Nose pimples

[antijam]

My '71 has a full complement of nose pimples i.e. the bumps caused by corrosion of the aluminium rivets securing the metal header bar to the glassfibre. They're not too easy to photograph but you can just make some of them out arrowed in this piccie....



Their presence is supposed to be evidence that the car has never suffered front end damage or been resprayed and are therefore a mark of authenticity. Mine may not have front end damage, but it has certainly been resprayed which I must presume was just done over the pimples without any flatting.

Anyway, if one wants to get rid of them, the perceived wisdom from the american forums seems to be to grind off the rivet tails from below, prise off the header bar and then winkle out the rivet heads also from below. Then to bond the header bar back in position while clamping a wooden batten across the bumps from above which will then be pushed back flush with the surface.
This process obviates the need to create holes in the nose surface that, after filling and respraying nearly always reappear as sink marks as the filler shrinks. Thus the original paint is undisturbed. Some owners claim to have completely eliminated the bumps this way, hence eliminating the need for a respray. I'm somewhat sceptical of this claim, believing that the paint over the bumps will have stretched and while the appearance may have been improved, there will still be some evidence of the bumps. Has anyone over here tackled this problem with success - with or without a subsequent respray?

 

[Oneball]

No idea but if you want a front end with riveted header to play with I’ve got one that’s going to the tip. I can save you the front bit.

 

[Daytona Vette]

I am not sure that the Header Bar was ever riveted at the factory - the Header Bars rust and then deform the fiberglass, you can often see a C3 and be able to see the line of the Bar deforming the fiberglass - Corroded Bars should be removed and replaced with new that is only bonded in place.

 

[antijam]

I am not sure that the Header Bar was ever riveted at the factory - the Header Bars rust and then deform the fiberglass, you can often see a C3 and be able to see the line of the Bar deforming the fiberglass - Corroded Bars should be removed and replaced with new that is only bonded in place.

As I understand it the header bars were rivetted to a glassfibre bonding strip which in turn was bonded to the nose section. This was done on '68 to '72 cars only. It seems Chevrolet were not initially confident that steel could be directly bonded to glassfibre, but by 1973 had decided that it could.
So, the pimple problem is only suffered by the early C3's. This is not to say that the header bar itself does not have corrosion problems but it is the galvanic corrosion between the steel header and the aluminium rivets that causes the rivet head to grow and apply pressure to the underside of the hood - producing the pimples. The cure proposed by Willcox Corvette in the States seems to have been widely adopted or modified by owners over there, but I'm wondering if it really works?

 

[antijam]

No idea but if you want a front end with riveted header to play with I’ve got one that’s going to the tip. I can save you the front bit.

Thanks for the offer Tim. If your front end is original with a riveted header, glassfibre bonding strip and pimples showing through the paint, it could be very useful as a 'dry run' to see if the pimples can be satisfactorally flattened. From the picture in your Racecar build thread, the bonding looks a bit as if it has already been replaced once? - I'll pm you.

 

[Oneball]

Don’t know what the outside looks like but this is underneath

 

[Oneball]

 

[antijam]

Thanks for the piccies Tim. Your header bar riveting does look original but no sign of pimples, so not of use to me. Appreciate your offer.

 

[Roscobbc]

Got me looking at my '68, interested in what has occurred over the last 52 years. I found only two 'pimple' marks - both adjacent to the outer edges of the hood opening. looking for the underside the header bar only seems to have minor surface rust discolouration. The rivets don't appear to have the powdery appearance you'd expect from atmospheric corrosion. I'd be very surprised it the car hasn't had some paint over the years.

 

[antijam]

This is a potential problem for all C3's built between '68 and '72 when the steel header was riveted to a bonding strip which was in turn bonded to the nose section. From '73 on the header was bonded directly to the car. Not all cars are affected and I guess those from the drier Stares like California are less susceptible than those often exposed to a damp environment. With most of these cars now around 50 years old a large number will have been resprayed at some time in their life and any evidence of pimples removed. This doesn't mean they won't necessarily reappear.

If the car was just flatted before respray and the 'corrosion cavities' not exposed then the corrosion will continue and the pimples eventually reappear. If the bumps were excavated, cleaned out and filled before respray there is a potential problem of 'dimples' rather than 'pimples' appearing as the filler shrinks with age.

The solution mentioned above of removing the rivets and corrosion from below without breaking in to the glassfibre of the hood panel itself and then either bonding a new, or re-bonding the old, header bar to the still in place bonding strip does seem the most likely to avoid future repercussions. A good time to do this would be immediately prior to a respray when any minor surface distortions remaining after the repair can be corrected.

My problem is that my car has been resprayed at some time in the past and the finish is still good enough that another respray is not warranted at the moment - except that the pimples were almost certainly not addressed the first time and they are still visible.