LUCAS 1950s

It is all about corrosion of steel.If the negative pole is earth, then the vehicule is charged up and thus the oxygen has to overcome both the Iron's oxidation potential and the batteries artificial potential for oxidation to occur, positive earth serves to increase the rate of oxidation of steel.

My impression is that the British motorcycle manufacturers attempted, as they later did with UNF fasteners, to follow the British car industry which in itself was mis-reading the future and slavishy following the U.S.factories where +/ve and -/ve earths had long been a bone of contention between GM and Ford...Didn't car radios have something to do with it in the end ? 

is something of a (rusty) red herring. The difference in corrosion between positive and negative earth is minimal - cars from the 50s, 60s and 70s rusted because they had no corrosion protection applied at the factories....

I prefer negative earth as it's consistent with modern vehicles and somehow seems more logical (yes I know that electrons travel from negative to positive!)

I believe that Nortons were negative earth up to about 1950, then went positive earth.  The wiring diagrams in the factory service manuals carefully avoid stating whether the bikes are pos or neg.  My bike was pos earth, and I chose to switch to neg earth.  Just reverse the battery and flash the dynamo.  Eventually I will reverse the ammeter wires so it reads correctly

Too soon to say if there is any difference in corrosion, or other effect. 

Paul

Once I read (forgotten where) that it was some difference in efficiency of spark on battery ignitions. Anyhow, it can be easier to change to negative earth, if fitting some modern electronics to our old bikes.

http://faculty.chem.queensu.ca/people/faculty/mombourquette/FirstYrChem/electro/index.htm

There have been a number of theories about the reasons for the change from +ve. to -ve earth.

1/ because of the use of transistor car radios....but early radios had a switch on the back to change the polatity for the car in which it was installed.

2/ needed because of alternators....but pedates this

3/ galvanic corrosion is reduced.

Above link explains this and as a ex-chemist , it was taught in ungraduate electrochemistry courses in the 1960's.

Al, I used UNF fasteners as an example of British motorcycle factories following the car manufacturers...and Commandos are mostly UNF - ask anyone who has used Dominator hub sleeve nuts on one ! They could just as easily have gone metric but thought that the U.S. market was more important.

 Whatever the scientific reason for the change to +/ve earth, the reason that the British industry changed to it was surely an attempt to join what seemed to be the winning side in the disagreement between the US car manufacturers where both systems had been common ?

I believe that GM had their own electrical division under the brand name AC Delco, and Ford used Motorcraft. The prince of darkness was, mainly, supplier to the UK manufactures like Austin,Morris, Riley, MG, Jaguar,Hillman , singer, Sunbeam, Humber, Standard, Triumph etc., Now all gone.ll.

Don't forget that Lucas also had local manufacturing in Australia. My sister's first job out of school was as a receptionist there.  I was, as a newly graduated industrial chemist, involved in supplying metalworking chemicals to the plant. They supplied most of the local automotive manufacturers. 

I still have a 1976 Holden fitted exclusively with Lucas o.e.m. equipment,  all of which is still the original fitment and still operating perfectly. 

I worked at Lucas Aerospace in the early '70s. I also wondered about the UNF/UNC threads being introduced.

Apparently, in WW2 the massive influx of American military vehicles meant a huge influx of A/F fasteners. Maintenance crews were forever picking up the wrong spanners, the wrong nuts and cursing the logistical requirements of stocking both at front line. Never again. Vehicles were also disabled by incorrectly connecting batteries.

NATO standard were quickly introduced after the war. Imperial threads were allowed only in extreme circumstance. The aircraft industry was fully UNF/UNC by early '70s.

The US military maintenance crews returned from WW2 mentally scarred by their meeting with BSF/BSW/BA nuts and threads. I'm sure many took civilian jobs in the motor trade.

And where were the motor industry products headed just after the war? Not the home market - you guessed it. With NATO leading the way, we were headlong towards UNF/UNC positive earth.

Peter

I am thinking that the question of commonality of components had something to do with the change.

If the largest auto manufacturers were going to positive earth systems then common components would change likewise.  I only made sense to have all the systems wired up the same to avoid costly mistakes in connections.  And the maker/suppliers of the components could reduce their inventory accordingly.

Mike

I think you mean -ve earth. Earlier custom was to use +ve. Just checked  1950's model 7 and 88/ 99 manuals. Show +ve earth

Negative earth was the norm prewar. Positive postwar, and now back to negative. When I put a radio into my 1957 Landrover the simplest way to make sure the antenna had the correct polarity was to change the LR to negative earth. Al would have been very upset to see red for negative and black for positive thereafter...