Exhaust tape - rust on stock headers?


13 replies to this topic
  • Suikerland

Posted July 29, 2007 - 12:44 PM

#1

I'm running heat tape on my stock XR650R headers.
I've been told that because they're mild steel, they're going to rust to hell under the tape.
True or not?
Anybody run heat tape on stock headers for a long period?

  • Frank ZX

Posted July 29, 2007 - 01:02 PM

#2

I heard that Honda uses stainless steel on all XR(I'm not sure it's true)..
Heat wrap voids ALL header warrenties,so I think it wolud trap some moisture and gunk under the wrap.

  • cleonard

Posted July 29, 2007 - 04:03 PM

#3

I've been told that because they're mild steel, they're going to rust to hell under the tape.


In order for this to happen there needs to be water. The UAE doesn't sound like a place where you have to worry much about rain or condensation. As long as the bike is kept dry I don't think that there is much to worry about. If you park your bike outside in a place that sees a lot of rain then rusting may be a problem.

  • TREADMARKS

Posted July 30, 2007 - 03:16 AM

#4

I used the tape on my then new white brothers stainless steel big tube header. It helped alot with heat, but after 6 months in south florida they crumbled like potato chips.

No more tape for me.:ride:

  • Suikerland

Posted July 30, 2007 - 06:55 AM

#5

In order for this to happen there needs to be water. The UAE doesn't sound like a place where you have to worry much about rain or condensation. As long as the bike is kept dry I don't think that there is much to worry about. If you park your bike outside in a place that sees a lot of rain then rusting may be a problem.


Not much rain, but a lot of humidity.




I used the tape on my then new white brothers stainless steel big tube header. It helped alot with heat, but after 6 months in south florida they crumbled like potato chips.

No more tape for me.:ride:


Stainless??? I thought stainless meant no corrosion.

  • Kyron

Posted July 30, 2007 - 11:27 AM

#6

Stainless??? I thought stainless meant no corrosion.


With enough salt in the air I've seem PVC rust

  • martinfan30

Posted July 30, 2007 - 11:33 AM

#7

why would you want to cover up that nice finish?

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  • Rman of 237

Posted July 30, 2007 - 06:33 PM

#8

What if you painted the header with BBQ pit paint, then used the wrap. Wouldn't this protect against rust?:excuseme:

Rman...

  • TREADMARKS

Posted July 31, 2007 - 05:14 AM

#9

From what I've read, if you wrap the header it will lose it's ability to cool off and the header them becomes exposed to more heat that it was designed to. I did paint my header with vht high temp black before wrapping it.

Here is something I came across:

THE FACTS:

Header wraps are designed to keep the heat in the header to improve scavenging of the cylinders. Keeping the heat in the header allows the exhaust speed to remain high. (the right idea)
There are no header manufacturers that I know of that will warranty their headers if any header wraps are installed on their products.
In most cases the header wrap damages the headers beyond repair. (I will explain below)
If you run a lean mixture, you "may" see a slim performance gain using header wraps. A rich mixture may show slim to absolutely NO gain in performance.
If you do not mind replacing your headers and header gaskets regularly, and you like that ugly look of a wrapped header, go ahead and use the heat wrap.
BACKGROUND INFORMATION:

In the past, almost all NASCAR and other racing engine builders used the header wraps for the added power gains. But, after having to replace the headers after each race due to the wrap being about the only thing holding the header together, they do not promote the practice any longer! They now utilize the thermal coatings that are chemically and electrically applied to the headers. Those include Airborn, Jet Hot, HPC, and others.

Imagine having to replace a $1200.00 plus set of headers after each race weekend! Few but the most financially well-off race teams can afford to do this. But, it is also in the downtime for remaking a custom set of headers. Most custom header makers do not have copies readily available.

I believe that the wraps are good to protect various items from heat, but not to hold the heat in the header. For example: you can use the wrapping for the protection of fuel and oil lines, wiring, etc.

Cool air needs to be around the header, and insulating it with a wrap to hold exhaust heat in makes the header material temperatures near molten. When you wrap the header you trap the heat in the header, but also in the material that needs to breathe to dissipate heat for it's own survival.

Engineers, Metallurgists, and other experts out there will state that there is no way that the material can fail because it can withstand, and it was designed to withstand, the internal temperatures of exhaust gases. TRUE! But, when the header is not allowed to cool so as to dissipate those extreme temperatures that the wrap is controlling, you have now developed a heat absorption that compares to thermal friction which will will continue to gain in temperature beyond the normal exhaust gas temperatures (EGT's). This is the same as with most any insulation.

Try this experiment ... launder a load of bath towels and then dry them. Immediately pull them out of the dryer and just toss them in a snug pile on your bed. Now leave them there for a day and then open them. You will find that there is still a considerable amount of heat left in the center towels. This heat, even though the outer towels and bed are normal room temperature have been able to contain their heat. This is a simple thermal insulation test, but with your headers you have an internal heat supply coming from the engine. The heat on the outside portion of the header material is trapped between the warp and the header and will continue to fatigue the header. This build of heat is amplified by the wrap. Towels do not need to breathe, header material does.

The EGTs stay the same but the properties of the header material changes in a way of amplifying the temperatures because of the insulation. This action goes against normal laws of thermal dynamics, but this effect is fact, and you have to pull the ears off most engineers before they believe you. This is the trouble with plenty of education, but NO "common sense"!

  • Rman of 237

Posted July 31, 2007 - 12:39 PM

#10

Thats a lot of good info. I think I'll just leave them alone. I was hoping to cool the engine off some by keeping the header heat from radiating back to the cooling fins, not so much for an increase in performance. There is a thread where a guy puts a XR400 oil cooler on his 650 and I will try that mod instead. I know for a fact that my 400 runs 50deg cooler than my 650.

Thanks,

Rman

  • Suikerland

Posted July 31, 2007 - 12:39 PM

#11

Man this whole header wrap issue is a strange one.
I've heard some people trashing header wrap like it's poison, others have used it for years with no problem. I dunno.

I'm using purely for cooling purposes, not to increase exhaust gas velocity. I ride in extremely hot conditions (often deep sand) so every degree of cooling helps. Header wrap reduces radiant heat a lot (some have measured up to 300 degress diffrence on the headers), I can fel the difference. I need to keep as much heat away from the cooling system, head and tank as possible.

My only worry is corrosion / metal fatigue - some say it happens, some say not. I can understand metal fatigue being a problem on wrapped superheated (red hot) race car headers, but on a slower revving thumper... I don't know.
I'll unwrap in 6 months and let y'all know...

I was just wondering if anyone has first-hand experience of corrosion on wrapped XR650R stock headers - so far nobody.

  • Rman of 237

Posted July 31, 2007 - 05:27 PM

#12

Hey guys,
After thinking about this for a while I have an idea that may apply to the reason that wrapped pipes don't last.
Back in tech. school I took a metalurgy class and learned about tempering and annealing. To create a hard end product you heat a metal to red hot then cool it rapidly in an oil bath for example, but to create a soft workable product you heat it to the same temp but you let it cool very slowly in the kiln.
On a header, the mfg uses an alloy that can reach extremly high temps and cools off in ambient temp (after you turn off the engine) at a speed that when it is cool to the touch, the header is the same as it started.
When the wrap is used the header is cooling off so slow that you're actually annealing the alloy over and over and over every time you shut down the engine. The headers alloy is now altered from its original hardness weakening the metal in all aspects including its resistance to corrosion.
When I think about it like that it sure makes sense to me,:excuseme:

Rman...

  • HeadTrauma

Posted July 31, 2007 - 08:25 PM

#13

I would never use exhaust wrap solely for the tiny performance gains unless it was the absolute last thing on the mod list and lots of contingency/sponsor money was at stake.

However, it is very helpful where heat is problematic enough to damage things. I wrapped a mild steel header on a Honda Civic I used to have in order to keep the A/C lines from melting on it. After two solid years of daily driving, I had to pull it off to pass emissions testing. It came off looking like the day I put it on(externally), minus the cheap heat paint that was on it. Keep in mind I had no way to see if the tubes were thinner. Even so, I recommend using heat shields if you can.

On a side note, yes stainless can corrode. Technically it oxidizes. The high temps and acidic gases present in exhaust make this happen and it can even erode superalloys like Inconel over extended periods. With mild steel it is much faster; that's how exhaust wrap can cause headers to become paper thin.

Suikerland, are you experiencing overheating problems right now, or is this a preventative measure?

  • Suikerland

Posted July 31, 2007 - 10:23 PM

#14

Just preventative - it was advised to me by a bike shop owner who preps race bikes (mainly CRF's) and regularly does desert races here. I don't race, but I tractor around in deep sand in hot weather...





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