As part of the the running gear refurb for the Mk5 4×4 RS000 I needed to re-zink some of the bolts so thought I would add an article on some of the different methods I have tried over the years to clean parts before dropping them off for zinking.
This is the process of feeding a DC current through the part you are cleaning creating a chemical reaction. do a quick Google and there are loads of websites and videos with instructions of the different ways to set up your tank and mix in 5 to 10 millilitres of washing soda per litre of distilled water and how to connect your power source.
After a couple of hours fizzing you can check your part and clean of any oxide with a soft brush and wipe, I used this method for the fan brackets below from my Mk2 Mexico heater box, before building it back up. the pictures below show the bracket after Electrolysis and before re-zinking and after build up.
You can see that if the metal was pitted before it will be pitted after, but once zinked still looks good
I also tried a small blasting cabinet as an alternative to Electrolysis, obviously it has a higher set up cost and more abrasive but is a lot quicker and a less faffing about! I’ve not got round to trying different media yet but the results are as good as electrolysis for the bits I’ve done.
While the methods above are fine for brackets and larger items they are a bit more of a pain for smaller bolts, washers and screws. For these I have tried a couple of different acids.
Citric acid is easily available and biodegradable so easy to dispose of when finished. Mix 5g citric acid with 400ml warm water (Can’t say I am very accurate on this bit!) I fill a jar add the bolts and then give it a good shake after a couple of hours.
leave it in until the rust is removed, normally leaving it for a few days and also giving the jar a shake.
When the bolts come out they look very black but wash them with clean water, dry them off and brush off the oxide and have a look at the results.
The bolts are a bit pitted depending on the amount of rust they had to start with.
No mixing for this one and nice and cheap! just fill the jar with distilled vinegar to cover the bolts and leave them, I tended to leave for a good few days like the citric again shaking every now and then and end with a wash and brush. Results to my eyes seemed better than the Citric acid but not much in it.
Been reading a few articles that say this stuff is better than the different acids for rust removal due to not removing metal once he rust has gone? But it costs a lot more than a bottle of distilled vinegar! but thought I would give it a try. Same process as before soak in a jar, until the rust has gone and then a good rinse in clean water and a wire brush to remove any oxide.
To test I did 3 of the front subframe bolts in Evapo-rust and 3 in citric acid soaked for the same time 4 days
The ones done in Evapo-rust are below on the left, Citric acid on the right and I think the winner is the Evapo-rust! Will see how many bolts I can do with this current bottle and see how it work trying to reuse a couple of times. If the rust is not that bad I would use the distilled vinegar.
Another tip from doing this test, these subframe bolts are a bit bigger and managed to crack both of the glass jars I’ve been using for smaller screws for ages while giving them a shake! so have upgraded to some plastic paint tubs from Wilco’s, Lots better!!