Loud engine knock...HELP!!!!

Hi everyone, I hope someone can help.

I just bought 2000 740I 160K. I drove the car for 2k miles and found that out I needed to replace the water pump. So, after reading up a little I started to replace the water pump and while I was doing that I took the intake off and put an new valley pan gasket and intake gaskets. I put the car back together aftrer runing it for about 50 mile my service engine light started flashing. I took the car to a reputal shop and the car showed a fule trim code and misfire code cyl 5 and 7. We replaced the plugs and that took care of the mis fire problem and the man at the shop said I would need to replace my cat. converter soon to take care of the fuel trim code. I picked the car up, drove 2 miles and all of a sudden I hear a loud knock coming from the motor , I turned around went back to the shop and it was determined that I had a sticking lifter on the driver side of the motor making the noise. I paid to have the lifter pulled out and the tech said they all checked out so we put the motor back together and I still have a loud engine knock.

The tech is now telling me that he thinks I have a rod bearing issue and he thinks the piston is tapping a valve on the exhaust stroke.

Does anyone have any advise for me, I have read things about lifters gettin air in them after a sharp turn, that is when this started.

Has anyone ever had this issue or something simalar? Any help is appreciated.

First I would ask for an opinion from another mechanic. Maybe somebody with more BMW experience. For some reason, from what you are saying, that mechanic, is guessing what the car has.

Similar issue: exhaust valve chipped or "burnt" . Check car for codes, you should get a clue. In my case it sounded like this:


There is a procedure to bleed the valve lifters for tapping sounds, post# 8 http://www.bimmerfest.com/forums/sho...ding+procedure

In order to do a real diagnosis, I would do a compression test or leak down test. They are both inexpensive.

Goodluck!

The simplest thing you could do right now is to check your spark plugs... Make absolutely certain they are properly tightened in. A loose spark plug can make a sound EXACTLY like a bent connecting rod, noisy lifter or other knocking-related problem. I recently did some work on my engine and events led me to believe I had bent a connecting rod - watch this video I recorded, everyone believed it was a bent connecting rod;



Turns out a couple of my spark plug were a bit loose. How loose? Basically I could put the spark plug bit on and without any kind of ratcheting attachment or anything, spin them freely. It was strange because I only just recently changed the plugs (as you have) and I KNOW for a fact that I tightened them properly.

All I can say is, check ALL of your spark plugs, tighten them good, make sure your spark plug boots are on solid and not splitting apart, then fire it up again. If the sound goes away or even just lessens, you're on the right track!

If you have access (or can hire) get a bore-scope and take a look inside the combustion areas. Saves a lot of heart ache.