Thanks for the ideas on my last thread about this. This was a job that I was not looking forward to... but when you open the petrol cap and see rust on the inner lip and rust / peeling sealant on the tank inside it starts to nark you after a while.
Forgot to take before pics so you will have to take my word for the start condition.
Stage one was getting the petrol tap off and then making a blanking plate to replace it (see pic) I did not want to refit the petrol tap whilst treating the tank in case it attacked the alloy or ruined the very fine nylon gauze filter which sticks up into the tank (unlike the Z1s and earliest 650s) which have a filter inside the tap. Incidentally I found out that the intake to the tap is about one inch up inside the tank - which explains how I ran out of fuel when I could still hear it sloshing around the tank - but that is another story.
Stage two was to fill the tank right up with descaler/ rust dissolver and slosh it round for a couple of days plus getting a long handled wire brush inside to shift the lose stuff. The rust around the inner lip came off pretty good (see below) and I have given it a light smear of oil to help protect it from going off again.
Stage three was to drain the descaler and treat the remaining sealant that was still stuck fast with nitromors - this loosened it and let the rust dissolver get beneath it when I put it back in. I didn't bother washing out the nitromors - but the descaler was water based and that diluted it away.
You need a long handled brush and a strong nerve to apply paint stripper through the tank filler hole!!! It would be far better to do it if the tank was being repainted altogether I guess - and there are obviously recesses where the brush can't get to - but I figured if the sealant was stuck fast and out of sight then let sleeping dogs lie. The final image shows what you can now see when you open the cap - which I think is fine for a 32 year old tank.
I then finished off by swilling some old petrol through and then topping it right up with new super unleaded - no leaks so far!! By the way I used a syphon to remove the solution from the tank until about a quarter left then you could tip it over and unscrew the blanking plug to let the nasty sediment out. The descaler I used was called Proscale 650, it comes in a 5 litre concentrate and you dilute it with water.
**** on the petrol tap watch out for the clear nylon washer that goes on the tap drain bolt - I nearly lost it and couldn't work out why it was dripping when reassembled!!****
and finally Esther!!! all back together again. Cheers again for all your tips - From Mark
