King main bearing clearance issue

[BLstangin]

I am putting together another sbc circle track motor. I tried the king hp bearings again in a fresh line honed block and i have a .0001 bore gauge i set to the crank size. I'm just running a cast scat crank. I have .0024 main clearance on the front four which I'm fine with, but the rear thrust main has .0036. I had this problem with a set of king hp bearings before and a set of clevites fixed it. I have an oil pump torqued on the main caps and the block was just line honed with arp main studs. Does anyone else see this problem with the rear main being bigger on the thrust main with king bearings? The crank is the same on every journal so it's not an undersized journal on the crank. I'm thinking about just putting it together but I might try a set of clevites first. Thoughts?

[wyrmrider]

.0035 works for me
I chamfer toward rear at parting line for thrust and/or drill a small hole through the thrust into the oil feed
if running much clutch pressure- or are you clutchless?

[FC-Pilot]

About 8 years ago I was putting together two similar engine, one with clevite and one with King bearings. Both were HP bearings. I noticed the kings seamed to have more clearance on the one engine. For kicks I swapped bearings and the kings showed .0005 more clearance on both engines on all of the mains. I don't know if that is still the case, but it was then as I had two sets of each on the shelf and I measured up all four of the sets.

I would run it and not look back if I had that clearance. It is not going to hurt the engine and will help to keep oil flowing across the thrust surfaces. I can't tell you if or how much power might be lost, but I would not imagine much with it only being on the rear.

Paul

[pamotorman]

chevy set up the rear main loser so more oil flows to the thrust surfaces of the rear bearing insert

[amc fan]

X2 with Pa.motorman on more clearance on rear main. Its surface is wider and with the thrust it can use the added clearance.Did you ever check rear main cap press in block register with pump on and then with pump off?

[Baprace]

I am putting together another sbc circle track motor. I tried the king hp bearings again in a fresh line honed block and i have a .0001 bore gauge i set to the crank size. I'm just running a cast scat crank. I have .0024 main clearance on the front four which I'm fine with, but the rear thrust main has .0036. I had this problem with a set of king hp bearings before and a set of clevites fixed it. I have an oil pump torqued on the main caps and the block was just line honed with arp main studs. Does anyone else see this problem with the rear main being bigger on the thrust main with king bearings? The crank is the same on every journal so it's not an undersized journal on the crank. I'm thinking about just putting it together but I might try a set of clevites first. Thoughts?

Normally the stock GM crank rear main size is smaller by at least .0005 - .0008, perhaps King is addressing an issue that may show up on aftermarket cranks.

[modok]

Same size OD bigger ID, must be a difference of crush or wall thickness.
If you check the wall thickness of the bearings you will know . I expect #5 will be .0005 thinner, but if not, could be a crush issue.

[pamotorman]

what I used to check bearing insert thickness. saves time when looking to change clearance. .0001 dial indicator.

[Cubic_Cleveland]

what I used to check bearing insert thickness. saves time when looking to change clearance. .0001 dial indicator.

Great tool!

[Racerrick]

Your clearances are fine for a street stock. the rear should always be bigger. run a std pump do not use a HV pump

[CharlieB53]

.0035 works for me
I chamfer toward rear at parting line for thrust and/or drill a small hole through the thrust into the oil feed
if running much clutch pressure- or are you clutchless?

I'd like to know more about drilling this oil feed hole.

[xanadu]

what I used to check bearing insert thickness. saves time when looking to change clearance. .0001 dial indicator.

That is very clever.

[Geoff2]

Are you sure the rear main did not bell mouth in the honing process? Why not try one of the other set of brg shells in the rear main to verify if it is a housing or brg problem.

[BLstangin]

OK guys I decided to check the line hone. I have a .0001 bore gauge so it's easy for me to see problems and needless to say I found it! The center three are all the same with .0002 max taper. The front one is .0003 smaller at the front of the cap and .0007 smaller at the back of the cap. The rear main is .0006 larger at front of cap and .0008 Larger at the rear of the cap. So that's almost .0015 swing from the smallest at the front to the largest at the rear. Needless to say it's back at the machine shop. Thanks for all the suggestions guys. I have a .0001 ball mic I use to measure shell thickness but at this point in time I'm pretty sure it's in the line hone. Needless to say just because it's new or just machined doesn't mean it's right.

[wyrmrider]

line hone is an art
I quit doing line hones without a line bore first
and tried to quit taking in quick and dirty FUBARed line hone jobs for repair
always sticker shock to the screwed customer
agree on slightly more clerance
1 bearing is wider
2 rear of crank can move around more (well other places can move around if the counterweights are not right)
3 all journals move some