as above really.

jamo

 

Basically its where the fuel and air mixture is ignited before the piston is at TDC (top dead centre) (at its highest peak on the crank revolution)... and therefore in basic terms it now explodes rattling the hell out of the piston rings and piston...causing PISTON SLAP..

Regards

joe

 

i think thats called pinking??????
not to sure


well if its the same as a motor bike then its when the rings wear down and the piston tilts in the bore not by much about 0.02mm. it normaly sound terrible. not so common on cars i think!

 

Sorry guys I am an idiot,,,I was thinking of Pinking!!!

joe.

 

gimp

 

the bore is slightly out of shape, which means the piston can slap about a bit while its cold, when its warm it expands and genraly clears up

mine slaps when cold, and so do a lot of other cars

its not half as serious as sum make out, as long as it clears when its hot

 

Out of shape or worn bores can cause it. MY98 cars had one of the cylinders with too large a clearance that caused piston slap. I think its mainly the cylinder nearest the turbo?

 

I've got some pistons hanging around taken out of my old slappy Rover somewhere. I've typed the full wind of this somewhere, some chappy has even posted it on a website somewhere....

In short, piston is too small/bore too big/out of shape, piston skirt makes contact with the bore at TDC and BDC, causes wear to piston skirt and bore. In the long run (and I mean VERY long run) it will cause oil consumption and a little loss of compression. Normally only something to really worry about when it's doing it whilst hot.