Blue Header pipes

Honda made double-skinned pipes to stop the outers bluing but they rusted between the skins. Any bike with chromed exhausts will discolour to some extent. I quite a bit of bluing - it's a sign that they're being used.  How bad are yours ?

Had a similar problem with my Mk 3 after a major engine rebuild fitting brand new header pipes without balance pipe. Right header just yellowed a bit but the left one really went blue. Dropped the needle down to bottom notch (to richen mixture) on left cylinder Amal carb only and fitted new header pipes with the balance cross-piece. Bluing disappeared with left pipe now just yellowed like the right one.

I have heard that Harpic Max works well on stainless although I have to confess am too scared to try it myself.....

Painting the inside of the pipes at the head end with high temperature cylinder head paint (matt black) has prevented my Speed Twin pipes bluing. The pipe on my ES2 is well blued, I didn't do it for that bike. I quite like it, actually.

All my bikes pipes are Blued , shows they get ridden and are not pampered exhibits.

If the discolouring is going down to the silencer joint then something is either very amiss or the pipes are not correctly made, highly unlikely as it can only be exhaust tube. With bluing this far back I would not be surprised if they glow at night. 

I know you have checked the settings, but if you can get to someone with a gas analyser they will tell exactly what the issue is. It will be quicker and easier than a strip. 

Ignition timing on MK3 should never be out using the slot on the crank viewed through the hole in the right hand crankcase. 

If you have an original failing MK3 cam, no matter what settings you have on the carbs it will make no difference. Surprisingly it will still deliver some performance even with a fair bit of a lobe missing, but the cylinder fill will be way out, most probably lean and may explain why performance has not been fully lost. I have kept my original cam as a trophy, I suspected something was wrong when I could not keep up with other Commando's at very high speed and yes it was well above 70. If you are using your MK3 up to this sort of speed, the cam condition will not be evident as many MK3 owners well know the surprise when see what is left of the original MK3 cam when stripping the engine.

Chromed Exhaust pipes go blue due to various factors. The usual causes being that the metal is too thin and/or the chroming poor. A weak mixture can also add to the misery.

Original Norton pipes were so well made that you could clean them with a wire brush before giving them a good polish with Chrome cleaner. The main tubing and flanges were generally of a decent thickness which also  prevented them cracking near the exhaust port. The base metal was copper coated and then a layer of Nickel followed by layers of Chrome added to give a durableand  shiny finish. I don't believe they are made this way anymore.

My 961 came with Stainless exhausts which both quickly blued near the headers with the remainder turning an almost uncleanable straw colour before making its first 500 mile service..

Phil,

The clue here is that the discolouring can go as far as the silencer clamp! Not good. 

When metal is heated it goes through colour changes. Clock makers of old would blue metal to give it an attractive appearance. The blueing of exhaust pipes is unavoidable due to the heating from the exhaust gases. On a good quality pipe it is normal to see the blueing around the bend in the pipe but this should not continue along the straight section of the pipe. 

Hello the Causes of Bluing it one over advanced ignition timing and weak mixture   of the carburetors  one or the other or both,                                Yours   Anna J  

Maurice, 

The set up you explain suggests that you will be running the rich side of OK, which should not be an issue. If using the black air box, remove the venturi's if they have not fallen out already, these are really restrictive. 

When the weather permits get some miles on it and get the bike on a dyno. For what a straight forward dyno test costs, it really does give a good picture of what is going on and saves the guessing. It will also enable a good base from which you can make changes, and have more confidence what that change will do. A decent dyno should be able to record the changes from tickover to full throttle and combine it with gear changes, the operator should check this prior to the full throttle runs, if the carbs are not metering correctly then there is no point doing the final runs. 

If the pipes still blue with your current settings, then I can only think of two things, unburnt fuel in the header igniting, or the pipes, could be many reasons, chrome, material or overly polished prior to chroming. I certainly don't think you are running lean. 

Maurice:

Can you say where you got your pipes?

Maybe others who have bought from the same source have had similar problems.

The bluing of the pipes can be caused from a number of different situations as I think you understand:

1. carb(s) out of adjustment re jets and needles

2. poor quality chrome

3. Air leaks on carb side resulting in a lean mixture

One step at a time.....

Mike

Thirty five years ago i fitted a SU carb to my first MK3 and the pipes turned blue after just a few minutes.

With the original Amals they were just slightly discoloured (single pipes, no balance pipe)

Fast forward to 2015 and I fitted a SU to my next MK3 and the same thing happened. I'm of the opinion that the SU enables the engine to run leaner. One has to use the choke on startup unlike the 'tickle and go' amal routine. I used to say that amals were the closest thing to uncontrolled fuel injection going. I sometimes wonder if my earlier bike had worn carbs? I have no experience of the new premier amals though.   

Correct me if i'm wrong, Didn't Bert Hopwood dislike the amals? and he fitted a SU to the Norton 76

as it improved fuel economy and hence emissions.

I know it amazes people when i tell them i regularly acheive over 80mpg         

Peter

SU are well known to be economical, and the Amal motorcycle carb is of course far simpler than most types used on large vehicles. The SU does need a pressure drop across it to hold the slide open so it is not as good for maximum possible power from a given engine size. In the real world that should be irrelevant because if you need to regain those few horse power you can just fit a bigger engine. But racing doesn't allow that, nor (often) do or did national motor vehicle tax laws. I'd say the worst aspect of racing formulae is that they artificially force designers to look for max bhp for a given engine size whereas logically we want max power we can afford to buy and maintain.

But back to blue pipes. Retarded ignition is a principal cause, because naked flames end up pouring out past the exhaust valves. Or to put it another way unburnt fuel burns after leaving the cylinder. It also seems unavoidable with modern lean burn engines with cosmetic pipes (like modern Triumph Bonnevilles).

And the chrome layer over the nickel base is extremely thin. There seem to be arguments about where the blue really is.  Either a crystal structure change within the chrome or an oxide effect on the nickel surface. Either way it comes to the same thing. It is not just on the surface and if it is polished away then that's the chrome you've got rid of. Indeed if polishes do work that pretty much shows it is a change in the chrome crystal structure and is less visible when there is even less chrome.

But I'd like to find a technical ( academic) write up rather than rely on forums on the web.