Is it overheating, then over expanding, then wearing of the culprit piston or something else?
If it is the above, how can the new bigger piston fix be a permanent cure?
Surely this will also overheat because it's in the same place and so wear in the same way, unless it'smade of a different material? Can anyone enlighten me?

 

Dunno what exactly causes it, but I do know that the new piston is made from a different material (teflon coated, so my dealer reckoned ) to prevent it from happening again. How do I know? My MY98's in to get it fixed right at this very moment...

 

It is the lack of length in the piston side skirts. Too much boost can also cause it with the increased pressure pushes the piston to one side.

Heat will reduce the piston slap because the metal expands.

[This message has been edited by submannz (edited 23 August 2001).]

 

On the scoob it's caused by the piston overheating. One cylinder runs hotter than the others and the piston in that cylinder gets too hot, distorts perminantly and hey presto, piston slap.

You get piston slap problems on the MY98 and prior N/A and Turbo engines.

The fix is to use a diferent material piston that is ceramic coated.

It usually starts to rear it's ugly head around 8000 miles on a scoob engine when its the piston overheating that causes the problem.

 

Another reason for the piston slap, normally associated with no.4 cylinder, is that no.4 runs quite rich, due to poor air flow caused by the air idle control valve restricting that leg of the inlet manifold.

This can cause "bore wash", which over time will cause excessive wear on the cylinder wall.

Mark.