Difference between main bearings?

[nicpaige]

Does anyone know the difference between the Clevite main bearings part # MS704P and MS1947P ? I have a 1985 12wt 4.2 crank and a 1999 4.0 HO block. Which main bearing set is the correct one? Thanks

[SilverXJ]

The MS704P is for the 258 and 87-90(renix) engines
The MS1947P is for the 91+ 4.0L

[nicpaige]

So for a 4.2 crank in a 4.0 block are you buying main bearings for the crank or the block? Or maybe it would be simpler to just ask which would be appropriate for my combo listed above?
Thanks again. Im in the home stretch. Final hone and Im ready to assemble.

[jsawduste]

Block

[IH 392]

Yes the main bearings MUST be for the BLOCK, NOT the crank.

[Cheromaniac]

All of the above posts are correct. You'll need the MS1947P main bearings for a '99 4.0 block as those have central locating tangs. The earlier MS704P main bearings have offset locating tangs and won't fit in '91+ HO blocks.
However, rod bearings and ARP rod bolts are interchangeable between 258 and 4.0 engines of all years as the 258 and 4.0 rods share the same big end dimensions.