HT 70 clinder head temperatures


Active Member
Jun 10, 2008
Just for the heck of it I bought an infrared digital thermometer and did some testing on my motor. At 26deg C or 79 deg F air temp doin a speed of 25 mph or 41 km on a 28:1 mixture and a 40T sprocket the head by the sparkplug was running 270-280 deg F. At idle it was about 230-240 F and flat out around 290 deg F. Saw 310 once after backing off flat out but it immediately started dropping from there. As a side note when I replaced my head studs I made them longer so as to be able to double nut them and install one at a time without having to pull the head off. Basically an extra 1/4-3/8 inch longer so they sit about the top of the cylinder fins. Probably doesn't do a heck of a lot but does aid a little bit more to disperse heat from the head with the air passing over it. Fwiw.
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Good info....thanks for posting....I recently got one of those temp guns too....been measuring pretty much everything....had not gotten to the bike yet tho!



Jun 22, 2008
i'd be interested in how fast it gets up to temp. I'm breaking in my engine and I start it and give everything a looksy over before proceeding.
1) check clutch cable adjustment
2) carb is tight-no leaks
3) chain tension is even and snug
4) no loose nuts, QRs, etc.

I'm thinking a 30secs to a minute to warm up? what do others do?


Active Member
Nov 17, 2007
Thanks for sharing your temperature readings. FYI, on model engine 2 stroke engines, I usually run them at a max 300 deg F on a non-castor based fuel and 325 deg F on a castor based fuel.

From a major 2 stroke manufacturer's website for their Saber oil:

Flash Point °C (°F) (ASTM D-92) 114 (237F)
Fire Point °C (°F) (ASTM D-92) 114 (237F)

The lubricating oil flashes at 237 deg F and burns at same temp. This means that the oil is not lubricating the engine component after it flashes. It only lubes when oil is in liquid form in the fuel.

Here is a synthetic oil that is blended with 20% castor. It is called maxima 927
Flash Point, °F 420
Fire Point, °F 480

At the temps you are showing, the oil will not flash before it is ignited by the fuel.

Common sense is the longer an oil remains liquid, the longer it lubricates bearings, rings, etc...etc. You decide what is best but don't be fooled by the naysayers who say that flashpoint is irrelevant. The same argument could be used to say that the boiling point of an antifreeze isn't important either but we all know it is.
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