Elusive knocking noise
 

I've spent 3 weeks trying to diagnose this noise without success, so I thought I would throw it out to the list.

The knocking noise started immediately after I changed cam pulleys and idler arm pulleys to take slack out of my cam chains. This accomplished the goal. When I installed the new adjustable cam sprockets, I had to time the cams. This means that I backed off all the valve lash adjustments to their max to allow the cams to move easier without pre-load. I set the timing on the cams, installed the carrera tensioners and put it all back together.

I then went back and set the lash adjustment to all the valves and installed the valve covers.

I started the motor and heard knocking. Normally, if you prime the carrera tensioners, you will not have cam chain slap, but I did not prime the tensioners and you could hear some slap. This went away after a minute or so, but the knocking was still there. It sounded metallic and it came from the drivers side, lower rocker cover. I removed it and found a loose rocker, set the lash and put it back together.

That fixed the metallic knock, but now I have a faint knock coming from somewhere on the drivers side, top. I checked all the plugs (in case one was loose allowing exhaust to escape), all the valve lashes again, the installation of the cam chain tensioner, cam pulleys, idler arm pulleys, spray bar (to ensure the cam was getting oil), head stud torque, exhaust leaks, intake leaks.

It's a strange knock too. When first started, the engine is dead quiet. The knock starts at 2000 (or so) rpm and actually sounds more like a "tic" base on one cylinder - kind of like an exhaust pinhole leak and stays when brought back to an idle. While the car is being driven and the engine is warming up, you can hear it around from idle to 3000 rpm and speeds up with rpm, then goes away or is drown out by engine/exhaust noise above 3000. When the car warms up solidly to operating temp, the ticking starts to go away or becomes much fainter (heat - expansion somewhere?). In fact, at idle, there is no more ticking. AFR's are exactly as I expect, oil pressure is right on, idle is perfect, acceleration is perfect all the way to red line under WOT, and so on.

I then rechecked everything again and even did a compression check with normal results thinking bent valve, burned piston, etc.

Anyone have any other ideas?

Thanks

Cylinder 1 or cylinder 3?

Most likely 3.

Do you have a stethoscope? Does it sound like maybe a rocker arm sliding side to side hitting the cam tower?

No stethoscope.

I guess it could be a sliding rocker arm but I would suspect the gap would have to be significant to get such as tic - loud enough to be heard over the sound of the motor. It does sound like it could be in the valve train tho.

I know it is a PITA. But the next time you are checking the valve clearance verify you don't have excessive side to side play. And I am sure you checked but just asking did you check the cam spocket offsets.

I know the rocker is a long shot especially not having this problem before. What about the scavenge pump for the turbo?

Hey Don,
can't help on the tic, but are you going to be at the Petit this weekend?

He needs to..... Get his mind off the markets and onto some R&R!!!!!

Don,
If you can get an ultrasonic mic, these things work great in in isolating sounds coming off the engine. These devices are more directional than conventional stethoscopes and have the added benefit of detecting exhaust leaks. They're expensive though, and a limited number of shops have them. More than likely, you are experiencing a header leak. Get under the car and search for any white traces that would emanate from any crack or gasket. On the other hand.....

When I had problems with valve lash on my car, I had little confidence in my technique. It turns out my technique was ok, but I was experiencing oil starvation to the cam. The wear on the lobes and rockers was accelerated and I found myself adjusting them more often than the norm. If you take the covers off, check the lobes for uneven wear. Check for ridges on each side of each lobe. The lobes should look almost chrome-like in their appearance.

I always have a good look at my top/inlet valve covers end to end for an equal amount of splashed oil. If they don't look even I run the engine with the covers off (wearing goggles) and check the spray bars are squirting oil. If I have any doubts I poke the holes with a pin.

Hi Greg - I doubt it. I have a lot of studying for my CFP board exam in Nov. I'm sure I'll see you at the Oct DE tho.

Good point - yes I did check the new sprocket offsets.

I drove it today and it sounds like like I have a playing card in the spokes of a wheel.

Nathan / Dave

Thanks. Maybe one of the aviation shops I work with have the ultrasonic mic. Good idea on taking the covers off looking for oil from the spray bars. It does sound like a dry rocker tapping.

Don,
Those cheap stethescopes you can get at a discount auto store are good for checking exhaust leaks. I have a Snap On stethescope and I take the vibration disc with probe off and add a length of hose to the end with the motor running and move the end of the hose around the header flanges and the area where the head mates to the cylinder. If there is an leak you will definetly hear it at that specific spot. You could also just simply take a flexable section of hose and hold one enf to your ear and the other as I discribed and get simular results. Again just an idea.
When you were a kid, did you try to put a whole deck on your bike?

That sounds exactly like mine did when the spray bar became partially clogged on cyl 5 & 6.
This is after the fact, but do you have an inline filter between the turbo scavenge pump and the tank? The stock turbo sump tank had a screen filter built into it and when I added the B&B headers, the tank provided did not have that feature.
Here's my horror link below.
http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/369989-clogged-spray-bar-autopsy.html

That's funny because it's always 5 & 6 that I've had doubts about too. There must be a reason particles end up there...

Nathan,
It's always going to occur on cyl's 3 and 6 and ultimately work it's way forward because the design of the top end lubing layout. The spray bars are closed at the ends. The better question is how particles get there in the first place. Because the oil is filtered only on the engine sump return line to the tank, one must make sure ALL oil is filtered before it's returned to the tank.

Sorry for going a little off-topic. Hopefully, this is not Don's problem. This is a PIA to straighten out.

I think the particles come from condensation around the oil filler neck. I try to wipe it out when I remember, usually when I check the oil level. I've seen cokey deposits there too, just like a normal car does. I actually removed my oil tank in my 930 and cleaned it out with fuel. I had my 911 one cleaned out approx 7 years ago when I understood how it all worked...

Don,
Any findings?