As the title states, it would be great if someone out there that had a drawing in Solid or some other CAD program, of the bolt pattern of the A12 transmission :)
If someone had a drawing in storage, that would spare me some time making one by my self.

I'm investigating the possibility of using an MX-5 5/6 speed on my A12

Best regards
Toby

It's not in CAD, but here is the factory blueprint

Never seen that before, thanks DD. I'll put that in my archive for future projects

Tboe I've been looking into the same thing as well; we have a 91 Miata and I have a spare motor, comparing the engine plates it looks like the bolt circle on the Mazda is bigger so could make an adapter plate. Additionally the input shaft bearing IDs are identical so in theory you could insert the A series input shaft into the Mazda front case for alignment purposes. Obviously there are a whole host of details that need to be worked out.

Tom

DD, Great Photo! I'll work from that to start with :)

Hey Tom, The bolt-circle I believe that the Mazda circle is a few mm wider. Within 300-335mm I think? I will try to get a factory blueprint, as all I made was just a quick mock-up.
Nice observation! I'll look into that. There will be a lot of details to work out, but I should know the right people to have it all sorted out.

Toby

Toby if you come up with an adapter let me know. I have a friend who specializes in Miata street and race cars. He's offered to loan me a front case,'I'm hoping we can use the 2mm A15 engine plate as a template, the Mazda engine plate as an adapter bolted to the A series plate and the Mazda case bolted to the engine place.

Tom

I'll be sure to let you'll know if I come up with one.
I'm working with Mr. Kolstrup (Invented Rotrex), and we just made an adaptor plate so that you can use a BMW 6-speed with the Miata motor ;) No more gearbox issues with high power engines!

Keep me updated with your progress also. Just so we aren't making the same thing on opposite sides on the planet.

Toby

Very interested in what you guys are doing.

I've also been collecting 5 speed MX5 boxes with the same view. Not a light box though, about 10kgs heavier than the series 60 box. I haven't done anything yet but have an auto bell housing that could be welded to the Mazda case.

I also wonder if bell part of the case could be milled where one of the two rings circles the entire case. Doing so and making a 3mm steel ring that bolted on with a lot of 6mm bolts similar to how three piece wheels are made. That could allow a range of steel mini bell housings being made for various engines. With ribbing and using 2.5 or 3mm steel the fabricated adapters could still be light.

With a steel mini housing, centralizing the input shaft to the pilot bearing would be simple. Two oversize holes with precise washers on opposite sides of the block, dial in the centre and a quick tack weld of the washers does the job.

Does anyone know who makes pressed steel cones that can be converted into bellousings? They are used in the USA in the making of larger adapters for heavy v8s.

Toby, will do.

Not sure where the V8 bellhousing raw materials come from. As for the weight of the trans, an extra 10kg is a good trade of for getting a modern strong box. The other plus on the Miata box is there are racing gear sets for those as well and the price is better as well.

Go see a metal spinner about getting a steel cone made, they'd have to have a pretty big machine for a decent wall thickness but they can make almost any axis-symmetric shape with minimal tooling.

You might also find an expired propane bottle with roughly the right size? They have heavy wall pressed steel ends.