Bubbling paint on bonnet
- Thread starter robrooster5
- Start date
Well found! As I've said, I didn't know the Z4 bonnet was aluminium. Now I do, this photo makes me feel better about it.flybobbie said:
My experience of aluminium was a Jaguar XJ8. A glorious, rumbling, responsive 4.2 litre V8, sadly in a steel, aluminium and plastic body, where stiffness had been sacrificed for lightness. The roof was so thin you could dent it with one finger, the doors so light they felt like thin plywood (albeit extremely well fitted plywood) and the open bonnet wobbled so much you could close it and miss one of its two catches.
Worse still, Jaguar never really overcame the problem of galvanic corrosion.
So, I wasn't wildly excited to learn of the use of aluminium in the Z4 and will be interested to hear the outcome of robrooster5's dealings with BMW about his apparently corroded bonnet.
(Since reading his original post, I've been over my 72k-mile 35iS with a fine-tooth comb and, including the stone chips I've already mentioned, there's no evidence of corrosion, galvanic or otherwise. And the aluminium roof panels, front side panels and bonnet are, thank goodness, really stiff.)
SV8Predator
Member
Pbondar said:
I'm sure Mr Google is your best friend! But have you any actual industry experience I wonder...?
Regarding stiffness and flow of aluminium alloy, what is your opinion on the best way to design the press tooling for vehicle panelwork, if the panel is to be alloy rather than steel?
You're obviously an authority, I'd be interested in your insight.
SV8Predator
Member
flybobbie said:
That's correct. The "perception" seems to be that alloy is very soft and therefore "flexible", when the opposite is true. Even today, it needs skilled design and very skilled "setting up" of the press tooling to successfully pop out alloy panels if they have a deep draw anywhere on the panel. As you said, tearing and cracking is common due to the low flexibility and elasticity of the metal.
robrooster5
Member
Been to BMW today, They measured paint and Reads 117 Micron, they are saying this has been resprayed and it should be around 80? Looked online and it seems like anything over 170 is a respray? What do people think to this?
Trying to duck the issue if that info is correct, get an independent inspection and report from an automotive engineer and if that states no respray then go back to BMW and fight your case.
robrooster5
Member
I also noticed it has done it slightly on the roof of the car in one place but this has no swirl marks..?? + on the bonnet, its all over not just one place and do not have the marks, this may be down to the light when taking the photo, im not sure?
robrooster5
Member
Fair enough thanks for the help guys
SV8Predator
Member
As I said earlier, you can see the swirls marks from a DA sander, not from a polisher, a sander. The marks are under the paint.
The panel has definitely been resprayed, no ifs or buts.
Might not be what you wanted to hear, but there it is.
Gasing a reaction to the paint underneath or from being wiped over by thinners to wipe off the dust.
I have used acrylic on acrylic and still had reaction. Perhaps acrylic on water based paints.
Seeing as in a line might some kind of run back from lifting the bonnet before respray. Might just be water contamination.
Take the car to a paint sprayer rather than BMW.
I have used acrylic on acrylic and still had reaction. Perhaps acrylic on water based paints.
Seeing as in a line might some kind of run back from lifting the bonnet before respray. Might just be water contamination.
Take the car to a paint sprayer rather than BMW.
