Miata Swapped MGB GT - The Cobbler's Child

I've had this MGB GT since 1988 and there's a long set of stories behind it. It's been a back burner project as I've worked on other projects for myself and customers, had a family, started a business, and various other distractions. I guess it's been a bit like the Cobbler's Child. I painted it in 1996, swapped a Miata engine in in 1999, had it running about 2001, and "finished" it in 2006. I used it to promote Eclectic Motorworks, as magazine story fodder for GRM, and loaned it to friends and potential customers because it puts a smile on everyone's face. I recently started using it as a daily driver and thought it would be good to put it up as a build thread as I make some repairs and updates to it for the first time in 18 years.

OK, me gusta!

I bought the car in the fall of 1988, right after I graduated from college.

As rough as it looked, it was a southern car and virtually rust free with a rebuilt engine.

I lived in a rental house with college buddies. It had a 10x16 foot garage out back that I used to work on cars. It had no electricity, so I ran 100' of 10 or 12 gauge wire to the dryer outlet. That gave me 220 for my welder and compressor and 110 for everything else. Anyway, that's where I reduced the car to a shell.

We had a place in town that would let you rent their big sandblaster. I remember taking the shell there the day after Thanksgiving. This this was moving fast--I had worked at University Motors in college and really learned how to hustle.

By March, 1989, I had the shell in primer and nearly ready for paint. A few months later, I bought my first house so the project went on the back burner as I worked on the house and restored a few cars on the side to keep up on the house repairs. 

After a few years, I was balancing this project with an even larger MGA project. When I worked at University Motors, John Twist would let us have used parts for free or cheap if he had plenty of them. I had pieced together almost enough MGA bits to build a body and chassis, just like Johnny Cash. When I would get tired of rust and welding, I'd move over to the mainly rust-free MGB GT. It had been hit fairly hard in the front earlier in its lift and clipped on the right side. And as the photo above shows, it had more damage to the front after that. So while it was solid, there was quite a bit of work to redo the clip and repair the rest of the damage. Let's say this is about 1992 or 1993.

I was now in the 24x24' garage in my backyard. I insulated, but still heated with kerosene. I straightened everything out and removed the old slam panel.

A new slam panel and valence went in quickly.

If you look in the background, the MGA was leaning against the wall under the blue cover.

Back then, it was really hard to find used bonnets and new ones were junk. When British Motor Heritage started making them again, they all came over with shipping damage. I had a friend who worked at Engel Imports, a large MG wholesaler about an hour away and he watched for an undamaged bonnet. One day, he called and said he had one. It was too good to be true after a long hunt. Keep that in mind for the next post. Anyway, the car was now about ready for paint.

So I got married and moved and the GT went back on hiatus. 

Love your work!  I showed my wife the pic of this car; we're looking for a driver for her this weekend at the Turkey Rod Run.  If you were selling this, we'd be all over it.  :-)

Now it's 1996, our first kid is on the way, so I better get this car done. We moved and now my shop was 24x30 with a real furnace. 

I've never liked rotisseries as they take up a lot of room. I like to tilt cars on their sides, and that's what I did with the GT. (Notice the MGA is still nearby.)

Back then, 3M made black rubberized undercoating that could be painted, so I used it with Centari acrylic enamel and that looked pretty much like the factory coating. At the time, this was going to be a factory-correct car.

The gray primer was PPG urethane high-build something or other. I was just switching from lacquer-based primer to the modern stuff and thought I'd risk putting it under old-school topcoats. For the topcoats, I used Centari for the door jams, interior, engine bay, underside, etc., and Lucite acrylic lacquer for the outside of the body. So here's the engine bay, wheel wells, etc. getting painted.

WIth all the jams and undersides done, I used PPG DP-90 epoxy primer as a sealer since I was a little worried about how the Lucite would get along with the urethane high build primer.

My chemistry plans worked and the lacquer went down fine. I had a good system back then and would thin the paint 200% and put down 20+ thin coats to a pretty high gloss even though it was lacquer. The next day, I'd buff with a course pad and course compound, then go over it again with a fine pad and compound without any wet sanding. The paint wasn't as nice as modern base/clear, but much better than factory and always got compliments (and side-jobs).

By the way, the color is Black Tulip, a 1974 only color that I think is the best color in the world. So my factory-correct restoration was now a little messed up as the car is a 1973. And I usually call the color purple.

Two weeks after I painted the car, I was up in the rafters and I dropped something. It landed on the dent-free bonnet I had gotten from Engel Imports. I was bummed and put a cover over the car, thinking it would be for a few months.

Awesome. Very much enjoying the ride, and taking notes as I've just dug my own '73 GT out and started noting the things that annoy me the most (it's quite a list) and deciding what needs correcting and what needs re-engineering/replacing.

Thanks for taking us along!

1999, two kids now, and somewhere along the way I bought another 1973 MGB GT that I gave what I call a shave and a haircut--paint and interior. And maybe I pulled the engine and did the engine bay, too. So it wasn't restored, but it sure looked that way.  It's the first car I sent out for bodywork and paint after I did the metalwork (it was rusty). Somehow, that seemed easier than fixing the dent in the bonnet and blending the paint on the purple car.

I'd long read GRM and Tim's Ro-Spit really inspired me. Since I now had a nice, stock MGB GT, I thought the purple car should get a rotary. I bought a $50 RX-7 and got so far as to test fit the engine. Then I realized that wrecked Miatas were out there and a Miata swap would have some advantages (mainly torque and longevity). I had a friend with a used car dealership that had Miatas and he let me take some measurements. I hadn't heard of anyone doing the swap, so all I had were those measurements and hope it would work.

Norman Garrett's book told me I wanted a pre-OBD 1.8 car, so I found the cheapest wrecked one I could ($3000! for a 1994) . I got it running again and cut down the wiring harness to the bare essentials before pulling the drivetrain, wiring, and computer. I sold the very bent shell to a Spec Miata guy for something like $1200. I know Miata bits are getting more expensive now, but they weren't very cheap back then either--they were too new.

A friend came over on a Saturday and we had mounts made up and the engine in by about 3:00. That's the easy part.

Soon after, I started Eclectic Motorworks and we had our third kid. Back burner again.

I remember the magazine coverage of the Miata swap, wiring, etc. It really inspired me in my quest for sensible and reliable updates to classics.

By about 2001, I was caught up enough that I made the radiator mounts, throttle linkage, clutch controls, and everything needed to make the car run and drive. So I made the car run and drive in the painted shell. I took it to the various regional and national MG shows as a calling card for Eclectic and it worked. It drew more attention than a finished car, so I didn't finish it. By about 2006, it was starting to get some nicks and minor blemishes from being loaded on a trailer and touched at car shows, so I thought I should make it a whole car before the blemishes got too bad. I was super busy with the business and kids' activities, but I had hired a pretty talented 25ish year old (Josh) who had a lot of free time, so he started putting the GT back together in the evenings. The other guys at the shop pitched in a bit too, especially Brent.

Notice the Classic Motorsports Modern Midget in the background. I was spending too much time on that one while Josh and the guys were helping me give the Cobbler's Child some attention.

To save time, I had a local upholstery shop put the Moss seat kits on the seats. And then I re-did them because they weren't on straight and they had goofy puckers in them. So much for saving time.

We made good progress and the car came together nicely.

For the car shows, I just sat on the floor of the shell to drive it around. Why didn't I put a seat in sooner?

I've since touched up the front pipe paint damage and adjusted the pipe. The car still looks very nice underneath.

After the car was "finished" in 2006, I drove it maybe 100 miles a year. It's been a great car, but I have other cars and my sons started getting into building yard karts and then autocrossing and project cars of their own, so the GT continued to be in the background. I was also building an over-the-top Miata-powered, supercharged, air conditioned MGB GT for a customer (I think I wrote more than 10 stories about that project for GRM). Every time that customer car was finished, he'd have us update it (it's had three rear suspensions since it was finished). By the time the pandemic hit, I was maybe driving the purple car 2-4 times a year.  Until about a month ago, when I decided to daily drive it.

The great thing about build threads is that they can help keep you accountable. And they help document the history and details of a build. So I thought I'd put this out there and maybe you guys can help me bring this car to the front burner where it belongs. The snow is about the fly, so it won't be my daily much longer. However, I plan to take care of some things over the winter and daily it next season. I'm also thinking about air conditioning, cruise control, and maybe forced induction, so there may be some upgrades.

In the short term, I have these things to sort out:

Upper door cap was coming loose, so I took it off.

Alternator charges, but the light no longer lights. Speedo stopped working. Why didn't I buy new switches with nice chrome around them? And why didn't I plug the hole where the choke used to be?

Heater valve is leaking.

Why did I powdercoat the aluminum bits? Now it's flaking off.

When I put the windows back in, I bought all new trim. The bottom windshield trim absolutely wouldn't fit, so I never installed it.

There are some other details I'll mention later. 

The first fix was to put the door cap back on. These are held on with very short #8 oval head sheet metal screws that strip the holes and commonly fall off. I was down to two of four screws holding the cap on, so I took it off before the last two holes stripped. 

I fixed the problem with very short #10 oval head sheet metal screws. Took me like three years and 30 seconds to do that. Cobbler's Child.

In reply to AngryCorvair (Forum Supporter) :

Thanks Angry. That means a lot, coming from you. I love the Monzora. 

In reply to Jesse Ransom :

Sounds like you need to put up a build thread so we can encourage and enable. 1973 is one of the best years, too. 

Carl Heideman said:

In reply to AngryCorvair (Forum Supporter) :

Thanks Angry. That means a lot, coming from you. I love the Monzora. 

Thanks man, I appreciate the kind words.

At the risk of being encouraged to get a room, I'm gonna say that I was shocked to learn that we are about the same age. Reading all your fab articles and seeing the quality of your work 20-some years ago, I assumed you must have had decades of experience back then. 

Forced induction? AC? Cruise Control?

I'm beyond in. Looking forward to how to do this stuff Cleanly.

What about the rear diff? I'd imagine you're nearly maxed out with stock Miata power.

In reply to wheelsmithy (Joe-with-an-L) :

People run 302 V8s in front of these axles, so I would expect that its good for a bit. How the car is used had a lot to do with how well it tolerates the new drive-train.

Big fan of this project and had lost track of how long it had been going on. Good to see it being put on the front burner.

Oh, the shame...

I am the cobbler...shame shame shame shame shame shame. Anyway, after draining this I did quite a flush on the engine block, radiator, and heater core. I also wrote, "I will change my coolant more frequently!" 100 times on the blackboard.

I powdercoated much of the aluminum like the thermostat housing and it has outgassed and built up corrosion behind it. 

So I bead blasted it an left it natural. I'll be doing that on other parts in the future.

Replaced the heater valve with a NAPA 660-1439 (about $65!), which was used on a lot of 1970s Dodge trucks apparently. I welded a little tab on it to reverse the direction from push-pull to pull-push to work with the stock MGB heater control and cable. 

Slightly less shame, but there is still more cobbler neglect to rectify.

If it's not too late, can you cut off the original arm on the valve that you're not using???   A little detail that I think would look very clean

Carl Heideman said:

Replaced the heater valve with a NAPA 660-1439 (about $65!), which was used on a lot of 1970s Dodge trucks apparently. I welded a little tab on it to reverse the direction from push-pull to pull-push to work with the stock MGB heater control and cable. 
 

oh man, future MonZora may get one of those when/if I add heat and defrost.

Taking more notes....

Two weeks ago, we had two feet of snow on the ground. Then we had unseasonably warm (40 degree) days and enough rain to wash the road salt away. I daily drove it again for a few days. 

The snow may come back next week, so I washed the GT and brought it in for some more uncobbling. 

I started with an oil change and underbody inspection. I don't think it ever had a nut and bolt after it was "finished" and there was more looseness than I care to admit. Although I guess I just did admit that. 
 

The worst part was the LH motor mount having 1 of 3 bolts and the 3rd loose. In other news, the occasional clunk from the exhaust/steering column is gone. 

The slave cylinder was weeping so I replaced it. 
 

The underside is still looking very good. If I spend a few hours with some soap and water and rags, it would look like new again. But that smacks of effort for another day.

Not shown but I adjusted the TPS and it's idling at 800 RPM with a nice Monza exhaust burble again. 

I've been splitting daily driver duties mainly between this car and my 1966 VW Beetle. Honestly, I've put more work into sorting/repairing the Beetle than this car, so it's still a bit of a cobbler's child. However, the uncobbling to date has made it so much fun and reliable that it doesn't motivate me much to continue to uncobble.

Enough jabber...I did work on uncobbling tonight by diagnosing the speedo, which stopped working soon after I first got it hooked up.

It takes about five minutes to pull the speedo in an MGB (or in my case, several years and five minutes), so I pulled it to see if the cable was spinning. It was not. 

 I'm spoiled and lazy, so I usually go right to a hoist, but I went old-school with a jack and jack stands to see the business end of the speedo cable. The gear in the trans was spinning the output (whew), so it had to be the cable.

And it is the cable. I had this cable made out of a stock Miata cable by some speedometer shop many years ago. I sent them a used Miata cable and they modified the end that isn't shown to a MGB fitting, and I just hooked it up. It wasn't reading quite accurately (as expected), so I was going to do the math and get a ratio adapter. Before I did that, it stopped working and I neglected it. I hope it broke just because it was an old, brittle cable.

So, I think I'm going to do the math, get a new cable made, get a ratio adapter, and fix it correctly. One less cobble on its way.

I did a little googling and ordered a new speedo cable from Deluxe Speedometer and Cable Service in Denver, CO.

I'm impressed. I called them and said I needed a 62" cable for a '94 Miata transmission mated to a 1973 MGB speedometer and one showed up in the mail 3 days later just over $100, shipped.

When the speedo was working before, it was 25-30% off in its calibration and I was planning to get a ratio adapter.  MGBs use speedos that are either 1280 turns per mile or 1000 tpm. Midgets are 1376 tpm, so that's another option.

 I couldn't find how many turns per mile a Miata speedo is, so I pulled out my stash of used Miata and MGB speedos and used a drill to try to figure out a what ratio I'd need.

I use a short section of speedo cable in my drill to check speedos. It requires running the drill in reverse--easy. Anyway, the Miata speedo ran about 25 MPH on the slow speed and 85 at the high speed. An MGB 1000 tpm speedo ran about the same, so the Miata must be 1000 tpm or near.

So, it looks like Mazda knew MGB owners would make this swap and they made it easy--just use the 1000tpm speedos from 74 and newer MGBs.

I cleaned up one of my used ones, put it in, and went for a ride. A GPS speedo app confirmed that it's pretty spot-on. It's nice when things work out like this.