Howdy,
I have a stick shift '94 with the 3.9. I want to find and rebuild another 3.9.And keep the 5 speed. Can I use an engine that was equipped with an automatic? Is the crankshaft the same or is there a difference because of the pilot bearing?
Although my search has just begun, so far all the engines I have seen are the automatic variety. Lots of them around.
Thanks for any response from people that know.
Larry

 

The pilot bearing recess may not be fully polished on an auto crank.

And that's it.

Here's a thread about it for a LA 318; principle is the same.

RwP

 

Im going to tell you what I think, but Im not 100 percent sure.

I believe the cranks are the same. In fact, looking at rockauto.com they only show one for the 94 3.9 dakota. manual or automatic.

I believe in older cars it made a difference due to how the pilot bearing mounted.
In older mopars, it was deep in the crank, and sometimes was not drilled deep enough or machined for the bearing or bushing.
In magnums, the outer section that would center the torque converter is used for the pilot bearing and its housing.
Below are two pictures that may make it more clear.
FWIW I have heard that when using the magnum in a older mopar, you can use the new style bearing and shorten the input shaft. So I heard.