Tank badge thread insert

[simonmurphy]

I'm recommisioning a G12 CSR. Inside, the petrol tank is a mess of rust and flaking sealant from an earlier restoration. One of the badge thread inserts has also partly corroded away and I'm obviously looking to repair it. Does anyone know of a suitable thread insert? And, Por15 or Redkote once the tank's cleaned out?

[jackstringer]

Many it the older tank sealants don't like the new ethanol fuels. So you may have to get a remover for the sealant and then treat and re-coat with a modern variant. I remember reading up on a place that sells the sealants but they also do rather good repairs, cutting the tank open to repair the rust and remove the sealant lumps that some people end up with. Ah here it is, https://www.biketankrepair.co.uk/

I have a 5ltr bottle of "Evapo-rust" rust converter stuff that does a good job of stabilising the rust before sealing.

With regards to the thread I am not sure, somone will be along shortly. I suspect BA or Cycle.

[simonmurphy]

Thanks Jack, I'll take a look at Evapo-rust

[bigwol]

tank badge thread should be 2BA I believe

[clive]

tank badge thread should be 2BA I believe

That was my thinking but I was not sure about later machines.

[dave16mct]

No It's 3BA up to 61, not sure if a bigger thread was used for the knee knocker badges. I'll take mine off later and have a look.
Dave.
PS what year is it Simon?

[dave16mct]

Just had a look and my '63 with kneeknockers has 2BA roundhead screws. Earlier models with round plastic badges etc.were 3BA raised head countersunk.
Dave.

[simonmurphy]

It's a 1963 (twin carb) with countersink screws for the badges. I've seen that some people use JB weld and then drill and tap a new thread. I was hoping to use a new insert but can't find anything suitable.

[simonmurphy]

managed to fit an M4 helicoil that the original screw seems to like.

[Groily]

Sounds par for the course if the originals are 3BA.
3BA = 4.1mm by 35tpi near enough, thread angle 47.5°.
M4 x 0.7mm = 36tpi near enough, at 60°.
So a 3BA screw would go in OK and probably stay put despite the angle thing. (Or a new M4 one if available in similar form?)