garetgax

iTrader: (3)

I know this probably sounds a bit numptie ish but If you dont ask and all that. What is Piston slap? Newbie to scoobies ( 3 days) and would like to make sure all the noises my engine is making are ok. The white smoke thing hasnt re-appeared since that one time so havent a clue what caused it. Anybody fill me in?

Thanks

wideybrook

What year model car do you have?

ALi-B

iTrader: (1)

Piston slap is basically when the piston is too small for the bore. And consequentally the bottom of the piston skirts hits/catches the bore at just after TDC (top dead centre) and after BDC (bottom dead centre) as the load angle on the piston changes from one side to the other. This creates a light metallic clinking sound, which is very difficult to describe. There is a sound file floating on the net of piston slap (and really a bad one of a GM V8 engine).

Piston slap on many modern engines is acceptable - only when COLD. This is bacuse of the engine design where the piston clearance is only very large when it is cold, once warm it expands and piston slap ceases. Examples of cars that have piston slap which is normal are Rover K-series, current Renualt Clios etc.

Cause for concern is when it is either very excessive, or it continues when the engine is warm. This is because the piston skirt is catching the bore, and thus causing wear on both the bore and piston.

wideybrook

Would you mind if I copy this and may use it on my web site, it is by far the best and most accurate description of piston slap I have ever come across.

Lee Jeffery WRX IMPORTS
http://www.wrx.co.uk

ALi-B

iTrader: (1)

Wow! Feel free I just typed off the top of my head. So please correct any spelling etc

Something I forgot to add: Is when trying to listen for piston slap, it will be heard mainly when you light;y rev the engine. You may also hear it at Idle. Whilst driving, you may hear it whilst gently acelarating.

HTH