Oil pump mounting

[Gregorypaul]

I was test fitting a new melling oil pump to my 94 Cherokee 4.0 block this morning (test fit no gasket) and noticed a definite rocking back and fourth on the mateing surfaces. Checked with a straight edge and it is in the block not the pump surface. :?:Wondering if anyone else has noticed this sort of fit on these particular year blocks? Goes to show the importance of proper torquing!

 

[superj]

i never had to break any of mine open that far

 

[Jester32]

Been there. Ive had to machine then on two of mine. I believe your allowed .001" if there a gasket and .00010 if theres no gasket like the Chevys

 

[Gregorypaul]

Looking at it again it appears the high spot is centered at about the oil pump discharge hole into the block, and between the mounting bolt holes. There is a .010" gap with a feeler gauge if the pump is pressed down at one of the bolt locations. Thinking about adding a .005" shim at the bolt hole locations. With all the wacky oil pressure issues with the 4.0 wondering if this is a partial cause?

 

[Jester32]

That's quite a bit usually they may machine a small difference to account for the torquing of the bolts and housing warpage when torqued. All my 4.0l are around 35 psi at idle and 45-50 at rpm. And that's using stock pressure high volume pumps clearancing the main and rod bearings according to the oil I run.