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Crank / Rod bearing Clearences

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I am currently rebuilding an engine, I have genuine Toyota manuals (its a 3SGTE) and am referring to these.

my question comes from the "old rule of thumb" and that's 0.001" of clearance for ever inch diameter.

now my journals on the mains are 1.889" nominal (im talking inches through out to try and keep it clear.)

this returns an oil clearance of 0.0018". now Toyota recommend 0.0006-0.0013" (although the upper limit ie when the motor is trash is 0.0031")

so the rule of thumb returns a rather large oil clearance. compared to Toyota.

im building the engine for track use, so my question is should I follow the Toyota tolerance and im for middle of the window? (0.0010")

that way I follow Toyota's recommendation for oil etc.

or change my tolerances towards the rule of thumb and run a thicker oil? (0.0015")

what do engine builders on here tend to do?

I love DIY, not to save money but its more rewarding. but these clearances seem to be a dark art.

No body?

I've always worked to the same rule of thumb as far as bearing clearances go. Some manufacturers do call for clearances quite a lot tighter than this though so you can't always take it as gospel. Generally I tend to aim a little looser than factory spec for a seriously modified engine that is going to see high rpm/high power.

You do need to be a little careful as increasing the clearances will tend to drop oil pressure and this can be an issue, particularly at idle.

Rule of thumb places it just above Toyota and below a 700hp/9000rpm 3sgte I've seen. Works for me. Happy middle ground. I'll aim for 0.0015-0.0020"

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