tap/knock series 1, 84k
 

On idle I have a knock/tap coming from my Bonnie. Sound is coming from the firewall side of the engine, can hear it on the valve cover and exhaust manifold with a mech. stethoscope. Standing infront of the car you can barely hear it, but from past the door/in the driver seat it is louder. Iit isnt always there, and under accel it goes away instead of getting louder. Car has 84k on it. Ever since I started thinking of getting rid of her for a newer one it has fallen to pieces, brakes/tires/surging/tap. Bringing down the trade-in value that I need. I might pull the cover to investigate further Any help as in what to look for, possible cause is greaty appreciated :oops:

Check the harmonic balancer.

Accelleration is the key. If you hear it on the passenger side, and it goes away when accellerating, Joe's advice above is sound. At idle, the harmonic balancer (when worn) can rebound off the mechanical stops. During accelleration, it goes away, as you take the 'slack' out of it.

Move your accessory belt. Does the OUTER portion of the crank pulley (harmonic balancer/dampener) move, but not the crank (bolt head)? If you look closely with a mirror and flashlight, do you see rubber cracking on the face?

When mine failed, I tried to find the source of the knock for a week. I would put the car in neutral or increase the RPM's, and the noise would minimize.