Test Dynamo/Generator

I have an LCD screen cheap multi meter from RadioShack and need to test my dynamo. Is this futile without a regular moving-needle type or can I make enough sense of what's going on with a digital meter?

I used the even cheaper (free) Harbor Freight LCD model - worked fine.

Main problem I ran into was corroded points inside the regulator that had to be filed. I used a tool designed for cleaning points called a "burnishing tool" (basically a fine file) but it was not coarse enough to cut the crud on the points. Finally just used a small fine file. Adjusting the regulator was lots of fun. Wound up with about 12.6 volts @ idle and about 14.5 volts @ 2000 rpm with lights and heater fan on - generator was not rebuilt just cleaned and re-used.

Good luck,
Eric

Ah - found the procedure in the bible

http://mgaguru.com/mgtech/books/pdf/Lucas_Generator_and_Control_Box_Tests.pdf

Just tested by removing leads from generator, clipping an alligator lead across the posts and then measuring from that point to the mount bracket. I got only about 50 Millivolts so something has gone wrong inside. I will pull the unit tonight and look at the brushes. I bet they have slipped out of place from the movement of pulling it out for my engine mount change.

Geoff - what about polarizing the generator field?

Russ

Geoff - what about polarizing the generator field? Barney says you have to do this each time you disconnect the battery.

Russ

http://www.youtube.com/watch?v=wH_yIeKsBSM&feature=related

John Twist has an easy test for the generator at about 3:40. Also helps to pinpint the electrical issue.

See also his video #40 where he diagnoses the generator internals. http://www.youtube.com/watch?v=sqCYcW0bAYA&feature=channel

I set my regulator using the manual linked in Eric's post. It looks overwelming, but just find your regulator and it should only be a few pages.

In practice, the only time you "might" need to polarize the generator is when you put in a new one or when you change to neg ground. The reason that I use the term "might" is that unless you are performing some diagnostic testing, the MGA circuit itself will energize the generator in the proper polarity. The generator does not need to be polarized. When you turn on the ignition, the system properly energizes the field in the "proper" polarity regardless of the predisposed "flashed" condition.

Only when you are testing the generator with any of the diagnostic tests before runniong the car for the first time, do you need to flash the generator. This is needed when the generator needs to run in a self-energizing mode. The regulator disconnectes the battery every time the ignition is turned off. So...replacing a battery would not necessitate reflashing.

The reality is you can restart a car that has been sitting for decades and if the electrical system is operational, the generator will function as demanded, pos or neg ground without any human intervention. You can reverse the battery ground polarity and things will work properly the moment you turn the ignition on. Now if things don't work properly and you decide to do some generator tests (without the regulator) then you may have to flash the gen just to perform the Lucas-prescribed tests.

OK, pulled and opened the generator and it was clear what the problem was clear immediately as I'd hoped. The wire has snapped off one of the brushes, and it looks too worn anyway. I don't suppose this is something I can find from a local supplier? I know they are cheap (Barney says $3, but they're $1.95 at Moss - even better), but $9 shipping for a small, light, cheap item would offend my cheapskate streak.

Geoff, do you have any Moss distributors near you? If so, have them order for you, they can combine it with other orders and pick up the shipping.

I'm not aware of any Moss Distributors near me. I'm two hours from the East Coast Moss location, so I figure I'm too close. Know how I could find out?

I tried to find some kind of list of Moss distributors but didn't come up with anything. You can probably just call and explain to them your issue, they may be able to point you to a Moss distributor closer to you.

Hopefully, someone on the forum will pipe up if they know of any.

Best of luck,
Larry

If you just wait a day or two you'll find something else you need. Every Time I made a small order to Moss I thought of more things to order just after I got their email saying "Your order has been shipped"

Napa list a brush for a early MGB generator that may be the same..


Generator Brush
Part Number: ECH E403
Product Line: Echlin Ignition Parts

Moss lists two different brush sets depending on the generator number. For "orig. generators marked #22700, #22704 " it shows the same Moss part number as they do for the MGB brushes. If yours is one of those numbers should be fairly quick to get it from the warehouse to your local NAPA store.

OOPS: looks like I can't post a direct link to the NAPA part, will have to go to www.napaonline.com and search for generator brushes for 1963 MGB.

The very early MGA generator 22258 uses different brushes. All 227xx generators use same brushes as the MGB through 1967. Generator brushes are $4 at NAPA.

I must need to learn the secret of searching the Napa site because I had already looked for generator brushes and found nothing. Thanks for the tip and the part number - it's showing as a warehouse item so I'll call as soon as they open.

Gary, I've done that "what else am I gonna need" trick at least once every other week for the last two months and have run out of ideas, but I'm gonna add an extra brush set to my next order. I should compile a list of small items you should just buy as soon as you buy a driver with unknown history. It would save $100 in shipping to make a $100 purchase up front just in case I bet.

Called in to Napa today. They said it'll be Monday at best, but they do have them at a regional warehouse. The stamped ID on the generator housing appears to be 22704, so I have the later type.

I've ordered so many "might as well" and "just in case" parts over the last 3 months that I'm not sure there is anything else I can excuse buying to make up for the shipping.

Thanks for the help again - I'll let you know how they turn out.

Geoff, How far is Ashburn from Petersburg? That's where Moss is. Best of luck. Basil

About 3 hours, sadly. My wife is growing suspicious of my attempts to find excuses to take trips down there.