10 replies to this topic

[Ratty165]

Hi all, I need to replace a positive earth battery on a Mark 1. Can anyone advise which cable I should disconnect first? The positive earth, or live negative? Many thanks if you can enlighten me.

[NikOett]

The opposite approach to what you would do with a negative earth battery. So take the positive earth off first. You'll be likely touching the body as you do this, so there is no voltage difference between the body and the terminal. Once the (positive) earth is disconnected from the battery, the body isn't held at a different voltage to the negative terminal, so there will be no voltage difference. Reconnection is the reverse of removal as they say.

[Ratty165]

The opposite approach to what you would do with a negative earth battery. So take the positive earth off first. You'll be likely touching the body as you do this, so there is no voltage difference between the body and the terminal. Once the (positive) earth is disconnected from the battery, the body isn't held at a different voltage to the negative terminal, so there will be no voltage difference. Reconnection is the reverse of removal as they say.

 

Thanks very much for clarifying, NikOett - I shall follow that procedure. 

[gazza82]

It's always Earth cable first ..

[Gaz66]

As a bit of a veer off topic......
Why was a positive earth adopted for the early cars?

[stuart bowes]

https://mgaguru.com/...ctric/et098.htm

 

interesting read (if that's the sort of thing you're into)

[Spider]

As a bit of a veer off topic......
Why was a positive earth adopted for the early cars?

 

My understanding was that it was felt that it led to less galvanic corrosion of the body and chassis.

[Tornado99]

https://mgaguru.com/...ctric/et098.htm

interesting read (if that's the sort of thing you're into)

Nice reading.
I will add that the statement all vehicles from the '60s on were negative earth is not correct. My '74 Norton Commando motorcycle was positive earth from factory. This has not been much of a problem for updated electronic ignitions, modern regulator/rectifiers, even LED lighting bulbs can be bought that are polarity insensitive.
Another quirk from the deep mists of time, many brit bikes had left RIGHTfoot gear shifting while Japanese and US bikes all had right LEFT foot snifters. No obvious rationale for the difference other than arbitrary historical convention. This lasted until '75 when Norton made the change to right foot shifting (still positive Earth though)...just before going out of business a year later.

Edited by Tornado99, 28 January 2022 - 09:31 PM.

[Quinlan minor]

 

Another quirk from the deep mists of time, many brit bikes had left foot gear shifting while Japanese and US bikes all had right foot shifters. No obvious rationale for the difference other than arbitrary historical convention. This lasted until '75 when Norton made the change to right foot shifting (still positive Earth though)...just before going out of business a year later.

 

 I fear you may have mixed up your right and left.

Virtually all Brit bikes, up until late '70s, had right hand gear shifters. My '73 850 Commando certainly did. My '76 Laverda Triple does, too.

The reason for the British bikes right change was that it allows you to put your left foot down when stationary, on the kerb/protected side. You need to engage a gear to move off, so you might as well keep the right foot on the peg. The Continentals and Americans tended to have left side gear shifts for the same reason.

Japanese manufacturers, with the US market in mind, adopted the left foot gearchange despite driving on the correct side of the road
 

[Tornado99]

 

 

Another quirk from the deep mists of time, many brit bikes had left foot gear shifting while Japanese and US bikes all had right foot shifters. No obvious rationale for the difference other than arbitrary historical convention. This lasted until '75 when Norton made the change to right foot shifting (still positive Earth though)...just before going out of business a year later.

 

 I fear you may have mixed up your right and left.

Virtually all Brit bikes, up until late '70s, had right hand gear shifters. My '73 850 Commando certainly did. My '76 Laverda Triple does, too.

The reason for the British bikes right change was that it allows you to put your left foot down when stationary, on the kerb/protected side. You need to engage a gear to move off, so you might as well keep the right foot on the peg. The Continentals and Americans tended to have left side gear shifts for the same reason.

Japanese manufacturers, with the US market in mind, adopted the left foot gearchange despite driving on the correct side of the road
 

 

Thx for correcting my switcheroo.

 

Also the Norton has atypical shifting sequence....1st engages with a lift up on the shifter, while 2-4 need it pushed down....going up a gear means pushing down on the lever. Apparently this has some advantages while racing and shifting in hard corners...probably the act of getting ones foot under the lever while leaned over hard at a high speed corner reduces ground clearance or something like that... . 

Edited by Tornado99, 28 January 2022 - 09:32 PM.

[stuart bowes]

I'm not a biker at all but I've definitely heard of 1 up 4 down before.. to be honest I thought that was the way with all bikes

 

but again I'm clueless I'm more than happy to admit