Piston Slap in 4.6is
 

I have a 4.6is X5 from 2003 with 30,000 miles on the clock, when cold it exhinits Piston Slap (confirmed by the dealer) and it seems to go away when warm, I am not happy as it will run out of Warranty eventually. The dealer says it is not bad enough to repair under warranty, I disagree, has anyone else has this experience?

Regards, Geoff.

If you notice it, and the dealer admits there is a problem, I don't why they shouldn't be forced to fix it. I think this is something you should push.

What is piston slap?

In simple terms, piston slap occurs when the piston is forced rapidly against the side of the engine cylinder wall. The more clearance between the piston and cylinder wall, the louder the knock.

Rob_

Piston slap is the perpendicular (side to side) movement of a piston against the side of a cylinder bore as opposed to its primary movement which is parallel (up and down). All combustion engines have a certain amount of piston slap but if you start to hear it that is usualy not good. That means there is an excessive piston slap due to much clearance between the piston and the cylinder bore. This is due to either wear or mismatched between pistons and cylinder bores at manufacturing.

The BMW regional engineer is going to hear it next, in these engines they have to replace the block and pistons, and that is a lot of money hence the reason they argue I think, I have seen articles that say I should not worry and articles that say I should worry, my 4.4 never had this noise when cold, the 4.6 is OK when warm. It does worry me, sounds like one cylinder only, but maybe two, ;)

Geoff.

I`m no expert but if the dealer admits it`s there then I think it`s letter writing time, with threats of legal action if they are unable to rectify the obvious defect.

If you're in the US all you have to do is report the problem before the warranty expires and it will be still be covered under warranty. I would suggest talking to BMW and seeing what their position is. Resale value will be impacted and they should be responsible for that. The problem may never get worse. If BMW was willing to give a doscount on a future purchase if the piston slap does not get worse, I would take it. If it gets worse then they need to fix the problem.