Cracks developing around hood fasteners

Hi,

The paint on my '71 Mach 1 is perfect except one thing: on the NACA hood, cracks are developing around the twist lock hood fasteners. The cracks are mostly radial and 1/2-1 inch long.

I have made sure the fastener inserts are not binding in the hood cutout/opening and that the fasteners only fix the hood but do not force it up- or downwards.

Is this a common problem or can it be traced back to some kind of mistake made by the painter (the car has been professionaly painted)?

If it is caused by the painter, what arguments can I best use to have him correct the problem (he claims that this is a weak spot and that it always will develop cracks)?

Do you have any tips or tricks how to avoid the cracks during a repaint?

Thank you, Manfred

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IMO: More likely the hood lock engagement was set too tight causing the sheet metal to "dimple" which over time will result in cracking. When I push down to engage the pins, the metal flexes just a little bit as they engage, but then it comes back to it's original profile - no dimple.

Click to expand...

QCode & Bill,

thank you for your replies. Although it was not that easy to take a picture that properly shows the cracks, I hope the one below is suffucient.

The painter has tried to "repair" the cracks by "flowing in" some paint with a brush which obviously didn't work.

Regarding the body work, I did the paint removal myself down to bare metal. I then sprayed it in primer to prevent it from rust. The body work has been handled by the same painter who did the top coat.

As I wrote in my initial post, I adjusted the twist locks such that they do not put any downward force on the hood. So they should not "dimple" the metal.

Click to expand...

Although this is not related to the prep work or how to resolve the problem, I just wanted to give my two cents on the subject about fastening the lock too tight.

Even if you adjust them so that they don't put any pressure on the hood, it will dimple as soon as you go fast on the freeway as the wind will try to push the hood open thus pushing it up against the locks or pins.

I had that problem with mine.

Usually the metal is flexible enough absorb this and will go back to it's original shape once you go slower.

On mine, the dimples stayed, so I reinstalled the original hood lock and just keep the hood pins for looks.

CAUTION, after reading this post.

The twist locks are for looks only you MUST have a regular hood latch / catch system.

Click to expand...

Although this is not related to the prep work or how to resolve the problem, I just wanted to give my two cents on the subject about fastening the lock too tight.

Even if you adjust them so that they don't put any pressure on the hood, it will dimple as soon as you go fast on the freeway as the wind will try to push the hood open thus pushing it up against the locks or pins.

I had that problem with mine.

Usually the metal is flexible enough absorb this and will go back to it's original shape once you go slower.

On mine, the dimples stayed, so I reinstalled the original hood lock and just keep the hood pins for looks.

CAUTION, after reading this post.

The twist locks are for looks only you MUST have a regular hood latch / catch system.

Click to expand...

I remembered after I posted this that I don't have the original style hood locks. I added the 60something Shelby style hood pins that are perfectly able to hold down the hood. Maybe that's why mine had dimples, as the base of these is much smaller so the pressure is not as widely spread as with the twist locks.

I have never seen twist locks in real life, so I don't know if they are only for looks. :blush:

Anyway, better to have the hood latch in place, I guess.

Click to expand...

Although this is not related to the prep work or how to resolve the problem, I just wanted to give my two cents on the subject about fastening the lock too tight.

Even if you adjust them so that they don't put any pressure on the hood, it will dimple as soon as you go fast on the freeway as the wind will try to push the hood open thus pushing it up against the locks or pins.

I had that problem with mine.

Usually the metal is flexible enough absorb this and will go back to it's original shape once you go slower.

On mine, the dimples stayed, so I reinstalled the original hood lock and just keep the hood pins for looks.

CAUTION, after reading this post.

The twist locks are for looks only you MUST have a regular hood latch / catch system.

Click to expand...

Hi OSM,

I have a regular hood latch / catch in place

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Looking at the picture it's a failure of the substrate or top coat...Did you use a 2k primer when you primed the car ? or lacquer ? did the painter remove your primer & re-prime ? How was the car stripped ? If it was chemical did you neutralize after stripping & then use a metal conditioner ? Also was the car painted in urethane ? & did you do a single stage job or base coat ..clear coat & what type of paint did you use..

Click to expand...

Looking at the picture it's a failure of the substrate or top coat...Did you use a 2k primer when you primed the car ? or lacquer ? did the painter remove your primer & re-prime ? How was the car stripped ? If it was chemical did you neutralize after stripping & then use a metal conditioner ? Also was the car painted in urethane ? & did you do a single stage job or base coat ..clear coat & what type of paint did you use..

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Hi QCode,

here are my answers (to the best of my knowledge)

Q: Did you use a 2k primer when you primed the car ?

A: Yes

Q: Did the painter remove your primer & re-prime ?

A: Don't know

Q: How was the car stripped ?

A: Sandblasted

Q: Also was the car painted in urethane ?

A: Sikkens CM 432 D4 (not sure about Manufacturer)

Q: Did you do a single stage job or base coat ..clear coat

A: Sigle stage

Q: what type of paint did you use..

A: see above

The painter is certified and does have a good reputation:

http://www.lackiererei-dauerer.de/

- Manfred

Click to expand...

IMO: More likely the hood lock engagement was set too tight causing the sheet metal to "dimple" which over time will result in cracking. When I push down to engage the pins, the metal flexes just a little bit as they engage, but then it comes back to it's original profile - no dimple.

Click to expand...

Bill...That' in it self won't cause crack's I can take a piece of metal that's prepped properly & sprayed properly & bend it back & forth without the paint cracking..His problem is too much filler applied in the area..poor quality primer...Incorrect reducers...mismatched materials....incorrect application of the top coat clear coat..with out a picture it's hard to say

Click to expand...

IMO: More likely the hood lock engagement was set too tight causing the sheet metal to "dimple" which over time will result in cracking. When I push down to engage the pins, the metal flexes just a little bit as they engage, but then it comes back to it's original profile - no dimple.

Click to expand...

Bill...That' in it self won't cause crack's I can take a piece of metal that's prepped properly & sprayed properly & bend it back & forth without the paint cracking..His problem is too much filler applied in the area..poor quality primer...Incorrect reducers...mismatched materials....incorrect application of the top coat clear coat..with out a picture it's hard to say

Click to expand...

Yup, I see and concede your point as the most probable cause. However I think having them too tight may have contributed. My sheet metal flexes as they engage (as you push down), but the paint has held up for 13 years with no cracking.

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