Crank Bearing Wear

First photo shows the worst three bearings. KZ750E

Second photo shows the others.

There is a nick in one of the bearings that concerns me, but otherwise the shiny marks don't seem to have suffered significant material loss.

What say ye? Replace or run?

I've reused before when there is wear and some light pick up but always use plastiguage to check the clearances, I take it you have marked the shells so you can re-position them?



does the crank look like? the nick in 2 is odd, has it been taken apart before? what are the big end shells like?

Those don't look bad at all. Some minor scoring but other wise good. If the crank journals look good your fine. You should check the clearances, plastiguage doesn't lie. And as Tyrell asked... do the rods look the same or better?

I would probably replace them if it were me, because then you would bring the bottom end back to almost new. I guess for you it would depend on what your building the bike for and how much time and money is going into it. So it's your call but I'd see no serious issue with re-using what you have shown... so long as the clearance are good ( and from the looks Id say it is).

...but also these kz shell / forged crank bottom ends are really strong, unless starved of oil . Any out of spec wear will be apparent with the plastiguage test -better than micrometers imo.

The soft white metal bearing shells and the oil wears out, the cranks just 'float' on oil pressure with no metal/metal contact apart from cold starts.

So for me, as an amateur I'd reuse them assuming your measured clearances are within tolerance. As a pro for for a paying customer then there is little incentive to take any risks here on what is a fairly inexpensive cost compared to that of a pro full engine rebuild.

Thanks for the comments guys.

I'm inclined to reuse these bearings and will do a sanity check via plastigauge. I'm fairly certain they will be fine since there isn't any significant material loss on either the bearing or crank itself. Just a little localized scuffing.