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MG MGB Technical - Lots of questions from new owner

Well I am now the proud/brave owner of a '67 MGB. The previous owner did alot to this car, but there are a few "little" things that need to be done.
A few questions off the bat:
How can I tell if I have a positive, or negative ground?
How can I tell if I can use unleaded fuel vs. using a lead additive? The engine was rebuilt about 100 miles ago, which was probably a few years ago.
There will certainly be more questions to come.
JordanB

Jordan, welcome to the world of B’s. Your first question is easy to answer. Take a look at the batteries, under the shelf, behind the seats. You will have one of two set ups. One will be the original set up with two 6-volt batteries, the other being with one 12-volt battery. Either way the earth strap will be connected to the positive terminal or negative one. Whichever way it is the way your car is electrically grounded. Originally the earth strap was fixed to the battery cradle and thus should be easy to identify.
I will leave the answering of the second question to someone who has undertaken the work on their car. I know you'll have to remove the head to see.
Ian Holliday

Jordan: Did the car come with receipts? Ask the previous owner, or the shop that did the work, if the head was redone using hardened valve seats, stellite valves, and manganese-bronze valve guides. The first is critical, the others are nice to have. If so, then you can use unleaded as without additives.
Andrew Blackley

Jordan - If your car is really a 67, then it is a negative ground. Check to see if it has back up lights, if it does it is a 67. My car is registered with the state of Washington as a 67 but is in fact a 66 and was positive ground when I got it. If it is positive ground and you want ot convert it to negative ground, send me a private e-mail and I can lead you through the changes. At to the head being modified to no led fuel, don't wory too much about it. My MGB has never been converted to no lead and it is driven every day, including trips to California onec a year and I have never had any of the "dire consequences" that everyone talks about. I am sure that the valves will start eating away at the seats sooner than if it had hardened seats, but I will wait for that to happen to do something about it. We have been driving the car, using no lead gas for close to 20 years and I am not at the point where anything needs to be done yet. If you are not already a member of the MG Car Club Northwest Center, check out this web site and consider joining, lots of like minded people there. http://www.mgccnwc.com/
Good luck - Dave
David DuBois

Dave. To the best of my knowledge, most, if not all, 67s were positive ground. It was in 68 that the 16AC alternator with external voltage regulator was introduced.

Jordan. Ian is correct. The way to check to see what polarity your car has is to see which terminal of the battery/batteries is connected to the chassis. But, remember, your car is now 35 years old. Quite a number of things may have been changed on it during this period. Generally speaking, a car having an alternator is negative ground. If the car still has the generator/dymamo, it could be either and the battery check is the only way to truly determine what you have. The generator may be polarized to work with either ground. Hence, Ian's battery check is your first and most reliable indicator. Les
Les Bengtson

Thanks for the help guys.
The car does not have reverse lights(is this illegal?), and there is a good sized alternator under the hood, but I have not opened the battery compartment yet. Won't the alternator also be grounded to the frame?
JordanB

Jordan,

The alternator is "grounded" via its mounting to the engine. The internal electrical components are "grounded" to the case, and the case bolted to the engine, which in turn is grounded via a flexible strap to the chassis of the car.

In other words, like most other items in your electrical system (assuming it is negative ground), the positive (+) "supply" side connects via wiring, whereas the Negative (-) "return" side runs back to the battery via the bodywork/chassis/grounding straps that the item is mounted/bolted to. The sheet metal becomes the "wiring" for the return path to the battery - hence the reason the ground/earth strap for the battery is connected to the bodywork. And why a "hot" wire will spark when it touches bare metal anywhere on the car.
Bob Muenchausen

Jordan,

It's not illegal if the car was never built with backup lights. I don't know about WA law, but here the CA Vehicle Code says cars manufactured on or after 1 Jan 69 must have one or more backup lamps.
Paul K

Jordan - Your car is "legal" in the sense that it had all the equipment necessary for when it was produced and sold. You do not NEED to retrofit reverse lights. But, as it has been over 35 years since the requirement was introduced, and most people have never seen a car without reverse lights, I would look carefully and twice before letting out that clutch, though.
John Z

Les - You are correct regarding the 67 MGBs being positive ground, I stand corrected. I took my information from the wiring diagram list in the British Leyland shop manual, which listed the drawing as "negative ground 67 - 68". They also listed a starting car number, which when compared to the listing in the Moss MGB catalog, shows that car number as starting in 10/67. This would make the negative ground cars all 68s in America. Cheers - Dave
David DuBois

This thread was discussed between 03/06/2002 and 04/06/2002

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