Crank journal stains... rust?

I might be wrong but this looks to me like the shells have picked up on the journal. Oil will acidfy if the engine is not run for some length of time and then stain and/or eat into the crank journal. Generally you get a pitting where this happens.

If you are going to fit new shells then you need to lightly roughen the journal surface to help the bedding in process. Similar to deglazing a barrel when fitting new rings. The good news here being that only a few hundred miles of running in is necessary.

Use a micrometer to check the journals before rebuilding.

dean

please don't roughen up the crankpins as suggested by phil ,the slight pitting you've got on your crankpin will do no harm,as long as it's under the surface (it's basically an extra oil pocket)

use a micrometer to establish that the crankpin is within service limits(ie not oval/tapered or barrel shaped)

If you feel the need to clean the crankpin up, use a very fine grade wet-n-dry and finger pressure or the cloth side of some clapped out emery cloth ribbon soaked in fresh oil.the idea is to remove only the corrosion and NOT any bearing surface area

when you fit the new shells to the crankshaft ,they should be able to drop under there own weight with no tight spots( 25 lbf torque)

steve

I'm with Steve on this one, a gentlelinish with some oiledVERY blunt 1200 grit wet and dry, or fine steel wool, only on the apparent stains, to ensure that the journal is smooth in that area, should be enough to put the crank back in service along with new shells. I definately wouldn't be trying to remove the stains, as they may go several thou deep, which would render the journal unservicable.

Paul

My mistake ....poor choice of wording. Polishing is far better then roughening. I generally use fine W&D and worn Emery.

The important point here is to establish what the stain actually is. The photo suggests, to me, a transfer of the big end shell white metal to the crankpin. In which case it must be removed or will chew up new shells very quickly.

It's on STD ? then I'd guess those marks pre-date the shells by quite a margin. They may have come from an even earlier set of shells or from a lay-up period. No one will ever know. Have a measure up with a micrometer and so long as they are not proud of the surroundings you have nothing to worry about. Journals need to be smooth as possible to avoid pick up in low pressure scenarios like start up.

Regards Rob.

If your journals are already below the minimum tollerence, surely while it's appart, it's a perfect oppertunity to have them reground? Undersize shells are no more expensive than std, which I asume you would be replacing anyway, so it's just the additional cost of the regrind. This will take care of all your issues & should ensure you won't have to worry about the bottom end for many years to come.

Regards, Tim