Hi Have finally got my 1961 C15 on the road my main concern is the charging , with a volt meter across the battery it reads 5.7 volts at low revs increases slightly as revs rise but never above 6V and then discharges significantly down to 5.4V as revs rise higher. Be very grateful for any advice on what the problem could be or a procedure to go through to check out the problem. Many thanks Tom.
I am no expert, but when I tried to connect a voltmeter across my old C15 battery terminals while it was running , I got readings all over the place which I put down to rectification causing big fluctuations in the voltage. I am not sure if that is normal or not!
It sounds to me you are just measuring the battery voltage with no output from the alternator/rectifier.
You can check the alternator by connecting each of the three output wires, one at a time to a voltmeter whose other terminal is earth to the frame, and give the engine a firm kick over...the voltmeter should move briefly in the direction of say 5volts...mine got to 3.8 ish volts, didn't kick to hard! Do this for each of the three wires.
If they all give about the same in the region of 4 to 6 volts the alternator is probably OK.
The rectifier could be faulty or you just simply have a bad connection, which is very possible.
I think my rectifier was probably faulty anyway and I have since converted the bike to 12v.
I don't think you can put a digital voltmeter across the battery with the engine running and get a correct reading.
I think the older analogue meters may be ok because they are damped.
If I remember correctly there is some mention of putting a 1 ohm resistor either across the terminals or in series with a digital voltmeter to give a correct reading.
Many thanks for the replies, I tried connecting a voltmeter to each of the three wires with them disconnected from the loom and did get a reading on each when kicked over but a very low figure 1 to 2 volts. I also ran the engine and measured the voltages at idle and recorded 1-1-1.4 v the max recorded when increasing revs was 2 volts. Looking at the ammeter when running normally it shows a very slight charge at low revs but swings to a significant discharge as revs rise.
Those readings do seem low.
If the stator wiring is intact, that would seem to suggest the rotor has lost some of it magnetisation which can happen with age or by reversing the battery polarity by mistake, for example.
As I have said, I am no expert and we really need someone on here with experience of these things to help us out!
Many thanks for that, the bike has had hardly any use in at least five years, if that is relevant.
Have you got the right battery polarity which is positive earth.
Yes positive earth, previous ownership a bit suspect so could have been wrong in the past!!.
I suggest the following;
Check the output as per the chart below which comes from the 1966 Lucas Alternator manual. The figures are with a 1 ohm resistor but you should get some idea without it The 1961 C15 original fitting would either be an RM13 or RM 18 for later in that year. You could use a 12 volt bulb to give you some idea.
Check all the wiring and connections, especially earths and repair as needed
Unless the regulator has been replaced with a modern unit suspect it - a replacement is cheap enough
If the battery is from 5 years ago suspect it
If the stator is an original exposed wire type carefully check it for damaged wiring. Inside a chaincase is not very friendly.
Switches deteriorate inside.
Many thanks I will work my way through that checklist.