Thread: spun bearing

Tweet

well i have alot to check out then. I havn't towrn it down yet. But i didn't check the side clearence or the oil holes. The machine shop was supposed to check that but thats my fault for not checking it myself. And it would run between 75 and 110 prolly. But i will have to tear it down. Thanks guys

Spun bearings have more than one possible reason:

- clearances:
Too tight will get you too little oil on the bearing and it might sieze up, too loose and the notches on the bearings aren't pressed into their proper place

- rod installed in the wrong direction:
Rods can only be built into an engine in a specific direction, because they have a chamfer on one side to accomodate the radius on the crank

- inside diameter of the rod eye
The inside diameter of the rod hole must be a bit smaller than the outside diameter of the bearing so the bearing is actually crushed a little. This prevents spinning

- oil problems
As already said: oil holes not drilled through, filled with debris, edges of the holes not deburred...

- bent rod

- crank journal out of round

- too high oil pressure won't normally spin a bearing. BUT: too high oil pressure has a cause, and that cause might also spin your bearing.

And any number of combinations of this list. Getting rods to stay put is one of the most critical and most difficult tasks on buiding an engine, specially if your using used parts. Who knows, maybe your crank journals were spun down to -.010 but you're using normal bearings? Sometimes it's the small things you don't think of...
Remember, we're talking thousandths of an inch here so use good tools for measuring...

Hope I could help,
Max