Salut à tous,Suis en train de terminer le remontage d une B de 1967 pour un copain
(j ai mis un OD entre autre).J ai changé la polarité (de+ à la masse ,j ai mis le moins)sans oublier d initier la dynamo.
Aurai-je des problemes à votre avis(compte tours pex)et pour l allumage j ai inversé les fils de bobine.Y a t il autre chose à faire.Merci
Pierrot
Changement de polarité
-
Pierre NOEL
- Messages : 955
- Enregistré le : 25 oct. 2005, 19:35
Pierre,
De mémoire, il y a aussi
- Une modif à faire au compte tour
- Vérifier que la pompe SU n'est pas une version polarisée (munie d'une diode).
- Inverser les connexions de la batterie ( c'est bête mais je le dit quand même).
- Il est préférable de remplacer tes vis platinées et tes contact de pompes à essence car ils ne survivent pas longtemps à une inversion de polarité.
- Le cas échéant, la radio.
J'avais une note trés complète sur le sujet, il faut que je cherche.
Pierre
De mémoire, il y a aussi
- Une modif à faire au compte tour
- Vérifier que la pompe SU n'est pas une version polarisée (munie d'une diode).
- Inverser les connexions de la batterie ( c'est bête mais je le dit quand même).
- Il est préférable de remplacer tes vis platinées et tes contact de pompes à essence car ils ne survivent pas longtemps à une inversion de polarité.
- Le cas échéant, la radio.
J'avais une note trés complète sur le sujet, il faut que je cherche.
Pierre
-
Pierre NOEL
- Messages : 955
- Enregistré le : 25 oct. 2005, 19:35
Et de un:
http://www.chicagolandmgclub.com/techtips/mgb/134.html
Et de deux:
http://www.chicagolandmgclub.com/drivel ... /tech.html
Et de trois:
Ground Conversion
I've not had to do this myself so what follows is what I've gleaned from elsewhere. The usual reason for converting is that the owner also wants to replace the dynamo with an alternator for its higher output, or fit modern electronic devices. It's possible to connect a positive ground radio in a negative ground car of course, but the case has to be insulated from the car body, and if any exposed part of the radio is at (radio) ground potential there is always the risk that this will be bridged to some other part of the car that is at car ground, which will result in a short-circuit and a blown fuse at best. You can also get inverters which convert polarity, but will need a pretty big output for anything but a basic radio. Of course, if you already have a positive ground radio, you will not be able to use it after the conversion.
The first consideration is the batteries. Before doing anything else make sure the battery ground connection is the first thing you remove, and the last thing to reconnect at the end. All the batteries I have seen have different-sized posts for +ve and -ve so in theory you cannot connect them the wrong way round, therefore the connectors will have to be swapped over or replaced. The original 'helmet' type that completely cover the post and are secured with a small screw that goes into the post expand and get loose with age and repeated removal and replacement, giving poor connections, and some resort to using silver paper to get a tight fit. Seeing as you are changing the polarity originality is not an issue, so if you haven't already replace these with the bolt-up type which give a much better connection. The other thing with the helmet type is that they are usually moulded on, these have to be cut off and replaced with the clamp on type, which usually have two large screws to secure the cable. This results in shortening each cable by about an inch but that shouldn't be a problem. If it is, then you will have to replace the cable(s). If you already have clamp-up type connectors remove these from the hot and ground connections and swap them over. Unless you have already replaced the twin-6v with a single-12v you will also have to deal with the interconnecting cable in the same way, and unless it can be physically removed from the car and reversed you will have to cut off and replace moulded-on helmet-type connectors, or remove and swap over the clamp-up type.
If you are retaining the dynamo this has to be repolarised so that it generates the correct polarity voltage. Disconnect the wires from the F and D terminals of the dynamo and with the batteries connected take a jumper lead and connect it briefly between the brown at the fusebox and the F terminal of the dynamo so as you see a small spark. Just one flash is enough, then reconnect the dynamo.
Cars after 64 had the electronic tach and this has to be converted too. You have to get into the case, find the supply and ground wires from the case to the circuit board, and reverse the connections. But note that some cars (e.g. a 67 B belonging to John Schroeder) have the circuit board screwed to the case and pick up the ground connection this way. In this case you have to isolate the circuit board from the case, move the original 12v supply wire from the terminal on the case to the body of the case, and provide a new wire from the ground connection on the circuit board to the 12v supply terminal on the case. John intends to publish notes and pictures of this on the Chicagoland MG Club website. In all cases you have to reverse the direction of the current pulse through the pickup and this also varies. On early models the pickup is external and a continuous white wire comes out of the loom, through the pickup twice (i.e. one turn) then back into the loom. With these carefully note the route the wire takes now, remove it, and reverse the direction of the wire through the pickup, but keeping everything else the same e.g. the position of the loop. On later tachs the pickup is external with two flying leads with male and female bullet connectors to match up with their opposite numbers on wires from the loom. As you are doing wiring changes inside the tach it would be neater to reverse either the ignition wire as it passes through the pickup, or the output of the pickup to the circuit board, whichever is easiest. But an alternative is to reverse the bullet connectors where the loom joins the tach. As to which pair, that is up to you. Since it is the car that has changed polarity it might make sense to change the bullets on the loom wires. But as you have to change the polarity of the power supply at the tach, it might make sense to change the bullets on the tach wires as well. The only advantage of doing the other way is that if you have to replace the tach in the future the pickup part of the polarity change does not have to be done again.
If you have the heater fan motor with black and green/brown wires these may have to be reversed at the connectors by the motor. If in doubt try them both ways (you can't do any harm) and if one way blows more air than the other that is how to connect it.
Finally fuel pumps. Originally the pumps had capacitor protection (reduces the burning of the points) and are not polarity concious. But if you have installed one of the later pumps with an 'X' in the part number e.g. AZX137 then these have diode protection (improved points protection) and need to be modified. Open the electrical end-cap and locate the black cube with two wires - one black and one red - coming out of the same end of the cube. These wires must be removed from the pump and connected the other way round. There is no immediate risk of damage powering-up without having done this change but it will largely disable the points protection so the points will burn faster than usual. Important If you have fitted one of the 'pointless' electronic pumps then you will probably have to replace the pump as converting the elctronics in these is much more involved, and changing the battery polarity without doing anything about the pump will result in the pump not working at best, or destroying the electronics and possibly burning the loom at worst.
That's it, unless you have any other electronic devices, which will be aftermarket and so up to you. The only possible other thing might be that the wipers now park in a slightly different place. If it bugs you then move the arms on the spindles. Start the car, check the tach is working, and measure the voltage on the brown at 3000rpm with minimal load. With a dynamo you should see in the order of 14.3v to 15.5v depending on ambient temperature (lower volts at higher temps), with an alternator you should see 14.3v to 14.7v.
Pierre
http://www.chicagolandmgclub.com/techtips/mgb/134.html
Et de deux:
http://www.chicagolandmgclub.com/drivel ... /tech.html
Et de trois:
Ground Conversion
I've not had to do this myself so what follows is what I've gleaned from elsewhere. The usual reason for converting is that the owner also wants to replace the dynamo with an alternator for its higher output, or fit modern electronic devices. It's possible to connect a positive ground radio in a negative ground car of course, but the case has to be insulated from the car body, and if any exposed part of the radio is at (radio) ground potential there is always the risk that this will be bridged to some other part of the car that is at car ground, which will result in a short-circuit and a blown fuse at best. You can also get inverters which convert polarity, but will need a pretty big output for anything but a basic radio. Of course, if you already have a positive ground radio, you will not be able to use it after the conversion.
The first consideration is the batteries. Before doing anything else make sure the battery ground connection is the first thing you remove, and the last thing to reconnect at the end. All the batteries I have seen have different-sized posts for +ve and -ve so in theory you cannot connect them the wrong way round, therefore the connectors will have to be swapped over or replaced. The original 'helmet' type that completely cover the post and are secured with a small screw that goes into the post expand and get loose with age and repeated removal and replacement, giving poor connections, and some resort to using silver paper to get a tight fit. Seeing as you are changing the polarity originality is not an issue, so if you haven't already replace these with the bolt-up type which give a much better connection. The other thing with the helmet type is that they are usually moulded on, these have to be cut off and replaced with the clamp on type, which usually have two large screws to secure the cable. This results in shortening each cable by about an inch but that shouldn't be a problem. If it is, then you will have to replace the cable(s). If you already have clamp-up type connectors remove these from the hot and ground connections and swap them over. Unless you have already replaced the twin-6v with a single-12v you will also have to deal with the interconnecting cable in the same way, and unless it can be physically removed from the car and reversed you will have to cut off and replace moulded-on helmet-type connectors, or remove and swap over the clamp-up type.
If you are retaining the dynamo this has to be repolarised so that it generates the correct polarity voltage. Disconnect the wires from the F and D terminals of the dynamo and with the batteries connected take a jumper lead and connect it briefly between the brown at the fusebox and the F terminal of the dynamo so as you see a small spark. Just one flash is enough, then reconnect the dynamo.
Cars after 64 had the electronic tach and this has to be converted too. You have to get into the case, find the supply and ground wires from the case to the circuit board, and reverse the connections. But note that some cars (e.g. a 67 B belonging to John Schroeder) have the circuit board screwed to the case and pick up the ground connection this way. In this case you have to isolate the circuit board from the case, move the original 12v supply wire from the terminal on the case to the body of the case, and provide a new wire from the ground connection on the circuit board to the 12v supply terminal on the case. John intends to publish notes and pictures of this on the Chicagoland MG Club website. In all cases you have to reverse the direction of the current pulse through the pickup and this also varies. On early models the pickup is external and a continuous white wire comes out of the loom, through the pickup twice (i.e. one turn) then back into the loom. With these carefully note the route the wire takes now, remove it, and reverse the direction of the wire through the pickup, but keeping everything else the same e.g. the position of the loop. On later tachs the pickup is external with two flying leads with male and female bullet connectors to match up with their opposite numbers on wires from the loom. As you are doing wiring changes inside the tach it would be neater to reverse either the ignition wire as it passes through the pickup, or the output of the pickup to the circuit board, whichever is easiest. But an alternative is to reverse the bullet connectors where the loom joins the tach. As to which pair, that is up to you. Since it is the car that has changed polarity it might make sense to change the bullets on the loom wires. But as you have to change the polarity of the power supply at the tach, it might make sense to change the bullets on the tach wires as well. The only advantage of doing the other way is that if you have to replace the tach in the future the pickup part of the polarity change does not have to be done again.
If you have the heater fan motor with black and green/brown wires these may have to be reversed at the connectors by the motor. If in doubt try them both ways (you can't do any harm) and if one way blows more air than the other that is how to connect it.
Finally fuel pumps. Originally the pumps had capacitor protection (reduces the burning of the points) and are not polarity concious. But if you have installed one of the later pumps with an 'X' in the part number e.g. AZX137 then these have diode protection (improved points protection) and need to be modified. Open the electrical end-cap and locate the black cube with two wires - one black and one red - coming out of the same end of the cube. These wires must be removed from the pump and connected the other way round. There is no immediate risk of damage powering-up without having done this change but it will largely disable the points protection so the points will burn faster than usual. Important If you have fitted one of the 'pointless' electronic pumps then you will probably have to replace the pump as converting the elctronics in these is much more involved, and changing the battery polarity without doing anything about the pump will result in the pump not working at best, or destroying the electronics and possibly burning the loom at worst.
That's it, unless you have any other electronic devices, which will be aftermarket and so up to you. The only possible other thing might be that the wipers now park in a slightly different place. If it bugs you then move the arms on the spindles. Start the car, check the tach is working, and measure the voltage on the brown at 3000rpm with minimal load. With a dynamo you should see in the order of 14.3v to 15.5v depending on ambient temperature (lower volts at higher temps), with an alternator you should see 14.3v to 14.7v.
Pierre
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