rcutclif's 1974 MGB-GT

If you don't want to make your radiator mounts, the easy button is to buy the factory rubber bumper radiator mounts. They're about $50 each from Moss. If you make them, I recommend taking cardboard templates from a rubber bumper car and then making a hammer form to duplicate them. That's how we do it at Eclectic, and I did a story about them for GRM many years ago:  https://grassrootsmotorsports.com/articles/grm-vault-hammerform-how-/

I'm glad your math matched mine for the clutch hydraulics. If you want some pictures with details of this or anything else from my swaps, let me know--I have about 1500 photos of the most recent one. I think you know my email address, which is the best way to contact me.

And, I'll just leave this here to remind you how much fun a Miata-swapped MGB/GT is...https://grassrootsmotorsports.com/forum/build-projects-and-project-cars/miata-swapped-mgb-gt-the-cobblers-child/260118/page1/ By the way, I started that one in 1988 and didn't have it finished until 2006, so you still have 8 years to finish yours if you go at my pace.

Keep going!

Really good to know about the fans! I will definitely take them apart and grease them up. If anything I prefer the way they look to a more modern puller fan on the back of the radiator.

I remember reading the hammer form article and I'll probably re read it again. I still have my early radiator surround, and my current plan was to use it to supply the material needed for the late mounting position. I'll make cardboard templates first to make sure the shapes are close enough first however.

More progress on clutching. 

I drilled the pedal, and also started modifying the pedal box. This was me mocking up the master in it's new position to make sure everything fits. And it does but barely. 

Next step is to weld in the new metal that moves the holes for the master!

Got some new metal welded in behind. Maybe not the prettiest cuts but it was hard to fit anything in there to cut this. At the end of the day, I'm really happy with the positioning of the master. And now there are actually studs so it only takes one tool to tighten (unlike stock mgb where you have a nut and bolt that both need a wrench, which I hate).

With everything sitting back in position, there is access to the bolts and the cap can go on and off. Nice!

Then I turned my attention toward a pushrod. I had one laying around that wasn't from a Miata (it's fork is a bit wider at the clevis) which was perfect because the mgb pedal is thicker metal. I was able to measure and shorten and now have a perfect piece.

It was finally time to turn my attention to the pedals themselves. You can probably see in the previous photo that I hadn't cut the end off the mgb clutch yet. Well I did now.

Then I decided to drill some holes in the pedals, because cool and grippy and weight reduction, and because the pedal cover pad on the clutch pedal was in bad shape. I figure if I don't like the holes I can always get new covers.

Only a few more things to hammer out and cleanup and then I can start putting the pedals back together.

With holes in the pedals, now it's a racecar!

speed holes!

More progress!

First, I recently read about how Miatas always have coolant flowing through the heater core. So therefore when I install a heater valve I need to get one that allows coolant to keep flowing out of the head and back to the water pump when the core is shut out of the loop. Like this:

I was also able to (I think) finalize the clutch and throttle pedal mating. 

First, there is a switch on the Miata clutch that is used for cruise control and maybe idle in the ECU. I want cruise eventually so I thought I'd grab it. This switch is depressed when the pedal is not depressed. 

The other switch is the safety switch for starting, which many people bypass on their Miatas to save crankshaft thrust bearings on cold starts... I dunno if I'll try to keep that one or not.

Anyway, the mgb pedals have a cover, and the brake light switch is basically just a bung in the cover. When the brake pedal is untouched, the back of the pedal hits the switch and the lights go out. I figured I could do the same for this Miata clutch switch.

Marked and drilled the hole in the right spot, then welded in a nut.

Makes me look like a robot, but job done!

I also was able to mate up the throttle cable. Here I just copied almost exactly the grm article (and honestly the Miata cable just about drops into the mgb). 

All that is needed is a small riser and it can be cut from 1 inch tube to capture the Miata plastic end. Weld on a plate at the bottom to screw into the mgb firewall and boom done.

Ok big progress here. 

Recently, nocones and singleslammer showed up at my shop and pushed me forward on this thing. Big time. I'll try to get everything but I am sure I'll miss some stuff.

1. First, I decided to move back to the CB subframe and steering rack. That meant subframe modifications were needed. Here's nocones, modifying subframes like a boss.

We eyeballed some lines, singleslammer measured pan clearance and gave the ok, and we tore into the cutting. 

On top of the pan clearance, we also moved the steering rack forward/down about 1/2 inch to fit the lower pulley. We cut the AC serp pulley off first because we thought it would fit, but that was a no go. Turns out moving the rack forward meant that cutting the pulley would not have been necessary.

It fit great, and there was plenty of slide in the column in order to take up the extra length needed. After a bit of heat and a very skilled dent in the header, it went back together. We steer again!

Sweet progress 

But wait, there's more!

I bought a 6 speed transmission recently, and it came with a nice exedy lightweight flywheel and clutch. So since we had the engine out for swap stuff, I decided it was the right time to swap in the 6 speed. #1, more speeds is bettererer, but also #2, I Believe the 6 speed will have better ratios to match the mgb 3.9 final drive.

While I had it apart, we replaced the rear main seal. It wasn't bad, but it was seeping a bit.

And then here we are with lightweight flywheel all loctited and torqued.

Aaaaaaaaaand, apparently I didn't take a picture of the pressure plate, but imagine a racy yellow one. Yes the setup was used but the clutch looked pretty good for now.

Next was making a bit more space in the engine bay. I cut and then welded. Not the prettiest, but there is more alternator space now.

Then, it was engine back in and time to compare shafts!

Amazingly, the Miata shaft just slid over the mgb unit, and we had a nice tight fit at the factory u joint weld for the rear u joint. We wrapped the front most part of the mg shaft with tape so it was a tight fit inside the Miata shaft and would hold itself centered while we welded.

We then clamped to a welding table to get the joints as close to in phase as we could, and we threw down some tacks. A final test install to check plunge, and we let the welder rip.

Here i am, doing a hopefully not awful job welding on my shaft.

Finally, while I didn't take any pictures - oops - we took way too long cleaning threads and reinstalling the transmission mount, and we also used a 90deg bend from an x1/9 exhaust pipe to connect my header output I made a few years ago to the rest of the mgb exhaust I had. We also reassembled the front suspension, minus shocks (need to buy new ones) and brake lines (should also get new).

Then it was time to see if we had fire! Ok maybe it wasn't time yet but we wanted to do it anyway.

Here's singleslammer, potentially in the middle of a late night fire dance.

After singleslammer told us how the ignition switch was supposed to be wired, nocones and I decided not to follow his advice and do it our own way. Which predicably didn't work.

When we finally tracked down our issue and listened to Jordan, we rigged up this old shop vac switch to do ignition duty while the clutch safety switch did starter duty for us.

​​​​​​

We had no fuel hooked up, but after a few tries with starting fluid, we had FIRE!

And then we decided to call it a success. Huge thank you to singleslammer and nocones for the push and the assists. I feel like we made an incredible amount of progress and my fire for the project has been relit.

Oh I almost forgot the alternator stuff. The Miata alt was still a bit too big to tension with the belt I had on hand. The 12a alternator was pressed into duty, but it's smaller pulley again left belt loose. However, the pullies can swap between alternators, so we put the big Miata pulley on the small 12a alt and bam - enough room to tension. 

I will be looking for a slightly shorter belt.

Hahahahaha, love the shop vac switch!

I'm in these pictures.

And I like it.  This car will be cool when finished.  But Robbie has much wiring to do.  

ok, how could I forget!! singleslammer also disassembled my rad fans and greased them for me. Big win. 

In this week's news, I have placed a few orders for parts. the first few should start arriving today. 

Nice nice nice!

Ok, lot of updates, and I need to get better at keeping the thread updated.

First, shifter. Here's the stock location:

And next, approximately where it needs to be:

Hole cut, and then we were making shift happen!

Then a bit more trimming and creation of a template for a cover up plate.

I ordered some 1/4-28 rivnuts to match the hardware so I don't have a hodgepodge.

I also decided to go ahead and do a new timing belt, because who knows how old this one was. An American branded Italian timing belt on a Japanese engine in a British car. Sweet.

I also took the time to clean up the front covers, and replaced the front crank seal as well as the two cam seals.

The gaskets were toast on the front covers, but, incredibly, I had received this gasket set in the grm new years game a few years back and it happened to be exactly the gasket kit I needed. AWESOME!!

And mostly back together:

I also decided to take the time now to clean up the front pulley we cut so it was no longer sharp. And then gave it a bit more paint for good measure.

I also have done a significant amount of wiring planning. Here's an entire Miata harness under an mgb gt.

I did a lot of looking and validating labels and connectors and checking to make sure I understood everything. 

I'm going to basically use the Miata battery/starter/alternator/main relay and fuse box as is. But I did remove all the plastic retainers since I will probably retain it differently.

Next I pulled out all the abs and airbag circuitry. Conveniently (other than 1 or 2 connections) Mazda made these harnesses blue inside of the larger harness wrapped in black.

So now I have a Miata harness. My plan will be to use most of the Miata harness, but I will tie into the mgb harness in some places. I really like how the Miata uses relays and modern fuses for stuff where the mgb basically just put a high amperage dash switch. This should also make troubleshooting any wiring very familiar to a Miata person.

One other thing I worked on was the driver seat. I pulled it out while working on the shifter hole, but it also needed to have the sliders greased and there was some broken straps on the bottom.

I took an old sheet we were throwing away and cut a new bottom for the foam since the original was disintegrated.

Here are the torn straps.

Luckily, I had an old timing belt just laying around.....

Better!

Now I've got my whole dash pulled apart, waiting on receiving some Miata wiring!

In reply to Robbie (Forum Supporter) :

Using the timing belt for that repair was brilliant!

Well done 

Biata makes so much sense. Love the progress.

There's no time like the present for wiring...

Here's me laying out the mgb and Miata wiring harness, and starting the integrations. I have snipped the Miata ignition switch connector and spliced in the mgb ignition switch. 

Next I want to install the harness to get a feel for how it all falls into the car. The Miata harness goes forward on both sides of the engine bay, so I needed to make a hole. My biggest hole saw (2.5inches) is a little small for the Miata harness bulkhead rubbers, but it will work great.

Added a hole on the driver side

Then, I needed to make the passenger side hole bigger. This is hard because there is not much access for getting tools in here. I looked at it for a long time until I had a good idea, just rivet the other cutout to the body to act as a guide for the hold saw!

Now, I just have this little mess to deal with.

Looking good! Good idea for the hole saw pilot. 

So I was distracted a bit by the speedometer - I found that the Miata drive cable fit right in but wouldn't seem to turn the speedometer...

After taking the speedo apart, I found this little white plastic gear to be nearly frozen in its bore. Tapped it out with a hammer (it should fall out once the retainer clip is removed) and cleaned it up and suddenly the speedo works great again. I remember the last time I drove this car the speedo would bounce, and I always thought it was the cable. Now I think it may have been this gear not turning well.

Anyway, I also found that if I macgyver some spacers and washers onto the mgb speedo, the Miata cable will clip on and drive the speedo correctly (win!) 

However, the Miata cable end is too large to fit through the holes in the mgb bulkhead (boo!) also, after switching to the Miata 6speed, I'd have to convert the trans back to a cable speedo too. I'm going to go ahead and put the speedometer to the side for a while so I can refocus on more important things in the short term.

I did get a smaller belt (by about .5 inches) and it fits perfectly with the Miata alternator. It's a 17350dr, which cross references to many cars. One of them is a Porsche 356. So we can call this a Porsche part, I think.

This may be a stupid question but are all speedo drives geared the same? That is, how do you know that the feed coming out of the Miata trans will be the right RPM to spin the MGB speedo?