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I've started stripping the scrapyard V8 with a view to keeping stuff that might be handy and binning anything that isn't.

I've discovered both exhaust manifolds have a small Flexi joint under the heatshield, and on both manifolds they are distorted and split.

Is this a common problem? My car has what sounds like a manifold leak, and my plan had been to clean up the faces on these ones and swap them in when I do the heads...

Is it worth trying to repair them? Anyone just sleeved with solid pipe instead?

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No-one seen this before?

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I've heard of it but never seen it. I'm not sure why they are there as nothing is going to move, the Classic and all previous cars the used the same V8 had cast iron manifolds. I suppose they might be there to account for thermal expansion?

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I had the problem (or half the problem) on my diesel, remember that they are double skinned so collapse may only be due to engine mount failure (or?), actual leakage in the case of the diesel is easy to see because of the soot .... on a V8 it may not be as obvious visually, but should be pretty easy to determine. The flex saves all the stress on the rest of the exhaust and a good flexi I would say is absolutely necessary.... V8's rotate quite a bit as I recall so I wouldn't be temtped to bypass it. .... just storing up trouble.

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if i was desperate i would weld it up in a heart beat or re sleave it. which ever is easiest. the exhaust is not sold mounted so room for expansion. let us know how you go.

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Sorry, I see this only now.
My 4.6 Thor is with a flexi under the heatshield, my parts Thor also, and a mate with another 4.6 as well.
Also, the material do not look to be cast iron, but steel. Might have to do as to why it has a flexi joint ...

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yeah i suspect the P38 manifolds are stainless, which expands a lot more than cast iron. The flange is also two piece. Presumably they've done it for fear of expansion causing problems in the manifold itself.

i'll need to see if i can source a replacement weld-in flexi, but super tempted to just sleeve it. I guess i'll need to use a cylinder head as a jig for welding to ensure it all stays in the right place.

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I'm pretty sure I have a leak in the right side/drivers side exhaust manifold. I can hear a ticking sound inside the car around the pedal area which gets louder with more throttle.

It's been like this ever since I've had it and has persisted even after an engine rebuild so I can only assume it's the manifold.

I haven't been able to find any cracks on the manifold on the car, after about 5 seconds it's far too hot to check. It's starting to annoy me so I may whip off the manifold and see if I can spot anything.

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if you want to find the leak just use a piece of garden hose . one end up to your ear and just prod about with the other , tape a piece of wire to it so you can reach in behind the manifold.

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mad-as wrote:

if you want to find the leak just use a piece of garden hose . one end up to your ear and just prod about with the other , tape a piece of wire to it so you can reach in behind the manifold.

I just went out to try that. I took the wheel arch liner off for better access but couldn't pinpoint anything. Whilst I was in there I checked the torque on the manifold to head bolts, all were ok. Perhaps it's not the manifold then, no idea what else it could be though.

I took a video near the manifold so you can hear what it sounds like at idle: https://youtu.be/Cpelii3yGNU

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Do you have access to a smoke tester? Something like this
https://www.amazon.co.uk/Machine-Automotive-Diagnostic-Detector-Motorcycle/dp/B074JMB6HK/

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Sounds more metallic to me, not an exhaust blow. One thing that can sound almost exactly like that is a slightly bent tooth on the CPS reluctor ring just touching the CPS tip. Take the cover off the lower part of the bellhousing so you can see the ring. Check each tooth very carefully but I suspect you will see one that isn't quite parallel with the others and, most likely, with a shiny spot on it where it has been catching. I only know because I bent one of the teeth on mine slightly when undoing the flex plate to torque converter bolts and it made that very same noise when I first started it after the gearbox change.

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if that's the case then put the hose onto the cover and you will hear it. some times they are a bit hard to pin point , you need to push the hose right onto the manifold , yes it may melt a little but you will find it.

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BrianH wrote:

Do you have access to a smoke tester? Something like this
https://www.amazon.co.uk/Machine-Automotive-Diagnostic-Detector-Motorcycle/dp/B074JMB6HK/

I don't have one but may be able to get access to one. After a quick search I assume you are suggesting to pressurise the exhaust with it and look for leaks? Sounds a good idea anyway.

Gilbertd wrote:

Sounds more metallic to me, not an exhaust blow. One thing that can sound almost exactly like that is a slightly bent tooth on the CPS reluctor ring just touching the CPS tip. Take the cover off the lower part of the bellhousing so you can see the ring. Check each tooth very carefully but I suspect you will see one that isn't quite parallel with the others and, most likely, with a shiny spot on it where it has been catching. I only know because I bent one of the teeth on mine slightly when undoing the flex plate to torque converter bolts and it made that very same noise when I first started it after the gearbox change.

I took the engine out around 3 years ago now so I would assume it would have clearanced itself by now? I did replace the CPS around 2 years ago but I don't recall any difference in the noise. I'll give it a check anyway. I agree that it sounds metallic though.

mad-as wrote:

if that's the case then put the hose onto the cover and you will hear it. some times they are a bit hard to pin point , you need to push the hose right onto the manifold , yes it may melt a little but you will find it.

I'll have another go when I have more time. Maybe I went wrong by not having it close enough.

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jacckk wrote:

BrianH wrote:

Do you have access to a smoke tester? Something like this
https://www.amazon.co.uk/Machine-Automotive-Diagnostic-Detector-Motorcycle/dp/B074JMB6HK/

I don't have one but may be able to get access to one. After a quick search I assume you are suggesting to pressurise the exhaust with it and look for leaks? Sounds a good idea anyway.

Yes exactly that, you don't have the heat issue then. I've used one to locate a vacuum leak on a Vauxhall that wasn't noticable apart from fuel trim errors at idle, once it got a few psi behind it the smoke appeared near the EGR valve, soon lead us to a bolt holding the flange on one site to have a totally stripped thread and whilst it was in the hole, wasn't doing anything useful at all.