SBC main bearing?

[rod]

working on this old 327. has main studs and am sure it was align honed. because I can see where the webs were chiseled/peaned to tighten the caps. so I pulled #3 cap. Clevite 77P bearing. the front half look 'unused' and the rear half down to the backing! I put the pan on and walked away. thinking about this...I am wondering if when the #3 cap was put on it was so tight it might not have gone on correctly or completely to seat. havent looked at the others yet. the cap could have been cocked 1 or 2 thou. and not been noticed. that would screw up a bearing in a hurry but not cause the crank to bind. thoughts?
thanks Rod in AZ

[pmrphil]

A bore gauge will answer your question. That, and a mike for the crank.

I've seen a lot of "trash" pinched between caps and blocks/rods.

[Adger Smith]

Could be taper on the journal or in the main housing.
With small journal I'm betting on crank flex.
Back in the early days when we ran those we had to put a little more clearance than what the big journal could get away with. Depending on lifter bore clearance & rod side clearance thin oil may not be friendly. I would rather have a thicker oil with good film strength than the miniscule amount of HP the thin gives.
As previously stated Dial bore the mains and put the Michrometer on the crank... Check the crank for cracks, too..
Good luck!

[Alan Roehrich]

A lot of old school guys stake main caps whether they align hone or not. You'll actually know it is align honed if you see the cross hatch in the main bores.The factory broaches them.


The condition you describe is more likely shaft journal taper. Micrometers and snap gauges or a dial bore gauge is what is required to correctly diagnose it.

[rod]

some observations. there is crosshatch, albeit very light. looking at the cap bearing I find most of what I thought was bad wear...,appears to be a lite polish on one quarter. [crank looks real good. but possibly the caps are not squared up.] a few scotch brite passes, and the bearing looks real good. except...the center where the oil hole travels. the oil holes received just a very lite edge break with a rotary stone. it almost looks like that area got work hardened [factory steel 327 crank] and the micro polish wouldnt cut it down. #s 2 n 3 main and several rod bearing all exhibit the same look. is that possible?
thought n comments appreciated.
thanks Rod in AZ

[Adger Smith]

Rod,
Those cranks are not near as hard as most after market. A good grit cloth shoud cut it then go back with the fine micro polish grit. Too much stock removal can get an out of round or tapered shaft. Be careful.. Might let a good crank guy that knows his stuff do it. What you are seeing in the middle bearings may be crank flex or whip. How you come out of the burnout can whip the crank and if you are "Hard" on the 2 step..
There is a reason GM went to the larger rod and main journals.
Don't be afraid of more clearance than "They Say" you should run.
A lot of factors at play with issues like you are having.
Keep digging you will figure it out.