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MG MGA - Distributor Model Number

I'm ordering the Petronix and the dealer is asking if the distributor is a 25D.

I've no idea.

The only info on the distibutor I can find is

40510 H

BN238 160
Tysen

Tysen,

The model is actually DM2.

See the Lucas Distributor Database:

http://www.telusplanet.net/%7Echichm/tech/lucas.pdf

But I think a 25D kit fits anyway, but I use Lumenition as they allow for more wear in the distributor shaft in my opinion.

Cheers <MARK>
Mark Hester

Thanks!
Tysen

Tysen. Mark is correct and that is the original distributor for the MGA. If you will look at the distributor body, where the vacuum advance can is attached, you will see the raised letters and number indicating "DM 2" there.

Jeff Zorn, of the Little British Car Company should, as an MGA owner himself, be able to tell you if the Petronix unit for the Lucas 25D4 will work with the DM2 distributor. He can probably get you a slightly better price than ordering directly from the factory.

Les
Les Bengtson

The pertronix for a 25D will work in a DM2, but you would either need a 25D points plate or cut off the raised fork on the points plate that used to hold the LT terminal. You can NOT fit a negative ground Pertronix to a positive ground car or vice versa. Us emust use the correct polarity model. LU-149 is negative ground, LU-149P12 is positive for the DM2.
Jeff


Jeff Schlemmer

Hi all. Since we're throwing distributor #'s around can someone tell me the correct model distributors for both the 1600 and the 1622 engines?

Al
A. Tirella

Al. The MGA 1600 used the Lucas DM 2 distributor to the basic specification of 40510. The one in my collection, out of my 61 MGA is a 40510H, but others may have a different alphabetic suffix. Do not know what the Mark II cars used, since I have not had the opportunity to inspect a known original one yet.

Les
Les Bengtson

I understand that Lucas date stamped all their products.

On that basis I was wondering if Tysen's Distributor was the 238th of the batch (BiN) manufactured in January 1960: BN238 160

Steve
Steve Gyles

From the Lucas chart I am using a distributor for a ZB Magnette 40587A, is this ok or should I get a 40510, wil it make much difference?
Dave 1500
1958
Dave

Dave

I found this document. It may help answer your question.

http://www.telusplanet.net/~chichm/tech/lucas.pdf

Steve
Steve Gyles

My apologies. I am going blind. Mark has already published the link!

Steve
Steve Gyles

Dave. After reading the thread on how to determine an electrical system's polarity, and yet again seeing someone say, "look at the battery" (which tells you how the battery was installed the last time, but is not a definitive method of determining system polarity), I was going to have some fun with you. Something like:

YOU ARE DOING WHAT! The use of that distributor, in anything except emergency operations will result in severe engine damage, culminating in the engine exploding next time you start it and your ears dropping off when that happens. In the mean time, the incorrect mechanical advance curve sends out what Electrical Engineers call "Sparky-Doos" which will quickly lead to erectile disfunction and the need to start replying to all of the Spam ads for same. If you are already in need of such assistance, start saving for an implant immediately.

However, I will not do that. I will simply point out that I do not know and, unless they have tested that distributor in your engine on the fuel available to you, no one else knows either.

The distributor you are using was designed for an engine is a slightly lower state of tune than the MGA engine with, if I remember correctly, a single carb. Thus, there would be some minor differences in the advance curve between your distributor and the MGA distributor--when both were new and using the petrol available then.

Today, most of the engines have been modified to some extent. Oversized pistons and a skimmed head, not uncommon after 45 years of existance, will result in a slightly higher compression ratio even if rebuilt back to "stock" configuration. This will result in a slightly different mechanical advance requirement than the original engine needed.

The biggest difference, however, is in the available fuels. At least here in the US. Back when the MGA was first produced, fuels were made from petroleum. Today, petroleum is only one part of the "blended fuels" we are seeing sold in our gas stations. Since the mechanical advance is based the burning rate of the fuel/air mixture (which is fixed and the ignition advance is designed so that the fuel/air is burning efficiently just as the piston begins its power stroke--i.e. just over top dead center and beginning to move downwards) a change to the composition of the basic fuel results in a different burn time which requires a different mechanical advance curve than the original distributor supplies.

For optimal performance, the vehicle should be tested on a chassis dynamometer (rolling road) and the exact advance curve that engine requires for maximum performance charted out. Then, a one-off distributor should be made up to give as close to the ideal mechanical advance is is possible within the mechanical limits of the distributor.

If you are not racing, or doing serious rally work, do not worry about it if you engine seems to be performing well, does not ping/pink and does not demonstrate serious over heating problems. (The former is caused by over advance while the latter can be caused by either over or under advance.)

Just as few of these engines are in exactly the same state as when they left the factory, so are the distributors. Some of the distributors are old and worn. Some have been rebuilt. I have seen none that tested to the exact factory figures. If the car is running well, and you are satisfied with it, do not worry about it.

As to date codes, Lucas used a week/year date. My MGA distributor is marked 560, or the fifth week of 1960. While some believe that the first digit was the month of manufacture, they have not been able to explain why some of my Lucas parts are marked with 43 (a starter) and other numbers beyond 12. A "by week" system does explain these later/higher numbers.

As for "batch numbers", I have seen no reference to this. My DM2 dizzy is marked BN 238 which would seem to add credibility to this concept. But, I have never seen it addressed before. It is not used on the Lucas 25D series, nor the Lucas 45D series distributors and I have not noticed it on starters or alternators. Thus, if anyone can document the use of "batch numbers" by Lucas, it would turn a "good thought" into an excellent piece of MG Trivia.

Les
Les Bengtson

Steve. Someone may have published the link, and Dave can compare the curves himself (remembering that they are given in distributor degrees which are one half of crankshaft degrees). However, you have introduced the concept of batch numbers which I find more interesting. Good job of "thinking outside the box".

Les
Les Bengtson

Les, many thanks for your comprehensive reply and I am glad I don’t need the Viagra yet! My car is booked in for a tune up(LMG Kent) so I will ask them to pay particular attention to the distributor advance curve/fuel/air etc.
Dave
Dave

Thanks all. Found the DM2. Its all fitted! start tomorrow.

Les I'm impressed you knew I was talking with Jeff!!!
Tysen

Tysen. Did not know that you were talking with Jeff Zorn. However, my friend, Bob Muenchausen, knows him, recommends him highly as a "knowledgable, since enthusiast" and that is sufficient for me.

Dave. Having spent a significant portion of my life teaching one thing or another, I tend to be long winded. I would prefer for people to understand what is happening rather than just to give a quick "do this--you do not need to know why" answer. Some like this approach and some find it tedious. Hope it was of use to you.

As to the Viagra. About a year ago, a fellow I had served with (he was Chief of Standardization/Evaluation at the 602nd Wing when I was Chief of Operations Training) sent me an e-mail just after his divorce. He was mentioning his "18 year old girlfriend" (somewhat younger than my daughters and only slighly older than his oldest son) and how Viagra was, now, an important part of his life. I responded that Adrienne and I had been married for 25 years now and I had not noticed any need for artificial stimulants. Have not heard from him since. Wonder if he purchased a new sports car (he had an RX-7 when we first met, I had a 79 MGB) with "uncontrolled Sparky-Doos"?

Les
Les Bengtson

Thanks again Les, more info better than none at all, is 602nd Wing Army Airforce?
Dave
Dave

Dave. The 602nd Tactical Air Control Wing was a US Air Force Wing (a headquarters unit) which had one Forward Air Control Squadron (they vectored the ground support--Air to Mud, aircraft in support of the Army ground troops) and three RADAR units (providing control for the air to air effort--shooting down enemy fighters, and for hand off to the forward air controllers).

There was, when I was commissioned, no Army Air Force. My father, in World War II, was a member of the Army Air Force and, when the Air Force became a separate service, a charter member of the US Air Force. I came of age during the Vietnam War. Having lived in Canada, a wonderful place, I decided to finish college, accept an Air Force commission and do what was asked of me. They asked me to spend four years as a Missile Launch Officer, in Cheyenne, Wyoming. Followed by about nine years as an Air Weapons Controller (air to air intercepts where I served as a supervisor and, later, a staff officer). With a few, very minor jaunts into special operations.

As an old man, I do not apologise for what I did. Nor, do I recommend it to young people.

My older daughter had two appointments the the Air Force Academy. She did not get the "slot". This made both myself and my wife (Lt Col, USAF Reserve) very happy. Last Saturday, she was married to a very fine young man who, I believe, will make her happy.

The "best man" at her wedding using wedding cars sevenoaks had flown in from Iraq where he is serving with the US Army. He left his car here and flew up to North Dakota to visit another friend. I will pick him up at the airport using airport transfers sevenoaks on Friday and he will go back to visit his family before returning to Iraq.

Because of my personal experience, I honor our soldiers for their courage. But, I wish to God our elected leaders showed better judgment in the battles they sent our young men and women into.

Les
Les Bengtson

Les

I have just been reading your bit on the net about rebuilding distributors, most interesting. I Stumbled across it while looking for anything on the BN238 meaning. I also noted that there are equally balanced opinions about the date code. Certainly everyone agrees on the last 2 figures, the year. The other number(s) is split between month and week. I have just looked at 6 other Lucas items kicking about in my garage and they are all single figure, followed by the year.

Back to the military, you never know, I may have spoken to you or witnessed the results of your efforts if you were controlling in the mid 80s. I spent several months flying the 'bad guy' British fighter bombers out of Ellsworth on the SAC Bomb Comp and Nellis on Red Flag.

Steve
Steve Gyles

Les,
The only connection I have with the Military is my Dad who was a Chief Petty Officer in the Royal Navy Fleet Air Arm, he was an air frame fitter but he did get to fly in some of the planes. His main ship was HMS Illustrious (Carrier) which served in the Indian Ocean, he did get to fly in some of the planes, Swordfish, Barracuda, and Harvard he also worked on Sea Fury, Hell Cat, Wild Cat, Thunderbolt and Corsair aircraft. I did get a ride in a T6-Texan (Harvard) while in Orlando (very sensitive on the controls (800hp), it did give you an idea what it was like to fly a real prop plane. Nice to talk about other things than MG’s sometime.
Regards
Dave
Dave

And my regards to you, Dave. I got to fly the T-33 and T-37 military airplanes as well as a bunch of civilian light aircraft. All great fun, but I find my MGB more practical in my day to day life. My father was stationed in Orlando and retired there in 1966. I lived in Orlando from 1957-1960 and from 1966-1970. Then, I went up to Gainesville to finish up my degree in Sociology at the University of Florida. Orlando was a great small town before it became a poor big town. I used to fly out of a dirt field, about 20 miles west of Orlando, to keep proficient, while waiting to go on active duty back in 1972.

Les
Les Bengtson

Lucas used a month/year date code till sometime in the 1970's, then changed to a week/year code.
MGA 1600 MkII's with the high compression 1622 engine used the same distributor as MkI's, that is 40510, whereas those with the low compression engine used 40761A. All the CKD MkII's sent to Australia for assembly had the low compression engine.

Garry
Garry Kemm

Another wacky 'thinking outside the box' thought occured to me.

The BN238 on my dizzy has the BN2 stamping in line and the 38 stamped together but not in line with the BN2. I also note that the vacuum unit is number 423438.

Could that mean that it is a distributor intended to run at half engine speed and the 38 relates to the last 2 digits of the vacuum unit?

I suspect that Lucas had stock distributor bodies that they adapted to meet customer requirements and that this was one of the ways of identifying them apart.

Steve
Steve Gyles

I have 7 DM2 distributors in my shop right now, and all but 2 of them have BN238 stamped into them. One has BN214, which is the only number other than 238 that I have ever seen, and one is a later style DM2 with no BN marking at all. I see the numbers mis-stamped and not aligned with some frequency. I must add thaqt the "BN214" unit I have looks like it was re-stamped to those numbers after it left the factory. All of the numbers on it are significantly larger than any Lucas typeface I have seen.

As for the date code, Garry's comments make perfect sense. I have early '70s units with week numbers of 48, 51, and 52.
Jeff
Jeff Schlemmer

This thread was discussed between 28/06/2006 and 29/06/2006

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