Author Topic: Positive or negative earth  (Read 2252 times)

Offline Adtrac

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Positive or negative earth
« on: 15.07. 2023 09:39 »
 Can anyone tell me if a 1953 BSA Gold Flash  electrics are positive or negative earth ,as the wiring on my project has been butchered beyond recognition *????*
SA hopefully getting a 53 A10 GF

Offline jhg1958

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Re: Positive or negative earth
« Reply #1 on: 15.07. 2023 11:02 »
My 1961 was positive earth and I am fairly certain that the majority of old British bikes (and cars) were.  I changed mine for a negative earth when I rewired mine. I also fitted an earth wire to just about everything as I have never been a fan of using the frame as an earth. I remember as a youth with bits of wet and dry trying to get continuity between components with lights working intermittently. 

Now that positive earth LEDs are available I am not sure of the benefits of changing over the earth.

Does anyone know why we have standardised on Negative earth?  Could it be anything to do with corrosion on components that are used as earth.

John
1961 Golden Flash S/Arm

Online groily

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Re: Positive or negative earth
« Reply #2 on: 15.07. 2023 12:48 »
From roughly the 1930s to mid/late 1960s, most British constructors used positive earth, believing that it reduced corrosion on electrical terminals, and that it was kinder to spark plugs - in coil ignition systems - to have negative sparks. (So says my 1967 edition of the Penguin Car Handbook, by Robert Ireson.)
The latter is true enough, but is irrelevant with a magneto, where you get one pos and one neg spark on a twin, or two and two on a 4 cylinder engine, whether you like it or not. 
By the 1970s all the manufacturers had pretty much gone back to Neg earth, which continental Europeans hadn't wavered from (and nor had Rolls Royce). Materials were better, so the 'issues' were now regarded as minimal.

Positive earth is often said to cause more galvanic corrosion to bodywork and so on, but every Brit car I ever had of either polarity from those years turned into ferrous oxide pretty darn fast  . . . steel treatment or lack of was a big part of it, and paint wasn't up to much, as all those businesses selling underseal products found to their advantage.

For no really good reason, I have my bikes wired positive earth, but it's just habit really. Negative can be helpful for attaching modern electrical gizmos I believe, although I don't have any, and was helpful for LEDs initially as mentioned.
Bill

Offline muskrat

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Re: Positive or negative earth
« Reply #3 on: 15.07. 2023 22:04 »
Can anyone tell me if a 1953 BSA Gold Flash  electrics are positive or negative earth ,as the wiring on my project has been butchered beyond recognition *????*
G'day Adtrac.
1953 GF would have been + earth.
Cheers
'51 A7 plunger, '57 A7SS racer now a A10CR, '78 XT500, '83 CB1100F, 88 HD FXST, 2000 CBR929RR ex Honda Australia Superbike .
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Offline Sakura

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Re: Positive or negative earth
« Reply #4 on: 16.07. 2023 08:59 »
My understanding is that the changeover from negative to positive earth occurred around 1950/51.
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Online Triton Thrasher

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Re: Positive or negative earth
« Reply #5 on: 16.07. 2023 12:10 »
Quote from: groily
and that it was kinder to spark plugs - in coil ignition systems - to have negative sparks.

But can’t you just reverse the spark polarity by swapping the low tension wires on the coil?

Online groily

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Re: Positive or negative earth
« Reply #6 on: 16.07. 2023 14:08 »
You'd have thought TT, yup. I guess folk slavishly followed the old SW and CB markings (or + and -) marked on the coil itself. (Or Mr Ireson hadn't thought about it a whole lot, his comment was only half a sentence.)
I remember wiring them for negative sparks back in the day, regardless of markings, using a pencil flare test if necessary to confirm polarity.
A  positive spark is said to be as much as 15% weaker than a negative one at the plug owing to the marked preference of ions to jump from 'hotter to cooler'. It is certainly the norm that the retarded spark on a V twin mag should be the negative one, to give it every chance, and so should the spark on any single.
Some say we should rotate the plugs on mag-fired twins every so often to even out electrode wear. Can't say I have ever worried much, but I usually stuff 'em back in opposite sides if I've pulled  them out for any reason.
I guess the issue could be relevant for anyone running trad coil ignition on a positive earth twin.
Bill

Offline morris

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Re: Positive or negative earth
« Reply #7 on: 16.07. 2023 17:46 »
My understanding is that the changeover from negative to positive earth occurred around 1950/51.
I’d rather go for end fifties early sixties as my ‘55 Isis came out of the factory with the + pole connected to the body
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Re: Positive or negative earth
« Reply #8 on: 16.07. 2023 19:16 »
My understanding is that the changeover from negative to positive earth occurred around 1950/51.
I’d rather go for end fifties early sixties as my ‘55 Isis came out of the factory with the + pole connected to the body

Your 1955 + earth car agrees with what he said.

Offline Sakura

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Re: Positive or negative earth
« Reply #9 on: 17.07. 2023 15:44 »
Morris Isis, we had a customer with one of those when I was an apprentice. Seem to remember the gear lever and handbrake being by the door. Presumably to avoid "mistakes" if a lady was sitting in the middle of the bench seat. Also remember changing gear on some pickup, when sitting in the middle, for the driver, with legs either side of the gear lever. Those were the days! Decoke at 30,000, full engine overhauls at 70,000 and only if less than 300 to the pint before BMC would consider fitting new rings under warranty.
63 RGS

Offline morris

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Re: Positive or negative earth
« Reply #10 on: 17.07. 2023 19:53 »
My understanding is that the changeover from negative to positive earth occurred around 1950/51.
I’d rather go for end fifties early sixties as my ‘55 Isis came out of the factory with the + pole connected to the body

Your 1955 + earth car agrees with what he said.
You’re right. I misread.
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'52 BSA A 10 Plunger
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Offline morris

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Re: Positive or negative earth
« Reply #11 on: 17.07. 2023 20:05 »
Morris Isis, we had a customer with one of those when I was an apprentice. Seem to remember the gear lever and handbrake being by the door. Presumably to avoid "mistakes" if a lady was sitting in the middle of the bench seat. Also remember changing gear on some pickup, when sitting in the middle, for the driver, with legs either side of the gear lever. Those were the days! Decoke at 30,000, full engine overhauls at 70,000 and only if less than 300 to the pint before BMC would consider fitting new rings under warranty.
Earlier cars for the UK market had a “bent over” steering column gear change which probably also didn’t contribute to its already low popularity.
Strange though because for the export markets they made them with a conventional column gear change pointing to the middle
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'52 BSA A 10 Plunger
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Offline Rex

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Re: Positive or negative earth
« Reply #12 on: 17.07. 2023 21:36 »
I always liked column change but I've never seen or driven one where the gear lever isn't operated by the driver's left hand.
The worst must be those awful Citroens and Renaults where the gear lever is a ball ended thing sticking out of the dash board.

Offline Sakura

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Re: Positive or negative earth
« Reply #13 on: 18.07. 2023 16:38 »
Column changes are, or rather were, ok when new but not so good when worn, as they were on all the cars I owned. 4 speed Ford Thames derivatives used to tangle themselves up requiring groping blindly about underneath by the roadside to free them up. One haulage company I worked for had some Saviem artics with crash boxes and column changes, not popular with driver's!
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Re: Positive or negative earth
« Reply #14 on: 18.07. 2023 17:03 »
My 1961 was positive earth and I am fairly certain that the majority of old British bikes (and cars) were.  I changed mine for a negative earth when I rewired mine. I also fitted an earth wire to just about everything as I have never been a fan of using the frame as an earth. I remember as a youth with bits of wet and dry trying to get continuity between components with lights working intermittently. 

Now that positive earth LEDs are available I am not sure of the benefits of changing over the earth.

Does anyone know why we have standardised on Negative earth?  Could it be anything to do with corrosion on components that are used as earth.

John

John, your Forum picture of the A10 in Nutley Blue bears an uncanny resemblance to my bike as it was pictured many, many years ago by a previous owner.  I was given the picture when I contacted him to investigate the history of the bike.  I'll see if I can dig it out for purposes of comparison.
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