Since my MGB GT is now negative ground it’s time to switch out the old Lucas generator and install a modern alternator. I expect many alternators will fit but decided on an AC Delco alternator from a mid 90’s Saturn as the conversion is well documented. These alternators aren’t exactly cheap but they produce mega amperage and are very well made.

Removing the old Lucas generator is very straight forward, no surprises here. The coil and bracket need to be removed as well, these will be remounted next to the old voltage regulator on the inner fender.

1967 MGB GT generator
1967 MGB GT generator
MGB engine with coil and generator removed
MGB engine with coil and generator removed
AC Delco 1994 Saturn alternator
AC Delco 1994 Saturn alternator

The pulley needs to be replaced with a v-pulley rather than the flat pulleys used on the GM cars. In theory this is easy as an air impact socket easily removes the nut and the pulley slides off. The tough part? The shaft size of the pulley on the alternator is .675 inches but the replacement pulley that I managed to locate was .66 inches. Fortunately a few minutes with a Dremel and sandpaper took the chrome coating off the inside of the pulley and everything fits nicely. You would think if they were planing on chroming a pulley they would make it the bore slightly oversize to compensate for the thickness of the chrome but this is what we get from China. Why a chrome pulley you might ask? It’s not for the bling factor, it’s what I could get in parts starved Canada within a reasonable period of time.

AC Delco with chrome pulley
AC Delco with chrome pulley

Apparently some MG owners are using an older AC Delco alternator that requires on of the mounting ears to be cut off. While this works I’m sure it voids any warranty and if you break down in the middle of nowhere and need to install a new alternator you’ll have to buy a hack saw as well. Some bright MG dude discovered on these newer Saturn AC Delco alternators that if you rotate the mounting plate 120 degrees they work perfectly. This is an easy procedure if you have female Torx wrenches but try and find one of those in small town Canada. After looking for Torx wrenches at places like Canadian Tire and Home Depot I finally decided an alternative was needed. Turns out a 1/4 inch socket grabs well enough to remove the 3 long silver bolts holding the alternator together. Easy to do at this point, without taking the alternator apart just rotate the mounting plate 120 degrees clockwise and reinstall the silver bolts.

AC Delco alternator with mounting plate rotated 120 degrees
AC Delco alternator with mounting plate rotated 120 degrees

A few alternatives are available to mount the alternator to the MGB engine. The alternator is quite a bit shorter than the generator so a spacer is needed to fill in the gap between the rear mounting bracket on the engine and the rear mounting bracket on the new alternator. Moss Motors sells a bracket that would likely work well although without accurate specs it’s really hard to know. I’m going to email them and try and get some additional information. In the meantime, I’m planning on using a long threaded rod with locking nuts and some pipe for additional strength, this should work well. Here’s a test fit and the pulley and old adjustable bracket line up beautifully.

AC Delco alternator test fit in 1967 MGB GT
AC Delco alternator test fit in 1967 MGB GT

Remember that this is a test fit only. I don’t think I would trust an installation like this for very long.

Part 2 coming up. Moving the coil and rewiring the positive ground system so everything will work.

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