Chatter marks on main bearings

[AC sports]

Pulled the sump off a motor for inspection today. Found some chatter marks on centre main. What causes these? I'm inclined to think the anti friction layer of the bearing may not have been perfectly smooth to begin with, and was a bit ripply from new. Any thoughts? I dont usually see this on the type of engines I build. Or maybe crank inbalance? Otherwise they look ok to me.

[BCjohnny]

They're not chatter marks but a facet of the 'rolling' process used in manufacture ......

Usually more visible in AlSn alloy bearings than bronze based

[Biteme]

That’s from the manufacture.
That bearing looks quite good.

[MadBill]

Judging by the shiny contact zone at the lower edge, the journal is probably a bit 'wasp-waisted'. Also, I'd be concerned about the integrity of the hydrodynamic lubricating wedge with those discontinuities being great enough to contact the shaft. (Although perhaps through running, they have been "steam-rollered" into uniformity and are no longer bottoming out...)

[BCjohnny]

Could be wrong but not entirely sure the journal is hourglass ......maybe looks more like crank flexure ......?

Has the crank got rolled fillets? Might go some way to explaining the witness. Four cylinder?

[modok]

looks like a king AL bearing
The amount of wave in the surface is probably far less then the oil film thickness, so it doesn't really matter.

[jed]

I have to agree with Modok. Modak has a very intuitive way of seeing, understanding and stating the obvious.
Wish I could.

[AC sports]

Cheers guys, I figured the same. They are not king bearings. They are Glyco. I've had very inconsistent thicknesses with king in the past and stopped using them. The king racing range seems better.
This is the first time I'm seeing this on Glyco bearings and I almost exclusively use them now in my italian engines.

[Dan Timberlake]

What engine ?

Visually the finish of the cap parting face is mighty ruff. Reminds me of Chevy rod cap machining in the 60s and 70s, unless you bought the "pink" rods.

[allencr267]

I first thought 'what a clean assembly', no wipe marks on the bearing at all, then wondered why cap has so many holes to F'up the hydrodynamic whatever, with a poorly finished insert's backing/base.
Does the varying thickness of the bearings overlay cause the wear pattern, being more compressible?

Heard about cracked rods, but cracked mains?

[AC sports]

The cap parting faces are actually ok. It's the pic. The block sat around and had oxidized. It also never had an oil change. When I built it, I dragged the caps along some fine abrasive after brushing to confirm flatness hence the look. You can barely feel the high low spots with your nail.

[dwilliams]

That's a ground finish. The OEMs like to use something like a 10 grit wheel and feed it hard; that's where the tears come from. Depending on which factory they came from, small block Fords sometimes had broached main caps; the broach is essentially a giant file and leaves a very slight wavy finish that will show up as parallel stripes when you rub the cap over sandpaper.