Rear lights alloy blocks

[Mr Spigot]

Like, I suspect, many others with an MM or early Series 2 Minors with Lucas 471 type rear lights, the alloy blocks under the rear lights are a source of problems. On my 1952 MM, the screws holding the bezels on are in trouble; 2 have sheared off leaving a stub inside the alloy block, one has a wood screw in it, so the thread is now shot and the 4th seems to be hanging in there. I have yet to try and take the light units out but I would not be surprised if the screws holding them in have the same problem. I recently managed to acquire another pair of blocks but these also have sheared and stuck screws.
As shown in the photos, several of the screws have sheared off leaving a stub stuck inside the block. I managed to take one whole screw out after several hours applying Plusgas and others are still being treated. The combination of steel screws with aluminium alloy threads is known to be problematic, and I wondered if there is any firm out there who could drill these out and fit helicoils, which would seem to be a practical solution.

[geoberni]

Not just the earliest ones.
My late SII was rebuilt around 1999, long before I brought him.
They must have given up on the oval alloy blocks and bodged a couple of bases from 1956-63 type lights. Hence the slight misfit appearance.
So I can appreciate your difficulties with the oblong bases.
.

20170828_195623A.jpg (142.54 KiB) Viewed 810 times

20170828_200046A.jpg (153.36 KiB) Viewed 810 times

.

I managed to get a pair of repairable Oval bases, clearly not from the same car given the paint colours , in slightly worse condition than what you have.

I'm removing the corroded parts and using Milliput epoxy putty to restore them sufficiently to then drill new mounting holes.
I intend fitting bolts from the outer surface (i.e. under the lamp base) possibly with countersunk heads, and nuts under the wing.

Milliput is a very useful hard wearing epoxy putty.

20241124_143330.jpg (1.19 MiB) Viewed 810 times

20241124_143314.jpg (1.27 MiB) Viewed 810 times

[Mr Spigot]

That is helpful. Is Milliput hard enough to tap new threads in? I had wondered about using JB Kwikweld.

[geoberni]

That is helpful. Is Milliput hard enough to tap new threads in? I had wondered about using JB Kwikweld.

I don't personally know about tapping threads into Milliput, and I've never used JB Kwikweld, so I can't directly compare.
I get a feeling Kwikweld is runnier, more like araldite when squeezed out of the tube, whereas Milliput requires slicing off like Plasticine.
There's quite a few videos of using Milliput on youtube.

The makers do claim "Once fully cured Milliput can be machined, drilled, tapped, turned, filed, sawn, sandpapered and painted."

[dp]

I've never found any of these substances to be particularly good at taking a thread and holding it. Better to either use the material to hold a metal threaded sleeve or nut. Or a threaded bar with a nut embedded in the stuff if you need a male thread sticking out.