Blowing exhaust manifold symptoms?

[daverclasper]

HI. I have an engine noise, that sounds like a muffled rattle. It is noticeable when the engine is under load, eg accelerating in higher gear (very much the same conditions that cause the pinking, tinkling sound, if ignition timing is too advanced). I didn't think it was timing causing this, as sounded different to pinking, though anyway, retarded it in various increments while testing on the road, and I couldn't notice any change.

I suspected a leaking exhaust manifold a few weeks ago, though the noise disappeared when the engine warmed up (metal expansion stopping the leak?) and is now worse?

What do you think. Any ideas to check this out?

Thanks

Edited August 5 by daverclasper

[dougbgt6]

Dave,

Probably Big Ends, it'll be fine. 

Once exhausts start to deteriorate they can go quite quickly, Is it stainless? They don't last forever, mine only did 30 years, it was guaranteed for life, but did I keep the receipt? 

I would monitor the situation, a blown exhaust is not going to do any harm,  except to your lungs. obviuosly.

Doug

[Iain T]

I suggest getting the car up on stands and getting underneath to check for leaks and clearance to prop etc.

Iain

[Nigel Clark]

Exhaust manifold gaskets can fail, and may make a sound similar to a loose tappet, or develop a chuffing sound as they get worse. 

What type of manifold has your car got? Original cast iron or tubular sports type? 

Nigel

[johny]

You havent mentioned that it can be heard with the car stationary Dave which I would expect with an exhaust leak. If its only when driving I think it would discount that...

[daverclasper]

6 hours ago, johny said:

You havent mentioned that it can be heard with the car stationary Dave which I would expect with an exhaust leak. If its only when driving I think it would discount that...

Thanks all. It's the original cast manifold, with a stainless exhaust, that was fitted around 20 years ago, I think?.

The noise is pronounced when engine is cold and stationary, not sure if it can be heard, when hot and stationary?

When cruising on a momotorway at say 2500 rpm (in overdrive, with a 3.27 diff) and I accelerate to overtake, it is certainly a lot more noticeable, and appears to disappear/go a lot quieter? when the overtaking speed is held, ie, no longer accelerating. 

Hope this makes sense!

Edited August 6 by daverclasper

[johny]

Ok then it would have to be a pretty big to be heard over engine, wind and road noise Dave - a good look round all the exhaust would certainly find the carbon marks you normally get with an exhaust leak👍

[Pete Lewis]

Dave try nipping up the flange nuts  (not too tightly)   but a new gasket seems the best route

Pete

[dougbgt6]

Dave,

What failed on my stainless exhaust were the internal baffles and some of the external welds.

Doug

[daverclasper]

Thanks Guys. I have two new manifold gaskets (I've read it may be a good idea, to double up, as are thinner than the original ones)

[johny]

Ive found it important on my mk1 to keep retightening the manifold to head fixings regularly as they seem to slacken off and then theres no quicker way to blow the gasket...

[trigolf]

I had a cracked cast iron manifold  - 2 quite long hairline cracks on my VitMk2. I gather that Mk1 manifolds are also prone to it. Something else to check for, if you don't find anything obvious.

[daverclasper]

Thanks. Removed the Air filter box, to check if was the triangular joint to the exhaust system. It was put, putting like a good un.

I replaced the gasket a few years ago with new as a matter of course. The new, was a thin, two skin thing that had de-laminated.

I had kept the original, which was thicker and the two skins were one piece joined around the edge. Replaced with a bit sealant on the gasket surfaces.

hopefully ok now?

[Pete Lewis]

you may find sealt will blow out     always best  fitted Dry 

let us know how well it works 

Pete

[johny]

Its another joint that might benefit from a retighten after a few miles Dave - not too much of course🙂

[Stratton Jimmer]

On 07/08/2024 at 11:47, trigolf said:

I had a cracked cast iron manifold 

I had a major crack in the cast iron manifold of my Mk1 GT6 years ago. I took it off and my dad welded it back together. He had just been sent on a cast iron welding course at Eutectic by his employer.

[johny]

wow result because not easy welding cast iron! I believe it has to be pre-heated doesnt it?