Line honing is a big point. You can't run a tight clearance on a motor if the main journals in the block are on both sides of the tolerance. That +/- .0005 tolerance can make one journal .001 bigger than another. If you don't try and keep the journals within a few tenths (.0001) then bearing clearance will be all over the map. So you have to open them up.

Bret

 

3 thousands clearance is pretty normal for a performance oriented engine. It has a lot to do with how much break in time it will see. If its a drag only motor where it would get maybe 30 minutes break in, I would go with the loose clearances. If its a long time streeter, then go a little tighter. Oil viscosity and pressure also will play a role in this. My theory is that you are better a little on the loose side than too tight.

 

Found a really good rule the other day that works perfect IMHO....

.0011 x main journal diameter = clearance. Add a little for the back cap on a chevy and you are set.

Bret

 

Thanx again guys. I was looking at running Mobil 1 this year.

 

Mine are at .0015-.0018 on the rods and mains and .0025 on #5, and my oil pressure is 30-35 hot at idle. No problems here, but it is more of a street-strip car, and I don't plan on pulling the motor each winter either. It's your motor, build it how you want it. I also run mobil synthetic 5-30 and 10-30 depending on the temp outside.

 

So a bit tighter than what they want to use would be better?

I want to use Mobil 1.

 

From what ive read in a couple places mobil oil is actually a little thinner than the exact rating they give. ex. thier 30 wts are more in the 20's