i think my car has it,but not sure.is it something to be worried about?

 

I think it's when the piston tilts from side to side within the cylinder bore - causing a slight slap on the bore. I think it's indicative of heavy wear.

But then I could be talking complete bollox - but I think I'm right.

What makes you think your car has it??

 

Danny,
It is commonly found on MY97/98 turbo engines, both Imprezas and Foresters.
It is something to worry about because a future buyer will either drop the asking price by about £2000, or your engine will sound so rattly that you'll do it yourself.
The undersized piston(s) eventually cause evenough wear to start high oil consumption and eventually the piston skirt may break up.
There are a number of wav files around of the piston slap sound. It is at its loudest from cold, particularly during the winter. If the sound stays even when the engine is warm then the slap is a bit advanced.
I have one off my old Forester if you want to hear it?

Nick

 

Generally considered to be harmless apart from the noise if it goes away completely when the engine warms up. If it does it all the time there is a problem though. This is Subaru's line, they won't look at doing anything about it unless it is there all the time.

The other thing to bear in mind is that the cost of fixing it to get rid of the noise will be pretty similar to the cost of fixing it if it does lead to an actual problem, since the parts you'll need replaced will be basically the same, i.e you'd be re-building the engine with new pistons and a re-bore or new heads to avoid a problem that would require you to re-build the engine with new pistons and a re-bore or new heads. So if it goes away when the engine is warm and everything else (i.e oil consumption etc) seems to be fine don't worry too much.

Uprated engines running Cosworth pistons are also known for being slappy due the design and clearances of the pistons, not really a problem, just a noise.

My '97 is pushing on for 80,000 miles and it slaps a bit when it's cold but is absolutely as sweet as a nut when it's warm, uses no oil and runs to the red line with only the first green light and flickers of the second on the knocklink.