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FL&WVMIKE · 12-14-2018, 12:36 PM

Tight is dangerous, a little loose is safe.

To run tight clearances, machining has to be SPOT ON. ANY incaccuracy in the rods, bearings or mains... and you'll have contact. Most machine shops have a tolerance limit of half a thou accuracy... 0.0005"... and some cannot even achieve that consistently. With the crank, rods and bearings all coming to the tolerance party, it doesn't take much for there to be a problem. I like AT LEAST 0.0020" if not 0.0030" clearance. 0.0010" gives pretty much zero room for error... and we haven't even mentioned crank flex.

The crank runs on a layer of oil. With looser clearances, as long as they are not excessive, you're a lot safer. Tight clearances are what spin bearings.

Good Luck

12-14-2018, 12:36 PM	#59
FL&WVMIKE Senior Member Join Date: May 2010 Location: Daytona Beach, Fl & Spencer, W. Va, Posts: 4,449	Re: Bearing clearance Tight is dangerous, a little loose is safe. To run tight clearances, machining has to be SPOT ON. ANY incaccuracy in the rods, bearings or mains... and you'll have contact. Most machine shops have a tolerance limit of half a thou accuracy... 0.0005"... and some cannot even achieve that consistently. With the crank, rods and bearings all coming to the tolerance party, it doesn't take much for there to be a problem. I like AT LEAST 0.0020" if not 0.0030" clearance. 0.0010" gives pretty much zero room for error... and we haven't even mentioned crank flex. The crank runs on a layer of oil. With looser clearances, as long as they are not excessive, you're a lot safer. Tight clearances are what spin bearings. Good Luck __________________ Mike Jr. here. I get on here every few months to check messages, and look through his almost 500 saved messages for information on the '29 and '34 I still have. A lot of very nice people on here. He truly enjoyed Ford Barn.