My left side pipe is very yellowed and has significant bluing patches...probably a result of the previous owner running that cylinder a bit too lean. Who has successfully removed it? How?
Autosol has a liquid abrasive polish for use on chrome or stainless steel specifically for removing bluing or stainless brown staining. It requires quite a bit of effort, but does work well with perseverance - an electric mop speeds things up. The drawback is that it works by abrading the surface and if repeated often, or the chrome is already thin, it will eventually break through to the nickel.
Thin-walled tubing seems to suffer more from bluing and a lean mixture making the cylinder(s) run hot will not help. Japanese double-skinned downpipes were one solution but heavy, and internally ceramic coating the pipe after plating to insulate it from the gas temperature is another option - at a price. I had been told by a plater (S&T) that when first fitting newly chromed downpipes, to start the engine allow it to get up to working temperature, then shut it down and allow the pipes to cool completely before starting again;this was supposed to prevent future bluing. I have not got to the engine running stage of my rebuild to try that yet, but plan to give it a go; it cannot do any harm, but I cannot help thinking it is just an old wives' tale.
The very word 'chrome' denotes the multiple colours available from chromium oxides. Since cosmetic chrome is essentially only a microscopically thin transparent layer over the silvery nickel plate, any abrasion will risk removing it altogether. I'd like to remove the blue from my 16H. If someone not associated with the snake oil sellers has a solution, I'm sure we'd all be using it.
I regard some exhaust blueing as an indication that the bike is used and used properly. If viewing a bike with immaculate shiny exhaust pipes, I would wonder if the engine is a runner or if so, if it has ever had more than a potter round the block. You used to see well thrashed Vincents where the exhausts were blued right round to the join but not any more. Too precious. A shame.
But that's just me.
Discolouration of the exhaust pipes near the exhaust outlet on any bike is perfectly normal. In fact its one of those fundamental science/physics things that occur when metal is heated and there is nothing that can be done about it. To be boring it is caused by the very hot exhaust gas heating the bend. The blue colour suggests that the temperature is somewhere in the range between 500 to 750 C range. A dark straw colour is somewhere around 200 to 400 C range if memory serves. These colours were used by blacksmiths as a guide when smacking bits of hot metal about on anvils, or for us more mature types when sharpening cold chisels and when hardening and tempering things in engineering workshops and the like.
As already mentioned if the exhaust it nice and shiny chrome it's either brand spanking new or it has not been used that much.
When I ride to Vincent meetings, I see a lot of them, some shiny pipes, some blue. Mine isn't blue, probably has always gone a tad rich. It's my preferred touring bike, more comfortable than any of my Nortons. Had to fit a new pipe to my Manx. Only took five minutes for it to get straw coloured, before I sorted out that it ran lean.
Earlier in this thread Andrew stated "and internally ceramic coating the pipe after plating to insulate it from the gas temperature is another option". A few years ago I replaced the exhaust manifold and downpipes of my BSA Rocket 3 and decided to try Kreem Blueshield to see if it helped to prevent blueing. I poured the stuff in all of the pipes with one end blocked-off and 'tumbled' the pipes to coat all of the internals. I left each coat for 24 hours and then repeated the process about four further times - the end result was that the pipes and manifold remained fairly un-discoloured (perhaps a little straw-coloured). This process only works with brand-new unused pipes. It's a bit pricey - £25.00 for 16oz bottle.
Opinions vary, but I was pleased enough ...
My Dommie has almost no sign of straw, and certainly no blue, after 20 years. My 16H went from bright chrome to dark blue in a matter of weeks. In fact it started to discolour from moment I first started it up after several decades of lay up. Side valves are notoriously hot, but the big issue at the beginning was that it was far too lean, and timing retarded, until the carb was sorted.
I use stain magic by yoshimura it removes all blueing and straw colouring, with no effort, but then you would need to set up carbs
Stain Magic by Yoshimura is an abrasive cream made for stainless steel exhausts and I for one, wouldn't use it on any chrome parts as it will almost certainly erode the surface.
I have an old container of Chrome Magic which was distributed in the UK by Auto Cavityseal, Manchester. This is an excellent chrome polish which produces a lustrous finish. Is this still available? There was a version for alloy too, AluMagic.