Mazdatrix has 3 different rotor bearings forthe FD.. Which do you suggest?



http://www.mazdatrix.com/b4.htm

Noone?

I have no idea why the FD would be different than all others. Some people use the engine without regard for the oil pressure requirements. The FD oil pressure at speed (I have read) is 110 pounds. The 50MM pump is more than adequate to supply that at speed. So what is the need?



If there is a choice, I would measure the crank and look for at least .003" more than that. For all out racing you could go .0035" on the mains and up to .004" on the rotor bearings, and you would never want less than 100 PSI at the block.



The object of the high oil pressure in racing is cooling. The additional oil moves overheated oil off of the bearing at a higher rate. The bearing overlay (the silver stuff) is soft and has a low melting temp. So, as long as it is not too hot it remains in place and does the job.



That layer is less than .001" thick, so some people machine it away, or sand it away with 600 wet or dry paper (done wet) so there is no soft stuff to move around or melt and plug an oil gallery. This leaves you running on the copper layer, but it works just fine. Years ago all Ford truck bearings had only the copper to run on, no indium at all. This makes the crank wear faster, but in racing you can pitch that one into the dumpster after the season.



For street driving the .002" to .0025" was fine. If you want to scream the engine every time its running, then go with the biggest clearance they have. Mazda is a bit timid on running clearances. The so called race rotor bearing is .0005" bigger than the street bearing. Not a giant step at all. The bearings are huge for the stress involved, and the additional clearance helps with crank flex also. With a dry sump pump and not less than 110 PSI you can run more clearance all around. I note that the racing Beat relief valve is set at 115 PSI.



My Fiat used .003" for rod bearings and .0035 to .004" for mains. We could break a rod and the rod bearing would still look good.



Lynn E. Hanover

nm-

unless otherwise specified, we'd normally sell the biggest one. like lynn says, its not much difference