Engine knock - video clip

[jamieduff1981]

Folks,

I'd like some informed opinions if I may...

Yesterday was the first time I've mounted the GoPro on the roof on the Cerb, and whenever I'm going slow enough not to have engine sounds drowned out by wind noise a loud knock is apparent at low RPMs under load - like this:

http://www.youtube.com/watch?v=5ZfAy-g4UOk&fea...

I've never heard this from inside the car and it never came through with the GoPro mounted on the doors etc or indeed inside the cabin.

What do you reckon this is? Detonation? I know I'm carrying a small crack on the O/S exhaust manifold which I need to sort, but on previous manifold leaks I've heard on various cars they sound more like firearms cracks than this. I'll be stunned if it's a bearing noise too as the engine makes excellent oil pressure.

[RAFsmoggy]

Is the camera really secure ?

Its difficult, put a screwdriver on the camcover, aircon & alternator& listen, plug lead/plug acting up? It could even be a spun bearing> Doubtful its a bearing if its only just started more like something is rocking slightly ....boot lid tight ???

Edited by RAFsmoggy on Tuesday 11th March 11:04

[ridds]

Bonnet up, very slight rev and listen on over-run.

Does it knock then?

That sounds very heavy which in my mind would male me think piston, rod, crank etc straight away.

[jamieduff1981]

I'll give it a go tomorrow evening after work.

I'm more surprised that I've never heard it previously. I couldn't hear it doing that drive with windows up or down. It's just the GoPro that's recorded it.

It makes 45psi oil pressure at hot idle so I'll be surprised if it's a bearing shell. It could be a slapping piston I guess.

[TobyLerone]

Before you panic, are you ABSOLUTELY positive its not either the camera mount and associated bracketry, or any movement in the bodywork panels?

[jamieduff1981]

To be honest, no, I'm not sure. I would have thought I'd have heard it somehow.

I'm going to have to look in to this properly. The timing isn't great, but it's manageable now the daylight is improving up here and it's looking to be sunnier.

[madjules]

For what it’s worth, my first port of call would be to fix your manifold. You’ve got a known fault, take that out of the equation and start your investigation from a good baseline.

Good Luck

julian

[jamieduff1981]

You're probably right - and it needs done whatever happens.

[FarmyardPants]

Just held the phone to my ear so not ideal but sounds a bit like one of the air boxes knocking on the bodywork. Is it a 4.5..?

[sonnylad]

You probably all know that common Cerbera brake knocking noise when traveling slow in traffic, well when i put the go gro on the front of the car it picks this up really badly and the only reason i knew what it was is when braking it stops.

Go pro is mounted just above front number plate on mine, but picks up that noise so clearly so yours may not even be engine related, have you tried recording it again but coasting along to see whether its speed or engine related.

[ridds]

Definitely and engine related noise as the sound happens before the car moves and in sync with engine revs.

[jamieduff1981]

FarmyardPants said:

Just held the phone to my ear so not ideal but sounds a bit like one of the air boxes knocking on the bodywork. Is it a 4.5..?

Ahhhhhh that may be a good shout. It is indeed a 4.5. I may put the GoPro back where it was and drive it back and forth in the driveway with the bonnet up and see what happens.

I'm quite accustomed to most of the usual terminal engine failure noises in lots of types and applications of engines and this noise doesn't seem to strike a chord with any of my past experiences. As Paul observes though, it's absolutely engine load and rpm related.

It just might be an airbox rattling on something though.

[RAFsmoggy]

Did you get to the bottom of this ?

[jamieduff1981]

I haven even looked in to it yet to be honest. I've been far too busy and both daily drivers are carrying issues I need to resolve first.