Cylinder head temp

[jetmech]

Anyone every measure their cyl head temp with a infrared gun? I recently got my 78 skunk running and the vm29 carbs run good but its pretty flat when giving it full throttle. I havnt done a plug reading but I'm not really concerned with the full throttle performance anyway. I just dont want to hurt it by being to lean. Anyways I used my infrared gun today after a long ride and it was 250*on the otbd cyl's and 280* on the inbd's. I dont know wether thats too hot or not. I measured it just next to each plug, figuring this was the hottest spot. Anyone know what the normal temp range should be? I know I need to take plug readings but havnt had the time or good weather yet. Thanks

[tkent02]

280 C or F?

[Steve]

I havnt done a plug reading but I'm not really concerned with the full throttle performance anyway. I just dont want to hurt it by being to lean. ... I know I need to take plug readings but havnt had the time or good weather yet. Thanks

Doing plug readings does not take a whole lot longer than getting temp readings, even with an IR gun.
And, ... your weather was good enough to get a temp reading? It was also good enough to get a plug reading.

You don't have to run the bike at full throttle to make it lean enough to affect engine performance and durability.
If your pilot circuit and needle circuits are too lean, you can fry the engine without ever seeing full throttle.

Your VM carb circuits are a little more flexible in tuning and don't rely on each other as much as the BS carbs do,
but you still need to check for proper jetting and operation on EVERY circuit for a happy engine.

.

[jetmech]

Lol

The temp reading was in F. And I knew I would be reminded to check the plugs. lol Which I plan on doing. But I only have about 2 tanks of gas on it (300 mi) since going thru the bike front to back, and I've just wanted to get some miles on it and see how it felt. Idle and part throttle are very good but like I said its flat under WOT. I guess what I'm asking is.. What is the normal temp that these bikes run at? Does 280*F sound hot? If this was a water cooled engine with that much water temp I'd be very concerned. But I swear I am going to check the plugs at all throttle settings..I'm just having too much fun right now

[tas850g]

i dyno'd my 850 and cylinder temps ranged from 195 to 210ish F about 1-2" outwards from the spark plugs with IR. I've been told the 200-220 is normal temps when dyno'd.

It's interesting by turning the air screws just 1/4 turn how much of a difference that makes on the air/fuel mixture on the dyno. I don't know how much that affected the cylinder temps though.

[81gs1100]

280 C or F?

Let us see... 548 degrees or 280 degrees, I wouldn't think someone would be able to sit on the bike with a 550 degree blast between thier legs.

Did you really need to ask F or C??

Go turn your oven to 450 Degress and sit it in

[Steve]

Let us see... 548 degrees or 280 degrees, I wouldn't think someone would be able to sit on the bike with a 550 degree blast between thier legs.

Did you really need to ask F or C??

Go turn your oven to 450 Degress and sit it in

Well, considering that the temperature of combustion inside the cumbustion chamber is well over 1500 degrees,
is it not possible that the temperature real close to the outside of the head might be over 500 degrees Farenheit?

.

[Agemax]

Let us see... 548 degrees or 280 degrees, I wouldn't think someone would be able to sit on the bike with a 550 degree blast between thier legs.

Did you really need to ask F or C??

Go turn your oven to 450 Degress and sit it in

haha like that!

[jetmech]

Thanks for the input guys. I did notice that the temp drops off quite a bit as you get closer to the edge of the cooling fin (obviously), more like the 210/220 F someone had mentioned. I'm just using the spot right next to the plug to be consistent. And man these things cool down pretty quick. After 5min I'll bet it drops 150*F. I'm not going to tune the bike just using this thing though. I had it, so figured I'd try it out. It is very useful and does help tuning though. Its kinda nice to read the exhaust temps cyl to cyl.

[Roger P.]

May not be directly applicable but guys on xs11.com have been reading about 300F on their cylinder heads, so yours doesn't sound out of line. I see almost 280F on my oil temp when stuck in traffic on my 1100 on a hot day.

[81gs1100]

Well, considering that the temperature of combustion inside the cumbustion chamber is well over 1500 degrees,
is it not possible that the temperature real close to the outside of the head might be over 500 degrees Farenheit?

.

Well, considering that the temperature of combustion inside the chamber is over 1500 for a nano second at the time of combustion and boyals law removes the heat via expansion and the oil, thin wall, and rings remove a bunch just before pushing it all out the exhaust by a fresh load of cool summer breeze.

The peak pressure and temp is only duing a few degrees out of the 360 of duration. Just slightly before top dead center compression, and a degree or so after.

How can you run your fingers through a flame of a candle or lighter and not burn it off. How many times can you run your finger through a flame before you start feeling its affects? 3 or 4 times a second, 8 to 10? And a flame is well over 800 degrees C in the center and 1400 degrees C around the outer core.

So no, I don't think it would be, and if it was there would be some problems popping up shortly thereafter.

[Bigbri]

I have been measuring the temp on my '79 850 with VM carbs at the base of the #1 and #4 plugs after fairly long rides. I felt that comparing those two plugs would give the most accurate readings. #1 is running at an average of 257 Degrees F and #4 is averaging 286 and the plugs reflect that difference. I just replaced the intake o-rings and need to sync the carbs again and address the lean plugs. Looks like plugs 2 & 4 are running lean.

[tkent02]

Let us see... 548 degrees or 280 degrees, I wouldn't think someone would be able to sit on the bike with a 550 degree blast between thier legs.

Did you really need to ask F or C??

Go turn your oven to 450 Degress and sit it in

Wadaya think?
C or F?

Sit on that.