alexdimen

iTrader: (13)

I've been specing out my rotor bearing clearances. The bearings have no visibly worn spots and have all the babbit (grey low friction coating) is intact. In other words, there is no brass showing and no uneven wear. They do however, have 127k miles on them.

The clearances I'm getting range from .0030 in to .0035 in (.076 mm to .089 mm).

The bearing bores also measure the same as a brand new FC bearing installed in a spare rotor I have.

The factory specs list standard clearance as .0016 in to .0031 in (.06 to .08 mm). The maximum clearance is .0043 in (.11 mm).

I think it's safe to say I'm still in standard clearance.

So... when do you pros replace bearings? If I should go ahead and get new bearings, which size of the 3 available should I get and why?

alexdimen

iTrader: (13)

I'm just going to ask atkins what bearing they recommend tomorrow. Since there don't seem to be any threads out there on this topic (fruitless searches), I'll post up what I learn.

EFS.O

I had the same question and got zero answer.At the end i bought and installed the ones with the biggest tollerances,but my bearings had visible wear.I am not an expert,but if mine were like yours,i would propably stick with the old ones.....

alexdimen

iTrader: (13)

Atkins says they use N3A1-11-B11. These are the largest of the bearings by a few ten thousandths of an inch. In other words, they give the most clearance.

I know, I'm tempted to leave them alone, but they have so many miles and it's the only thing I didn't replace the first time around.

I'd like to have the peace of mind and if they keep the engine running tighter for longer, I'm more likely to meet my mileage goal for this rebuild.

Chadwick

iTrader: (12)

The clearance you list is fine for a used bearing. If you don't see any brass color wear spots showing through they are fine to re-use. It is always better to use a seasoned bearing when they are not showing wear and are within spec.

alexdimen

iTrader: (13)

Well, I've ordered the bearings. I can always leave the old ones in.

I think I'll take a look at the old bearing surface under magnification before I decide. The car sat for a long time and there was chemical or electrolysis damage to the main bearings. It was really weird.

The rotor bearings looked decent and measured out fine, so I used them. Now the engine is apart again after only 1500 miles (compression related failure) and I'm double checking everything.

FD7KiD

iTrader: (8)

hey everyone, bringing this back up to get some guidance.

my noob question is, will getting more clearance in bearings help with oil flow similar to the race spec rotor bearings??

or

is there a easier/proper way to find out which rotor bearing is the best to use. I'm currently rebuilding engine with a single turbo for a 400+ hp goal. (FD rotors, street port)

my options at the moment are:

N3A1-11-B11 3.0mm (-0.005 to -0.010)
This will give more clearance than stock

N3A2-11-B11 3.0mm (0.00 to -0.005)
This may give more clearance than stock

N3A3-11-B11 3.0mm (+0.005 to 0.000)
This may give less clearance than stock

IRPerformance

iTrader: (41)

Really you should measure the eshaft to find what clearance you need. I use the N3A1-11-B11 large clearance yellow stamped bearings in most of my builds. The larger clearance helps them retain more oil. I've never had a bearing issue in a motor I built since I've been building motors some 16 years ago. Why someone wouldn't replace bearings during a build is beyond me. They are a wear item and relatively cheap.

j9fd3s

iTrader: (3)

the way Mazda lists the clearance is a bit weird, the 3mm they mention is the thickness of the bearing shell, so its 3mm give or take, which probably means that they just grade different batches. the Eshaft might have a stamp in it that mentions what bearing Mazda used originally, although we don't know how to decode it.

you can see about 1:30 they measure the main bearing and stamp the shaft.

FD7KiD

iTrader: (8)

@j9fd3s: thats a really awesome video!!

@IRPerformance: i was planning going in that direction of getting the N3A1-11-B11 large clearance yellow stamped to retain "more" oil; similar to that of getting the race spec bearings but without having to pay triple for each bearing; but, i wasn't sure if going with the larger spec would have any type of negative affect.

it just seems weird to have other clearance options if your only option is to go a size larger, since you cant just go with the smaller of the three and not have it fit on the e-shaft.

or

is having a tight fit rotor bearing on the e-shaft the preferred way for all applications?

thank you all for your help on this

IRPerformance

iTrader: (41)

I always go larger. I've actually had brand new eshafts that wouldn't fit with the smaller bearings. Mazda had different size bearings because of manufacturing tolerances in the eshafts but it is proven that the larger bearings retain a ticker film of oil and are better for performance applications.

FD7KiD

iTrader: (8)

@IRPerformance: Thank you very much for this piece of info!!! I feel more confident in getting the yellow stamped bearings N3A1-11-B11 3.0mm (-0.005 to -0.010) since it'll have a similar affect as those of the "race spec" bearings racing beat sells.

My follow up question:

Is there such a thing as "too much" clearance for a rotor or main gear bearing??

thank you again for your time and consideration in helping me.

IRPerformance

iTrader: (41)

Yes there can be, but it would take a significantly worn eshaft. Max clearance is around .0031-.0039".

alexdimen

iTrader: (13)

FWIW I've had great results with the N3A1-11-B11 bearings. 25k of street driving, auto-x and HPDE's. Original e-shaft... actually I think it's from an FC.

FD7KiD

iTrader: (8)

@IRPerformance: thank you again for your help on this, I really appreciate it a lot.

another follow up question:
can this method be applied to the main gear bearings as well??


@alexdimen: thank you as well for your experience, it seems like the yellow stamped bearings is a no brainer to get. especially since my rotor bearings are showing large amounts of copper.