I called a few local places and got the runaround from a few Facebook marketplace remanufactured engine sources. Does anyone have a recommendation for Illinois or at least the Midwest where I could find a reliable quality rebuilt BP-4W (99-2000) NB1 engine?

 

Miata engines are not horribly complex. A good machine shop can rebuild them.

 

And equally, a bad machine shop can butcher them.

Ensure a couple things if sending in your longblock for a rebuild:

• If cylinders need boring, ensure that the block setup uses round bar to level the crankshaft journals for a perfect perpendicular bore
• That they use a proper fly cutter for resurfacing the top of the block
• That they know and understand proper RA surface finishes for MLS head gaskets