I'd reckon theoretically you could use a manual one. One benefit would be retaining the hole in the side for the throw out bearing if that was the route you were taking.

From what I've read, youd have to basically completely disassemble the 5/6 in order to remove the front bell. I guess if you have a big enough bandsaw you could just crudely cut and mill it even. Or take some sort of cut off wheel to it lol

Yep
but not lol because you could crudely just cut it off because your next step is to machine the cut edge to the height you need for welding the plate

yeah if my initial plan worked out it would have been beneficial to use the auto bell if I was going to do anything with that hole in the center to align everything up but doing is this way by just by welding on an entire adapter plate yeah a 5 speed housing wouldn’t have any downside really, could just lop it off with a band saw or grinder.
by auto bell housing I’m referring to the automatic Miata transmission as the bellhousing just unbolts.
I know this post got kinda all over the place but I’ll try and straighten it back up since I’m hoping to make real progress on it some time soon, just waiting on a few things to get here.

A few pictures in case anyone was interested in the progress, first time ever messing with a mill let alone boring a hole with one, It did however end up fitting perfect and the measurement of the hole in the plate to get it to fit right was 4.6840". One side note that might turn into a bad thing is I cannot find any offset dowels if it does need to be offset not sure how accurate different engines/castings were but guess ill find out, with the runout specs on the tremec being so tight I find it really common to need to use offset dowels to get it within spec assuming i can build the bellhousing straight enough hopefully it wont need any.

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Looks like a solid fit. That other thread I was mentioning showed a good way to center up the input spline with the crank using a bolted sleeve. I'm sure you'd be able to make one on your mill

Probably would need to make the dowels yourself. IIRC the factory one is just on the right side of the motor and is hollow for one of the bolts to go through. The auto trans just has those two ~7mm holes that I presume are dowels for the auto cars

Another thought I just had, did you account for the thickness of the aluminum spacer in your measurements? The one that is typically between the motor and transmission

I was going to center it the same way you index it every time you bolt it to the motor with a dial indicator and mag base on the crank/flywheel like described here https://americanpowertrain.com/gener...-instructions/ Except in my case im doing this with the plate then with it zeroed ill tack it all into place and go from there. Hoping the process of welding it doesnt warp or make it draw up on the other side too too bad or i might have to have someone deck it and get it parallel with the other side.

The way i measured it by just measuring from the face of the bellhousing to the splines on the input shaft and matching that with a stock 5 speed which didnt didnt need to take into account that spacer, as long as i got them both to match then using the spacer will be just as it would be with a 5 speed. And yeah the dowels will be the same as long as the housing all lines up straight and what not, I bought some new ones, auto and manual ones are the same.

bit more progress, just to see if I could do it I got the center runout within .002 which is beyond good however I have to shim and parallel it tomorrow then re center the plate then I can tack it but have to clean up the housing a bit first. Pulled out another motor from the shed seems a little better condition the last one I tried mocking with the bearings were so bad I don’t think the crank ran straight…I have collected a few blown up parts engines over the years, all I got or tear the engine back out of my car to do it with which I don’t want to do again..
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Unless you are not planning on welding it 100 percent around, I think you will have to face the plate side after welding. It is just a matter of how much the welder can manage the heat.

Ill be the one welding it, im by far not the best out there but i think i can do it. I plan on doing it all the way around the outside and the inside but plan on taking my time on it and giving it plenty of time to cool between sections.

Thank you for the write up. Has anyone spoken to Holley/Quicktime to negotiate a group buy for the RM-4097 bellhousing? I find it unlikely that they discontinued the product unless the tooling saw severe damage and volume wouldn't recoup the repair/retooling costs. Maybe a large sum of upfront crowdfund cash could convince them to run another batch.

Does anyone have the link for other threads documenting a successful TKX swap?

Something this niche would likely need support of a vendor IMO.

I'd think someone like American Powertrain selling the TKX swap as a complete Miata kit would be my best guess as someone to approach. I'm interested but not a buyer yet, still waiting for my 6spd to die first.

ive randomly talked to a few people in various places that also got hit with the same 3200$ fkoff price from holley/quicktime. Im sure a swap kit including everything would likely be very expensive and not sell well. With the transmission being 3000$ alone im sure a bellhousing, crossmember, shifter extention, driveshaft, PPF delete solution of some sort and posibly a clutch would make that easily 5-7000$+.. Id say the amount of people in the miata community willing to drop that much on a swap kit is very slim because you know "thats more than i spent on my entire car" 😂

If there is money in any vendor for it seems it will be a company already selling complete install kits that has a lot of the needed parts already on the shelves for other applications and is familiar with custom applications.

Even if it doesn't come with driveshaft and PPF delete since that will vary some depending on peoples setup they could make a kit with bell, trans, shifter, hydro throw out bearing. (They do sell custom length driveshafts though if needed.) My buddy used them for a swap behind his SBC and was very happy with the service.

The people needing a setup like this have likely already put 5-7k+ into a engine setup alone making 400+ and are tired of swapping stocks trans in every other event which are only getting more expensive and parts harder to find.

It would be great to see another vendor like FM or 949 jump on the band wagon and buy 15-20 of the bells to sell over time but seems unlikely? Would love to be proven wrong, they bells work for a variety of transmissions so while they might not fly off the shelfs they are useful for more than tkx swaps.

Since it measured out damn near perfect so far and as long as the welding process goes smooth ive really enjoyed making this one and would love to crank more of them out and could decently quick now that i have all the tools which has been most of the time holdups but the issue would be 1. its not certified in any way (i think the quicktime was the only sfi certified housing out if that matters to anyone, idk i dont race anything so doesnt matter to me) and 2. idk the liability of selling such a thing if something was to happen with it.. the rest of the kit wouldn't be hard its mostly basic components minus the crossmember which also i dont forsee being very difficult after the first one is figured out

I would be interested in a bellhousing once you get it ironed out. I saw @bbundy has made a PPF adapter for his application.

i've been keeping an eye on his post as well, would be cool to see more pics of that ive seen a few setups of ppf's to crossmembers before. Part of me hates dealing with the PPF in Miata's for me its like 70% of the time dropping a transmission is fighting the ppf and just wanted to make a simple ppf delete, It looks a little jank but i seen a post of someone cutting the ppf off right at the diff and just connecting the diff to the subframe with a heimjoint and claimed it worked fine. Im going 8.8 one of these days but with axles and rebuilding the entire diff aswell as the whole tkx swap got a little pricy for the moment and wanted some time to recoup and didn't want to put a ton of effort into keeping a stock diff although if it meant if there was that much interest id possibly look into that but i have to get 1 for my car all up and going and test first of course.

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I imagine it is similar to the pieces used on the SR20 engine swap kits. But I will let him expand on that.
Part of me also hates managing the PPF during transmission service but with this new robust solution I hope it will become a thing of the past.

Bit of an update, only a few tacks but it’s starting to take shape, keeping everything within spec when welding it is going to be the worst part by far
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looking pretty nice man! I'm still waiting on adapter from Domi works ;-( Next one I'm just going to do it myself like you're doing.

I got it welded over the past couple days, The welds turned out like total shit, Aluminum didnt weld the best in the world lots of junk and my 200a welder certainly wasn't enough but made do i guess , also welded along the inside but dont have any pics, As long as it holds i suppose.. Keeping the center within spec was super challenging, welding one side would throw it out over 10-15 thou then have to weld the other side and keep going back and forth. Being one big heatsink basically it just cools down quick when trying to preheat it. When i was done had to wash over alot of spots to try and draw it back into shape.. At the end i ended up keeping it to .007 center runout which is within their standard spec not quite the "high performance 7500 rpm spec" but every engine is going to be different, Currently fighting to get it parallel, even after decking it its .006 out at the highest spot which is 3x+ the spec.. Going to try it on a differnt engine soon and see how far off other motors are from each other, I suspect im going to have to dive down the rabbit hole of making offset dowel pins to realign everything. I believe the Mock up engine i used to build this the oil pan doesnt sit flush with the block by a few thousandths which is what makes the back sit higher when bolted on but indicates fine on the mill.
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