paint cracking during assembly HELP!

david perez · Post by **david perez** » Sun Jul 07, 2002 12:30 pm

use washers under bolt heads and nuts.
some builders use (in addition to the washers), a rubber gasget under the washer.
alot of "show cars" are not driven and nuts and bolts are left lose.
some parts (supention ect,) are assembled THEN painted, alot of making os involved!
I have seen aftermarket fenders crack upon install, this is why I don't use them on MY cars.

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David, aka, HAPPY HOPPY of Happy Hoppy's chop shop
cut, hammer, weld, drive.
not necessarily in that order

ChrisK · Post by **ChrisK** » Sun Jul 07, 2002 11:46 pm

A friend restoring a bug has some paint cracking issues. I noticed the same things in the past with my cars whenever stuff is painted but since none of mine were 'presentable or show quality' it wasn't an issue.

Anyways, the problem is this: during assembly the paint cracks where the pressure of the bolt is applied to it. I'm referring to everything from the pan bottom when putting the shell on to body panels, suspension components, etc. Obviously this is due from the bolt pressure BUT what to do about it if anything? After spending thousands on a resto this is an annoying little 'bug' in the process. How do the pros deal with this on their concours restos? Or is this inevitable? (Did I mention my friend is a stickler for perfection?).

ChrisK · Post by **ChrisK** » Sun Jul 07, 2002 11:48 pm

BTW, he did use good quality paints, sealers, primers throughout (PPG, ,etc).

ChrisK · Post by **ChrisK** » Mon Jul 08, 2002 12:30 pm

This happens too with bolts with washers. Sure, they probably help by spreading the load over a larger area but they do not eliminate the problem.

Also, what about the factory? I went with my friend to a few dealerships to look for this efect on new cars and guess what...no cracking. How do they do it? Obviously they don't assemble and then paint.

I figured as much about show cars...if you left the bolts a bit loose or used a rubber gasket....but what about a car meant to be driven. The biggest worry is that water will seep into the hairline cracks and start corrosion.

ChrisK · Post by **ChrisK** » Mon Jul 08, 2002 12:31 pm

One other thing about assembly and painting. If you asssemble and then paint you're limited to a brush which leaves brushmarks or risk overspray on other components...

Bucko · Post by **Bucko** » Mon Jul 08, 2002 12:37 pm

I know that when a paint shop paints parts such as front bumbers (on the newer cars), the add a "flex agent" which allows the paint to flex when you press on it. Case in point: look at any of the new cars today that have painted bumpers; if you press on them they flex, yet the paint doesn't crack. I've been told though that this flex agent makes the paint fade sooner. That's usually why the bumpers on a car discolor sooner than the rest of the car.

Perhaps this is what the "restorers" are using?

david perez · Post by **david perez** » Mon Jul 08, 2002 7:49 pm

if you wait very long the paint hardens and could crack, if you put it together soon after painting , (not wet) it should be O.K.

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David, aka, HAPPY HOPPY of Happy Hoppy's chop shop
cut, hammer, weld, drive.
not necessarily in that order

ChrisK · Post by **ChrisK** » Thu Jul 11, 2002 11:01 pm

Thanks all. Good info/tips.