Using phosphoric acid prior to undercoat

Hi,
This might of been covered before but wasn’t able to find any reference to it.
When prepping Lister D for painting, I intend to wire brush crankcase to bear metal, then apply a diluted phosphoric acid solution
What I would like to get clarification on, (1) do you wash it off before it dries, and (2) would it react to the undercoat if left on? I will be using Paragon Anti Corrosive Zinc Phosphate Grey Primer
I’m more inclined to wash it off, dry, give casting a final quick rub down then apply undercoat
Once again your comments greatly appreciated!
Mark

Hi Mark I'm not at all familiar with the stuff but I do wonder why you think you need it?
Since starting this hobby a little over a year ago I've stripped back to bare metal 7 engines and 5 water pumps. Before priming I wash them with white spirit and kitchen towel until there's no blackness left on the towels then leave to dry.


I buy this 6 cans at a time making it very cheap. Its almost £12 a can locally so a big difference
https://trade-mart.co.uk/products/action-can-rx-90-red-oxide-primer-ral-3009-500ml


As with any painting method try it on something that's not important firs.

If you're stripping back to bare metal mechanically there won't be any rust left that the primer won't fix

Thanks Andy, yes brushing to bear metal, then a rinse with white spirit does seem an easy option, just I know there will be some small hidden areas that are rust traps ready to jump out! So using phosphoric acid to get to thoses areas was my intention.
I could still apply phosphoric acid, rinse dry then go over with white spirit prior to painting
I do like the undercoat spray you mention! Any idea what temperature that will stand up to?
Mark

No I don’t know but it’s on all my engines so as hot or hotter than any of them

The worst that can happen is the green will go darker over time.

Maryalice