Engine Bearing Clearance

[Chad E532]

I just finished tearing down my engine for a ring and bearing job. When I put it together last I needed to run a combo of a standard and .001 rod bearing to get the clearances to 0.0025. So I put the thicker bearing to the top of the rod as was recommended from a blueprinting book I was using for a reference. Now it is time for bearings and everything is measuring the same as last build so again the combo of a standard and 0.001 will be needed. My question is does it really matter if you put the thicker bearing to the top? I have a full set of the left over bearings that will give me the correct clearance but I will have to run the thinner bearing to the top.
This is on a large journal small block chev.
Thanks,
Chad

[Rich Biebel]

If clearance adjustments need to be made, use either an extra clearance part for more clearance or an undersize part for less clearance. It is permissible to mix sizes if less than .001" adjustment in clearance is desired. When mixing sizes for a select fitting: a) never mix parts having more than .0005" difference in wall size; b) and always install the thickest wall shell in the upper position if installing a rod bearing or the lower position if installing a main bearing. When working with a reground shaft, always measure assembled bearing ID's first. Next have a shaft sized to produce the desired clearance since there are no extra clearance parts available for undersize shafts.

http://mahleclevite.com/techinfo.asp

[BillK]

Chad,

I just threw 2 complete sets of .001" lower half Big Block Rod bearings away on Friday for the same reason. I figure if Clevite tells you to run them that way, there must be a reason. The engineering side of me says that the thicker bearing will conform to the diameter of the crankshaft better and will result in a larger bearing area as compared to the thinner one.

[Chad E532]

Thanks guys, that is what my gut was telling me, so I ordered up a couple sets of bearings to mix and match the correct way.
Chad

[Greg Reimer 7376]

Years ago, when I was a line guy at a Chevy dealer, the front main saddle on 350 blocks would move as the block seasoned on new cars and trucks. An attempt could be made to bring them somewhat into line by juggling over and undersize bearing inserts as long as the block stabilized. In extreme cases, the front main spun.This ruined the block, the crank and sometimes tossed the #1 rod as well. In an attempt to cut costs and be cheap, the thinwall castings weren't very stable, then were machined, then the casting moved and the critical dimensions went out of spec. That was a factory warranty fix to juggle bearing shells to move the hole back into place. Sort of an indictment on quality in the mid 70's.