I don't need this pressure on - but I like it anyway

Inspired by Bostik, I decided to fit oil temperature and pressure gauges. The question was, where to?

The sump has three M16 oilway blanking plugs and the original 1/8NPT hole for the standard pressure switch. The pressure and temperature sensors I bought were both 1/8NPT and one of them (can't remember which) came with a clever but rather bulky four-way adapter block, drilled and tapped to 1/4 NPT and with four 1/8 to 1/4 NPT adapters. I fiddled around for ages with various alternatives for fitting the sensors. I decided to try using two M16 to 1/8 NPT adapters in place of two of the three oilway blanking plugs. I chose a drilling beneath the mesh filter for the main supply for the oil temperature sensor, and a drilling adjacent to the standard pressure switch at the rear of the sump for the pressure sensor. I think the latter is intended for an oil pressure test gauge because it doesn't blank a drilling in the sump casting that serves any other obvious purpose. 

I fitted the standard pressure switch and plug beneath the mesh filter for the oil cooler with permanent thread lock and torqued up nicely.

 The 1/8 NPT to M16 adapter plug for the temperature sensor should have been straight forward. Unfortunately, the one I bought had a fairly short thread and the blanking plugs in my sump are headless allen fittings which engage with a thread that doesn't start until approx 10mm into their respective holes. In other words, I got only two turns on the adapter before its head locked against the casting. Also, because these are tapered threads, the threads that were engaged were extremely loose. I've opted for two remedies. I ground down the head of the bolt to effectively lengthen it by about 4mm. I then wound PTFE tape around its threads to help take up some of the remaining clearance, if any, between the threads. I hope this will do the trick (clearly) but I'll have to wait for the start up to find out. This drilling is to an oil way before the oil pump so the oil will not be under pressure here. Unlike the take off for the oil pressure sensor ...

1/8 NPT to M16 brass adapter plug ready for temp sensor

The pressure sensor is pretty bulky and the exhaust headers run very close to the sides of the sump casting. There is a bit of room at the rear so I figured that would be the most likely place to fit it without interference between it and the hot pipes.

Aluminium 1/8NPT to M16 adapter plug with brass
three-way 1/8 NPT adapter, allowing a 90 degree bend
for the pressure sensor.

Even so, a test fitting of the sump showed very little room so I needed to put an 90 degree adapter in between the sensor body and the 1/8NPT to M16 bolt.  This aluminium adapter bolt was included in the gauge kit - a nice long tapered thread so no problem with engaging this one. I used PTFE tape again to give it the best possible chance to seal.

Pressure sensor body in place on the brass three-way adapter

Test fitting of pressure sensor, lined up against exhaust headers

I tagged the pressure sensor feed with
green tape so I wouldn't confuse it with
the temp sensor feed

Rats nest of wires sprouting in all
directions - 20 stripped ends to be
tinned for joining or termination

The sensors use a blue wire to connect to their respective gauges, the temperature sensor also has a white wire to connect to earth. The gauges need a 12v switched supply, earth and feed from their respective sensors. I made up two little looms to do this. I used 5amp blue wire to extend the temperature sensor, black for the earth and green for the pressure sensor.

The sensor mini-loom was for carrying three wires up from the sump to terminate above and in front of the battery. After scrutinizing the wiring diagram in my manual, I worked out that one of the connectors for the third ignition coil (unused on the four-cylinder models) is switched 12volts. It is a red female spade connector. The other one is brown with a yellow tracer and loops to the ignitor box. Not one to play with. Anyway, this unused coil connection runs very close to a place where the main frame tube joins to the box-section rear frame rails, next to the battery. There is a bit of room just here, above a useful little bracket that mounts the starter solenoid. Ideal for keeping connections out of the weather and tidy.

The gauge mini-loom was for carrying four wires (positive from switched supply, negative/earth, and two sensor feeds) from above and in front of the battery to the gauges which will be mounted between the standard clocks and the top yoke.

Four wires for gauge mini-loom: brown for switched supply,
black for earth, blue for temperature sensor feed, and
green for pressure sensor feed. 

Gauge loom ready for wrapping with electrical insulation
tape. I used heat-shrinking tube to seal the soldered joints and
additional, larger section heat-shrink to cover the whole joined area.

Sensor mini-loom, heat-shrink tube installed under the sump,
the other three wires (green for pressure, blue for temperature,
black for earth/negative) ready for wrapping. 

Termination of sensor mini-look: M6 ring for earth, male
bullets for sensor feed wires. Heat-shrink added to protect.

Cleaning threads with M6 tap prior to installation of sump

Pressure (left) and temperature (right) sensors in place on
sump with loom held out of harm's way with a cable clip. 

When I test fitted the right-hand exhaust, I discovered that the sensor body just touched. It might have been OK - but represented too big a risk of frying whatever is inside the sensor body. So I decided to remove a bracket the helps to locate the exhaust headers and to rotate the 90 degree adapter half a turn so the pressure sensor is now centralized behind the sump. In the picture below, it looks as though it is in contact with rear suspension drag link - in fact there is about 5mm clearance. So, no more interference, wiring in place - the job should be a good one. Only time will tell. If not, I'll have to replace the M16 plug and admit it was an adventure that failed.

Final (for now) position of the oil pressure sensor