Topic: Wear marks on pistons normal???

[murdrcycle]

Are wear marks like these normal?  If not, what are the possible causes?

[calj737]

They are an indication of the piston rocking as it travels. Can be from worn wrist pins, rod bearings, piston rings, cylinder bores, etc. Micrometers tell the tale. 

[Pat_at_APE]

Also the pistons could have worn away the taper. 

Pistons are smaller at the crown and larger at the bottom of the skirt by design.  When that taper wears they will rock and rings wont seal. 

Pat

[PeWe]

Easy to think that those pistons runs too tight when it is opposite.
I learned here on this forum that too much clearance will affect the oil film to not lubricate bore vs piston when the gap is too wide.

[rotortiller]

You have some mechanical marks from tooling on the  pistons from mishandling. Sometimes debris can go through the engine or high spots of the mechanical damage can break away causing scoring. Dirty oil can do it too. Sometimes bits of carbon can break away and cause damage. I doubt it is from loose fitting pistons, however clean it up, measure and if good put back in-service.

rt

[murdrcycle]

Thanks for the advice - I'll put the mic on it.

[70CB750]

Polish them away only in the direction of those scratches.  They are quite nomal, I seen the in both my CB750, usually only "skin" deep.