Smiths Twincheck

[bjm38]

Hi everyone,

I've bought a NOS Smiths Twincheck dual gauge off eBay, it has an oil pressure gauge and water temperature gauge with all the fittings, wires and hoses in the box. The pressure gauge is mechanical, so I'm right enough with that...but what of the temperature gauge - will it be polarity sensitive? Our car is still positive earth. The temp gauge has a voltage stabiliser on the back, and the instructions make no mention of battery polarity. It just says to wire the sensor to one terminal and the other wire to the battery. This Twincheck thing looks pretty old skool, at least 30 years old and quite possibly up to 40.

I suspect I might have to dismantle the voltage stabiliser to answer this one, but it's worth asking!

Many thanks

Bernard

[mike.perry]

The only Smiths dual gauge that I know of is the oil pressure/water temp gauge which is mechanical. The oil pressure is fed by the tube which connects to the sensor location on the block and the temp is from the capillary sensor which connects to the block below the thermostat housing, on a 1098/1275. The only electrical connection is for the backlight Original gauges were in deg F then deg C and the latest were plain HNC[frame][/frame]

[bmcecosse]

I agree! And have never heard the expression 'twincheck?) - so yes - there will be a capillary tube from the temp gauge with a sensor bulb at the end which is fitted to the cylinder head (usually requiring an adapter) in the port just below the thermostat. This capillary is easily damaged, and sadly - often missing........which renders the gauge useless......

[bjm38]

I couldn't find very much on Google at all, I suppose they weren't that popular? The gauge kit itself is in the car in the garage (work beckons!), but here's one of the pics from the eBay advert:
[frame][/frame]

...and a couple of close-ups from pictures of the instruction sheet I found online:
[frame][/frame][frame][/frame]

The voltage stabiliser connections are stamped "B" for battery and "I" for instrument, which reminds me of the markings on the old polarity-insensitive metal-can flasher relays. I strongly suspect the stabiliser will be the old bi-metallic strip type, but I'm worried of breaking something by fiddling. If it *is* capacitors, would wiring it backwards toast it?

Bernard

[kennatt]

if its that old it may be designed for positive earth,most cars were ,back in the day.Looking at the diag.isn't the volt stab only for the warning lights,the feed to the actual guage is straight to the transmitter. Could you not test rig it and not use the connection to the stab. then which way the gauge moves would be enable you to work out polarity. allthough if its hard up against the stop it may not move backwards

[bmcecosse]

Ahhh right - so it's just two electric gauges side by side.... it is just bi-metallic strip so not polarity sensitive. You won't damage it.

[bjm38]

Success!!

The temp gauge doesn't give a jot about polarity - here's a pic of the back:[frame][/frame]
The voltage stabiliser is the black bit at the top, I've still to wire up the backlight.

It was a complete and utter mare to screw up the oil pressure switch tee-piece in such a way as the side tapping was accessible, so I decided to ditch it altogether and just make do with the gauge. The engine's probably b*****ed by the time the dash oil pressure warning light comes on anyway, surely...? I've yet to warm up the engine with the pressure gauge fitted, but 70psi cold at a fast idle sounds fairly healthy to me.

Thanks for everyone's input.

Bernard

[bmcecosse]

It's the strangest thing I have ever seen - but well done getting it all working!