Well, half of one really. It was important to do something about the problem gauge which has now wasted an awful lot of time and quite considerably delayed our getting Our Trike back into check. Just so people know what I’m talking about, this is what the gauge looks like.
Cylinder Head Temperature is shown on the left hand scale and Engine RPM on the right. The gauge is a used replacement as the original had been damaged, and as the connections had also been messed up, I’d not been able to get it working after replacing the wiring as I didn’t know which wire was supposed to be connected where.
I had the idea a few weeks ago of asking for advice on the BMAA Forum and within a very short time was pointed towards the manufacturer’s web site where there is a diagram showing the connections for a similar model. This is what the connections on the back of the gauge look like.
The gauge is in effect two gauges combined. The RPM connections I was advised, consist of a link to the magneto (which creates the engine spark) on one side and an earth on the other. The CHT connections go straight to a thermocouple (remember from school, two dissimilar metals that are in contact that create a small current when the junction is heated up). The thermocouple is held against the cylinder head by being screwed down under one of the spark plugs – pretty simple really but quite effective. It was easy to trace the thermocouple connections and according to the gauge manufacturer’s diagram, they should then be connected to the pair of connections on the back of the gauge numbered 3 and 4. Simple.
That just left connections 2 and 5 for the RPM gauge, with the ‘live’ on 2 and the earth on 5, according to the diagram. Marvellous! 🙂
Dave on the BMAA forum had suggested that I checked things out with an electrical multimeter which was a good idea that hadn’t occurred to me even though I have an excellent Robin at home. So that’s what I did. Disaster!. It seemed to me that with the connections as they were, they were all ‘shorting’ out! The only way I could prevent it was by breaking the RPM ‘live’ connection, so back I went to the BMAA forum.
‘Yes’, said Dave, ‘It would appear that way but actually they’re not’. I had asked if anyone knew where I could get an ‘official’ wiring diagram for the Robin engine that showed exactly how the connections should be done and almost straight away, Ginge posted the following one.
I’d said that the original connection had been made into a yellow wire which was in a group emerging from the magneto housing, and if you look carefully at the area ringed in red, you’ll see that that’s exactly how it should be. Dang! I’d broken that connection so now I’d have to remake it. 😐
And that’s what I did this afternoon. And guess what – afterwards we had an Engine RPM readout!
But still no CHT reading. And then I remembered. When I bought the gauge, the seller also gave me a Rotax Water Temperature gauge (which Our Trike doesn’t need because it’s air cooled) and a rolled up length of what I’d thought was old wire. When I got it out and unrolled it, sure enough it was a thermocouple. So the question is, is our existing thermocouple not compatible with this gauge and will this ‘new’ one work? I don’t know – I didn’t have a plug spanner with me so I couldn’t swap them over. That will be a job for next weekend.
But at least with Engine RPM I’m half way there. So it’s half a Hooray! anyway 😉