Early 258 12wt Crank to TF999

[ag4ever]

I am considering rebuilding an engine for my '83. ('98 4.0 block, 12 counter weight 258 crank, custom pistons...)

In researching this I found, "The early 258 crank was designed for use with the Borg Warner automatic, and requires an adapter to be used with a Torqueflite automatic."

Is there any truth in this? What is needed to mate a TF999 to a 1971-1981 258 crank? I think I also have a engine that I could scavenge a post '82 crank from (I think it might be an '83 or '84, but I don't remember off the top of my head), but would rather the additional rotational inertia afforded by the 12 wt crank.

(And don't fret, I will keep the original engine, possibly rebuild it and bag it for future use to enable it to be 'bone stock')

Also planning to rebuild the TF999 while I have everything out, but that is another story. Would be nice if I could find a donor TF999 to rebuild so I can have everything ready for a swap and just have the Jeep down for a single weekend and shelve the stock parts for the future.

 

[FLCJ8]

In researching this I found, "The early 258 crank was designed for use with the Borg Warner automatic, and requires an adapter to be used with a Torqueflite automatic."

I take this to mean the '71 was for the Borg-Warner and the '72 - '80 were for the TF


This corresponds with part numbers from supply houses as well.

Not sure about the '81 to '88 counterweight quantity though.

 

[ag4ever]

Are those casting numbers or part numbers?

I’ll have to look at the crank I have to see if there are any markings.

 

[John N]

I’ve got an ‘81 with the original TF999. It came with a rebuilt 258 of unknown heritage. I swapped it out to an AMC 360 (3 times, but that’s another story). Very swap, install, was totally straightforward. Just had to use a 360 flexplate and make sure that the bushing sleeve for a T400 wasn’t still in the crank. No adapters were necessary. I don’t know if this helps or relates to your situation.

 

[FLCJ8]

Are those casting numbers or part numbers?

I’ll have to look at the crank I have to see if there are any markings.

This is the header

I had cut the top off as it went back to 1965 and thought all the other engine info would be confusing.

 

[ag4ever]

Found the casting number 3214723, so I should be good to go. Thanks!

Now I need to strip down my 4.0 and take the block, head and crank to the machine shop. Hopefully they will all be serviceable.

 

[FLCJ8]

Found the casting number 3214723, so I should be good to go. Thanks!

Now I need to strip down my 4.0 and take the block, head and crank to the machine shop. Hopefully they will all be serviceable.

So, are you building a stroker?
If so a build thread would be interesting to follow.

 

[ag4ever]

First step will be to get the block, head and crank cleaned, magnifluxed, and given the green light. If all that checks out, I plan to build it up as a stroker. Just need to do a bit more research to be sure the v belt accessories will work on a 4.0 block before I send the parts to the machine shop.

Since it would go in the overlander, I want it to appear stock. If the v belts don’t work on a 4.0, I’d probably postpone the stroker (for an ‘81 build from spare parts) and just do a straight rebuild on another 258 I have.