Smiths Instruments Removal

[element]

I'm well underway with removing the old dash & all the switches and instuments but I have hit a hurdle on the final instrument - the oil pressure/water pressure gauge...



On the back of it there are two feeds, the first is for the oil pressure:



It has a plastic or nylon tube joining it which seems to be tightly fitted onto the brass spigot. At first sight, I thought, perhaps it has that hexagonal shape to allow one to put a spanner around it to tighten it on / loosen it off the gauge.. However not wanting to do it wrong first time I thought I'd better ask you guys that have been here before.. So - to remove the gauge from the old dash - do I simply undo/unscrew the hexagonal stud OR - do I cut the pipe and then remove the tube and to refit (eventually) do I just heat up the pipe and slide it over the spigot once more?

Question 2:

There is a water sensor wire that enters the gauge, it has a spiral wire protective sheaf running its entire length..



To remove this from the guage - does the lower brass sleeve simply unscrew?

Many thanks!

[dcunn]

Re: Smiths Instruments Removal

The brass nut should come free with care, not a problem, it should spin on the spigot.
However the water temp wire is best released from the engine end and the wire retained attached to the gauge - unless of course anyone else knows different !

[element]

Re: Smiths Instruments Removal

Yes thanks for that - pretty much what I already thought.. The water sensor wire is awkward but not impossible to remove from the other end & then thread all the way through - and back again; it actually connects to a sensor near the radiator...

[greyV8pete]

Re: Smiths Instruments Removal

To remove this from the guage - does the lower brass sleeve simply unscrew?

Many thanks!

This type of gauge is a sealed system so do NOT attempt to separate the capilliary tube at the gauge. They use to contain ether (maybe something more fancy these days?) that expanded when it warmed up and actuated the gauge, like a pressure gauge works.

They are normally installed with a two turns pigtail at the engine end to avoid vibration fracturing the pipe.

If you decide to replace it in the future with an electric type be sure to get the sender unit that matches the gauge. Also check whether it needs raw 12volt supply or has to be fed through a voltage stabiliser like Ford used to do. Peter.

[element]

Re: Smiths Instruments Removal

OK, so I don't remove the water connection at the gauge but I can undo the hexagonal stud for the oil pipe (without damaging the actual pipe itself)? OR I undo both at the other ends and feed them through...
Your explanation Peter makes sense as it explains why the pipe is coiled up (out of picture) - there's enough to do another 2 metres easy!

[Cameron F]

Re: Smiths Instruments Removal

Yes as above. These gauges are available new but are astronomically expensive so be careful. They were fitted to MGBs midgets early mini and much more so they do come up used from time to time. When you remove the armoured capillary from the car (it wont separate from the gauge) its a good idea to attach a bit of string to the end so you can guide the pipe back into place when refitting it. You can curl it up but be careful (especially near the ends) as they can go quite brittle and as Peter says, may contain ether if old. The point being you wont be able to reseal it if it breaks and that means a new gauge..

[greyV8pete]

Re: Smiths Instruments Removal

OK, so I don't remove the water connection at the gauge but I can undo the hexagonal stud for the oil pipe (without damaging the actual pipe itself)? OR I undo both at the other ends and feed them through...
Your explanation Peter makes sense as it explains why the pipe is coiled up (out of picture) - there's enough to do another 2 metres easy!

The hex oil pipe union nut on the back of the gauge is best as it eliminates the need to remove the rigid oil pipe to the engine which can be a pain. The union nut should not be excessively tight but do remember to refit the oil pipe when the gauge is replaced. Someone forgot this on my Dad’s old car many years ago and he didn’t enjoy the experience of engine oil all over his legs! That said I have seen diaphragm type valves available (maybe for racing / fire prevention?) that fit in the oil line to prevent raw and very hot oil escaping into the passenger compartment in the event of a crash. Peter.

[lil_red_roadster]

Re: Smiths Instruments Removal

There may be a tiny leather sealing washer under that oil union, if so don't lose it..!

[element]

Re: Smiths Instruments Removal

Had another look at it tonight & the water temperature gauge receives input through a very small bore brass tube (around 1/ 1.5mm diameter) which is then protected by its steel coil sheath throughout its length. The 'other end' of which is attached by an identical looking crimp sleeve at a radiator water pipe union. The union has a hexagonal nut sleeve around it & it looks as though I have undo it and then very, very carefully, thread the pipe length complete with the nut sleeve (which will remain on the pipe) all the way through the engine bay and through the bulkhead, through a rubber grommet and out complete with the guage from the old dash. Fitting the dash in the new dash will be the reverse procedure... My only hope is that the entire length of this very fine water pipe is not actually filled with water because if it is I will never be able to refill it again! I'd like to think it isn't & that the water temperature rising - increases pressure throughout the tube (even if filled with air) and this acts on a sensitive part inside the guage..

[greyV8pete]

Re: Smiths Instruments Removal

Had another look at it tonight & the water temperature gauge receives input through a very small bore brass tube (around 1/ 1.5mm diameter) which is then protected by its steel coil sheath throughout its length. The 'other end' of which is attached by an identical looking crimp sleeve at a radiator water pipe union. The union has a hexagonal nut sleeve around it & it looks as though I have undo it and then very, very carefully, thread the pipe length complete with the nut sleeve (which will remain on the pipe) all the way through the engine bay and through the bulkhead, through a rubber grommet and out complete with the guage from the old dash. Fitting the dash in the new dash will be the reverse procedure... My only hope is that the entire length of this very fine water pipe is not actually filled with water because if it is I will never be able to refill it again! I'd like to think it isn't & that the water temperature rising - increases pressure throughout the tube (even if filled with air) and this acts on a sensitive part inside the guage..

The sensing bulb, capilliary tube and up into the gauge is a sealed unit and was originally filled with ether. Maybe later ones used something else? As the temperature rises the ether vapourises and expands causing a bourdon tube in the gauge to "uncurl" and as that is connected to the gauge needle it makes that rotate around the dial to give a "temperature" reading. The gauge is actually working as a pressure gauge but calibrated in degrees of temperature.

If the tube is fractured then the ether escapes and the gauge will not work so handle it carefully! Years ago there were companies that could refill and seal these units but I suspect that is now a dying art? Peter.

[element]

Re: Smiths Instruments Removal

Yes its very very very careful fingers this evening! So both are filled with ether.. If I do fracture either one at least it'll initially numb the discomfort of having to get a replacement electronic one

[dcunn]

Re: Smiths Instruments Removal

No ! The oil pressure one has oil (under pressure) so don't get any leaks !

There are many instances of engine oil coming out under pressure when someone is driving, you don't know it, and then the inevitable happens to the engine

[element]

Re: Smiths Instruments Removal

All ok it wasn't as difficult as it could have been, some 15 cable tie wraps to cut then undo the 21mm nut around the water temp sensor housing, then withdraw the sensor:



... and slowly bit by bit feed it all the way through the 2" rubber grommet - getting the 21mm nut through was the hardest bit! Done and out now still in one piece. The oil pipe was easy by comparison - 13mm spanner, 2 turns and it unscrewed by fingers and was out in seconds. Now on with the dash...

Looking at the colour of the sensor I think a good flush and coolant renewal would be a good idea...