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.