Main bearing oil clearance measuring out of spec
 

Can somebody help me figure out why my main bearings are measuring out of specification? Both my used OEM and new King bearings are measuring DOUBLE the oil clearance specified in a 2017 Toyota 86 service manual.

2017 BRZ FA20D, 44k miles, performance rebuild.

Main bearings journal OD, specified: 67.985-68.003mm
Main bearing journal OD, measured: 67.986, 67.990, 67.990, 67.990, 67.989

Main bearing ID, not specified.
Main bearing ID, measured, used OEM bearings: 68.030, 68.046, 68.038, 68.038, 68.033
Main bearing ID, measured, new King bearings: 68.033, 68.046, 68.046, 68.051, 68.033

Oil clearance, specified: 0.013-0.031mm
Oil clearance, calculated, used OEM bearings: 0.044, 0.056, 0.048, 0.048, 0.044
Oil clearance, calculated, new King bearings: 0.047, 0.056, 0.056, 0.061, 0.044

-Ambient temp and block is 20.8C
-Block halves torques together per manual.
-I’m measuring the crank main journal OD directly with my micrometers after checking micrometer with the included gauge pin.
-I’m measuring the bearing ID by checking micrometers with a gage pin, setting the micrometer to 68.000mm, then zeroing my bore gauge to the smallest value I can get between the micrometer, then measuring the smallest value inside the bearing. My bore gage is inch so my math is 68.000mm+(measurement*25.4).
- Oil clearance = bearing ID - journal OD

Help. [emoji17]https://uploads.tapatalk-cdn.com/202...6445e95fd7.jpg

Run 0w40 and call it good.

I don’t have engine assembly experience, but some triage thoughts for you to check if you have not already - once in a while a naive eye can help:

https://www.ft86club.com/files/BRZengine.pdf

This is presumably for at-launch 2013 engines; page EM-120 is where you’re at; your journal diameter measurement is in bounds. There are other measurements recommended, all the way back from EM-107 forward; are they all in scope as well? Especially re: piston diameter and crankshaft tolerances, though this is where I declare inexperience and tap out.

My 2019 service manual has a different/tighter upper tolerance on crankshaft journal diameter (max 68.003) on page IN-15. I didn’t check the other figures (though I see one of the crank shaft bearing thickness limits tightened as well) but duly noted since you’re probably across the facelift boundary.

Chances are, you’re already familiar with all of this, so this is unhelpful; but if somehow it pans out, cheers.

Having never done an oil clearance measurement, I don't know how big a difference this would make, but I would suggest bypassing the gauge pins.

Just zero your bore gauge to wherever your micrometer ends up from measuring the journal OD. Then the bore gauge just reads the oil clearance directly. If I understand your procedure correctly, you're including two more measurements (the two involving gauge pins), and their associated errors, into your final calculation.

One would hope these errors don't overwhelm the actual measurement in which case you'd get the same result, but if the result turns out different - hopefully closer to spec - I'd go with that.

I did and it worked so far, but I’m taking so many other risks I can’t afford to risk something simple like this.

Yep, 2017+ car so I’m going off a 2017 Toyota manual. The engine looks great after 63 track days and 44k miles with no measurable wear, except this one oil clearance.



Thanks. Yeah I asked this on some facebook groups and I got a similar response. I’ll update the original post but it did not make any significant difference. If anything, it confirmed that my measurements were pretty consistent and that some main bearing 3 and 4 are particularly bad.

Do the original bearings show any visible signs of wear? I see the difference between the Toyota and BRZ specs. I'm with Tokay on this. I'll go a step further. Since I first became aware of how much engine speed affects oil temperature, I've quietly assumed that it is a direct result of dumping the same amount of work into a fraction of the oil volume seen in previous generations of journal bearings.

I bet the original bearings were fine,

How are you measuring the ID of the bearings without the engine assembled? Using a micrometer on an uninstalled bearing is your problem. They got to be compressed, installed in the journal to get an accurate measurement. Do it right, use plastigauge like everyone else.

If he compresses them, there will be even more clearance. Plastigauge is for a amateurs who don’t have the correct measuring equipment.

I had similar issues when assembling my engine.
The ACL race series bearings come in both 0.025 oversize and undersize sets.
I ended up using 1/2 a std set and 1/2 0.025 oversize set to get all clearances good.
Expensive and time consuming getting it all good but it can be done.

I think the block relaxes after a couple years of heat cycling so they're never quite the same as a new one.
I also had issues with alignment as I removed all the dowels to make it easier to set up on the machine for sleeves. This was a mistake! I ended up having to make offset dowels to get the tunnel to line up true again. A huge amount of work but probably still less than line boring it.
I have all the leftover bearings from my build listed for sale in the australian classifieds section.

Another tip for fine tuning clearances.
If the std bearings are to loose and the 0.025 oversize are to tight, you can use one of each shell on a journal which gives you 0.012 clearance increments.
Be very careful if using this trick on main bearings as you may create alignment issues if thick and thin shells end up on opposing sides of the tunnel.
Rod bearings no problem, run the thinner shell in the cap.

Incorrect, but thanks for trying. Main & rod bearings are slightly larger than the journal, when bearings are seated in the journal the tension from this holds them in place. Then when you set the crankshaft in place and torque the block halves to the correct value you will get the true clearance. Anything else is just guessing.

It's no wonder there are so many failures on "garage" rebuilds for this engine...I'm still 0 for 150+

lol. “uSe PlAsTiGaGe! yOuR dOiNg It WrOnG”
The guy has actual measurements with high quality direct and indirect precision measuring tools. Why on earth would he use Platigauge? It has its place. That place isn’t here.

Plastigauge isn’t perfect but given the OP’s measurements I would have used it to double check myself in that situation. At least one rod or main would have been plenty to verify.

Plastigauge isn’t perfect but given the OP’s measurements I would have used it to double check myself in that situation. At least one rod or main would have been plenty to verify.

My question is has the measuring tool been calibrated/reading correct? I would double check with another tool, yes plastigauge would be a good double check.

Main bearing oil clearance measuring out of spec
 

I measured everything again, using the crank pin journals as baseline instead of the gauge pins and no meaningful difference.

I guess the plan for now is to use the 0.026mm tighter bearings by King Bearings. This conveniently puts my measurements back within the looser end of specifications or just slightly outside of them.

With the block assembled and torqued, without a crankshaft. I’m not sure how you would measure a loose bearing as you described.

I don’t get my equipment calibrated but, I have an assortment of gages and multiple calipers that overlap gages, and everything measures within 0.002mm. Plastigage measurements have been within 0.005mm of micrometer measurements.



You are correct. The original bearings measured oversized the same amount as the brand new King bearings and show almost no wear. A few little marks that look like they had some embedded debris at one time, but nothing of concern.
https://uploads.tapatalk-cdn.com/202...1de1f8ed08.jpg



Cheaper than machining anything! This is the route I am going, but will be all 0.026 tighter.

Yeah, it does almost seem like the block loosened up, unfortunately I don’t have bearing bore dimensions to verify!

Good to know. It looks like I’ll be running all oversized so no worries.

There is always the chance that the clearances were all out of spec from new. Maybe subaru is a bit sloppy building them. Maybe that's why they're a bit more prone to failure than other engines.
Oil pressure at idle spec is about 7psi according to toyota, crazy low. With main clearances set at middle of spec, 0W-30 oil and a WRX pump I get 12-15psi at idle.

Who wants to buy a couple of new short blocks, strip, measure and post the data. I'm sure we'd all be very appreciative! :)

That is enough double/triple checking to say your measurements are good.

Whether the micrometer he's using is calibrated or not, it almost irrelevant. He's setting the mic to the crank pin diameter, and zeroing the bore gauge to it. Are suggesting the bore gauge may not be tracking correctly over a <.002" stroke?

I was wondering if that main clearance was a cause of failures as well. Extra main clearance, means lower oil pressure for both the rod and main bearings. Then when someone gets rod knock it gets blamed on abuse or neglect.

I wish there was more data on what the main bearing shell bores should be. It seems like a pretty vital piece of info to leave out of the service manual.

Luckily this engine still had 20psi idle oil pressure with 0W-40, and down to maybe 16psi at worst idling immediately getting off the track and 240F oil temps.

Is the table at the end of page EM-115 about taking an *indirect* measurement of this? (I’m asking to check my learning from this thread, so please don’t feel compelled to reply if it’s any trouble.)