Knocking noise at idle

[Paul240480]

Righto thanks, good luck with yours

[PTJS]

Hi Paul

My hearings not too good but is it a low throaty sort of noise thats concerning you? When I blip mine on tickover thats what I get and I can also hear it on pickup when going through the lower gears. I've wondered if it was something to do with the advance and retard set up but the car performs well. Still i suppose when the big bang arrives I'll find out what it is. Seriously though, I could do with a top 240 cove to check it over and pinpoint what the problem is but where do you find one of those these days?

Good luck

Phil

[Paul240480]

Originally Posted by PTJS

Hi Paul

My hearings not too good but is it a low throaty sort of noise thats concerning you? When I blip mine on tickover thats what I get and I can also hear it on pickup when going through the lower gears. I've wondered if it was something to do with the advance and retard set up but the car performs well. Still i suppose when the big bang arrives I'll find out what it is. Seriously though, I could do with a top 240 cove to check it over and pinpoint what the problem is but where do you find one of those these days?

Good luck

Phil

Hi Phil. Yes, that is a good way to describe mine, the 'low subtle throaty knock in the background'. It's been there for some time now & can only be heard from outside the car on tick-over once it is well warmed up.

Anyway it, clearly is not the same as Cliffords issue. I'll keep on a plodding & hope the 'big-bang' doesn't happen................ at least for another 50k or so

[Clifford Pope]

I've just tried changing the oil to 20/50, and the noise has gone. Perhaps 15/40 really is just too thin for an old fashioned engine on 255,000 miles?

That seems to confirm it is cam-shaft related. A thinner oil would have a more copious supply but at a lower pressure.

Curiously the idling speed is now slightly higher - no other adjustments made. You might have thought a thicker oil might slow an engine down.

[c_lee]

A handy tool to have for ones armoury is a basic stethoscope which can be easily made very cheaply.

The one I made years ago used a length of flexible plastic tube a couple of feet long and a length of rigid small bore copper pipe about the same length to fit into the end of flexipipe.
Soften the end of the flexipipe in hot water to allow it to push onto the end of the copper pipe.

The rigid pipe allows you to poke in areas whilst keeping your hands away from things that could injure you or to listen closely to things that are not easily reachable.

Put the open end of the flex pipe to your ear and it will concentrate your hearing in the area of the open end of the rigid pipe.
Beware of the wind noise effect from your radiator fan though if in that area.

Even when you have no strange noises it's quite interesting to poke around different things while the engine is running to hear sounds you wouldn't normally be able to isolate from the jumble of background sounds.

( THINKS - We could start a reference sound library of normal engine noises.
IE: this is what it SHOULD sound like - could be quite useful for anyone trying to diagnose a fault.
If anyone has some form of portable recording device that will do mp3, wmf etc it could be a good project for you ).

HTH ( or is it a can of worms ) - Colin

[Clifford Pope]

Excellent idea, I'll give it a go.
I've always ignored the possibilities of stethoscopes (long screwdriver) in the past feeling that all you get is a jumble of sound transmitted through the engine block, with no certainty that the noise is actually coming from the point of contact. But I may well have been maligning the technique.

I'd like a giant stethoscope about 10 feet long with remote control to try and pinpoint the chronic rattle somewhere at the back of the car.
But it knows I'd be after it - to someone sitting in the boot the noise appears to be coming from the front - in fact it is always somewhere else !

[honestjoe]

Just being silly but!!..you could record your engine and take the recording and put it through a graphic equaliser omitting lower end rumble!!...I know its thursday!!..cheers hj.

[PTJS]

Originally Posted by Clifford Pope

I've just tried changing the oil to 20/50, and the noise has gone. Perhaps 15/40 really is just too thin for an old fashioned engine on 255,000 miles?

That seems to confirm it is cam-shaft related. A thinner oil would have a more copious supply but at a lower pressure.

Curiously the idling speed is now slightly higher - no other adjustments made. You might have thought a thicker oil might slow an engine down.

I'm intrigued by this Clifford as it could make a lot of sense to combat niggly rattles which develop as the engine wears at higher mileages in this way. When my 240 was new, in its early years it was serviced by the Volvo main agents and they used 10/40 oil which was ok then. Since I've largely been self maintaining in the past 10 years I switched to 15/40 which had a quietning effect on engine noise. Now, at nearly 200k, maybe its time to give 20/50 a crack. Anyone else any views on this and of any risk of oilway blockage in using a heavier grade oil?

Cheers

Phil

[PTJS]

20/50 ok anyone? 20/50 ok anyone?

Cheers

Phil

[Clifford Pope]

I always used 20/50 on my previous cars as a matter of course - habit really, because I have always had old/classic cars, and that just seemed the natural oil to use. My previous 240 did 425,000 miles largely on the cheapest 20/50 I could find.
But I changed the oil every 3-4 000 miles, and the filter at every alternate oil change.