This Does Not Sound Good ....

[conrod]

Dear All,

Further to my previous post re my "embarrassing moment", I decided to remove the exhaust header gasket and replace it - this time not using any RTV silicone sealant.

I started the engine, and the banshee wailing was still there. I've uploaded a video to YouTube here.

It's not at all obvious where the noise is coming from - but it sounds like a bearing to me. I removed the fanbelt and it made no difference - so that rules out the alternator and water pump. I've tried holding a stethoscope against various parts of the engine - but it doesn't magnify the sound at all.

I did get a high pitch whining noise a couple of weeks ago, which was intermittent. That noise definitely seemed to be coming from the rear of the engine - so I suspected the distributor. I removed it and regreased the top rotating plate. The noise disappeared, until this one started - but I've probably only driven about ten miles since, with all the wet weather.

Any ideas anyone?

[Noel]

Hi Alan, sounds like you've got the dogs b*ll*x of a supercharger fitted?

Sorry I can't help but you've had some problems with that engine?

Didn't someone have some problems with a carb sucking air through a gap and making an awful noise recently??

[conrod]

Noel,

Yes - that was Paul Wilburn. But he has even bigger problems now ...

The same thought went through my mind, especially as there is play in my primary throttle spindle too. But it's not coming from the carb.

I can't understand why I can't hear anything through a mechanic's stethoscope - I just can't pin the noise down.

The jobs I've done recently are:

1) Adjustment to clutch slave cylinder to cure clutch slip. I moved the slave cylinder back by inserting spacers to the bracket mounting bolts, and inserted a spacer at the rear of the slave cylinder to get it lined up better. This cured the clutch slip and the stiff clutch pedal. I've tried depressing the clutch - it makes no difference to the noise.

2) Regreasing the top plate in the Mallory dizzy - which involved removing it and reinserting it. I had to turn the oil pump shaft slightly to get the dizzy back in its original position - but everything fired up OK (timing checked and spot on).

3) Removal of RH headers to replace the gasket (twice!).

4) I also removed the RH rocker cover as I thought this was where the original noise may have been coming from (which I later diagnosed - maybe wrongly now as it happens - as the dizzy). I noticed a slight leak from the rear of the rocker cover gasket, so I turned the gasket over (i.e. so it was then effectively the other way up) with the leaking side now at the front so I could keep an eye on it until I get a new gasket.

I'm getting depressed now - just as the sun comes out .......

[Purple AK]

Hi Alan. Might be my ears but the whine seems to momentarily disappear as you blip the throttle? That would point to an intake leak as the vac decreased. A squirt around with WD40 might help to pinpoint it. Other than that if it is mechanical, It's probably something small as it's not a deep sound. Re your original assumption of Dizzy, maybe a bob weight spring let go and rubbing?

[conrod]

Originally Posted by Purple AK

Hi Alan. Might be my ears but the whine seems to momentarily disappear as you blip the throttle? That would point to an intake leak as the vac decreased. A squirt around with WD40 might help to pinpoint it. Other than that if it is mechanical, It's probably something small as it's not a deep sound. Re your original assumption of Dizzy, maybe a bob weight spring let go and rubbing?

Chris,

I was thinking along the same lines myself - and I've just got back in from the garage checking the various vacuum pipes. Although it sounds like a metal-on-metal screech, it doesn't vary much with engine revs - so an air leak would fit the bill. It would also explain why I can't pinpoint the noise with a stethoscope.

I'm now starting to think that this could also be related to the "popping on the overrun" problem. I read somewhere that, although this is usually caused by an air leak in the exhaust system, it could also be caused by an inlet manifold leak.

I drove it straight home after the noise started, which was only about a mile. I noticed that it would disappear only when I put my foot hard down on the accelerator. This further suggests an inlet manifold leak as the probable cause, as the inlet manifold vacuum goes to zero under those circumstances. My vacuum gauge still seems to be reading normally though .....

[wilf]

Drop the fan belt off and run it (for a short while only) to eliminate anything associated with that.

As Purple said, it seemed to go away as the throttle was blipped, so I also would suggest a vacuum leak somewhere.

You have to love these cars!

[Steve]

the way the sound picks up slowly definately sounds like air leak, not mechanical to me.

split vac hose?

[Purple AK]

Long Shot, but try pulling the PCV valve out and blanking it off with a finger.

[conrod]

Originally Posted by wilf

Drop the fan belt off and run it (for a short while only) to eliminate anything associated with that.

As Purple said, it seemed to go away as the throttle was blipped, so I also would suggest a vacuum leak somewhere.

You have to love these cars!

Wilf,

Been there - done that! I removed the fanbelt and the noise was still there. I've just whipped the carb off and fitted a new base gasket, and also gave the inlet manifold bolts a tweak. Again the noise is still there It seems to be coming from the rear of the engine - but it is very difficult to tell. The noise stops as I blip the throttle, and it only rises in pitch slightly with increasing revs - not proportionally. So all this does indeed seem to point to a vacuum leak - but who'd have thought it could make such a bl00dy racket!


I'll go in search of an inlet manifold gasket tomorrow. Then I guess the process is:

1) Drain the cooling system.

2) Disconnect all hoses.

3) Mark and remove the dizzy (at base and rotor position).

4) Disconnect throttle and choke cables and remove the carb.

5) Remove the twelve bolts.

I guess I should also check the manifold with a straight edge to see if it's warped. If it is, I assume it's just a case of taking it to a machine shop to have it machined flat?

Thanks for your help guys - any other ideas/suggestions welcome.

And in answer to your last point Wilf - yes you do indeed! I remember being in a BMW showroom looking at paint colours for the Cob I'd just ordered from DB, seeing a Z4 and thinking - I could buy one of those for similar money. But one look under the bonnet was enough for me - how the hell could you tinker with that lot? And that is, after all, half the fun - eh Dave?

[Sidecarbod]

Originally Posted by conrod

I guess I should also check the manifold with a straight edge to see if it's warped. If it is, I assume it's just a case of taking it to a machine shop to have it machined flat?

There will be quite a narrow margin that the manifold can be machined.

Russell Ram explained this very well on the forum once. Basically the engine can be viewed as a square standing on one point, the two lower sides of the square are the two banks of cylinders, the two top sides of the square are each side of the manifold. If you shorten the two top sides of the square too much then basically its no longer a square! (I guess a few thou would be OK).

I also agree that it sounds like an air leak. I think that WD 40 could help resolve what's going on.

Pete