How to properly measure Head Temperature

Discussion in 'General Questions' started by StrontiumEthics, Apr 23, 2012.

  1. StrontiumEthics

    StrontiumEthics Motored Bikes Sponsor

    I have installed a PUCH high compressure head and have been doing some testing. To my surprise i've getting some weird numbers like 450fah, when my mixture is properly tuned (according to spark plugs). Prior to this the engine temperature was never tested. I have a Nieko IR thermometer.

    In short, how does one properly use the IR thermometer? these temperatures are definitely not normal

    Also, is there another way to accurately measure head temps?

  2. StrontiumEthics

    StrontiumEthics Motored Bikes Sponsor

    also 650fah exhaust temperatures. lol outrageous. I didnt bother starting things up.
  3. jaguar

    jaguar Well-Known Member

    If I recall right, up to 500 degrees is OK for a head temperature. It gets higher with more compression.
    Some people use thermocouple washers under the spark plug to measure the temperature.
  4. MikeJ

    MikeJ Member

    Don't be too quick to question your measurements. Your meter is closer to reality than you think.

    I looked up cylinder head and exhaust gas temps from a Lycoming air-cooled aircraft engine site. Your head measurment is in the same ballpark. And keep in mind that gasoline burns at 1300 degrees to a lot hotter, depending upon how rich or lean your mixture is. I have seen lawnmower exhaust pipes glow cherry red when running the engine hard. So your 650 F reading is really too cold. A thermocouple device about 2 inches into the exhaust gas flow from the cylinder would give a more accurate measurement. So scan your exhaust pipe real close to the cylinder; the reading will probably still be low.

    Maybe a calibration check: scan a pot containing boiling water. I will bet your meter displays real close to 212 F.

  5. Cavi Mike

    Cavi Mike Member

    Exhaust temps get ridiculously hot. So hot it can make iron glow bright red. Not-so-much on a 2-stroke but 650 even seems low to me.
  6. StrontiumEthics

    StrontiumEthics Motored Bikes Sponsor

    Wow! I must say that I am shocked none the less. I was reading here that optimal head temperatures were around 250- 300 fah and was freaking out. I just ordered some SIG castor oil. Going to put a touch of that alongside my royal purple synthetic oil.
  7. corey872

    corey872 New Member

    If you're using an IR gun, several factors can come into play. I won't go into all details here. You can read up if you want:

    But the two main ones to deal with are field-of-view and emissivity.

    In short, the gun looks at a certain field and measures it's temperature. Even if you have a laser dot, the temperature comes from an area around that dot. Generally guns have an ~8:1 or 9:1 ratio...8 inches away, you're looking at a 1" diameter spot, 16" = 2" diameter, etc. Trouble can arise when things like the spark plug, exhaust pipe, carburetor, cooling fins, etc get into that field of view and could skew the reading either higher or lower than the actual head temperature.

    Second, emissivity - basically how 'bright' a material shines in IR light. A perfect radiator is 1.0 - most everything else is less. Most guns are calibrated to about .95 which approximates quite a few surfaces, general paint, etc. Shiny aluminum, stainless steel, spark plug porcelain, etc will usually make for a error.

    For the best IR reading, you'd need to paint the head flat black (.95 emissivity) and take a reading close enough that only the metal of the head is viewed, not the spark plug, exhaust pipe, fins, etc.
  8. Fabian

    Fabian Well-Known Member

    Hi Strontium

    Send me a PM and i'll send you a link detailing how to set your bike up to accurately measure cylinder head temperature and Exhaust Gas Temperature as an accessory option for the bike.

    The worst i've seen has been 557 degrees Celsius with around 480 to 500 Celsius in normal operation - Exhaust Gas Temperature
    Cylinder head temperature sits around 220 Celsius with max being 285 Celsius using a Dellorto No68 jet.

    Since changing to the Rock Solid Engines Billet CNC Reed Valve Intake, i have needed to jet up to a Dellorto No74. Low and midrange torque has jumped significantly with the engine running much more consistently as well as maximum exhaust gas temperature dropping 50 degrees Celsius to 500.

    Last edited: Apr 23, 2012
  9. Harbor freight has few small engine readers and they actually are pretty precise
  10. jaguar

    jaguar Well-Known Member

    HF has two cheap ones to consider but the cheapest of the two only reads up to 482 degrees F. So this is the one to get since it reads almost to 1000 degrees:

    If you want to be even more accurate, since using an infrared device will just read the fin temperature since the frame will be in the way of getting the reader in the centerline to read the meaty part of the head, you can buy a thermocouple spark plug washer for $45 and use a digital voltmeter to read its voltage output (while riding which is advantageous) and use this formula to determine the Fahrenheit temperature: temperature=((voltage-0.61)/0.03075)+100
    Pegasus also sells an analog gauge to use with the thermocouple for $65:
    Last edited: Apr 28, 2012
  11. Ya I would only need the cheaper one that reads up
    482 F since I ride very short distances
  12. jaguar

    jaguar Well-Known Member

    for a few dollars more you can have the better one. short distance is not important. an engine with too much compression or too advanced ignition or too lean can get to maximum temperature very quickly.