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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: DavidATL on January 21, 2018, 09:12:38 PM
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Maybe you have some data?
A month or so ago, I was goofing around with my IR temp gun waiting for the K75 t-stat to open and for the fan to start cycling. I wanted to confirm proper operation of the coolant system after changing the cap and cleaning it out. I discovered that the exhaust header temperatures varied from cold in front to hotter toward the rear cylinders.
After a 70 mile ride today, with everything hot and reasonably stable, I left the bike idling in the drive way and checked the temperatures. #1 (at the front) was around 230 deg F, #2 and #3 were around 320 deg F (all measured about 1" down from the flange on a 45 degree angle to the bike centerline). Well, a difference of 90 deg F didn't seem like a good thing. I searched the net including this forum for normal header temperatures, but came up sadly empty handed. I see that RBM, Martin, and alexis921 have noted temperature differences among the 3 or 4 pipes that led in some cases to injectors needing attention. However, other than referring to things as "cold", I didn't note any specific temperatures listed.
Example
http://www.motobrick.com/index.php?topic=10674.0
I don't have a manometer and I have no idea if the throttle bodies have every been checked or balanced. There are light blue paint seals on various adjustments and they don't appear to have been disturbed. All three Bosch spark plugs look normal and quite similar and were recently changed to baseline them. Long therm, I'd like to investigate using the thermal IR gun to adjust the throttle bodies but should eliminate injector issues first.
So, does anyone have some 'normal operating condition' data? Temps of #1, #2, #3, and #4? What temperature does each of your cylinders run when warm?
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What's more important is even temperature between header pipes. You need to take the temperatures after a fast run and at idle. you need to take the temperatures as close as possible to the cylinder head, all at the same point. On my bike a K75s I need to remove the belly pan in order to get accurate readings.
Regards Martin.
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I don't have numbers from my bike I'm afraid, I used a plastic cable tie which clearly showed that number 2 cylinder was colder at about 1" from the cylinder head. I know that my throttle sync, tappets, injectors, spark plugs, piston crowns and compression pressure are ok because I've checked them. I haven't swapped or replaced plug leads or coils.
Regarding your measurements, having spent many years testing engines on dynamometers, 90F is a significant difference, particularly at idle. The more important test though would be under load and at higher speed - hard to do unless you've got some instrumentation. How do your plugs look? That might give you a clue to fuel mixtures. Do you have an endoscope so you can look into the cylinders?
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The unknown mileage Bosch plugs are attached. Replaced with new Bosch in December with same part number.
Bike has 21k miles.
The temperature delta was present before the plug change and has not changed much if any.
Should I interpret 230F as cold and possible leaking injector *or* 320F as hot/lean and a leaking throttle boot (not checked for yet) or throttle plate imbalance?
I know the delta T is likely a bad sign - the unknown for me is which extreme is bad?
A project on the back burner for me: thermocouple data capture (via arduino) of all three exhaust ports while in motion, under load, WOT, etc.
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Hard to say about the absolute values of the temps without knowing more about how they were measured, though 230F looks low. This is supported by it being different to the other 2 cylinders. The plug pics look ok to me but there isn't really enough detail to be sure. If you can log temperatures under load as you suggest then that would be great. If you can measure gas temperature in the centre of the pipes that would be ideal but you'd need to weld on thermocouple bosses to do that.
Unless one of your plugs looks wildly different to the others I wouldn't worry too much at this stage. I would recommend a cylinder pressure or leakdown test though, if only to put your mind at rest a bit!
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Measuring 1" down will induce variations, I don't know why. But after trying various positions I concluded the best position to get consistent even reading was as close to the cylinder head as possible. And in order to do so I had to remove the belly pan.
Regards Martin.