I recently put a rebuilt engine in this truck following failure, and am now tidying up “odds and ends.” I have a junkyard header panel (what the cosmetic grill and headlights bolt to) from the local “Pick a Part,” and it is 95% intact; a definite improvement over the original! However, there is a small piece on the new one that’s missing that I overlooked when pulling it. As a consequence, the passenger side headlight is secured by only 2 of three points and wiggles in use.
So my intent is to use adhesive to patch in the small part of the original that isn’t damaged. To do this, I need to know what plastic it is, and what adhesive to use. So far, I can say:
-black plastic
-where broken, it has “granular” appearance, like cast metal might if broken.
-Red-hot fork tine produced minimal melting when applied to plastic
-When exposed to flame, burns with small, yellow flame. Just barely sustains combustion on its own. There is some black smoke, but not overwhelmingly sooty. Not much of an odor; just a hint of “sweet, chlorine-ish” scent. (Like chloroform, only way less so.)
Is this ABS? Or some sort of thermoset? What would be a good adhesive to use?
In one of my service manuals it listed how to identify the type of plastic but must be buried somewhere. Fiberglass won’t work so maybe JB which seems to stick to everything or possibly the bumper cover repair which is a lot like JB.
Any name brand 2-part plastic epoxy should work. I once did a temporary repair on a broken plastic radiator coolant inlet for my '98 Jeep Cherokee that lasted for years. I was going to replace the radiator but never had to because it never leaked.
So this stuff burns but does not melt?? Or did I read that wrong? If it melts, it is a themoplastic, if it only burns, it is a thermoset plastic.
And it is structural? Must be because the headlights are mounted on it.
Maybe SMC - a thermoset plastic sheet. I’d test a small spot with polyester resin intended for fiberglass. If it sticks well, fix it with that. If it doesn’t stick, try an epoxy fiberglass resin like used for boats. That stuff sticks to anything! And the fiberglass cloth will reinforce the area and make it way stronger than JB Weld alone
One thing I have learned from doing these type of repairs in the past is that the mechanical bond of the adhesive alone may not be sufficient. At a minimum, I drill some holes through both pieces, inside of the area that will be bonded with the epoxy. Then make sure to force some of the adhesive through those holes to both sides. Those holes will act like rivets to hold the two sides of the JBWeld (or whatever adhesive chosen) together and to the base material. Of course, some structural metal bonding plate is better and can use the same approach but I’ve found it really enhances even just the epoxy strength if used alone. Considering a heavy lamp assembly will be working against this mounting point, some structural enhancement would be preferred for a lasting repair…
If you have some scrap material to work with (I guess you do from the tests you already ran on the material) try to find a solvent weld like they use for plastic plumbing drain pipe. Try and get as much overlap as possible. If you have to butt ends together, try and cut an extra piece to overlap the butt joint.on both sides. Solvent weld (if it works) is the best stuff I can think of. I have used the plastic bonder and JB weld before, and solvent weld works much better. I have never been able to break a solvent weld.
For added strength use small (1/8 or smaller) screws and nuts on the overlap like . If you position it first, drill your screw holes next, then weld it together using the screws as a placement guide, you assure correct alignment of the part… Look in the plumbing section of any plumbing store/department for an “all purpose” solvent weld that lists several types of plastic it can be used on.
Based on your description of the header panel, it must be a thermoseting polymer. Rough up the area you apply the adhesive repair to so that it sticks better.
