header pipe

Not open for further replies.
Sep 20, 2005
Country flag
Hi guys

Why would one header pipe (left) on my previously rebuilt 1975 mk 3 commando get way more discolored than the other one?

Check the carb adjusts/air leaks...sounds like one barrel is running weaker/hotter than the other...discoloration/rainbow appearance of the pipe is a result of high temp, which all pipes will be exposed to....think new pipes will all do this to an extent....but if only one does it....points to temp/mixture differences :wink:
thanks for the reply, I will have a look. the plugs look the same though and the bike runs really really strong
hewhoistoolazytologin said:
Maybe then I'm off in left field...but it does seem to be a temp thing.

thanks hew, I believe you are right. I just pulled off the carb (single mikuni) and put new gaskets on the head at the manifold and I also checked the exhaust (which was tight). I dont know what else it could be. The bummer is that the header is already blued up a lot so I dont know how to check if I have fixed it or not. Any Ideas?

Think some chrome polishes advertise that they will remove the bluing on the pipes. I've seen blue pipes many times over the years and they all seemed to be new pipes...with apparently a too lean mixture to thank for it....but maybe it's just a "new pipe" thing too, to some extent, could be they just aren't made to the same specs as the original ones, or maybe they just need to "cook in". I have never had it happen and if it ever did...I couldn't remember it now anyway......my pipes are still the original ones......original scratches....original missing chrome and lots of original rust...if mine ever got "blued".....only an archaeologist would know....... :lol: :lol:
You say you have a Mikuni......you are not the only one in the forum with a single Mikuni...and different symtoms on each barrel.......Hummmmmm......Alice had it right when she said "Curiouser and curiouser"......
Polish it out and let us know what happens...if it happens again....might have to learn to like it :lol:

At the risk of starting something ugly again :cry: , here's my two cents;
Still running points? check the timing, one cylinder might be running advanced and that will make it run hotter. The bluing is caused by the copper plating migrating through the chrome as a result of high temps. Even when the motor is running spot on this will happen but when it happens to one side only there's something amiss.

Thats what makes this forum work! Scooter has a really good suggestion and I bet he's right about his thinking you have points....and...... we won't start any nasty stuff here again either.....WILL WE......???????

Please not........

Jason has a point too...if I recall correctly..... :lol: :lol: :lol:
thanks all, I do have a boyer in the bike. I will try to polish it out a bit and report back after running it up


were the header pipes bought at the same time form the same place? I have heard of differences in chrome quality causing dofferent colour changes on pipes
Geoff said:
were the header pipes bought at the same time form the same place? I have heard of differences in chrome quality causing dofferent colour changes on pipes

Hey Geoff, they were indeed bought from the same place at the same time.
if you can get a temperature probe like a non contact infrared handheld setup or an exhaust temperature setup from a snowmobile and stick the thermocouples up through the pipes close to the ports you can measure the temperatures of the individual cylinders and compare them to see if its a chrome thing or if the cylinders are running differently...a cylinder head temp guage will also give you similar results...also check to see if your valve settings are the same for both cylinders or take a really good look inside th head and make sure that you have the pushrods properly seated in the rocker sockets and that the rocker shafts are put in in the right orientation...a compression test or a leakdown test will tell you if one cylinder is running differently than the other...might be a bad valve or a broken ring but normally that would make one cylinder run cooler than hotter....put a timing light on each plug and check to make sure that the timing is really the same for both cylinders..maybe try 2 different plugs or switch them side for side .we wont get into the boyer thing just yet but be sure and let us know on this one...good luck barry
thanks barry, I did do a compression test and both cylinders are the same. I did just adjust the valves. How do you check the pushrods without pelling off the head? I will check the timing on both cylinders also. I wont beable to run it up till next week but I will post when I do

The only Nortons that i have ever seen with shiny exhaust pipes were on trailers. I believe that if you ride them they will get discoloured.

Checking temperature is not as easy as you think unless you use seperate cylinder head gauges. You will drive yourself crazy trying to use a hand held unit . Just ask my shrink. The distance over 1 inch can be 50 to 75 degrees different on the same pipe. I always figured that setting the carbs would be so easy by dialing in the temperature. When my bike ran well there was 100 degrees different from side to side. That was confirmed using two different pieces of equipment . If you go that route i would think that you will find the temperature about 550 degrees F at 600 rpm when you check 3 inches out from the exhaust nut. Bring lots of beer along because you will go crazy trying to figure out a way to get both temps the same . You just won't rest until you do.
off hand...I'd reason this isn't going to get solved for fourperf.....by all he says, the machine runs well and the only complaint is the color of the pipe. Ron might be right...readings will be so questionable that in the end all you will have is a headache from the beer, an overheated motor, an angry wife and still no answer. Check the basics.... skip the beer, and go for a ride...polish as directed......

PS....the rocker shafts, and the seating of them, can be seen through the exhaust rocker covers...it is indeed possible to put on a head with one of them not seated....just ask me....I know :lol:
thanks for all the replies everyone. I think I will live with the one discolored header. Everything else seems fine
hey fourperf.....if you take off the rockerbox covers you should be able to see inside with a flashlight...its pretty crowded in there and i cant remember whether its through the front or the back you get the best view...think its the back...been a while...you might ned a mirror to see around all the frame stuff but when you get the covers off its pretty obvious as i recall...anybody else got any tips on this? barry
Not open for further replies.