Knocks and pings are almost always bad, but some can be decieving, but I alreasy think just the fact that you find it abnormal says something.
Cars have Knock sensors so the timing can be advanced while using low octane fuel without damaging engine. The knock is from, "Detonation" which is when the cylinder timing is so advanced of fires too early and the piston is still travelling up and it will put a hole in the top of the piston in no time at all. Knock sensors can hear this and retards the timing until it stops. Sometimes piston design can be noisy. Is it a knock from the bottom end or a tap or ping from the top end. To check this a long screwdriver with your ear at the hadle end and the other end at different points can help to find the area that the noise is coming from. The tope end can make some tapping noises and is a little noisy, not that it means that it is okay, but compared to bottom end. The bottom end is pretty smooth and a knocking noise is not a good sign. The cam chain/belt can cause top end tapping or valve rattling and timing issues if it is damaged or has a faulty tensioner.
So, unfortunately, it is somewhat objective as diffent engines make noises that are okay, but noises that are excessive are generally a problem. Smaller motors are noisy, etc.
However, does the BMW dealer have another Cooper S with same motor to listen too? He can find one at another dealer as they work together to trade sales stock and are not strangers to helping each other out. So, more than likely, you can find a new Cooper S with the same engine. Will it be one with a WORKS tuning kit? It should be, are they that rare? If not, it does not really matter unless the kit makes the motr knock louder than without it.
They should pull the trouble codes from the car and see if anything shows up. You should also look in the oil and see how much metal is in it. During break in there is some. But, I think BMW does break in at the factory with engine on a bench. However I may be wrong and they may not do it for Cooper. However, even the amount of metal shed at break-in should be tiny specs and be silvwer in color. If they are small chunkcs or brassy colllored, this means there is excessive damage from the chunking which is probably piston material as it is cast aluminum and tend s to break off in chunks and brassy colored metal is the last layer in the engine bearing and indicates bearing failure. You can look at dipstick after car has ran and sat for 5 minutes. Look at it in bright light or sunlight and move it around as the particles are small.
I think getting the trouble codes and demanding to hear another Cooper S that is new sound the same are your best arguments and ways to see if it is normal. Even if you have to drive an hour or so, tell them you are willing to go to another dealer. Tell them they have to call ahead so that you do not have to spend time explaining the situation which is courteous to the other dealer so a Salesman does not waste his time thinking you might buy one until he sees yours. A Tech should really hear the two same cars side by side. Dealerships work together all the time trading cars for stock or a sale, so its not a stretch to do this.
Go on an enthusiast forum and see if other owners have the same complaint.
Let me know how it goes.
Friday, November 18th, 2011 AT 3:02 AM