"If it's too tight, everybody knows. The main bearing journal should be 2.3982 to 2.3990 , checked all the way around . In reality, the right way to check bearing clearances is with the proper tools. At about 10 passes, it gets down to about .0035, which is why some racers re-size them or replace them at this point. I have read in many engine repair books that a used rod bearing that checks less than.004 is OK I regularly set up engines for drag strip use that have .002 on the rods and .003 on the mains and they run fine. The oil film is supplied by splash coming off the rapidly rotating crankshaft. Quote Reply Topic: 401 Main Bearing Clearances - Too Tight Posted: Sep/27/2010 at 10:58am: Fellas - I'm about to start reassembling my 401 - it's a moderate steet build with stock rods and crank (.010 on rods and mains), Speed Pro forged 2380's, 291C … Rod side thrusts have the same effect. The bearings may be too tight or too loose in the bores. If the crank pins are within .0002 and the bearings show .0015-.002 clearance , I would button it back up! I have seen mention that too much splash may not be good for an engine breaking in. Although thrust bearing run on a thin film of oil; just like radial journal (connecting rod and main) bearings; they cannot support nearly as much load. A spun rod bearing may also be caused by wearing down of the bearing with time, or even due to improper assembly in the engine. There is also a spec for that clearance. Be advised that Rod clearance is smaller than main clearance because of the diameter difference. Ex. Remember your piston skirts and wrist pins are splash oiled! The time-honored formula for determining bearing clearance is .001-inch for every inch of crankshaft main journal or rod journal diameter. Pair a STD half bearing with either a .001 or STDX half bearing to obtain your clearance. Radial play is the clearance measured perpendicular to the bearing axis or more specifically: average outer ring raceway diameter minus average inner ring raceway diameter minus (2 x ball diameter). Main bearing clearance should be .0009 to .0028 early and .0008 to .0015 late 70's motors . slightly loose isnt gonna kill it.too tight will kill it in a hurry. Too loose, and you know," quotes Himley. Ex. I'm thinking I need to leave about .008 to .010 id clearance to allow for any warping and slight misalignment. .002" bearings and some shimstock will put you back in spec. Pair a STD half bearing with either a .001 or STDX half bearing to obtain your clearance. I would say that your oil pump is working fine, the bearing clearances are too great. Bearing friction will also likely be great if the clearance is too negative, and thus the bearing may fail from excessive operating temperature. I would not want to spin a large 3.00" 351W main bearing too fast with a relatively tight 0.0015" clearance. Remember, you can mix bearing sizes offered by King to achieve desired oil clearances. The crank journal should be miked to ascertain it's size and to make sure it … IMO, 0.003" isn't too much oil clearance, and is what I would have spec'd in the first place. Too much bearing clearance combined with heavy loads 3. Too little bearing oil clearance 2. Putting together our new 501 with an Eagle crank and Eagle H-beam rods. To speed things alog when checking this clearance I put the bod bolt in the rod without the rod cap . If you feel that you need more clearance then use one shell from .0010" set to adjust the the vertical oil clearance by .0005", which should give you a clearance of .0025" Amount, quality and viscosity of the oil 4. When damage to a rod bearing … .0020" rod bearing clearance is fine, as long as your journals are in good shape. 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