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MG MGB Technical - Temperature sender thread

I have found links in the archives that state that the diameter and thread count of the sender unit in the head of an MGB is 5/8"18. Am currently searching for an adapter that will allow me to use an aftermarket gauge's temperature sender in the same hole which is 1/8NPT. Anyone know of such a source for this type bushing/adapter(5/8"-18 male X 1/8" NPT female). Also while searching for this was looking an the Pegasus Racing site and saw mention of the closeness of 5/8"-18 and 3/8" BSP. Is there any chance that the thread count in the head is actually 3/8" BSP and not 5/8"-18? Thanks,'
Frank
Frank

Apparently, 3/8" BSP is 19 TPI ... see

http://en.wikipedia.org/wiki/ISO_228
Geoff Everitt

"Is there any chance that the thread count in the head is actually 3/8" BSP and not 5/8"-18?"

In a word, no. While the thread count may be close (BSP is 19 TPI), the thread form is different and a 3/8 BSP has a 0.030" larger diameter. They are not interchangeable. For a chart of standard threads (American, British and Metric) see the Standard SThreads chart in the Other Tech Articles on my web site at: http://homepages.donobi.net/sufuelpumps/ Cheers - Dave
David DuBois

David,
Sorry about that should have been a little clearer. Was more wondering if perhaps the archived threads are wrong and really the hole in the head is tapped 3/8 BSP since they are so close in size and thread pitch. After all the car is British. Still looking for a source of a bushing to go from 5/8-18 to 1/8 NPT if anyone can help with that as well. Thanks
Frank
Frank Mooring

Frank - Perhaps both of us could have been clearer. I have checked the threads on several heads and all are 5/8 - 18. The vast majority of threads used on the B series engines are SAE or NC. That said, there are a number of odd British threads found on them. You can see a listing of these British threads in my web site at: http://homepages.donobi.net/sufuelpumps/ in the Other Tech Articles section. Cheers - Dave

David DuBois

Frank. You are not likely to find a bushing, designed in the style of the original probe, which seals on the front bevel, that is drilled, reamed, then tapped to 1/8" NTP thread. Such a bushing would have to be custom made by a shop that can have both the factory sensor (as a pattern) and the new sensor (to see how it must fit into the bushing) as part of the machining process. The bushing, made out of brass, would be relatively easy to make on a manual machine. But, it would take a fair amount of time and that would make it expensive.

Les
Les Bengtson

Hi Frank if you need one making up i can do it next week at work and post it to you .just cost you the post price ,you can send me that when you recive the bush. if that helps cheers. Malc
Malc Fox

Malc,
I will send you an e-mail with my address. Thanks so much.
Frank
Frank Mooring

This thread was discussed between 31/12/2008 and 03/01/2009

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