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Old 1st December 2019, 12:20   #1
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Default Exhaust heatshield problem

Having cut my old exhaust off prior to fitting a new one, I thought I'd whip the heatshields off and sort out the odd blip of surface rust underneath the edges, mostly around the bolt holes.

I discovered the shield itself has been attacked by moths, or at least that's what it looks like. There seems to have been some sort of chemical reaction where the steel bolts go through the aluminium sheet. I don't want to put it back on like this as it can't be taken off again without dismantling the exhaust. Three of the four RH bolt holes are like this to some degree - oddly enough the LH holes aren't.



It if was flat I'd bolt two strips of aluminium sheet along the RH side to act as clamps - that would solve the problem. It's not flat though.

Last edited by Blink; 1st December 2019 at 12:23..
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Old 1st December 2019, 12:51   #2
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I made aluminium washers from an old ECM casing, to avoid accelerated electrolytic corrosion however pan menders are just as good

It's not the worst I've seen

Brian

P.S. your exhaust assembly paste will allow for subsequent dismantling of the exhaust if required
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Old 1st December 2019, 15:09   #3
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instead of two strips I used one and bent it over. Drilled for the bolt hole then offered it up so the bolt hole lined up, drilled through in two places and riveted the two "strips" together. Then bolted to the car

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Old 1st December 2019, 15:34   #4
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Quote:
Originally Posted by marinabrian View Post
I made aluminium washers from an old ECM casing, to avoid accelerated electrolytic corrosion however pan menders are just as good

It's not the worst I've seen

Brian

P.S. your exhaust assembly paste will allow for subsequent dismantling of the exhaust if required
These might help provided the edge is rounded off so that it doesn't cut into the heatshield. I think that's half the problem - the washers on the original bolts have a sharp edge and it cuts in as the rest of the heatshield vibrates up & down. You can see it in the post 1 pic.

PS. Good news re the paste.

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Originally Posted by macafee2 View Post
instead of two strips I used one and bent it over. Drilled for the bolt hole then offered it up so the bolt hole lined up, drilled through in two places and riveted the two "strips" together. Then bolted to the car

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I'm not sure I understand . Do you mean you sandwiched the edge of the shield between one long strip bent in two (doubled over), then bolted through the sandwich?

If so, how did you match the contour of the shield - it's not flat, there's a long hump between each pair of bolt holes, i.e.

  • Front pair: distance between bolts centres = 33cm / hump length = 28cm
  • Rear pair: distance between bolts centres = 20cm / hump length = 14cm
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Old 1st December 2019, 15:35   #5
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PS. Ooh, Xmas smilies. Lovely :icon_r olleyes::icon_questio n::lipsrseale d:

Looks like some of them don't work.
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Old 1st December 2019, 15:49   #6
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I just put two long metal jubilee style clip/ties around the whole pipe and cover to give extra support and eliminate the rattles. Worked a treat.
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Old 2nd December 2019, 12:03   #7
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Quote:
Quote:
Originally Posted by Blink View Post
Having cut my old exhaust off prior to fitting a new one, I thought I'd whip the heatshields off and sort out the odd blip of surface rust underneath the edges, mostly around the bolt holes.

I discovered the shield itself has been attacked by moths, or at least that's what it looks like. There seems to have been some sort of chemical reaction where the steel bolts go through the aluminium sheet. I don't want to put it back on like this as it can't be taken off again without dismantling the exhaust. Three of the four RH bolt holes are like this to some degree - oddly enough the LH holes aren't.



It if was flat I'd bolt two strips of aluminium sheet along the RH side to act as clamps - that would solve the problem. It's not flat though.
Make up some larger alloy washers and use those to stop corrosion in the future use under the shield and on the surface.

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Old 2nd December 2019, 12:09   #8
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worth while plopping some goo / sealant between the shield and the Chassis and the washer and the Shield to help/ slow the dissimilar metal corrosion.
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Old 2nd December 2019, 13:58   #9
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Quote:
Originally Posted by Arctic View Post
Make up some larger alloy washers and use those to stop corrosion in the future use under the shield and on the surface.
Good idea Steve - especially the moulded washers. I see you've used flat sheet for some washers and some bits cut from another heatshield for others. I don't have either of those so I'll have to buy something. What thickness flat sheet did you use?

I'm still toying with the idea of using flat sheet strips running between each pair of bolts - a bit like the strap on the fuel tank. If I can get the 'humps' exactly the right height it'll clamp the whole contact surface between the bolts. Each strip would be 40mm wide and (say??) 2mm thick.

Here's one supplier (see Flat Bar or Sheet options) - https://www.metalswarehouse.co.uk/custom-cut-metal/?gclid=EAIaIQobChMI-se1mIOX5gIVCLTtCh0bdwDXEAAYASAAEgJMgPD_BwE


Quote:
Originally Posted by ceedy View Post
worth while plopping some goo / sealant between the shield and the Chassis and the washer and the Shield to help/ slow the dissimilar metal corrosion.
Good idea again, although I'll be painting the area underneath the heatshield anyway and I'll use stainless steel bolts.
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Old 2nd December 2019, 14:05   #10
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Quote:
Originally Posted by Blink View Post
Good idea Steve - especially the moulded washers. I see you've used flat sheet for some washers and some bits cut from another heatshield for others. I don't have either of those so I'll have to buy something. What thickness flat sheet did you use?

I'm still toying with the idea of using flat sheet strips running between each pair of bolts - a bit like the strap on the fuel tank. If I can get the 'humps' exactly the right height it'll clamp the whole contact surface between the bolts. Each strip would be 40mm wide and (say??) 2mm thick.

Here's one supplier (see Flat Bar or Sheet options) - https://www.metalswarehouse.co.uk/custom-cut-metal/?gclid=EAIaIQobChMI-se1mIOX5gIVCLTtCh0bdwDXEAAYASAAEgJMgPD_BwE




Good idea again, although I'll be painting the area underneath the heatshield anyway and I'll use stainless steel bolts.
I use a blanking grommet with a hole pushed through. It helps to absorb vibration and reduce tearing

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