Unofficial Royal Enfield Community Forum
General Discussion => Tech Tips => Topic started by: fredgold52 on February 07, 2008, 08:14:59 pm
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I've seen pipes turn sort of yellow and I've seen them turn deep blue. Can anyone provide a simple explanation of what the colors mean / what causes them?
Thanks,
Fred
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I think it depends on the exhaust header manufacturer as to whether it is single or double skinned. Then there is the question of mixture and is it weak or rich or perhaps correct!
The deep blue normally says it is getting very hot so might be running weak or the timing is out. Straw coloured I think is fine (Ie mixture and timing correct).
Lots of variations on a theme here!!!!!
I stand to be corrected so................. :D
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I think it depends on the exhaust header manufacturer as to whether it is single or double skinned. Then there is the question of mixture and is it weak or rich or perhaps correct!
The deep blue normally says it is getting very hot so might be running weak or the timing is out. Straw coloured I think is fine (Ie mixture and timing correct).
Lots of variations on a theme here!!!!!
I stand to be corrected so................. :D
I didn't say which sort of pipe I was asking about. I meant to ask about our RE pipes which are single layer.
Good to hear about the 'straw' color. Mine's developing sort of a yellowish hue as I gain miles.
I saw a picture of one of our Classics here. Great looking bike but the pipe was very discolored and dark blue looking. That's what made me ask the question.
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Mine is 'straw' at about 1700 miles with some very light blue 'rainbow'. This is just at the first bend out of the head.
My dealer checked the carb float needle and balanced the idle circuits after fixing the sticky throttle problem under warranty. So my pipe color is assumed normal and I'm not running lean on my box stock Sixty-5.
My plug readings are normal.
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My experience has been: Yellow first, then if they get hot enough, purple. My favorite were the headers on my '72 Yam 650 XS2: Pretty purple, blue and yellow.
Yellow = hot
Purple = real hot
Or as I like to think of it:
yellow = fast
purple = real fast
IOW, "Purple Pipes Mean Fast Bikes"
OK, it makes about as much sense as some other biker stickers...
Kidding aside, the extreme lean running conditions of modern engines sure lends to purple pipes!
Matt
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OK, so what I'm learning from this so far is, Yellow = Normal, Decently Tuned, Jetting is close. Blue or Purple = Too Lean, Timing too advanced or too retarded.
Is that close???
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I have always preferred jetting to be a little on the rich side, but usually my pipes blue. I think it happens when I'm stuck in a lot of traffic. I time my engines by ear and exhaust backpressure, It has worked very well over the years.
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OK, so what I'm learning from this so far is, Yellow = Normal, Decently Tuned, Jetting is close. Blue or Purple = Too Lean, Timing too advanced or too retarded.
Is that close???
Blue and purple don't have to mean too lean. They just mean hot.
All of this depends and several factors, not the least of which is pipe construction. How thick are the walls? Does it have an inner lining?
Unless it has an inner lining most modern, OEM-tuned bikes will have some discoloration - and usually with some purple. They run lean (and hot if air-cooled) - but all within design parameters. No harm no foul.
My bikes with purple pipes have run hot - but some (like the RE) are not running lean - and are running well. Color is not always an indicator of the state of tune.
In past years aftermarket free-flowing header pipes were often thinner than OEM and without a liner, hence the purple discoloration. This is where (in my mind) purple was equated with fast. The fast guys had always popped on a Kerker or SuperTrap as part of their performance upgrade so they were fast and purple! (maybe I should have explained that up front....)
Matt
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I can tell you that I watched my brand new pipe turn yellow on the FIRST exhaust stroke after it was installed. Then at idle, by 15 seconds it was blue, went out for a ride and it came back yellow, which is how its been ever since. Go figure. I dint think the colors mean anything about engine state. But probably says something about pipe construction, materials, etc.
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I agree, Cyrus. Pipe construction is absolutely a critical part of this equation. But if we restrict the discussion to the stock RE pipe, that should take some of the variation out of the process. What you describe sounds wild. Went yellow right away, then blue and finally yellow again. I wouldn't have thought it possible.
Mine is just the lightest yellow, but it really hasn't been exposed to any heat yet. All my 150 miles have been done in 40 degree F and colder air.
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The quality of the chrome job has a lot to do with it also, and I have noticed that the Indian chrome in general is lousy. I didn't add that some of the chrome instantly blistered like house paint, also on the first few strokes.
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Mine doesn't seem to be changing colors yet at 260 miles.
jon
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Mine doesn't seem to be changing colors yet at 260 miles. jon
Sure, Jon, but wait until you go out for a longer ride when the temperatures are above 50 degrees (can't come too soon for me!).
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Very hot summer days and creeping in stop and go traffic will turn the pipe. Even some slight brown patina on the cylinder head - just like the old BSA and Triumph days.
Thank goodness for synthetic oil!
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Good point.
jon
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"Thank goodness for synthetic oil!"
But only after the break-in/running in period has been completed to your satisfaction!
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Sooo,What do the colors mean? Don't know, but I can tell you in the metals world blue and purple are cooler than yellow(straw).
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Sooo,What do the colors mean? Don't know, but I can tell you in the metals world blue and purple are cooler than yellow(straw).
But in the 'real world' of engineers blue and purple are definitely HOTTER!!!! ha ha
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Really? heres my world....
Metal Temperature by Color
--------------------------------------------------------------------------------
Color Approximate Temperature
°F °C K
--------------------------------------------------------------------------------
Faint Red 930
500
770
Blood Red 1075
580
855
Dark Cherry 1175
635
910
Medium Cherry 1275
690
965
Cherry 1375
745
1020
Bright Cherry 1450
790
1060
Salmon 1550
845
1115
Dark Orange 1630
890
1160
Orange 1725
940
1215
Lemon 1830
1000
1270
Light Yellow 1975
1080
1355
White 2200
1205
1480
--------------------------------------------------------------------------------
Use of this site indicates you accept the Terms of Use
Copyright © 1995-2003, Process Associates of America. All Rights Reserved.
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Really? heres my world....
Metal Temperature by Color
--------------------------------------------------------------------------------
Color Approximate Temperature
°F °C K
--------------------------------------------------------------------------------
Faint Red 930
500
770
Blood Red 1075
580
855
Dark Cherry 1175
635
910
Medium Cherry 1275
690
965
Cherry 1375
745
1020
Bright Cherry 1450
790
1060
Salmon 1550
845
1115
Dark Orange 1630
890
1160
Orange 1725
940
1215
Lemon 1830
1000
1270
Light Yellow 1975
1080
1355
White 2200
1205
1480
--------------------------------------------------------------------------------
Use of this site indicates you accept the Terms of Use
Copyright © 1995-2003, Process Associates of America. All Rights Reserved.
You're talking a heating temperature color that disappears when the metal cools. And it looks like a ferrous metal chart. Bikers are talking crome plated mild steel with a permanent hue to the chrome plate after cooling. It's all in the chrome! ;)
Think your pulling our leg! :D
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They are heat treating temps, as you can see blue and purple (being cold colors) are not even on the chart. If you take a piece of polished steel and slowly heat it you will see all those colors. Note that I said polished, just like the pipes. Blue and violet are allways the first colors to appear, and at a temp you can get in a household oven.I blue clock hands in this manner,You only see the colors vividly if the metal is highly polished. Try it yourself.
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They are heat treating temps, as you can see blue and purple (being cold colors) are not even on the chart. If you take a piece of polished steel and slowly heat it you will see all those colors. Note that I said polished, just like the pipes. Blue and violet are allways the first colors to appear, and at a temp you can get in a household oven.I blue clock hands in this manner,You only see the colors vividly if the metal is highly polished. Try it yourself.
That is simply not true in my experience. My motorcycle pipes have always yellowed. Those that have thinner walls in the exhaust header and/or have run much hotter go on to blue.
Matt
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Hey, whatever, these are just some facts that might apply. This table might apply even more to the pipe colors.
[old attachment deleted by admin]
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Hi Cyrus,
Your second table seems to line up more with what I always thought about exhaust pipe colors. It does seem to be almost the opposite of the heat treat color table you posted first. What is the second table talking about and why is it different from the first table.
Now I'm all screwed up. Possibly information overload, it'll do that to me ya know.
:)