Where did the earth come from.

Reunited Chris

Reunited Chris

Senior member
Location
Sydney
I've just been working on a hard to start 120 Jota. If the battery was fully charged it would reluctantly start, once running it was fine.
Suspecting a faulty earth I checked for an earth lead to the motor, nothing there. Given that the motor is rubber mounted there is no connection to the earth, so how was the startor motor able to turn over all be it slowly. The only earth connection I can see is the neutral indicator switch. also how did the spark plugs fire at all if there was no earthing to the ignition module.
Interested in any enlightenment.
Bike starts and runs well now.
 
Chris plucking this out of my arse, my starter motor has a welding cable that connects from the starter motor to the earth on the battery. Guess what Electronic Juru fitted that.
 
Reunited Chris said:
I've just been working on a hard to start 120 Jota. If the battery was fully charged it would reluctantly start, once running it was fine.
Suspecting a faulty earth I checked for an earth lead to the motor, nothing there. Given that the motor is rubber mounted there is no connection to the earth, so how was the startor motor able to turn over all be it slowly. The only earth connection I can see is the neutral indicator switch. also how did the spark plugs fire at all if there was no earthing to the ignition module.
Interested in any enlightenment.
Bike starts and runs well now.
Click to expand...
No idea what to suggest as all things electrical remain a perpetual mystery to me. When I saw the title of your post I was immediately intrigued to read it thinking that it was a deep, philosophical question! Hopefully, somebody will be able to resolve your earthing question but anybody out there got an answer to the other mystery ..... where DID the Earth come from? Answers on a postcard please from Alpha Centauri or somewhere that no man has ever been before!
 
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Reunited Chris said:
I've just been working on a hard to start 120 Jota. If the battery was fully charged it would reluctantly start, once running it was fine.
Suspecting a faulty earth I checked for an earth lead to the motor, nothing there. Given that the motor is rubber mounted there is no connection to the earth, so how was the startor motor able to turn over all be it slowly. The only earth connection I can see is the neutral indicator switch. also how did the spark plugs fire at all if there was no earthing to the ignition module.
Interested in any enlightenment.
Bike starts and runs well now.
Click to expand...

If you don’t have an earth strap from motor to frame, earth could well be finding a path via: gear change mechanism, drive chain, throttle and choke cables and stuff like that. Like how with some bar mounted electrics, earthing is done through steering head bearings etc.

Not ideal, as you know
 
Copper was expensive in the very early 20th century, steel frame was applied as a "return" path back to magneto or Kettering secondary cell battery systems, think early kettering were primary battery ( non rechargeable ). Seems unlikely sundry mechanical cables would support many hundreds of amps cold crank starts, let alone any I/R voltage drops.

Seen under the battery tray a high current cable on various later 120 motors, which corrodes as well known. Usually a short link starter capable to the rear crank case in some form, leaving the aluminium oxide surface to carry 200-300amps, Natural Anodizing is a very good insulator, good for up to 300V insulation capacity..... proper compression lugs on welding cable sorts the electrically challenged Laverda factory notions of how electricity flows, or does not flow in the case of oem notions... starter motor mount fastener to battery negative. Possibly, Vince was one of the first to get this engineered solution, bit of a pioneer in the day was Vince, a history of some degree...grin.

Warning, story... in electronic schematic drawings there is/was a propensity to simply draw a symbol for the return path to the energy source or similar, an infinite paper current sink i used to call it, paper conducting all the return current. Rather, draw all the conductor paths as lines and junctions to my students, correct your technicians and engineers at work, as is unenlightened understanding of electrical principles. Suspect that is a follow on from steel mechanical frames and chassis as infinite current sink return path to energy supply. j
 
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