Radial GT

iTrader: (16)

Hello,

I am rebuilding my engine and the previous owner did not change the oil often enough. All of my bearings need to be replaced. I had to also order a new eccentric shaft. Anyway, my question is when I go to Mazdatrix they have different sizes for the main bearings.

I am getting the idea that you have to measure your eccentric shaft and then subtract the tolerance that you are looking for and that will give you the size of bearing you need. However I am unsure on what a good tolerance is for the bearings. This is a street car, and don't want it to be all crazy or anything, but I just want to make sure that I have the right parts. Any ideas?

Thanks!

Mitch

GoodfellaFD3S

iTrader: (213)

I'd recommend going to Ray at Malloy Mazda for all your FD parts needs. His # is 888 533 3400.

He offers very deep club discounts, ships promptly, and owns two FDs (one a 20B) so know these cars inside and out.

arghx

iTrader: (3)

Download the workshop manual. At the very end is the technical data section. It has specs for the bearings and e-shaft. If you are actually trying to do this measurement you will need high-end micrometer(s).

GoodfellaFD3S

iTrader: (213)

For a street car, Ray will make sure you have bearings of the proper thickness. Tell him you have a new e-shaft.

Radial GT

iTrader: (16)

Good stuff, thanks Goodfella.

I think that this Mr. Ray could end up becoming a good friend. The reason that I ask was I am just curious to how important the tolerances are. The service manual makes it seem fairly black and white, if it is larger than this replace it to make it to the correct measurement. I just didn't want to have any problems arise down the road with the bearings. That is an ugly ugly beast when they go bad.

I do have access to high end micrometers so the data that I would collect would be spot on.

Thanks

GoodfellaFD3S

iTrader: (213)

We press brand new rotor and stationary gear bearings in with almost every build at IRP, IMO they're essential to a quality build, especially the stat gear bearings.

Carlos Iglesias

iTrader: (6)

First off, to echo Rich on Ray... you WILL NOT go wrong with defaulting to him for parts.

To do the measurements correctly you'll need tools to measure the 43mm +/- .06mm Stationary Gear Main Bearing bore (telescoping guage/micrometer)and respective e-Shaft race (outside micrometer). This means more than likely:

- 25-50mm or 1-2" (outside) micrometer
- appropriate telescoping guage

Once you have those, measure the inside and outside dimensions of both the front and rear main bearings. Do the same on the e-Shaft. Subtract the e-shaft diameter from the respective main bearing bore and the resulting clearance should be:
- outside: .08-.11mm but never >.13mm
- inside: .06-.08mm but never >.11mm

If out of clearance, replace with the appropriate bearing.

BTW, the rotor bearing and respective e-shaft race measure 74mm +/- .06mm. Though a telecoping guage will work, unlike the smaller main bearing bore, inside micrometers are also available at this size.

I'll leave discussion of the benefit/offsets of new vs used (within clearance) bearing for a different time/place.

arghx

iTrader: (3)

I can tell you that rotary engine builders don't sweat bearing clearances anywhere near as much as on a piston engine

GoodfellaFD3S

iTrader: (213)

One thing I've noticed over the years, rarely do we have teardowns with bearings that pass the visual inspection. We don't even need to bust out the mic for bearings in most cases. Usually when a car comes in for a rebuild, they have the original bearings because the last guys didn't want to mess with them, or didn't deem them bad enough to replace at the time. So you're looking at 20 year old bearings with 50-100k miles that have lived a hard life.