Originally Posted by Guinnless

He's not correct though in what he's written. Oil slapping the pistons indeed

You get piston slap on 2WD engines is because the gudgeon pin is located centrally and the piston 'rocks' until it warms up and expands. A central location is desirable on a high revving engine hence why Cosworth built it this way.

4x4 engines were changed as the Motorsport requirement was no longer there hence the offset gudgeon pin to reduce piston slap.

The slap doesn't cause any harm and is actually mentioned in the Owner's Handbook.