Trying to figure out loud knocking noise

[sileighty]

Hey everyone. My new to me 325is has what sounds like a knocking sound coming from the valve cover. I did a lot of googling and read a lot of threads here but haven't been able to figure it out. Here's some key points:

1. Sound matches engine RPM (I used one of those bpm tap apps to confirm, it's around 650 or so at idle which matches idle rpm.
2. Sound starts immediately after starting the engine. Doesn't change at all after warming up. After a long drive, it's the same sound when I'm about to turn the engine off.
3. Sounds like it's coming from the valve train, just under the valve cover.
4. I tried adjusting the valves. Nothing seemed to be way out of adjustment (measured clearances between the eccentric and valve stem). Same noise afterwards. I did notice one of the rockers (cylinder #1 intake) was pretty loud when I rocked it.
5. Listened to the engine running with the valve cover off. The sound definitely came from either cylinder 1 or 2.
6. Car has Castrol GTX 20W-50 put in from previous owner.
7. As far as I know, it hasn't run low on oil. At least not since I've owned it.
8. The car runs very well. No sputtering etc.

I'm currently uploading videos but my internet is pretty slow right now. Anyone have any ideas? It seems like rod knock is WAY louder and nastier (judging by YouTube videos), and piston slap changes with engine temperature. I'm hoping to do a lot of autocrossing and other events with this car so I'm worried that this is going to cause my engine to blow up...

Video of me rocking the rocker

https://youtu.be/50FGxIm-nSg

Video of it running

https://youtu.be/lozvOeZfK9c

[AndrewBird]

I would be it's an improperly adjusted valve. It is quite hard to set them correctly unless you use the BMW spring tool as it is all about feel.

Did you adjust them cold or hot?

[dnguyen1963]

Check the oil feedline to make sure that it is not clogged.

[sileighty]

I adjusted the valves cold. I checked the oil bar and it seems fine. Took it out and sprayed carb cleaner through it. Put it back in, started the car and the oil drips onto each pair of rockers just fine.

While the engine was running I collected a few more data points :

- Pulled spark plugs one by one, the knocking/tapping sound didn't change.
- Tapping speeds up with RPM when I give it gas
- no difference when I push the clutch in
- Definitely Loudest at the first cylinder, not second.
- Sound is definitely up in the head, I got under the car and it was harder to hear.

- I tightened the #1 intake to 0.008 but no difference. I'll try tightening #1 exhaust now to see if I can provoke a difference

[dnguyen1963]

You might have an uneven wear on the eccentric. Replace them to see if that makes a difference.

[redlightpete]

Nice idea with the beats per minute app. A rocker noise should be at half the engine speed, since that’s how fast the cam is turning. What did your exhaust clearance test show?

[sileighty]

Nice idea with the beats per minute app. A rocker noise should be at half the engine speed, since that’s how fast the cam is turning. What did your exhaust clearance test show?

The exhaust was 0.010", so that was fine.

You might have an uneven wear on the eccentric. Replace them to see if that makes a difference.

Here is a pic. It was really clean around the area where it contacts the valve stem.



Anyways, I figured out what the problem was. Keep in mind that the only thing I've done since I bought the car was change the timing belt, cam shaft oil seal, and water pump.

..I forgot to tighten the torx bolt for the cam sprocket. That was causing all of the noise.

I know why I forgot though. When I changed the camshaft seal, my plan was to crack the torx bolt loose with the old timing belt still on, remove the belt, remove the sprocket, replace the seal, and put everything back on with the torx FINGER TIGHT so that I didn't move the sprocket until putting the new belt on. Once I put the new belt on I was so excited at getting it on properly, and I went ahead and rotated the engine several times to verify the timing was correct, then I proceeded to put everything back together... but I forgot to tighten that torx bolt. The reason I forgot to tighten the bolt is because I couldn't immediately torque it down when I reinstalled it, I had to get the belt on first. All the other bolts I could torque down right after threading them in, but this was the exception, so I screwed it up.

Oh well, lesson learned. With the torx bolt loose, the ignition rotor had a lot of play and when it spun it took chunks off the posts on my distributor cap. Check out the carnage...











That was a brand new cap and rotor too! However the car was running fine with that damage. Since it's easy to replace the cap and rotor, I'll just keep the old parts in the trunk and swap it out if I have any issues.

I figured this out because I was searching YouTube and found a guy with the same sound. He said he forgot to tighten that torx bolt.

https://youtu.be/a1gITP6aIRo

Thanks for the help everyone!

[Kershaw]

Good thing you figured it out before catastrophic damage occurred!