C3 Rivet Bumps

[Patrick B.]

Has anyone developed a method of dealing with the bumps that occur on 68-72 C3's due to corrosion of the aluminum rivets on the headlamp support bar that does not risk damage to the front surround panel. It seems to me that it would be possible to cut off the peened end of the rivets and remove the steel bar leaving the bonding strip attached to the surround. Next, a spot weld cutter (a very small hole saw with spring loaded pilot) could used to make a 1/2" hole in the bonding strip beneath each rivet to remove the corroded rivet from beneath without cutting the into the surround panel. The steel bar would then be bonded to original bonding strip using whatever kind of adhesive that was used on later C3's to attach the headlamp support bar without the use of the corrosive rivets. The integrity and paint of the surround panel would not be affected, and I am hoping that bumps may settle down at least partially over time on a car with only a few mild bumps. Certainly it would prevent any further growth of bumps.

Has anyone already tried this idea?
What was the adhesive used on 73-81 C3's without rivets.
Does anyone know where I could get a piece of a wrecked surround with the headlamp bar in place to practice this idea?

[Dick W.]

Re: C3 Rivet Bumps

Lord Fusor adhesive

[Paul O.]

Re: C3 Rivet Bumps

Patrick if you are going to go thru the trouble of separating the metal header bar from the fiber glass bonding strip. You can remove the whole assembly as one unit. I have done it several times you have to remove everything that is attached to the header bar. Lights, horn, fender supports etc. I would then use several different widths and length also flexible putty knifes. Breaking the bond from the surround and the bonding strip you have to take you time and a lot of patience and persistence but it can be done.

With the header bar out I would then separate the bonding strip and metal support drilling out the rivets. When that is completed and you glue the 2 section back together make sure to remove the excess adhesive from the rivet holes. You then can take several rivets and cut sections of shaft off then flatten and expand the rivet to appear as the one you originally removed then glue them at the rivet holes. This give it a original appearance now you can reinstalled the header panel.

The adhesive that was used later I do not know what type it was but there are many brands of adhesive available today.

As far as practice panels swap meets are the best but you may find some locally on you local Craigslist.

Paul 18046

[Patrick B.]

Re: C3 Rivet Bumps

Thank you Dick and Paul. I went to the Lord website and they show many kinds of Lord Fusor. The type 116 was intended for attaching metal to plastic so that must be what the factory used.

I had originally thought the thing to do was to take the metal bar/bonding strip assembly off the front surround and replace the aluminum rivets with stainless steel, but I was warned that this was a dangerous approach if one wanted to keep their original paint and avoid possible damage to the front surround. Paul, were your successful experiences with cars that were being restored and repainted or those that being treated to avoid the progression of the bumps without repainting?

[Paul O.]

Re: C3 Rivet Bumps

The cars I worked on were full repaints but did this before the original paint was removed with no ill effects to the existing paint. but like I said this was a long and tedious process moving slowly and with great caution. We are talking days not hours if I added the total time in hours would be around 18 to 24.

Paul 18046

[Michael D.]

Re: C3 Rivet Bumps

...Patrick if you are going to go thru the trouble of separating the metal header bar from the fiber glass bonding strip. You can remove the whole assembly as one unit. ...

I agree. No need to replace the rivits. Bond the header to the bonding strip and reinstall. The bonding agents available today are stronger than what was available back in the day.

[Patrick B.]

Re: C3 Rivet Bumps

Paul: Did you have to take any precausions regarding the fit of the hood to the surround panel during the operations you described. Does the nose droop with the steel bar removed? Does the clamping of the bar/bonding strip assembly during adhesive curing introduce any waviness to the surround where it abutes the hood?

[Joe L.]

Re: C3 Rivet Bumps

Has anyone developed a method of dealing with the bumps that occur on 68-72 C3's due to corrosion of the aluminum rivets on the headlamp support bar that does not risk damage to the front surround panel. It seems to me that it would be possible to cut off the peened end of the rivets and remove the steel bar leaving the bonding strip attached to the surround. Next, a spot weld cutter (a very small hole saw with spring loaded pilot) could used to make a 1/2" hole in the bonding strip beneath each rivet to remove the corroded rivet from beneath without cutting the into the surround panel. The steel bar would then be bonded to original bonding strip using whatever kind of adhesive that was used on later C3's to attach the headlamp support bar without the use of the corrosive rivets. The integrity and paint of the surround panel would not be affected, and I am hoping that bumps may settle down at least partially over time on a car with only a few mild bumps. Certainly it would prevent any further growth of bumps.

Has anyone already tried this idea?
What was the adhesive used on 73-81 C3's without rivets.
Does anyone know where I could get a piece of a wrecked surround with the headlamp bar in place to practice this idea?

Patrick------


My expectation? I would expect that in the process of trying to remove the rivets from below there will be inevitable further damage to the exterior paint surface.

[Patrick B.]

Re: C3 Rivet Bumps

Joe:

Certainly there is a risk of cutting deeper than the thickness of the bonding strip to free the rivet head. But I think a pressed-on collar around the spot weld cutter could be used to limit its penetration to a safe depth. This method seemed less dangerous to the surround panel than splitting the bonding strip from the surround with the skillful use of putty knives. Of course the reason I am looking for a hunk of a wrecked car for practice is to discover the complications before attempting this on my own car. Do you see any rivet bumps on your car or have you solved the problem somehow?

[Rich P.]

Re: C3 Rivet Bumps

One of the problems I see with this is that as the rivets have already expanded causing stress on the top surround and weakening each spot you will be still left with bits of contaniments in the hood surround when you remove the rivets. You have to remember the factory shot blast the underside of the hood surround to aid in bonding the header. When they did this the fiberglass coat was opened and now you will still have bits of corrosion left in the glass. You would be suprised at how far the corrosion travels in the underside of the glass.



Rich

[Paul O.]

Re: C3 Rivet Bumps

Patrick have not been on for a few days but when I did the removal we still had the bumper and all the supporting items still attached. From what I could tell there were no changes to the position of the surround after reinstalling the surround the fender supports at each end of the bar were in the same position.

If you leave the header bar off for a few weeks and let if warm in the sun or some heat lamps the raised rivet areas in the fiber glass almost disappear and after several months the were totally gone.

For the reattachment I used some wooden strips on top and had to use very light clamping pressure and had no ill affects.

Paul 18046

[Patrick B.]

Re: C3 Rivet Bumps

Thanks Paul. Your experience is very encouraging.

[Joe L.]

Re: C3 Rivet Bumps

Joe:

Certainly there is a risk of cutting deeper than the thickness of the bonding strip to free the rivet head. But I think a pressed-on collar around the spot weld cutter could be used to limit its penetration to a safe depth. This method seemed less dangerous to the surround panel than splitting the bonding strip from the surround with the skillful use of putty knives. Of course the reason I am looking for a hunk of a wrecked car for practice is to discover the complications before attempting this on my own car. Do you see any rivet bumps on your car or have you solved the problem somehow?

Patrick-------


There is not even a hint of a rivet problem on my car after almost 42 years. However, my car has lived in California for its entire life. I think that road salt-induced corrosion is the main "instigator" of corrosion for these rivets and my car has never experienced road salt.

[Terry M.]

Re: C3 Rivet Bumps

I believe salt air/mist can do it too, as can any moisture. Coastal areas or places with high humidity would lead to this problem, but Joe is well inland. The same can not be said for all of California.

The principal corrosion source is galvanic action between the aluminum rivet and the steel support. All that is required is the presence of moisture, as in high humidity and rapid temperature changes, to create a primitive battery between these dissimilar metals. I can't get into the chemistry of this action, but I know materials that are far apart on the Periodic Table are prone to this phenomenon. The rest I will leave to those with a chemical dependency. I know there are several Chemistry PhDs on here, and they can go into it further if anyone is interested.

[Kenneth B.]

Re: C3 Rivet Bumps

I believe salt air/mist can do it too, as can any moisture. Coastal areas or places with high humidity would lead to this problem, but Joe is well inland. The same can not be said for all of California.

The principal corrosion source is galvanic action between the aluminum rivet and the steel support. All that is required is the presence of moisture, as in high humidity and rapid temperature changes, to create a primitive battery between these dissimilar metals. I can't get into the chemistry of this action, but I know materials that are far apart on the Periodic Table are prone to this phenomenon. The rest I will leave to those with a chemical dependency. I know there are several Chemistry PhDs on here, and they can go into it further if anyone is interested.

I agree Terry. I am not a Chemistry PHD but I did stay at a Holiday Inn. Aluminum will oxidize & form a white powder salt like substance. Look at aluminum valve covers & trany castings on a car that has been setting a long time. My 70 coupe from MI.with original paint has no bumps nor my 454 from OH.but my 70 conv. from NC. did have them. FEB,March & April builds.
KEN