Annoying knock V8

 Help......... 1999 E39 V8 535 72000mls.

When engine  is warm it emits slight knock from front cam cover area. Ie  oil filler cap/ cam sprocket drive area.  This is particularly audiable when on tick over waiting at traffic lights etc.  The left bank is noisier than the right. If you place end of screwdriver on cam cover, place ear to it you can hear it and also slightly "feel" it. No knock when cold. Not sure if noise goes away when higher as it is masked by other normal mechanical noises (fan etc). MAIN TIMING CHAIN TENSIONER has been replaced by specialist but NO CHANGE.

Considering mileage bit surprised there is a problem at all.!

Any ideas. ........At present the only solution appears to be to replace every thing on a try and see basis. Which is a bit hit or miss and expensive.

 No misfire, not lumpy, runs perfectly smooth.

Considering the area the noise eminates from, I can understand to a degree why the guy replaced the chain tensioner.

But it sounds to me too deep seated, or solid, not tinny or chainy if you know what I mean for it to be the chain itself

Are these things prone to camshaft wear, I just have an orrid feeling ts something along those lines.

One other possible factor is a change from fully synth. oil, to semi synth. I cannot be positive, but maybe the noise has got worse since  this recent change of oil type.

I suppose if you were really clever you could pin down fequency of knock relative to engine revolutions. ie does knock occur every chain sprocket or cam shaft revolution.

Nothing worse than having an undiagnosed problem with a car... Been bugging me for days

Might also be a rogue hydraulic tappet. I have an E34 540i V8 that came with full history. 3 months later I had a knocking noise from 1 bank of the engine that sounded like cam knock or a stuck hydraulic tappet.

I cured it by adding 2 cans of Wynn's Oil Treatment-it flows like bitumen-warming the engine up, then bouncing it off the rev limiter to raise the oil pressure enough to 'unstick' the rogue tappet. I then changed the oil after 1000 miles and everything's been fine since.

Sounds violent but it worked. Problem with hydraulic tappets is they fill with oil but, by design, only bleed out a small amount. So any crud that gets into the tappet usually stays there. Raising the engine speed increases oil pressure and can shut up a sticking tappet, only for the noise to return when the engine is idling.

I took a gamble with my 'fix' but it worked and has been fine for the past year of hard driving. I have the early non-Vanos V8 so can't comment on Vanos noises, but I imagine a faulty Vanos would affect the way the engine 'feels', as it's purpose is to alter the valve timing and give good low-rev 'grunt' with storming top-end power.

Timing chain tensioners usually rattle or clatter, but don't give a rythmic 'knock'. A steady 'knock' at the top end of an engine is usually camshaft or hydraulic tappets-this was common on the very first M40 4-cylinder 1.6 & 1.8 litre engines from 1988. The V8's have 32 hydraulic tappets, and replacing them involves removing the camshafts (2 camshafts for each bank of the V8!) whilst not losing the orientation of the cams or their timing-not a job for the faint-hearted! You can see why I added syrup to the sump then made the V8 sing it's heart out at 6500rpm :) Hope this helps.

Camshaft End Float????    Don't know if there are spacers which need adjusting or whatever but some bike engines suffer from this and they make the same type of annoying "serious" type noise.

Just an idea....

Good luck

 Going to show my ignorance here...........

I assume the vanos unit is oil pressure "operated" similar to the timing chain tensioner, but is set by electrical impulses from the engine management system. 

Is the knock (normal or otherwise) likely  to be cured by simply replacing the vanos unit it self. Or is it going to be mechanical bits on the cam/drive that the vanos units re "times" to alter the value timing.

Put simply would screwing on  new vanos units cure  it.?

Thanks for the offer.

We are only at Amersham so might take you up on the offer.

Many thanks

Malcolm.