As I recall, a bit looser was better because you got more oil flow,
which helped carry away the heat. Also we were running harder bearings
that didn't allow particles to embed in them like babbit does. So
larger clearances let larger particles flow through the bearing.
I read that stuff a long time ago. Practices may have changed.
Jim Juhas wrote:
> I'll weigh in on the question of clearance. I think "tolerance" is the
> wrong word here.
> The shop that did the bearing work on my 5.0L ford engine for my Cobra
> replica selected bearings individually for each journal to give me
> greater clearance than the middle or low end of the tolerance range, his
> premise being that an engine being pushed harder develops more heat and
> should have proportionally greater clearance at cold. He builds lots of
> race engines.
> Larry Colen wrote:
>> When Armando did my crank, he machined the rod journals to tighter
>> than stock tolerance, and told me to use thinner oil. The premise
>> being that with the blower, the tighter tolerances will allow less
>> room for the rods to pound on the crank.