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Mazda BP MBSP
By Randy Stocker
Mazda added a Main Bearing Support Plate (MBSP) to the 2001+ Miata. Often called a "girdle" it help keep the main bearing caps aligned and helps minimize failures from crankshaft flex and ultra high rpm usage. It is part # BP-6D-1040Y.
The 2001+ MBSP can be easily retrofitted to earlier Miata BP motors since the main caps already have drilled bosses to accommodate it (it was actually an OEM piece on the rare 323 GTR - although a front sump design). All you need is the corresponding 2001 oil pan.
If you cannot locate a correct 2001 oil pan the MBSP can be modified for use with the earlier 1994-2000 oil pans. It is not recommended but is possible.
The 'dimples' stamped in the MBSP to give clearance to the crankshaft counter weights need to be removed since the earlier pan is not cast to accommodate them.
The 2001+ MBSP also covers the entire circumference of the block while the earlier windage tray only fits partially with locating ridge machined in the oil pan. This requires either putting the earlier pan on a mill or belt sander to flatten the locating ridge or sacrificing the earlier windage tray to cut spacing strips to fit into the machined recess. Either way the two rubber oil pan seals on either end of the pan will not fit properly so some creative use of RTV will need to be used to seal the pan.
Special Thanks to Sheldon Engelhorn for the retrofit info and some of the pics!