Hi all,

I'm having the classic "engine tapping" conundrum that a lot of 6G owners seems to face. However I think this may be a little more serious..

The knocking or "tapping" sound seems to be definitely coming from the right (rear) head, and occurs once for every revolution of the drive belt.

So far I've done the following (in this order):

- Engine flush, Lifter free, Oil and filter change to 15W (previously 5W but I think that's much to thin for an engine that's done 280,000 + ??)

- Tried the lifter priming method (revving up to x RPM for 15sec and dropping the throttle for 15sec up to 30 times) - the neighbors loved this :facejump:

- Re seated the EGR line (back of the intake manifold) and found that the gasket was leaking. I have since fixed this. It's also not the EGR valve.

- Removed the right (rear) rocker tubes and cleaned them (they weren't blocked at all, no sludge) rocker arms, primed and replaced all 12 Lifters ($6.60 from Repco!). There doesn't seem to be excessive wear on the rocker arms / tubes

However since replacing the lifters, the tapping noise seems to oscillate when reving up to around the 2100RPM mark..

I'm not sure if this could be an exhaust manifold leak, or if its something more detrimental like the timing belt has slipped? :headbange
Also there is no loss in power or feel to the car..

I'll be buying a 6g75 with a manual bolted to it from Mal in the next week or two, so it's not hugely important.
Thanks!

-Mitch
:happy:

The knocking or "tapping" sound seems to be definitely coming from the right (rear) head, and occurs once for every revolution of the drive belt.
If it's once per revolution of the drive belt, it's unlikely to be anything internal, since the engine does multiple revolutions per drive belt revolution. A damaged drive belt, perhaps?

If it's once per revolution of the drive belt, it's unlikely to be anything internal, since the engine does multiple revolutions per drive belt revolution. A damaged drive belt, perhaps?

Thanks for the reply!

I would feel silly if it was lol Hmm well when I bought the car, the drive belt had actually cut into the timing cover.. I've obviously replaced the covers and belts since.

Still it seems to be coming from the other side of the engine bay. I did take a quick glance at the belt and pulley system to begin with though, I'll have a proper look.

Any other suggestions on what this could be?

So.. I dropped into the mechanic today to see what their opinion was. He had a quick 5 minute look at it and advised that I shouldn't drive it at all, that it sounds like a piston hitting a valve..
Could this have been caused by the timing belt slipping?

If the cam positions aren't correctly positioned vis-à-vis the crankshaft, it's quite possible for valves to start hitting pistons. An engine in that state probably wouldn't run very well - or for very long before doing serious damage. Belts slipping on their sprockets or not being installed correctly can certainly cause that.

Various things come to mind. Use a bit of hose to listen at various points. disconnect the battery, remove sparkplug from possible source area, remove wheel, use 22mm (about) socket to turn crank shaft, mark a point on belt and harmonic balancer pulley, turn and note moment of sound, inspect through plughole piston top or use a screwdriver to feel the location of the piston top, look at the distributor point in relation to relevant cylinder... wait till you have the next engine in and then check it out.

<edit> that it sounds like a piston hitting a valve..

If the piston hit the valve with all that revving I'd be amazed that the engine could run with normal power...

Since the noise is near a particular RPM I'd think it is more like a loose bolt, engine mount, exhaust shield? anything that can rattle at that RPM.