Build Thread 1978 Mercury Cyclone. The pig is in the pen.

Now that the pan is done, I have to start considering the trans swap. The engine came with a 4 speed auto, but it isn't really up to any big power capacity. It's also fully computer controlled.

And I like my manual shift auto. With converter L/U, it's almost like I have a 5 speed.

Adapting the 4r70 is gonna be true Monster-typical stuff though.....as I've thought this out for the last two weeks there are two possible paths to take...one is better than the other, but it has a fairly big "con" that can't be reversed,mane once I start down that path and it don't work.....

I'm phcked.

So, let's talk about the other way where I'm not.

Plan A: I build an adapter plate that sandwiches between the back of the 2j block, and the SBF bell pattern of the 4r70. Right now, the plan for how thick that plate will have to be is still up in the air. The problem with keeping it thin is that the 4r70 converter pilot is bigger than the pilot hole in the 2jz crank. And, according to the place I got the converter from, the converter cannot be turned down to fit inside that hole without cutting through. So,.....I have to have a stepped up adapter built that will center on the pilot hole of the crank, and step up to the diameter of the converter snout, so that the converter will have something to center in.
The thickness of that will depend on how far the converter's hub sticks past the flex plate when it's bolted up.
And that will determine how thick the sandwiched adapter plate will have to be.

And that could end up being really thick. ( like 1" or more)

If there is a 1" thick adapter between the two mating surfaces, the converter feet would also have to be commensurately thick.
The one thing you learn when contemplating this is that the stock starter mounting surface is part of the block. You want to try and keep the stock starter in place,..you want to use the stock Flexplate, hence all of the rearward spacing off of the block.
It’s a bunch of custom made stuff...completely in line with the Monster theme.

The other version uses the stock A340 removable bell. I’d have to cut the existing bell housing off of the 4r70, and use the front pump as a mounting surface for a plate that I’d use to bolt the stock bellhousing to. While this is more desirable to me, the problems arise when you have to consider the difference in the crank pilot versus the converter hub. With this scenario, I don’t have the spacing to accommodate the difference between two. The converter would have to bolt up to the Flexplate as is, as I can’t imagine that I’m gonna have enough room for a pilot adapter in the back of the crank.

So,....no worky. It also destroys any chance of bailing out, or going back once I cut that bellhousing off.

a91what said:

lets start with the converter... why cant you have someone make you a converter with the correct size hub? I would start here and then move onto the other items on the list. once this part is figured out a 3/8 steel plate could be drilled to make the adapter. of course you have the flywheel to figure out but if you have a friend with a lathe they could cut the centers out of the jz and SBF flexplates and you could then weld the JZ center into the SBF flexplate and have it balanced...

I know it sounds crazy

Click to expand...

Nope, not crazy at all. Excepting your advice to have a custom converter made ( read:1000+ dollars) the thought process of bolting the two flex plates together has already crossed my mind. the converter in the 4r70 is a 10" L/U IIRC, i paid a little over 550 for the thing already. I'm not gonna sell that off at 50% if I can make it work. This Saturday will be the start of the process. I'll pull the remnants of the Monster engine, and start trying to fab up some sort of jig so that I can start attempting the marriage between the 2j, and the 4r.
I'll know soon enough what lies in front of me after that.

KZGUNS said:

@CarMichael Angelo Send me a drawling and what material. I won't charge you anything really unless its some pricey material lol

Click to expand...

And man, I appreciate that.
I have to get the two of them together in order to know what I need thickness wise.
But I'm thinking itll end up being a 3" diameter disc with a " outtie" that will fit into the pilot hole in the crank, and an " innie" that will allow the converter to pilot into. I'm thinking that itll just float ( I hope) and that the converter will force it to stay in the crank once its bolted onto the flex plate. If the pilot is deep enough, ( the japanese converter pilot looked to be maybe maybe in the crank at least .750", and if that fit is close enough, it shouldn't try to wobble since its spinning with the crank.)
This piece is the start point for the adaptation process. Once I get something in the tail of the 2j crank that will allow the converter to line up with and fit into, the rest can be done by me.
Just thinking about it, I'd bet that the thing will start at maybe 2" thick, and finish with the pilot in the crank .750-1.00, and the remaining hub between .500-.750.
I need to keep the spacer at the finish depth of regularly available bar stock so that I can just go out and buy that junk when I need it to build the adapter plate itself.