Has there been any definative reason given as to why the 3.6 TDV8 exhaust manifolds warp?

I am in the process of having to replace mine and was wondering if there is any mod can be done to stop this happening again in the furure.

Thanks in advance

Once the manifolds have warped, they won't warp again (same as Td5 )

Either, the studs snap and the manifold warps, or the manifold warps and the stud snaps. It's difficult to say

Either way, we skim the manifolds, new studs, nuts and gaskets

I see, thanks.

The 'skimmer' who the garage uses wouldn't take it on, so had to buy new ones as time is an issue, but a machine shop that my lad uses in Grimsby is going to have a go, and also look into the possibility of making up a set in stainless steel.

Will come back if the latter proves viable.

I think we pay around £300 per manifold, so it's not cheap, but a fair sight cheaper than a new part

Tell me about it, £678.06 +VAT each, and every factor we spoke to gave an identical price.

'Our' engineering shop intends to use a grinding machine, not actually skim, apparently.

Update.
Manifold too small to fit in machine, so no luck there.
As for making up in stainless, too costly for a small run, so also a non starter.

I had a quick look at a picture - assuming they look like the L322 ones (that was the first pictures I found) it seems like they'd be a nightmare to hold square, but once you'd sorted that out, anywhere with a Bridgeport and a fly cutter ought to be able to skim them..

Work holding is probably why they cost what they do to get skimmed, though. Of course, finding an old-school engineering shop with a manual mill who will do a one-off job is hard, these days

If you really needed it done I'd suggest a trawl of the places at Bicester Heritage.. but if you already have a replacement, and since Bicester isn't exactly near you, it's probably not worth the trip? 2014 BMW 530d Touring, 2006 BMW 650i, 2018 Mini Cooper S