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DonE DonE is offline
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Join Date: Mar 2004
Location: Brooks, GA
Posts: 1,211
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
Old 09-27-2008, 03:50 PM
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