HOW TO MODIFY A 2001+ MAIN BEARING SUPPORT PLATE TO FIT A 1994-2000 MIATA ENGINE

PARTS NEEDED:

- (1) MBSP, Mazda part #BP6D-10-40Y for 2001+ models (list price is $93 each, Miata club discounted price at local dealer was $66 each)

OPTIONAL PARTS TO HAVE A #3 MAIN CAP THAT BOLTS TO THE MBSP:

- (1) used #1, 2, 4, or 5 main cap (1994+) with the two OEM holes tapped for bolting to a MBSP bracket
- (1) A second MBSP to steal a bracket to enable bolting the MBSP to the #3 main cap

INTRODUCTION:

On 1994-1997 Miatas, there's a flimsy sheet metal oil baffle sandwiched between the block and the oil pan and below the crankshaft. The oil pickup tube is bolted to the underside of it.

In 2001, Mazda replaced that oil baffle with a sturdy steel plate called the Main Bearing Support Plate (MBSP). It acts as a "girdle," linking the block, oil pan, and #1, 2, 4, and 5 main caps. There is no accomodation for bolting the MBSP to the #3 main cap.

Like 2001+ Miatas, 1994-2000 engines had #1, 2, 4, and 5 main caps with two tapped holes for bolting to a MBSP, even though there was no MBSP on 1994-2000 engines.

In the course of modifying a MBSP for installation on a 1994-2000 engine, you can optionally repurpose a salvaged #1, 2, 4, or 5 tapped main cap as a #3 main cap and add a bracket to the MBSP in the #3 main cap position. The most cost-effective way to do so is to obtain a second MBSP and steal a bracket from it.

INSTRUCTIONS:

The most challenging part of this project is to get the lip of your oil pan milled down by the same thickness of the MBSP which gets sandwiched between the oil pan and the block.

If you don't do this, you will find out the hard way (as I did) when you attempt to re-install your engine that the bolts that attach your tranny bellhousing to your oil pan won't align vertically.

Even though you're going to want to go crazy with the silicone when installing the oil pan to the block, to prevent leaks you want to start out with as perfect a seal as possible between the oil pan, MBSP, and the block.

You could file down the lip of the oil pan by hand, but for peace of mind, it's worth having it milled at a machine shop (for about $50). Or if you're rich and lazy, you could go down to your local Mazda dealer and buy a 2001+ oil pan.

The MBSP has four bulges pressed into its sides and the 2001+ oil pan has matching indentations. The inside walls of 1994-2000 oil pans are flat. So unless either the MBSP or the oil pan are modified, the MBSP will not lower all the way down so that it seats properly on the lip of the oil pan.

Grind flat spots on each of the eight bulges in the MBSP at their widest points (about 1" vertically from the lip) so they don't contact the inside walls of the oil pan:

Drill out the eight spot welds and wedge a chisel or screwdriver blade between the bracket and MBSP to release the bracket:

The "stolen" bracket bolted to a #3 main cap replaced with a #1, 2, 4, or 5 tapped main cap:

Mark a hole to allow access to the new bracket:

The X-shaped hole, cut with a Dremel. Bend the "tabs" over by giving a twist with ViseGrips:

Bolt the MBSP to the main caps to confirm proper alignment and weld the new bracket into place on both sides:

My modified MBSP after it was silver zinc-plated. Looks like a stock part!: