SOHC.co.uk Forums > CB500/550

To blast or not to blast

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Ashdowner:
My 1978 Keihin P46A carbs have got the battleship grey coating on them. They look pretty grimy compared to the rest of the bike which is shining up nicely. Has anyone had similar carbs blasted and if so was it just a clean or did you get the grey coating blasted off as well? I worry that if the coating is removed the carbs would oxidise pretty quickly and look grimy again. 

kent400:
Soda blasting carbs is the only safe method but ideally you need to totally dismantle them. I recently remove the float chambers on my 400f to replace the float valves and found quite horrible stains inside the chambers so inside the ultra sonic cleaner they went but it didn't have much effect on those stains. Looking around I found a bottle of clean spirit, stuck some in one, left it for half an hour with an occasional brush around and it shifted the stains. Pleased with the result I washed the whole carb bank off with the stuff, to be fair they weren't too bad but even so there was a significant improvement.

Clean spirit does not smell and it's water soluble. Available from B&Q and Homebase. Can't remember the cost maybe £4 for 1500 ml. Might be worth a shot!   

royhall:
Totally stripped my 750 carbs and had them Vapour Blasted by a company that really knows bikes (you dont want some muppet blasting the insides). They came up like brand new so I was really pleased. Six months later they were back to the exact same battleship grey they started at. That was 2.5 years ago and to date they haven't oxidised.

Trigger:

--- Quote from: royhall on February 28, 2017, 07:08:02 AM ---Totally stripped my 750 carbs and had them Vapour Blasted by a company that really knows bikes (you dont want some muppet blasting the insides). They came up like brand new so I was really pleased. Six months later they were back to the exact same battleship grey they started at. That was 2.5 years ago and to date they haven't oxidised.

--- End quote ---

The carbs don't oxidise as much as the engine alloy. And to get a good coat of oxy, the bike needs to be left outside in all weathers.
As Roy as said, to have anything vapour blasted, you need to know that the blaster knows his job. Otherwise it will end tears  :'( :'(

andut:
Soda blasting is the safest method as it's much easier to remove the blasting media, but the finish is a matt grey whereas aqua blasting with fine glass bead will provide a like new satin sheen to the aluminium that I personally prefer.  The downside to wet blasting is you have to be very very careful to ensure all the media is washed out, but it's perfectly possible if you make sure you completely strip the carbs and make sure you know where all the cross drillings go so that you can flush and blow them clean.

Maintaining the satin finish following wet blasting is an on-going routine though and requires regular cleaning, so if you'd rather not do that, or you're not confident in getting to all the drillings in the carb bodies, then I'd suggest soda.

Andy

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