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Thermocouples and CHT


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Hi all, I don't know if anyone else uses a cylinder head temperature gauge, but I do. The standard sensor is a copper washer affair that bolts down underneath the spark plug. This is OK, but if you have to swap your plug in and out, you are putting the sensor under a fair bit of movement stress, with the risk of it breaking.

Having done a fair bit of reading on the subject, I have come to the conclusion that a perfectly reasonable alternative is to use one of the cylinder head bolts instead. The differences in reading are slight, and although the readings might lag slightly, you are only talking by a few seconds. This is unlikely to affect the great scheme of things, and an EGT sensor is likely to be the only one to respond fast enough to save your piston in the event of an over-hot condition, but you will be able to keep track of trends.

This then leaves you with the problem that you need a new sensor that has a hole to match the diameter of the cylinder head studs, and depending on the source, they don't come right cheap. I solved this by buying some thermocouple wire, welding the conductors to form a new sensor tip, and then crimping it into a home made, substantial, copper washer. The addition of a little solder and some heat shrink sleeving, and you have a pucka custom sensor (note, you can't solder the wire directly). I have bolted it down with one of the studs on the exhaust side of the cylinder, reasoning that this side is likely to run hotter of all of them.

Not having a running engine, I can't give function reports, other than to say that a hot air gun produces the expected readings.

I have sufficient thermocouple wire to make another sensor if anyone would like to go the same route. It is type 'K', and I'll make up the copper washer to order. Connection at the other (meter) end is your responsibility. Postage will only be pennies, so I'll do this gratis if anyone has a requirement. If more than one person wants one, I'll buy some more wire and do them at cost which would only be about a quid.

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  • 2 months later...

Hi Phil,I would like to buy a thermocouple sensor if you have enough wire to make one for me please,

I too am interested in fitting a CHT gauge , Which one do you use or recommend Phil.

Thanks Phil my tel no is 01239612370 if you would like to give me a call.

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