Low drumbling at tickover

[Psychobert]

This ones got me foxed.. When just ticking over, I've started to notice a low grumbling for maybe a second, then a brief pause then it repeats. I *think* I can feel a vibration, but I may well just be paranoid by now. It seems to happen whenever the engine idles, even the slightest revs above idle and its gone, (spent quite a while in the car car with it 200 rpm over which is a tricky thing to hold when freezing your nuts off outside..)

Oil pressure on the guage isn't great, but as the guage flaps around a lot I've never really paid a huge amount of attention to it. Its not using any more than usual which seems the important thing.

Only way I can think of describing it is as a slight harmonic to the usual tickover. Pretty sure its not mechanical, (was a little worried about bearings and so on but I presume that would be constant even if it went away at different revs).

She's due a service soon anyway and as everythign else seems ok, I'm not that worried, but its one of those 'what the hell is that?' things..

[GreenV8S]

The only things that come to mind are crank rumble, or a resonance in the exhaust system. Crank rumble would come from worn main bearings which may also cause lower oil pressure, and would normally be more apparent at higher revs.

[v8_oatz]

check the exhaust manifolds for cracks or pinholes

[honourablepickle]

i agree with green , crank shaft noise is usually more obvious at say 4000rpm with no load i:e rev it up and let off - crank noise usually shows up as the revs drop - best guess by internet ESP - exhaust
might not be a bad idea to test the oil preasure just incase the mains are gone and it's about to throw the crank - peace of mind and all that
reb

[psychobert]

Exhausts been off recently and I've only noticed it since then.. It also took a bash on the way out of a garage a while ago.

Hope it is the exhaust, crank sounds a bit of a job..

[HarryW]

I'd say exhaust too, mines been realigned so many times.
Every time it gets bashed it seems to home into the chassis NS of the gearbox and gives a low rumble to begin with. Once bashed again there is no mistaking it , it then seems to be in permannet contact with the chassis and you tend to notice it :hehe.

The other point you made about the oil pressure gauge bouncing a bit, personally I wouldn't be happy with that, get it sorted . Saying that, if idle is set too low the uneven firing of the RV8 can give poor(bouncy) pressure which is not good imho.................. does it stabilise with revs

[Psychobert]

HarryW said:

The other point you made about the oil pressure gauge bouncing a bit, personally I wouldn't be happy with that, get it sorted . Saying that, if idle is set too low the uneven firing of the RV8 can give poor(bouncy) pressure which is not good imho.................. does it stabilise with revs

Pressure is fine when revved higher and fine when under load. Its just when it drops to tickover or is first started it tends to wave around a bit.

That said, I've a vague feeling its a bit lower than the V6 used to be.. Just about to start my weekly 200 mile drive to work so will keep an eye open and report back later with figures..

[nawarne]

HarryW said:

I'd say exhaust too, mines been realigned so many times. Every time it gets bashed it seems to home into the chassis NS of the gearbox and gives a low rumble to begin with. Once bashed again there is no mistaking it , it then seems to be in permannet contact with the chassis and you tend to notice it :hehe. The other point you made about the oil pressure gauge bouncing a bit, personally I wouldn't be happy with that, get it sorted . Saying that, if idle is set too low the uneven firing of the RV8 can give poor(bouncy) pressure which is not good imho.................. does it stabilise with revs

Whilst I can see where Harry is coming from, I would say to use the gauge as a guide only - rather than absolute figures. I had a calibrated wet line gauge put on my engine after re-build and found the dash mounted item reading 10.5 psi LOW!
Nick

[HarryW]

Thats good Nick, I have confidence in my gauge as the pressures it gives me match those given from when it was rebuilt and bench tested .
I found that a lumpy cam and low tick over can give irractic readings which in my simple mind means irractic oil delivery .

Back on topic; Out of interest what pressures are you getting warm/hot mine is 25 at tick over and 45-50 at revs, cold it is 35 tick over and 55 at revs.

[Psychobert]

HarryW said:

Back on topic; Out of interest what pressures are you getting warm/hot mine is 25 at tick over and 45-50 at revs, cold it is 35 tick over and 55 at revs.

Mines not too different.. Maybe I'm ok afterall..

Cold 25 tickover, doesn't get revved above 3K until the temp increases but then it sits at about 40 when revved. Warm/hot 25 tickover, 45 at revs.

At motorway cruising speeds, (2.5K which equates to 75mph indicated), it behaves slightly over tick over, say 30 there or therabouts. Were I to have taken it to 5K revs it sits at 50.

The guage still flaps around though when the revs change. I'm wondering if I've got a blowing exhaust and a dodgy wire somewhere..

[HarryW]

Psychobert said:

HarryW said: Back on topic; Out of interest what pressures are you getting warm/hot mine is 25 at tick over and 45-50 at revs, cold it is 35 tick over and 55 at revs. Mines not too different.. Maybe I'm ok afterall.. Cold 25 tickover, doesn't get revved above 3K until the temp increases but then it sits at about 40 when revved. Warm/hot 25 tickover, 45 at revs. At motorway cruising speeds, (2.5K which equates to 75mph indicated), it behaves slightly over tick over, say 30 there or therabouts. Were I to have taken it to 5K revs it sits at 50. The guage still flaps around though when the revs change. I'm wondering if I've got a blowing exhaust and a dodgy wire somewhere..

DAft question levels OK isn't it?

[Psychobert]

That was at about halfway between full and fill up, (if you know what I mean). Topped it up 150 miles ago this morning and its still bang on the full line..

Discovering the disadvantage to a sports exhaust is that when playing around with the car, I can't actually hear anything but the exhaust. Trying to work out if its blowing is nigh on impossible.