Bearing Tolerances

[Da67goatman]

I have a question that is a little out of the ordinary.  How do bearing clearances change with temperature?  I am assuming the recommended range is for room temp 70f but I'm working in roughly 10f so should my tolerance be the same or should i stick to tight end or loose end of the range?

[Stewart G Griffin]

Which bearings?   Main?

[Da67goatman]

Specifically for rod bearings.  But the rule should apply to all, shouldn't it?

[Stewart G Griffin]

My opinion---and this is just my opinion only---i have very little experience rebuilding engines, is that this temp variation isn't going to make a difference.  Now, if we were talking about 200 degrees (or however hot the oil gets) vs. say, -32 degrees, then yes you would have to compensate.

But i really don't know.  This is just my gut feeling.

[Captkaos]

Are you building a motor?  If so follow the recommended tolerances.  Remember it comes up to operating temp when running...

[Da67goatman]

I already built it and after about 100 miles it generated a knock which i am still investigating.  i was hoping it was a faulty part not faulty mechanic

[srozell]

Are you building a motor?  If so follow the recommended tolerances.  Remember it comes up to operating temp when running...

That is mostly true. The issue is that the metal doesn't always expand and contract evenly, so if you torque bearings at a low enough temperature, it will expand and be over tight at the higher temperature. You are compressing them into place, and if they've shrunk up, they'll go in further than they are supposed to.

I'm not sure how much temperature variation will cause a problem however. I'm not even sure where to look that up.

[jaredts]

.000007 per inch growth per degree Fahrenheit increase in temp for steel.  I don't think this would likely be your problem, but you could do some math after you find the source of the knock.  I think bronze grows slightly more at .00001/in/deg F.

[pholliday1]

When trying to diagnose a "knock" its helpful to listen to he knock first in park at slightly different rpms then put it in gear keeping your foot on the brakes the slowly push on the gas to "load" the engine. It should help pin point the source.

[Da67goatman]

Found out what my knock is...  I dropped the oil pan to find 5 rod bearings loose.  I don't know if it was me or the parts but I still have to drop the diff to get the pan all the way off.  It will be a while till this get resolved.  This is what you get when you cut corners.  Miccrometer EVERYTHING then Plasti-gauge it just to be sure.

[Dr_Snooz]

This thread makes me sad. :-(