While this is not today but over the last weekend I thought it may be of some, if limited, interest to anyone with an appreciation of old Moto Guzzi’s. This may go on for a bit so my apologies in advance.
Went to go out for a ride having re-registered my old Guzzi and what do you know, she no start! Turns out I have a flat battery. Now this has never happened before but given my slightly reluctant charge light I think I am going to have to delve into the wiring and the charge system to fix this.
Now one thing I did notice, when I last rode the bike as I was pulling up to the house, she was a bit “fluffy” and I initially thought it might just be a blocked pilot jet, but now I'm thinking if its not charging then a flat battery would definitely cause a running issue.
Sat the bike on charge for a few hours in the hope that would be enough to fire her over, but no go. The no go manifesting as a clicking starter solenoid. I did try the “percussional adjustment” method but to no avail.
So next thing remove the starter motor and fiddle with the solenoid to get the starter to turn over off the bike. All seems OK so put it all back together and used a spare battery as a jump starter and she fired up fine.
Lo and behold with the ignition on I have no charge light, and once checked with a multi meter it's definitely not charging. So, time for more investigation. Now, just to be clear, if the charge light doesn’t come on with the rest of the idiot lights when the ignition is turned on, then there is no supply to the alternator rotor field windings and the bike will not charge. This is a particular problem if the fuse blows while out for a ride.
So the next thing after lots of internet reading and fault-finding exploits from the “experts” in Guzzi land I started doing the basic checks.
The first thing I find is that the charge light basically doesn’t, so hoping it might just be a blown bulb I pulled the dash apart. After a bit of fiddling about I discovered that the bulb is OK but the wiring is not making consistent contact so more fiddling and crimping later and the bulb now lights up consistently with the ignition on.
I now just have to get it to go out with the engine running!
Looking over the wiring and can’t see any issues and no signs of wiring failure or loose contacts there, so next thing is to look at the generator rotor and stator.
Pulled the brushes off the slip rings and check across the sliprings for a resistance measurement. It should be in the order of 3.4 Ohms. I'm getting some very inconsistent readings so I don’t know if its fried or not. I did try a different meter but it was still inconsistent.
While I was fiddling with the alternator stator, I noticed that one of the brush connecting wires in the brush holder had broken, so I had to resolder it in place. Stator off and sit at the dining table and resolder it back together. Managed to get it metal glued (solder) back together and a continuity check seems to show its working. So, some limited success but its still not charging. Bugger!!
Just to recap, thus far I have fixed the charge light connections so that works, and re-attached the brush connections so the rotor should now become an electro magnet. I had another check of the rotor for resistance and after cleaning up the slip rings I can get a consistent reading of 4.7 ohms, which is not quite right but should still give me an output of some kind. I checked the output from the stator across all 3 fields and it should have been about 40 vac, but I got nothing so this points to the stator windings being cooked.
I then checked all the resistance readings across the fields and got exactly what I should, about 0.4 ohms on all 3 fields, then I checked the winding insulation and again across all 3 fields I got infinite resistance so they are not grounding to earth, so that’s good. Next thing was to flash across the slip rings with 12v direct from the battery which apparently is called field flashing and helps put a residual magnetic charge in the windings. I have done this previously on DC generators but not an AC one.
Then I put a direct feed from the battery to the DF spade on the brush holder and checked for charging again. Nothing, I'm now starting to doubt myself.
I then decided to re-establish an earth wire from the brush holder. Now, for as long as I have had this bike there has not been an earth wire but the wiring diagrams and all the fault-finding schematics show there to be one, so on one goes.
I put it all back together with the fuel tank on so I could run the bike a bit longer than just the fuel in the float bowls, connect the voltmeter across the battery, turn on the ignition (charge light comes on) and hit the starter. Charge light stays on, but the voltmeter is registering some activity, a bit of a rev and the charge light goes out and I'm seeing about 13.5 volts across the battery. Happy days!!
So, it’s now charging, not as much as I would like, but it is charging. Its enough for me to call it done and I shall put it all back together through the week and head out for a ride.
I am wondering if the slightly higher than should be resistance across the rotor slip rings is the cause for low output, but for now I shall live with it.
again my apologies for the boring read and if you have made it this far then thank you and Happy Easter!!
