Rebuilding the 12a from my 84 GSL.

Cleaning the rear iron and removed the rear bearing.

I noticed there is a two-tone appearance on the inside: silver and copper colors.

Is this normal? Should I be concerned enough to replace it?

 

The silver is the babbit material, the copper is under the babbit.

Some of the more experienced guys will chime in, but the mormal bearing with acceptable wear usually does not have so much copper showing. Typically the only copper showing is at the key joint. If you can get a bore guage to measure it and calculate the oil clearance it would give you a better idea of how to proceed. Some of the higher authorities on the forum may be able to look at the pic and give you an idea.

 

Looks like a lot of copper showing in there Tim, but Robert is right, a measurement is in order.

Here's what that copper stripe looks like more typically. These were replaced.

 

Ray, Robert,
Thanks.

My rotor bearings have the one copper stripe, nothing more.
Attached images of front bearing.

They are not the expensive from Atkins, but the Atkins ones don't have the copper strip. Aftermarket as opposed to OEM?

 

Find a good used set. They are pretty cheap.

 

http://www.ebay.com/itm/Mazda-RX-7-Rotary-Engine-Parts-12A-Stationary-Gear-Set-/321276175508?pt=Motors_Car_Truck_Parts_Accessories&hash=item4acd8d6494&vxp=mtr

 

I'd replace them with new bearings if it were me. 24 hours in the freezer and a few minutes on the press will do that engine good.

But check your shaft for wear as well.

 

if they aren't scored and oil pressure was good before pulling it apart, I'd run 'em again.

The only times I've had main bearing issues were when I had a low/no oil pressure problem one time, and one other time when I pulled the stat gear out and it didn't go back in 100% straight, so it wore cockeyed.

Get out your measurin' tools. The one that had low oil pressure was from the front cover O-ring blowing out, and the bearings were scored and had .007" clearance. Normally, when they are worn to copper, they generally don't wear any more than that so you can just keep on truckin'. They're pre-race-clearanced.

Bear in mind that new bearings are a "traumatic" event and they always have high spots that need to be broken in (worn down!) which is why Mazda recommends a breakin period 2-3 times longer than a rebuild with reused bearings. And use an RX-8 front cover gasket so you don't have to worry about the front cover O-ring...

 

peejay,

I can see score marks, but after cleaning I cannot feel anything resembling a minute scratch.

At idle,750-800rpm oil pressure would be about 12 on the dash gauge. Running 1500 and up it would hold near 60 (midpoint) on the gauge. Does that sound normal? Its been that way since I inherited the car from my father 8 years ago.

 

12 is a little low, although the dash gauge is woefully inaccurate. (I discovered my issues with the one engine after installing a mechanical gauge. Dash gauge was reading much higher than reality)

Measure at several different diameters, front and rear (especially rear) and do the same for the eccentric shaft. If the oil clearance is over .004" then go bearing shopping.

 

I believe I need a micrometer and bore gauge set.

As micrometer repeatability is more important than absolute accuracy, I'm only looking for relative differences, do you think I can get by with a micrometer set with .001 increments?

There is a significant price jump going to .0001.