different cylinder temperatures? Should I worry?

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Nielsen

Nielsen

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Oct 2, 2013
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Partly as a result of advice here, I scrapped my incorrect manifold and Amal carb for a new manifold and a 34mm Mikuni, new cables, plugs, wires, etc. on my '74 'Commando'. The Norton now starts on the third or forth kick, and I suspect that'll only improve. Starts first kick after it is warm. Here's the thing: I took it for its first highway run, a fifty mile jaunt at a pretty steady 60-70 mph. It ran really well. When I got home I discovered that the left exhaust had blued quite a bit--which it wasn't before--but the right hand one seemed just the way it was before. I can only assume that the left cylinder was running hotter. How can that be with a single Mikuni? I have a Lucas electronic ignition. I pulled the plugs and both looked the same. Should I be concerned about this or is it much ado about nothing? here are photos of the two exhaust pipes:
different cylinder temperatures? Should I worry?
[/urldifferent cylinder temperatures? Should I worry?
 
Since we have to assume both jugs are now running at equal mixture, the other variable that can have a direct impact on exhaust temp is ignition timing. If you have access to a timing light, check both sides for equal full advance.
b.t.w., mine went from a steady 48 mpg with the stock 932 Amals to 58 mpg with the single Mikuni. And, no; the Amals were not running overly rich.

Nathan
 
I have seen greater differences than your, mine for instance.
I have read here on more than one occasion that the left burn slightly hotter simply cause it is on the far side of the lubrication. I really am not sure about that but it seem common the left does burn hotter on many bikes.

I think that a simple plug change on the hot side to an 8 from a 7 might bring some equality.
Unless it gets really bad, which yours seems not too bad, then I would not be overly concerned.

However, you should make sure that everthing, carbs, valve gap and the like are in good nick.
 
if you have an intake manifold leak on one side that lets in more air, it would account for a leaner, hotter cylinder.
 
One carb means same mixture r/l and electro ignition gives same spark time on each side. As bluing is before the cross over consider exht air leak &/or more guide oil leaking in LH to lower combustion temps on that side even if not visible smoke. Its possible for push rod tunnels to leak air into one side though don't know if so much it can cause pipe to lean blue.
 
It might be worth picking up an infrared thermometer to see how much difference there really is...it won't be terribly accurate on a reflective surface like a head pipe but seeing the relative difference is useful. You can get a decent one for $50 or so and they are handy for all sorts of things...

different cylinder temperatures? Should I worry?
 
A compression test to ensure that both cylinders are working approx equal could be useful too.
You have checked your tappet clearance (on top of the valves) that they are all in spec ?
 
Nater_Potater said:
Since we have to assume both jugs are now running at equal mixture, the other variable that can have a direct impact on exhaust temp is ignition timing. If you have access to a timing light, check both sides for equal full advance.
b.t.w., mine went from a steady 48 mpg with the stock 932 Amals to 58 mpg with the single Mikuni. And, no; the Amals were not running overly rich.

Nathan
Click to expand...


I got 63 mpg out of my twin amals, riding very quietly though I must admit. Surprised me.
 
I asked the question why my 850 had blue pipes and my 750 had gold pipes. The answer was the 850 was running rich. I proved that when I got the 850 running better. Its on the lean side of perfect. the pips are slowly changing back to gold.
Go figure. [ I could not argue with the comment made to me, but now I can confirm it. ]
all the best. Dereck
 
I have seen greater differences than your, mine for instance.
I have read here on more than one occasion that the left burn slightly hotter simply cause it is on the far side of the lubrication.
Click to expand...

LOL go look up Harley head cooling by over expensive extensive oiling experiments to see how silly that concept you read on this forum. Oil can not cool or heat combustion chambers and exhaust temps, it can only cool springs and help friction heat a slight bit. Cdo oil flow though head is so restricted there is nil temp difference from which side gets oil fed in and none on combustion temps unless some getting into chamber and tend to stifle combustion as seen by clean metal on combustion surfaces where oil get in. If enough oil to smoke then of course can coke up whole surface.

Both pipes bluing or tanning don't relate to one sided differences. The blue side is the most common color seen on well tuned hi throttled cycles so it might be the tan side out of whack.
 
Nater_Potater said:
Since we have to assume both jugs are now running at equal mixture
Click to expand...

A single carb doesn't necessarily guarantee both cylinders get the same mixture.

I'm not saying this is the problem, only that it is a possible cause: spark-plug-color-t7699.html
 
I would make very sure that the tappet settings are the same (set evenly allround)....

Blue pipes = retarded to me (and hot) and or the valve is closing very late due to big lash gap or worn cam lobe!!

That what i think!
 
L.A.B. said:
A single carb doesn't necessarily guarantee both cylinders get the same mixture.
Click to expand...
I agree with L.A.B.
I would think it's very unusual to get equal mixture distribution to 2 cylinders from one carb.
You can usually fix it by facing the carb more toward the lean cylinder. Mill the manifold flange on an angle.
 
You will have to excuss my old age...but i allways thought slightly rich was cooler? 50 years and had it wrong all this time :oops:


kerinorton said:
I asked the question why my 850 had blue pipes and my 750 had gold pipes. The answer was the 850 was running rich. I proved that when I got the 850 running better. Its on the lean side of perfect. the pips are slowly changing back to gold.
Go figure. [ I could not argue with the comment made to me, but now I can confirm it. ]
all the best. Dereck
Click to expand...
 
I agree with bluto about actually checking the two pipes' running temperatures before going through a lot of questionable work to maybe solve a non -problem. The plugs looking the same is more of an indication that the mix is equal than one of the pipes being a little bluer indicating it is not. Another reason to wait a bit is the pipes themselves. The aftermarket what it is today does not always equal original standards no matter where the parts come from. The two pipes could very likely have been made and chromed at different times with especially the chrome plating being of different qualities = pipes of different shades with the same heat.
 
LOL its essentially Impossible to get enough unequal mixture to cause one side only to thermal stain pipe from a single carb on a Commando d/t the very short-clear manifold path - unless something leaking badly or blocking badly - don't waste much time on that dead end. On engines with 3 or more cylinders a single carb is well known to feed each one somewhat to a lot differently d/t the longer differing manifold paths to each jug. We have a # of reports of missing a inner manifold bolt that went through engine unknown and no pipe color or performance evidence, discovered by surprise going in for some other reason. Valve sealing or timing, air leaks intake &/or exhaust or ring sealing and internal gasket issues are about only one sided factors on single carb, cross over pipes with electro dual wasted spark engines. Its rather expensive to get an IF temp sensor that can read over 1000'F for header temps but cheap thermo needle in pipes for EGT and plug rings for CHT with combined or separate needle meters such as ultra light air craft or go cart guys sport.
 
The color of the chrome IS an indicator of temperature. Chrome forms oxides that depend on the temperature of formation.....purple hottest, then blue, then gold, etc. Once the oxides form, the process is not reversible... that is, blue does not turn back to gold if the temperature is reduced.

In my experience, all normally tuned motorcycle engines eventually had their chrome pipes turn some shade of blue-purple/blue. Vee twins always had the rear pipes a deeper shade, or the color band extended over a longer length of pipe. I am wondering why Nielsen's right pipe has remained gold.....perhaps not enough time at temperature....perhaps a lower temp than left cyl. It is the mis-match of temperatures that is abnormal, not the blue color.

Hobot and others have made good points regarding mixture and timing .... that is, hard to attribute temp diff. to mixture (one carb) or timing (EI). That leaves a leak as likely cause.

A clamp on thermocouple, attached just forward of the exhaust nut in the same place relative to both cyls, would be a way to measure exhaust gas temp. difference between cyls. I realize this equipment is not available to most.

Slick
 
There is some reason the fuel/air mixture is burning at a different rate in each cylinder. Ratio of mixture, ignition timing and compression will affect the burn rate. A compression check may be in order.
 
possible there is nothing at all "wrong", nothing to be concerned about

could well be that, as often happens, the application, the thickness, of chrome is just different from one header pipe to the other

this is frequently discussed on many MC forums
 
Hm now there's a thot nothing wrong at all as such a small blued section might of just been direction of wind hitting LH most on this short period of use so far. Amend on thermal stains being permanent unless rubbed off till running out of chrome layer. Really over hot by mix or spark or both leaves a foot+ long deep blue-purple shine. Beware some chrome remover pastes leave a dull finish that more distracting than shiny colors. I got exhaust wrap when gets too ughly or even rusty to deal with, which interestingly makes front of engine clanging/ring-tinging sounds distinctly dulled down to pleasant exht note more apparent.
 
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