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MG MGB Technical - Lucas - Saturn Alternator Conversion

Converted my 69 MGB from the original Lucas alternator to 91-94 Saturn alternator over the weekend. Got most of my ideas from Darryl McLendon:

http://www.onefastmgb.com/pages/6/index.htm

Results excellent. My red idiot light now no longer comes on at anything less than 1300 rpm. For more details and photos:

http://web.ics.purdue.edu/~fishertr/alternator.html
T.R. Fisher

T.R.-- Good, easily understandable instructions. I'm a novice at this electrical stuff and have some questions. To begin with, I got my '78 B three years ago. Outside of the normal Lucas problems, the car is doing great. I have noticed on some mornings, the car is a little slower turning over, even when the outside air temp is above 45 degrees. I bought a new battery when I got the car. Will the increased amperage (100 vs 30) conversion help the B turn over easier (more residual power)? Is a newer battery required? How does this conversion benefit the B or me?

thanks

Shook
Shook

Hi, Shook:

I did this project mainly for enjoyment and the satisfaction of knowing (perhaps "expecting" would be a better word) that I'm improving performance. As I said, my red idiot light no longer comes on at low rpm. This is true even when I have the headlights on, the heater fan running and the radio playing.

I am not an engineer so I don't know about your question about improved engine turn over. I wouldn't think you should need a new battery. Beyond that, perhaps someone else can answer your specific questions.
T.R. Fisher

The Saturn alternator will simply have an easier time keeping the battery charged for when you try to start, and for providing current beyond the battery's capacity when the engine IS running. An alternator doesn't do much else for you at start up until the engine is spinning it past about 600 rpms at which time the alternator kicks in (but not before). Starting is dependent on the battery for all of the car's electrical needs until it gets running.

The Saturn conversion is a boon to those with large power demands while their car is running (super power stereos, other high current accessories all on at the same time) but if all it does is meet OE demands, then you may never really use the higher current it is capable of. Daryll's site has helped a lot of folks, especially those with very early alternator or generator charging systems.
Bob Muenchausen

Hey guys, I hope I'm not sounding sour here but I'm not sure I know what the "normal" Lucas problems are, having never had an MG electrical problem that couldn't be explained by extremely advanced age, wear, neglect, and/or abuse. With a normal Lucas alternator, my idiot light stayed off at idle and the car started normally.

Shook, if you just replaced your battery and if your 28 year-old Lucas alternator is still working properly (not unusual for Lucas products!), I would suspect your 28 year-old starter. The 33 year-old starter in my '73 B/GT is finally dying. My fault - the manual says to replace the starter every 30 years or 200,000 miles - whichever occurs first.

Now, I too did the 105-amp Saturn alternator conversion, but not because of any fault with the Lucas. I added A/C, two radiator fans and halogen headlights to this car, which I fear would have taxed the 43-amp Lucas unit beyond capacity. I continue to use the little "Group 26" single 12-volt battery, and don't think there is any need to replace it with something larger.

I confess that I'm replacing the starter with a modern gear reduction unit. The old ones are sturdy, adequate and reliable. The modern ones are better. For similar reasons, I'm inclined to upgrade older MGs from dynamo to alternator: Lucas, Delco, Bosch, or whatever.

But, back to the thread. T. R., you're right about this conversion. It's beautiful, easy, looks somewhat original, and supplies gobs of overkill amps. Oh, and I forgot to mention - it's cheap. One more thing: I'm not sure those brown leads will carry all that new amperage back to the connection at the solonoid. The addition of a #10 lead helps. Incidentally, I added a voltmeter with this conversion, and I find it VERY informative!

FWIW,
Allen
Allen Bachelder

Retired, most of my drives are the one-mile trip to the shopping center --- and there just isn't enough time to recharge the battery. So I now have a Bosch knockoff to put those starting amps back in the battery a bit more quickly.


Dan Robinson

Allen, et al,

There isn't any real need to change from Lucas on account of quality of the original build or materials. People like myself did Bosch conversions years ago to those Bs and As which either had generators or which had the early 16AC and 16ACR alternators. The main problem with the early alternators was not their ability to keep the battery charged, but showed up in circumstances where it was possible to be running all the high current options at the same time ~ places like Idaho, MN, MT, ME etc. where one could have halogen headlamps, rear window defogger,wipers, and heater blower all going at once to try to make headway some winter's night.

We found the the Achille's heel of the early units was that they were set up to cut-in at about 1000 rpms ~ OK under "normal" circumstances to run on the battery only at idle, but too low a cut-in rpms under stress. We would watch lights dim, wipers slow, defrosters fall off, and defoggers drop the voltage from the battery down to as little as 8 VDC (I use a voltmeter too, good idea, it's how I concluded I needed to replace the 16AC alternator OE for my 68GT) which in itself caused poor running or even stalling of the engine. Not a good thing to happen in a snow storm at -25F at night in some regions.

It was suggested by one of the former posters here that simply changing to the Ford Fiesta Bosch unit would resolve this problem and it did as it cuts-in at about 400 rpm. What I learned later, after creating a website on how to do the Fiesta conversion (from Dan Masters, I believe), was that simply converting to the later 18ACR Lucas Alternator would accomplish the same thing as Lucas had resolved this problem with those units.

There is really no real advantage to using a Bosch unit of any origin in normal usage, but some folks like to substitute, and so I have left the website up for those who still believe that the problems they have are because of Lucas design, even tho my own experiences have indicated that Lucas equipment is the equal of anyone else's given half a chance, and in many cases, a lot better.
Bob Muenchausen

Shook

Check ALL of your connections starting at the battery posts and all the way through the starter. Corrosion on one or more of these can cause the type of performance you describe. Lots on this in the archives. If all of your connections are bright and clean then you might want to pull your starter and take it to a local auto electrical shop and have them test it.


HTH

Larry
Larry Hallanger

Thanks for the education. The B wouldn't start again this morning. Only 55 degrees in the morning. Cranked it up last night for ten minutes insuring (hopefully) of a quick start this morning. I'll first check connections to the battery (been two years) and then starter. If nothing elese, I'll take the alternator to the nearest Advanced Auto Parts for diagnosis. I don't plan on adding anything electrical is the car that wasn't there in '78. Advanced has the LUCAS OE going for $65.00. As Allen says, the manual says to replace the starter every 30 years or 200,000 miles - whichever occurs first. Not up to either, but probably wouldn't be a bad idea to replace for piece of mind. The only upgrade I 've made is a Pep Boys AM/FM/CD in-dash player.

Thanks for the electrical discussion and opinions. As always, this forum brings together different mind sets and theories.
Shook

Sounds more like battery rather than starter to me, especially if the cold slows your cranking. If the connections are OK, either the battery isn't holding charge or the alternator isn't charging it properly. Your ignition light is there to warn of the latter, and a voltmeter will diagnose either (they are really cheap and a very useful piece of kit). Have a look at http://www.mgb-stuff.org.uk/ for the detail.
Steve Postins

And, Shook, of course it's possible that your new battery is defective. Also, contrary to my starter diagnosis: very often a weak starter will fail more often when hot rather than cold.

Larry's advice about checking connections is right on the mark. Make sure that includes the ground lead from the battery to the frame, cleaning both ends as well as the frame where it connects. Next, don't ignore the engine ground strap! Is it clean and bright at both ends? And bolted down tightly?

I have long been an advocate of rebuilt parts from Advance Auto, but recent experience has been contrary. I bought a rebuilt windscreen wiper motor from Advance and found nothing more than a dab of new grease and a paint job. The motor itself was seized. Even if one of their new alternators works; how long will it work?

FWIW,
Allen



Allen

Ditto on cleaning the ground connections (biggest single cause of "normal Lucas problems").
Carl Floyd

The first thing I did when I got the car three years ago was to replace the battery. The PO was a fair weather driver and let the car sit over the winter months. I've never inspected or cleaned the ground connections because Ive never had a reason until now. Sounds like a couple hour/beer job. Since I haven't inspected the battery since it was installed, this will also be a good time.


Thanks again for the advice to a B Plebe.
Shook

Hi Guys,

I'm no expert to all Lucas gremlins, just want to share some experience.

When my BGT was rebuilt 5 years ago, the electrician put a Denso 45 amp alternator to the car with some home-made brackets. The B is equipped with A/C and running total 3 electrical fans, 2 for cooling the engine and one for A/C condenser. But never has charging light on even with 700 rpm idle. In addition, the starter was dis-assembled for cleaning the contact between the brushes and armature.

Until last few months, the car suffered from starter problem. Sometimes it cranked to start beautifully, sometimes just with a sound of "clip" when cold/hot starting. The electrician asked me just to replace the starter soleniod, of course I did it at once with a USD35 japanese made soleniod sourced locally. The car started at once without any hesitation after soleniod replacement.

Just with curious, I dismantled the old soleniod, the contact point inside it was so severely pitted after serving 36 years and that account the poor current conducting!

Ennio
Ennio Wong

Shook,

Do you know for a fact if the current battery is a single twelve-volt (group 26 - as most of us are now using) or if your car still has the twin six-volt batteries as originally equipped? If you have the twin sixes, you'll have two more battery post connections to clean. Also, if you have the twin sixes and find you need to replace them, I would strongly recommend the single twelve-volt instead.

It's not really normal, but quite possible, that your three year-old battery/batteries is/are tired out. But check those connections first and post back with your results. The brand of beer you use may affect your results: Old Speckled Hen or Newcastle Brown work best. Bud Light might corrode the terminals. 8^)

BTW, up until about a month ago, my son lived in Colorado Springs. Nice town - he enjoyed it. Now he's trying, in vain, to find similar housing at something remotely close to the same prices where is new job is, in Amherst MA.

Cheers,
Allen
Allen

Allen,

I replaced the previous single/12 volt battery with the same size/amps. I'll clean the terminals and any other connectors involved. I've been fortunate with the car--no electrical demons since I've owned it. Might even be time to replace the ground straps for added insurance.

BTW, I'm two miles from the Air Force Academy if your son asks.

Thanks again

shook
Shook

ALLCON,

The B wouldn't start again this morning. Got on-line with Advanced Auto in search of a new battery. They list group 24 as the battery for the B. As Allen mentioned, the group 26 battery is the correct choice. What's the difference between the groups? Physical size?

shook
Shook

Gotta love Google ;)

http://www.rtpnet.org/teaa/bcigroup.html

I use the smaller one. Easier to get in & out.
Carl Floyd

Mr. Floyd,

I never thunk about using Google. I thought the different Group #'s related to amp ratings.

Thanks for googling this info.
Shook

Mister? I ain't that old! Even my dad will tell ya to call him Herren (& he's 71). The name's Carl. Kids call me Coach Carl.

New website, for me, too, with good info. Glad it helped.
Carl Floyd

Got a new battery from Advanced Auto yesterday, plugged it in, and the B fired right up. I'm not holding out all hope that the new battery fixed the problem. Sound cynical, but in the three years I've owned the car, this and the horn stalk are the only two Lucas maladies I've had to deal with. I'll keep my eye on the alternator just in case.

Thanks for the battery size info and diagnostics.
Shook

This thread was discussed between 22/05/2006 and 26/05/2006

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