Probable Piston Knock


I just had my car shipped from Oklahoma to Cambridge, MA. When the guy took the car off the truck, I hear a knocking sound. I have owned this car since it was new and have never had any issues at all with the power train. I backed the car up and as the RPMs went up, so did the knock. I let it idle for a few minutes with the hood open. The sound was certainly coming from the engine block and to me sounded like one of the pistons was knocking on something. I then closed the hood, and backed up the car further to park it so it wasn’t in the middle of the street. After parking the car, the sound was gone. I drove it around the block, still no sound. What gives? The car has 47k miles on it and is still under its manufacturers warranty, so I think I’m going to take it in anyway, but what could cause this issue and how concerned should I be about this?

If it is light piston slap as it may be more commomly known as, there should be cause for little or no concern. I recently traded a car that had light piston slap for most of its life which for me was over 140K miles. The noise was more pronounced in cold weather but about a mile of driving would see it gone every time. It did not get louder with added mileage but the noise was not apparent when I bought the car new.

For a long time I thought it was a slightly loose valve lifter and knew from past experience that hydraulic valve lifter noise must not be judged until the engine is warmed.

GM had an issue with piston slap a while back and fixed it, as I understand, with a smaller production clearance between pistons and cylinders.

That sound more like a valve tapping than a piston knock. I have had several cars do the very thing you’re talking about but they usually had 100k or more miles on them. Do get it checked out asap. Remember, If you run the car like this you will almost certainly do at least some damage the engine.

I think this model uses hydraulic cam followers (lifters if you prefer) and just offhand it sounds like one of them bled down while the car was en route.
The followers pump themselves up with circulated oil from a running engine. It’s possible that the bouncing the car took could have disturbed the mating surfaces inside the follower and allowed oil to drain.

A few minutes of engine running will perk a good one right back up. At this point I would not worry about it at all.
If the problem does happen to resurface then you might consider using an additive in the engine oil as any sludging, even very minor, can affect a cam follower.
The best additives (and cheap too) are Berryman B-12 and SeaFoam. Add a can to the engine oil, run it for a 100 miles or so, and then change the oil and filter.

Just being curious, but what part of OK are you from?

Is this a one time never happen again situation? most likely, I am curious as to how long the engine was inoperative,

I had a feeling I just may find something so I checked TSB’s and sure enough there is one SB 11-09-07 (you did not state the year so I used 2007) and it is a TSB explaining why the hydraulic valve lifter assembly may at times make noise. The TSB says the engine will not be damaged and they will pay a tech too bleed the system up too 5 times. I will not delve into my typical spiel about how important it is to check for TSB’s. If you miss a TSB in a BMW shop the hounding is relentless, you may as well go home for the day.

yep, I agree. All the vibration from shipping tends to make fluids settle to the bottom. No big deal at all, most likely.

I was moving from Lawton, OK. I just separated from the Army and moved out this way. Thanks for the help on this. I’m not as worried about this anymore. It’s due an oil change in 2k miles and I’ll ask them about SB 11-09-07 when I take it in. I feel much better about this.

This was a one time thing so far. It is a 2007. When I take it in for the next oil change, assuming nothing else makes me bring it in first, I’ll get them to bleed the system. Thanks for the help.