view of the '99 fuel rail input. This is not designed for a clamped connection. After 2000 miles (about 5 weeks) of use, the fuel hose fell off and no amount of tightening of the clamp would hold it on. Even after replacing with a new length of hose, it would not stay on. The resulting spray of fuel in the engine compartment was quite undesirable! Interestingly, the hose on the '94 FPR fitting with the flared and clamped connection was leaking too! This meant that my problem was two-fold.

After doing a bit of research, I found that there are a multitude of SAE specifications for fuel hose. There is hose designed for high pressure (injected) applications, hose designed for clamped connections, and some for connections using barbed fittings (picture below). Some hose is designed to be compatible with diesel, gasoline, and ethanol, some is not compatible with all of those. So, you really need to understand the specs and make sure you get the hose for the application. Any fuel hose you buy will comply with one of these specs, however when buying online the spec is very often not indicated and you don't know what you're going to get. The hose pictured here is the "right" hose to use in this application. The spec is SAE 30R9. It is designed for a clamped application, high pressure, and low permeability to petroleum distillates (to meet environmental regulations). The original hose I bought was SAE 30R7, which is all of that, but NOT for a clamped application. This is why it eventually let go from my FPR fitting, even though there is a flare there and the clamp was tight. On the fuel rail supply fitting it was even worse. The lack of a flare meant there was no chance of it staying put and on my second try with this hose it fell off after literally 5 minutes of running.

So here's the fix. For the '94 FPR connection, it's important to use SAE 30R9 fuel hose (Gates P/N 27085), so the clamped connections will work. For the '99 fuel rail input, the 30R9 hose is fine, but you need to make the connection with one of these. It's DORMAN part number 800-081.5. It's a nylon 5/16 inch 90 degree barbed fitting. It needs to be 90 degrees because the space under the fuel rail is very tight and a straight fitting doesn't fit. I got 5 of them from Autozone online for about $12. It was a special order item so I'm not sure if you'll find them at your local store.

Here's the assembled hose and fitting. It JUST fits in the space under the fuel rail. The connector gives a very reassuring and positive click when engaged.

This shows how I ended up routing the hoses. It had to change a bit with the 90 degree bend at the end of the supply hose. From the hard lines on the left, they both run back behind the intake manifold and then run forward right on top of the fuel rail. Finally, the supply line goes forward and makes a gentle 180 to go under the end of the fuel rail and make the supply connection. It's not ideal as I'd rather the fuel hoses were more concealed, but I had to take the route with the least sharp bends and the right approach direction to the fittings. You might find a suitable route under the intake manifold, but there's very little room to make the connection down there and I was being conservative because I needed this to be fixed!

Flat-bed Blues

A truly rare sight! This car has not been on the back of a flatbad since 1997 when I crashed on track at Laguna Seca. I detected a strong smell of gasoline this morning when I got to work and then at lunchtime it wouldn't start at all. Investigation revealed both fuel lines to be very loose on the fittings at the fuel pressure regulator. In fact, the supply side had popped off completely! Fuel was gushing quite vigorously and creating a pretty nice puddle of gas under the car. After some attempts to replace the hoses, it became apparent that they would not stay tight no matter how hard I screwed down the clamps. These have been fine for over 2000 miles of city driving since I put the car back on the road in January, so I'm really not sure why this happened. The hoses are fine on the supply end, but at the fuel rail they won't grip the fitting at all. Very strange. I think it's just the hose I used is somehow not right so I've ordered some more 5/16" fuel injection hose and some better clamps and will redo the fuel connections.

'99 Miata Camshaft Confusion!

With the help of a couple friends, I figured out why my new '99 head was making such a racket. It's got the wrong exhaust cam in it. I got the '99 head from a friend of mine. It's been in storage for over 10 years and its exact history is a little fuzzy. It came completely assembled but the cams were just loosely held in the journals with the bearing cap bolts finger tight. As seen much earlier in this blog, I took it apart and lapped the valves, checked the bottom surface for straightness, and put it back together.

What I've been hearing since I first started it up was what sounded like excessive valve lash. It was quite loud so I knew something wasn't right. I had checked all the clearances when I installed the head and they were pretty good. If anything a couple of them were on the tight side, not loose. Nevertheless, I figured I had screwed something up so this morning I popped the valve cover off and measured the clearances. None were above the maximum spec, but a couple were below the minimum, so I fired up my spreadsheet and plugged in all the numbers and identified 4 shims I could swap with each other that would bring everything within the factory specs. I was able to get the shims out without completely taking out the cams or having to re-do the timing. If you loosen the bearing caps and rotate the engine you can sneak the shims out from under the cam without removing the timing belt.

I was very glad to get the clearances better adjusted. Most of the valves are in the bottom half of the range. Alas, the noise was unchanged, so I put out a mayday to some gearhead buddies. One of them asked if I was sure I was using the right cams because the cams for NA and NBs have a different profile due to (or at least coincident with) the change to solid lifters in '99. I just used the cams that came with the head, but I realized that I took it on faith that they were the right cams.

From Solomiata.com:

Note the NB cam on the left has a more rounded profile, while the cam on the right from an NA is more pointy.

So, I pulled the valve cover off again and held a cam from a '96 next to the cam installed in my '99 head. They look the same to me. It was starting to make sense.

Next to the intake cam in my '99 head: The known '96 cam looks a little more pointy compared to the intake cam in my '99 head, as would be expected.

To seal the deal, I spotted the marking on the intake cam, BP4W, which is indeed the correct intake cam for the head. On the exhaust cam is BP06, which is an NA cam. Bzzt. Wrong cam. So I'll be ordering up an NB exhaust cam and I'm debating whether to also order the BP5A (aka Mazdaspeed cam) for the intake side. Would be easy to swap it out as long as I'm in there swappin'. Hope this helps save someone some trouble sometime. Never assume!

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.