916 Etc Headlight Glass Replacement

Having been unlucky enough to have a stone take a chunk out of my dipped beam lens I was faced with prospect of trawling EBay to find a complete headlight unit (expensive) or replacing the damage lens. There’s loads of guff on the web about removing car headlight lenses for various reasons so having been lucky in getting given a 916 headlight unit from BOOTSAM with an intact dipped beam lens I thought to give it a go.

Most of the web posts will tell you to heat the unit up in the oven at around 110C and the lens will push out of the housing, the first thing I can tell you is that this is bollox. It may work on some car lights but certainly not the two 916 headlight units I’ve tried. The adhesive used to secure the glass into the plastic housing is some sort of thermoset material; this means that once cured it will not return to a liquid state by heating it again ( rather like trying to unscramble an egg by reheating it).
I tested this by cutting a piece of the “overflow” material from around the glass and put it in the oven at 185C for half an hour; it stayed solid and didn’t change state in any way. I didn’t bother to test at higher temperatures because there was no way that the plastic housing would take it without distorting.

So faced with the fact that conventional wisdom wasn’t going to do the job, the only way of getting the lens out was to cut it out. Maybe there’s a solvent but it would probably destroy the housing too. Fortunately the adhesive is quite easy to cut: unfortunately the plastic housing is brittle so any levering snaps the thin sections off. The glass lens is fitted into a U channel in the plastic housing so there is adhesive on the 3 sides.

Step 1: It’s easy to get a thin blade knife into the outside edge and run it around the glass.

Step 2: Next, Dig out most of the outside adhesive with a small jeweller’s screwdriver to reveal the bottom of the channel. In theory you could skip this step but it gives you more room to get the knife in for the next step.

Step 3: Get a reasonably sharp kitchen knife, heat up the end to red hot and bend the tip of the blade (about 6mm-see pic) at a right angle. This stops your woman from stabbing you with it when she sees what you have done to it. You could of course point out that it was either the knife or stinking the house out for hours heating plastic up in the oven ( this would be pointless but she doesn’t know that).

Step 4: Not ideal but necessary: cut a small section of the outside lip of the channel away (see pic) so you can get the knife in to cut the adhesive at the bottom of the channel. The cut-out only needs to be wide enough to accommodate the end of your bent knife blade and a screwdriver (see Step 6)

Step 5: Run the knife around the glass, cutting through the adhesive at the bottom of the channel. A fair amount of force is needed in places but a bit of twisting and pushing should see it go all the way around. As mentioned earlier the outside of the channel is thin and brittle in places so try not to do any twisting and levering there.

Step 6: Now we only have the inside edge to deal with but after cutting away 2 sides the adhesive bond is quite weak. Get a screwdriver under the glass in the cut-out you made for the knife and twist. You should see the glass start to move and by pushing a thin blade (I used a 1mm thick by 20mm wide stainless putty knife) between the glass and the outer lip, lever gently avoiding the thin side walls. Gradually work the blade around where you can whilst increasing the size of the “twisting” screwdriver to suit. Worn down old screwdrivers without sharp edges are best to save the glass from chipping too much. Your lens should now come free.

Step 7: Cut and scrape the rest of the adhesive out of the channel and off the glass. At this point you can get the fog off the inside of the lens with a toothbrush and glass cleaner.

Step 8: Clean the glass and channel and stick the glass in with the adhesive of your choice. I used a black Gutter and Roofing sealant from Wickes and let it cure for 24 hours with tape wrapped around to hold it in place. I guess any silicone sealant / adhesive would do the job.


Tools Needed

Bent Knife

Cut-Out in Channel

Headlight Glass Removed