ORIGINAL: Skypilot_one
ORIGINAL: William Robison
[b]JVB:
Using a thermocouple in contact with the cylinder head, up to 250F is safe with synthetic oils, using castor oil 325F, even 350F can be survived. Do remember, the internal temperature will always be higher than that read on the outside. And there are many other ways to detect overheating.
When you use an infra-red thermometer you are reading an average that the sensing unit sees, since the outer tips of the cooling fins will be cooled by the air stream to a greater extent than the base of the fins, the non-contact thermometer will always read a number lower than the thermocouple in direct contact at the base of the fins. The amount of the variation depends on too many things to say one temperature is OK and the next bad. The height of the fins, just the thickness of the fins will make a difference. Even in engines otherwise the same (Saito) an AAC cylinder and an ABC cylinder will give different IR temperatures while the contact thermometer reads the same.
I have a Fluke 52 and my buddy borrows a thermal imager from work. How do you hold the thermocouple probe to the engine without putting it under the plug gasket?
I forgot to ask about four strokes and exhaust temps. My Enya 155's have the hottest exhaust temps I have ever seen. That's with them adjusted 100 rpm down running a Cline regulator. Those Enyas even after four gallons showed no ring or cylinder wear at all. All the machine marks in the ring was still there. I've never seen anything like it.
On mine I use a crimp-on copper wire eyelet and place the Thermocouple sense in the barrel where the wire would be inserted and crimped. A 1/4" crimp-on fits the glow plug perfectly and I just use a smaller crimp-on connector to get under one of the head bolts to get temps farther out from the chamber center. I also use that connector to check the case at the back plate, etc.