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MG MGA - Plug for water temp sensor in block

What thread is in the engine block where the water temp sensor goes? Does anyone make a blanking plug for this hole?

Thanks
GS Swindell

GS, I don't remember right now if it's 3/8" standard pipe thread or 3/8" bsp or bspt thread, but plugs for both are availabe at McMaster-Carr. http://www.mcmaster.com/
Standard pipe threads are tapered, the bsp is an untapered thread and would need a gasket or O-ring to seal.
Bill Young

GS, the british pipe threads are available in both a straight thread and a tapered thread.
John H

I am looking for the same info and got nowhere. I have MGB 3bearing engine and I like to plug the thermo connection. I measured the dia of the thermo nut, it is .620IN. 1/4 BSP dia is.520 and 3/8 BSP dia is .660IN. I have both and nether will fit. It is 19TPI but there is nothing close to it. The closest I see is 5/8 18TPI - special order. Will it fit? 3/8NPT is too big. Hopefuly someone knows what it is. The gauge is made by JAEGER, they may use they own tools.
Martin
martin

Martin. On the 68 and later MGB the 5/8"-18 is standard. The seal is provided by the end of the thermocouple to the block. I have verified this on a number of MGB engines. Do not know why this sould be a "special order" as it is a standard thread.

Les
Les Bengtson

Gentlemen - I just went down to the basement and measured the jam nut from an early MGB temperature gauge. It measures 0.6175" dia and has 18 TPI as measured with a gauge for American threads, it is also a straight thread, not tapered. A 5/8" SAE thread measures 0.6250" - 18TPI, a 3/8 NP (straight threads) measures 0.6620" - 18 TPI and a 3/8 BSP (straight threads) measures 0.6560" - 19 TPI. Based on this, I have to vote with Les, even though I was originall sure that the jam nut was a 3/8 BSP. This same thread is used on the heads of all years of the B series engines as used in the MGAs and MGBs. Martin, the 5/8 - 18 SAE bolt will should fit fine, but I would suggest aht you have a taper put on the end of the bolt to match the taper of the seat in the head so that no damage is done to the head and it will provide a better seal. Cheers - Dave
David DuBois

Same question was posted sept 04. I have 3/8-19 BSP tap and die and I know that it will not fit. It is dificult to measure TPI on 1/2IN long brass nut due to stretching. My error. 5/8-18 UNF is not listed as per McMaster-Carr. They go only to 1/2IN size. Is SAE and UNF same? Just for the curious 5/8 thread can have 11,12,14,16,18,20,24,27,28,32TPI with that many designations after the basic size.
Martin
martin

Martin - SAE and UNF are the same threads. the standard threads for a 5/8" bolt is 11 TPI for UNC and BSW, 18 TPI for UNF/SAE, and 14 TPI for BSF. The other thread count you see are speciality threads, of which there are many.
Cheers - Dave
David DuBois

Martin. The Society of Automobile Engineers was started in the early 20th century and undertook to standardize thread patterns and sizes in the US. When the Unified National system was adopted, most of what was adopted was based on the SAE standards then in effect.

As to tapering the front of a bolt to provide a good seal, this would be very important. It would also need to be done on a lathe to work properly. You need an exact mating of the bolt/thermocouple and block surfaces to prevent leaks. Were I to do this, I might consider a 5/8"-18 set screw rather than a hex headed bolt. It would make a neater installation. I would also taper the front of the bolt/screw to the same taper as found on the current thermocouple. Then, I would assemble the piece to the head using some good quality epoxy. That should both prevent the bolt from backing out and provide a little additional protection against water leakage.

Les
Les Bengtson

Sorry G. S. Swindell I stole your thread. I hope you have enough info to do whatewer you planed.
I thank all involved to put me straight.
My machinery handbook was new in 1971. A lot changed since then. Thank you Dave.
Martin
Martin

I mentioned this to my next door neighbor - he's from Britain. Unbelievably, he went into his garage and fished out a british pipe thread hose bib that fit the hole perfectly.
GS Swindell

Why not just drill it out and retap it to your chosen thread??

CP
Colin Parkinson

This thread was discussed between 10/03/2006 and 17/03/2006

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This thread is from the archive. The Live MG MGA BBS is active now.