classic motorcycle forum

Motorcycle Discussions => British Bikes => Topic started by: popstar1 on August 10, 2016, 11:08:34 AM

Title: Charging system T140e change over model
Post by: popstar1 on August 10, 2016, 11:08:34 AM

The  charging circuit  is only making 12.8 volts on my T140  Bonneville at the battery  terminals at about 4000 rpm and as soon as I switch the lights on the engine dies  i've checked the Earth terminals and I all seems well there the only thing I can think of is the alternator is faulty or there is a problem with the  rectifier , because this bike is a change over model there doesn't seem to be any suitable wiring  diagrams in the manuals , The bike is fitted with its original rectifier  and original Zena, are only two wires coming up from the alternator a green yellow and a green white if anyone has any ideas I will be grateful . Otherwise the five runs  really well . The bike has a positive earth.

Title: Re: Charging system T140e change over model
Post by: L.A.B. on August 10, 2016, 11:25:52 AM

Quote from: popstar1 on August 10, 2016, 11:08:34 AM

because this bike is a change over model there doesn't seem to be any suitable wiring  diagrams in the manuals

A 1978 T140E wiring should be the basically same as the late ('77-'78) T140V. As it's positive earth and has a two wire stator, then the charging circuit (assuming no modifications?) will be identical to the T140V electrical diagram. 

The wiring only changed significantly on the 1979 'E' models (from HA11001) when the electrical system changed to negative earth with three-phase alternator charging and Lucas Rita electronic ignition.   

Title: Re: Charging system T140e change over model
Post by: Rex on August 11, 2016, 08:38:59 AM

The most obvious thing to check is the battery. Stick it on charge overnight and try again. 12.8V is far too low.

Title: Re: Charging system T140e change over model
Post by: popstar1 on August 11, 2016, 12:18:54 PM

 Hello thanks for that I've already checked the battery though and all seems fine it's holding a charge well but the output  is still only around 12.8 volts  at 4 to 5000 rpm

Title: Re: Charging system T140e change over model
Post by: L.A.B. on August 11, 2016, 12:42:56 PM

https://www.scribd.com/doc/157399591/Fault-Finding-Lucas-Motorcycle-Charging-Systems-Aug-2013

Title: Re: Charging system T140e change over model
Post by: Rex on August 12, 2016, 09:57:08 AM

Quote from: popstar1 on August 11, 2016, 12:18:54 PM

Hello thanks for that I've already checked the battery though and all seems fine it's holding a charge well but the output  is still only around 12.8 volts  at 4 to 5000 rpm

That's not really conclusive either way. With a charged battery, how long does the headlamp stay bright with the engine not running?