What does header temperature tell me?

[ChicagoRob]

Howdy.

I bought one of those HF non-contact laser temp things and measured the temp on the header right by the head on the boy's 80 550L after a shakedown ride. The temps read as follows:

1 - 235
2 - 280
3 - 280
4 - 200

What's that telling me? 2 & 3 too lean? too rich? Nothing at all?

Thanks,

Rob

[mike-s]

The inner two cylinders regularly run hotter than the outside two as they have less surface area to cool them. They are also usually run a little richer than the outside two to have a cooler burn and have the excess fuel that gets spat out help draw extra heat away.

[ChicagoRob]

Thanks.

I get that #2 and #3 should be a bit hotter but, boy, there is a pretty big differential here.

I guess what I'm trying to do is find a "The Proof is in the Pudding" test to see if I have all of the things that control combustion setup properly. I'd think that if everything is good and in sync, the temperatures across all four cylinders would be roughly the same. Granted this isn't the same as measuring the actual exhaust gas temp, but it should be a good indicator.

For example, #4 is running much cooler than the others. Doesn't that indicate some sort of problem with it or maybe the others?

Rob

[spyug]

Have you looked at the plugs? I'm thinking 1 and 4 are bit far apart and one will be richer than the other ( or leaner depending on your point of view).I'd be thinking they should be within about 5 degF (give or take) with each other. I'd also think the inners versus outers would be a tad closer too but I don't think it really worth worrying about. Bottom line is they are never going to be all bang on the same.

Interesting post.

Cheers,
Spyug

[Big T]

I agree, you now need to pull all 4 plugs, so a comparison can be made

[ChicagoRob]

I agree, you now need to pull all 4 plugs, so a comparison can be made

I guess that it's time to add plug chopping to my repertoire.

Is there a definitive guide on how do it ?

Rob

[850GT_Rider]

Howdy.

I bought one of those HF non-contact laser temp things and measured the temp on the header right by the head on the boy's 80 550L after a shakedown ride. The temps read as follows:

1 - 235
2 - 280
3 - 280
4 - 200

What's that telling me? 2 & 3 too lean? too rich? Nothing at all?

Thanks,

Rob

All of these non-contact pyrometers are dependent on what's called "emissivity", or the ability of the material being measured to radiate energy.

To keep it as non-technical as possible, a shiny surface and a dark surface will radiate differently at the same temperature. If one exhaust pipe is shiny and one is dulled even slightly, a non-contact pyrometer that is not compensating for emissivity will produce different readings on the two surfaces. Even the angle at which the pyrometer is at in relation to the pipe can affect the displayed temperature.

I would not place much stock in the different readings and certainly would not try to tune the bike that way.

Plug chop instructions are here:

http://members.dslextreme.com/users/bikecliff/images/highest_rpm_plug_chop.html

[ChicagoRob]

Thanks for this.

The first time that I read it I called BS. Sure there would be some error but it surely had to be within what I'd consider acceptable. (Say 5%)

To test it out I safety wired the probe style thermometer that I use for candy making to one of the headers (#4) and started the bike. I let it run for a bit then shut it down. The contact thermometer stabilized at 154. The non-contact read 101! Ouch, what a piece of crap.

I checked the inners and the probe read much lower than the non-contact. Grrr.

Back to the drawing board.

Thanks again for pointing this out.

Rob

[850GT_Rider]

No problem.

The non-contact (infrared) pyrometers we use at work cost many hundreds of dollars, but we use them primarily to identify temperatures in a broad range as opposed to precise measurements. (More interested in "Is is 250F or 350F?") Even at that, the setup requires compensation for emissivity.

On the chart in the link below, look at the difference between polished nickel (which is comparable to chrome), and then oxidized nickel - it's almost a 10-fold difference. So varying amounts of oxidation would have significant effects on infrared emissions and therefore on displayed temperature on the pyrometer.

http://www.engineeringtoolbox.com/emissivity-coefficients-d_447.html

[OldVet66]

The accurate temperature readings may be way off, but they can be used as a guide. fairly consistent readings would at least let you know that you were getting close. I wouldn't use it to determine if you were rich or lean, but when you do get it tuned properly the readings however inaccurate will be fairly close for each pipe with 1-4 being a little cooler.