Aussie P5NC restoration - help needed

Hi all, First post.

I have a set of P5’s which are around 30 years old I believe. During disassembly, this noob managed to shear off a couple of heads off of the 1/4" pan head screws, leaving the shanks in the bell ends.

In order of success, the following have been attempted at extracting the shanks:

WD40 & PB blaster (both a waste of time)
Drilling out the core of the shank, welding a nut and attempting to undo the screw (failed miserably as the nuts sheared off the shanks)
Simmering/boiling in alum… for days (waste of time)
Soaking in 70% nitric acid (not concentrated enough), had a small effect which seemed to wear off.

So now I see two options:

  1. Fuming nitric acid (>90% concentration), or
  2. Reverse anodising in sulfuric acid, to dissolve the steel

Has anyone had success at either? I’ve garnet plasted the horns back for painting, have new gaskets and seals, and the removal of these shanks is the last step. Would anyone know what grade of aluminium was used by Nathan with the new cast horns? I may need this for the anodising company.


Welcome to the forums. Congrats on the P5’s.

Sounds like you’ve had a pretty good go at it. I am not familiar with the different chemical methods that you mentioned. If you have access to a drill press, you can attempt to drill the bolt out completely. Try not to veer off into the threads. If the threads get damaged, you can always drill and tap for a helicoil insert.

Good luck - and keep us updated with your progress.

Welcome to the forum. I think ear2ear covered it well enough. DBO is in Australia and he might have some input.

Thanks for the comments guys.

I have drilled out some shanks to basically the minor diameter of the screws such that I stopped there with fear of running into the aluminium. So the next step was a chemical one. I understand helicoils are an option, but I’d like to keep the horns original if possible.

Greetings and welcome to the forum. That bolt saga doesn’t sound like fun. Drilling them out is probably still your best option. Sorry… can’t offer much help on that topic from the net.

What are you thinking with the anodizing? … I approached a few people in Brissy with wanting a Leslie done and they all advised against it. They reckon the alloy won’t color evenly and look quite patchy.

Thanks DBO,
Anodising is not for a surface finish, the process is to dissolve the remains of the screws out. Then the horns will be painted.

Oh OK. Sounds serious - never seen anodizing used that way.

… lol, we’ll find out if it works, or simply results in a pile of aluminium particles at the bottom of the anodising tank.

I’ll keep this forum updated as I progress the resto. I also have an ex RS-3L and Wabco A/B horns in the works.

I am sure you will get the screw remains out. Just be careful of the chemical dips…Some years ago an acquaintance soaked a rare-as-hens-teeth Leslie A-125-3E in a chemical bath and came back the next morning to find only the bronze bracket…The aluminum horns had completely dissolved…

Yes, it pays to understand the chemistry, otherwise bad things can happen!