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MG MGB Technical - temperature sender fixing nut

I have just put the temperature sender back in my '68 roadster and I cannot get the nut far enough into the head to get the sensor nice and tight. there is still some movement in it even with the nut fully home. I note that there is a recess in the back of the collar of the sensor bulb where the fixing nut has presumably worn a channel. It appears that the nut runs out of thread to tighten up fully. Have other BBSers come across this? And what was their remedy?
Steve Church

Never a problem on my car, can you find a washer around your garage which would allow you to tighten and seal the bulb?
Stan Best

Where exactly does the seal take place? Between the front of the bulb flange and the head? The back of the flange and the nut in conjunction with the nut thread in the head? If the later then a washer (which would have to be slotted) would make up the gap but not provide a seal.
Steve Church

Have you had the temp gauge repaired? If so then he has used the wrong nut. If it came out of the head and was OK then it should go back - ha ha -never seems to work like that. Suggest that you find a copper washer that just fits over the bulb - possibly one from the lower gasket set. You may have to file a bit off the outside.
Garth
Garth Bagnall

Gentlemen - The seal is on the tapered portion of the head and the front of the sensor. A washer in this position would only interfere with the sealing of the sensor. Steve - try a bit of anti-seize on the threads of the nut. cheers - Dave
David DuBois

Thanks Dave, I wasnt helpful enough to put a spanner on mine and look at it, while its not leaking
Stan Best

If the 'nut' really is going in as far as it can and the bulb is still loose, then short of sending it back (if it is a replacement) you will need packing *behind* the bulb not in front of it. The ID needs to be smaller than the bulb of course, and the OD smaller than the ID of the nut if the bulb fits inside the nut, or smaller than the OD of the nut if it doesn't. Cutting through one side of a suitable spacer then fitting it over the tube may work. Could be the bulb being too short as well as the nut being incorrect.
PaulH Solihull

The midgets were fitted with an adapter between the sensor and the head - if you can't get the nut in far enough to seal then you could use one of these.

http://www.mgocspares.co.uk/acatalog/MGOC_Spares_1275_167.html#l45

45 - Adaptor- Thermal transmitter 11K2846
Chris at Octarine Services

Having been away for a couple of weeks I've resolved this one. The small amount of play I felt in the sensor when it was tightened up was not play in the actual bulb but in the crimped skirt that covers the capilary tube/bulb junction. This was not a solid crimp so it gave the appearance of the bulb not being firmly held. I found this out when I took the thermostat housing off and checked the bulb from inside the cylinder head. However this was not before putting a packing washer between nut and bulb (no difference) which then got stuck in the head when I tried to remove it (the washer that is). This had to be drilled out. I can now not get the bulb out as there appears to be a small ring of metal securing the bulb in (presumably formed when the washer was inserted) and I don't want to risk the integrity of the bulb by forcing things. I'll leave it for now and hope I don't need to take the head off. If I do I'll try to figure out what to do then. I need to get this engine running as I've had the car for 3 months now and am a bit behind schedule.

Other questions following later.
Steve Church

Resolved? Hmmm, maybe 'got round', until the next time you need to remove it ...
PaulH Solihull

Yep, definitely a temporary solution but it does give me a bit of time to think how to get the bulb out if I need to (which I will of course).
Steve Church

This thread was discussed between 06/09/2010 and 24/09/2010

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