Having had a frost plug blow-out and serious overheating without warning from
the mechanical hot water gauge (low water in radiator), I decided last fall to
install a NOS electric water gauge in the head. Hoping to keep the appearance
of the engine compartment vintage, I began pondering where to fix the
electrothermal sensor. The obvious position was in the threading for the water
tap, but this required removing the brass tap supplying the heater.
I think I've developed a work-around that is inexpensive and quite neat
looking. The total cost for the sensor ,brass parts, tap and pilot drill about
$50. Various chrome bezel black-face quadrant water temp gauges in good
condition come up on EBAY frequently at reasonable costs. When done, you have
a handsome brass stand-off for the hot water tap which stands 1.1"+/- off the
head. The coupling has 1/8" beaded ends and is 1" in diameter, which prowhich
is just a little shy of the outside diameter of tap's hexaonal body.
For those interested in doing this, the esoterica of archaic and/or British
pipe thread conventions require consideration. The 100-4 water taps are 3/8"
BSPT , not 3/8" Pipe Tread, as I originally assumed. The BPST (really a
Whitwirth thread) is 19 t.p.i, not 18 t.p.i. for standard pipe thread. You
also cannot substitute more contemporary UNF/SAE threads, which are also 18
t.p.i. and of slightly less diameter so they thread into the head, but do not
seal. 1/8" NPTF is a stock American threading.
A 1/8" NPTF electric water temp sending sensor is available from Holden. This
is threaded into the side of a 1.05" x 1" cylindrical cast brass coupling with
rounded ferule ends that appears quite 'vintage'. The coupling has 3/8" BSP
female threads one of which receives the traditional water cutoff valve, and
the other of which receives a 3/8" male-to-male close nipple that is all but
invisible and connects the coupling to the head. You bore a hole into the
coupling with a D pilot drill, and thread with a tap for 1/8" NPTF. All the
brass parts and the tap and pilot are available on-line from Mc-Master.com.
Here is a parts list:
McMaster-Carr http://www.mcmaster.com
(1) 4978K133 BSPT 3/8" low pressure bronze thread coupling
$ 2.69
(1) 4824K113 BSPT std. wall 3/8" nipple, sched 40
1.41
(1) 2525 A213 taper pipe tap 1/8"-27 NPTF
12.40
(1) 2940 A527 carbide tipped jobbers twist bit (D)
12.40
(If you want to see the parts, use McMaster's on-line catalogue, type in
the part number, and then hyperlink to the techical drawings for dimensions)
Holden Vintage http://www.holden.co.uk
(1) 070.016 Temperature Sender threaded 1/8" NPTF (27 t.p.i.)
11.80 BPS (~$20)
(e-catalogue is a little hard to use at first, but well supported with
photos of many items)
Both vendors take major cards and ship promptly. Holden has a wealth of gauge
and light pieces for Lucas/Smiths etc, all pictured on-line. You can order
all the parts in half an hour; then drill, tap and assemble the
coupling/sender in about an hour -- assuming of course you don't get lost
cruising McMaster-Carr's 2500+ page catalogue of pipe fittings, stock, and
machining tools, etc. or looking over Holden's incredible inventory of Lucas
and SMith's guage and lighting parts you thought you had to buy at flea
markets.
Similar approaches can be undertaken to install oil temperature sensors in the
oil pan (more easily done with stock 1/8" NPTF bulkhead fittings available
from American hardware stores).
Allen Miller
BN2-M
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