SS Exhaust problems AMV8 - Any advice
Discussion
[Before I begin - Let me clarify this AMV8 is old school (1981), not the new baby]
Basically the flange between the manifold and the downpipes keeps blowing out. When rebuilding the car I chose SS manifolds as replacements for the cast ones that were standard. From the downpipes it was all SS anyway so now all the exhaust is SS. The problems is the manifold flange to downpipes (4 into 4 each side) has blown out 5 times. My mechanics have tried; skimming, higher torque, cement, Hymol (sp?), but she still blows. I also removed the rear silencers (one each side) and replaced them with straight through pipes which should have improved the breathing and reduced the pressure (sounds great!). Alas she has blown again (Comedy moment) - "Thar she Blows".
Apart from going back to the manifold manufacturer and asking them to sort it. Anyone got any ideas, experience or thoughts?
Basically the flange between the manifold and the downpipes keeps blowing out. When rebuilding the car I chose SS manifolds as replacements for the cast ones that were standard. From the downpipes it was all SS anyway so now all the exhaust is SS. The problems is the manifold flange to downpipes (4 into 4 each side) has blown out 5 times. My mechanics have tried; skimming, higher torque, cement, Hymol (sp?), but she still blows. I also removed the rear silencers (one each side) and replaced them with straight through pipes which should have improved the breathing and reduced the pressure (sounds great!). Alas she has blown again (Comedy moment) - "Thar she Blows".
Apart from going back to the manifold manufacturer and asking them to sort it. Anyone got any ideas, experience or thoughts?
Maybe tightening the bolts even more is the wrong way to go. The joint needs to expand evenly to maintain a flat surface and a good seal. What type of gasket are you using? can they not modify the flange, i.e., make it a slip over pipe as opposed to a flange.
The problem with the 4 bolt flange is that when overtightened at the corner's, they tend to bow in the middle and leak, over tightening only makes it worse. Modern exhaust's often use a longer bolt with a spring, so the load is set by the spring and it allows for expansion.
The problem with the 4 bolt flange is that when overtightened at the corner's, they tend to bow in the middle and leak, over tightening only makes it worse. Modern exhaust's often use a longer bolt with a spring, so the load is set by the spring and it allows for expansion.
I would look very carefully at the exhaust mountings, because as the engine revs especially with an engine as tourquey as yours it 'twists' the engine on its mounts.
This in turn will twist the exhaust and the point of greatest force will be at the mandold to downpipe flange as this is the link that joins the horizontal (manifold) to the vertical (main system).
This is made far worse with a stainless steel exhaust because it is inherintly much harder than mild steel and once fitted has much more resistance to twisting so what may have worked in mild steel is no good in SS.
This is a well known problem on American V8 muscle cars fitted with SS tubular headers and systems and what you need to do to cure it is to loosen the rigidty of the exhaust sytem or introduce a flexible joint.
On most cars by far the simplest solution is to replace any rigid mounts with rubber which enables the exhaust to flex with the engine or swap hard rubber mounts for softer ones..
Tighteneing the flanges or using cement will only make your problem worse.
When you build the system up do not use cement or a hardning compund use proper engineering grade silicone sealent as this will flex with the system and not crack this is the favoured method by drag racers and muscle car enthusiasts the world over..
This in turn will twist the exhaust and the point of greatest force will be at the mandold to downpipe flange as this is the link that joins the horizontal (manifold) to the vertical (main system).
This is made far worse with a stainless steel exhaust because it is inherintly much harder than mild steel and once fitted has much more resistance to twisting so what may have worked in mild steel is no good in SS.
This is a well known problem on American V8 muscle cars fitted with SS tubular headers and systems and what you need to do to cure it is to loosen the rigidty of the exhaust sytem or introduce a flexible joint.
On most cars by far the simplest solution is to replace any rigid mounts with rubber which enables the exhaust to flex with the engine or swap hard rubber mounts for softer ones..
Tighteneing the flanges or using cement will only make your problem worse.
When you build the system up do not use cement or a hardning compund use proper engineering grade silicone sealent as this will flex with the system and not crack this is the favoured method by drag racers and muscle car enthusiasts the world over..
It's a common problem on the V8. The flange on the manifold where it joins onto the downpipes is uneven. Usually happens in manufacture when they weld the pipes onto the flanges, it distorts the face. Only proper fix is to remove them from the car and grind them smooth, then reassemble. Temporary fix is to use two flange gaskets to make up for the uneveness. Also check to see where it is blowing by on the gasket, this will tell you where the flange is uneven.
Roo
Roo
All good ideas.
The update on this is my mechanics in London have discovered that the 4 into 4 pipes are out of alignment which is causing a massive pressure build-up. The result is a blow out. Manufacturer fault
so now their problem to fix.
Noted :-)
- we are using Hymol flexi sealer
- mountings are all flexible spring loaded
- gaskets used are AML, but they are very thin copper sandwich and a temp fix could be x2 each side
The update on this is my mechanics in London have discovered that the 4 into 4 pipes are out of alignment which is causing a massive pressure build-up. The result is a blow out. Manufacturer fault
so now their problem to fix. Noted :-)
- we are using Hymol flexi sealer
- mountings are all flexible spring loaded
- gaskets used are AML, but they are very thin copper sandwich and a temp fix could be x2 each side
If anyone is still interestd in this post then read on:
Puddleducks supplied the manifolds as manufactured by PD Gough. I offered to contact PD Gough directly as Puddleducks are a small business and I wanted the issue resolved quickly. PD Gough have nothing short of blunt in their refusal to deal with the matter despite their much advertised Transferable Lifetime Guarantee.
The big question who is liable to pay for the removal and shipping of the faulty parts and the reinstallation of the new correct parts?
I'm still waiting for a resolution and any advice is welcome - meanwhile if you hear an extremely loud, but not sweet sounding AMV8 then you'll know who it is.
Puddleducks supplied the manifolds as manufactured by PD Gough. I offered to contact PD Gough directly as Puddleducks are a small business and I wanted the issue resolved quickly. PD Gough have nothing short of blunt in their refusal to deal with the matter despite their much advertised Transferable Lifetime Guarantee.
The big question who is liable to pay for the removal and shipping of the faulty parts and the reinstallation of the new correct parts?
I'm still waiting for a resolution and any advice is welcome - meanwhile if you hear an extremely loud, but not sweet sounding AMV8 then you'll know who it is.
I know this does not help you Dr.Jock, but I've also had problems with this. I have standard mild steel manifolds. I replaced the studs with stainless bolts. After coating the gasket with sealer, I clamp the manifold/downpipe flange tightly with mole grips and then tighten the bolts. This has lasted for 3 years so far (inc 3 track days 
) and also makes separation easier.
) and also makes separation easier.I know this is a bit late, but might help someone else with the same problem! My new manifolds (from puddleduck) also blew the standard flange gaskets - turns out they are all now made to Vantage spec and therefore you need a Vantage gasket, which is solid copper, not a sandwich like the original. I think you might struggle to fit new manifolds onto and old non-Vantage downpipe because the pipes won't line up quite right.
Tim B
Tim B
Hey there - you are quite right and the solution is to fit heavy copper gaskets. RS Williams have them for £80 each side, which is very pricey for a bit of copper, but they work. If I had known all this months ago it would have saved me a ton of money as the exhausts blew out 4 times.
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