421 main bore ?

[rogerleejr151]

hi I purchased a 421 chevy engine and was rebuilding I have rebuilt several engines but am no expert what ive ran accross is main bearing clearance that is too large and found it do to the main bore being linehoned out of spec it is a 400 block with a 350 main crank was wondering if I could use additional shim stock of .0005 under the bearing spacers too correct the size and crush any info would be appreciated thank you

[let-r-eat]

How large are the clearances?

[rogerleejr151]

I have anywhere from .0038 to .004 on number 1 through 4 and the rear main is at .005 I am more worried about having correct bearing crush though. before I tore engine down we tried to run it with wet sump set up and 20-50 oil and only had 45 lbs at idle and after a good warm up would drop to 10 lbs and would not climb with rpm increase

[let-r-eat]

My experience says that a main line clearance that wide isn't going to cut the pressure like your seeing although it is too wide. You could use x bearing in there and cut that down. If the housing bore is too big overall I would cut the cap and re hone. I would check lifter bore spec and cam bearings. If it has a real small base circle cam since it's a 421 I would make sure the lifter bands aren't bleeding off as well. You may need small base circle cam lifters. *they have the altered band for the lifter to set lower in the bore.*It takes a hell of a leak to only have 10 pounds of oil pressure on a chevy.

[go2fast]

when we used bearing spacer we would line hone the mains to 2.840.8 i thank it goes like 2.840.5 to 2.841.5

[grayarea58]

with only 10lbs pres warm, id look at cam bearing not in the right spot or check valve in pump. clearence may be a lot but the should still pump the oil.

[powerslide]

Try the x bearings.