Bearing clearances
 

I just got the bottom end of my 01 VVT block disassembled with the assistance of my little helper.

The crank loos great, nice and polished with no scratches or score marks. Plastigauge checks of the rod clearance showed 0.002"-0.0025" and main clearance showed 0.025"-0.003". These measurements are below the 0.004" limit, but at or above the normal maximum range of 0.0027". I am debating on getting the ACL Race 0.025mm (0.001") undersized bearings to reduce the clearance on the rods and the mains. My only concern is that my measurements are with worn bearings. For example, if I slap in a standard bearing would I already reduce my clearance by say 0.001" or have too little clearance if I take away another 0.001" with slightly under sized bearings?

I measured the crank out of the block and both the main and rod journals were right at the bottom of the minimum numbers in my manual. This makes me think that I would be OK with a 0.001" undersized bearing.

What do youse smart fellars think?

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You can combine std and 0.001 bearings to get the clearances you desire.

If you are going to the trouble of getting clearances right an extra set of bearings is a small cost in the scheme of things.

Those bearings will do the opposite of what you want. They're designed to increase bearing clearance for high performance applications.

Actually it looks like they offer both +0.025 and -0.025. I would absolutely run standard bearings on a turbo BP with your current measurements though.

I would probably go with standard sizes.

One other thing though. Put a little bit of locktight on your oil squirters and make sure those are torqued to spec.

I guess I will try standard sized bearings first. I can always get the 0.025mm smaller bearings later if my clearances end up too tight.

Still trying to determine if the oil squirters are staying or going, but that is another thread that I am drafting.

I went with standard bearings and clearances are just under the maximum allowed 0.0027". It think it will work.

Do I need to have the crank polished? The crank looks good with no scoring. I don't really want increase bearing clearances at all so I would rather not polish the crank. In previous stock rebuilds I have always had my machinist tell me to leave the crank alone if there is no scoring and no need to turn it down.

Race engines and other heavily stressed engines are typically built with loose bearing tolerances. This lowers the oil pressure a little but is normal. Using a higher volume VVT pump will compensate if you are conservative.

That's what I am thinking too. I could not find a good number on what "loose bearing tolerances" really are, but figured the higher limit of Mazda's recommended clearance range should be OK. I am running the Boundary Stage 2 pump with higher flow for the VVT motor.

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I forgot to upload a picture of the crank earlier. Does this crank need to be polished or would I see any benefit from getting it polished?

# 4 main and the crank flange could use polishing IMO.
That groove that the rear main seal made could be minimized.
Polishing shouldn't remove more than .0002 and I usually have cranks polished.
I try to use standard cranks as well.
Machining removes any heat treating the factory did, polishing should not.

I would polish it. It's cheap.