MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGA - DM2 distributor is a 40510 A not 40510 D

I need information regarding the DM2 distributor I just received, it is a DM2 40510A not 40510D , it looks identical to my original 40510D except the vacumm advance has the screw on fitting instead of push on , the person I purchased it from says the "A" is an original dealer replacement for the D. the manufacter date stamped is 1156 BN238 so I question his explanation since it was manufactured 1156
can anyone shed some light on this for me?
thanks joe
joe williams

The original A dizzy does have a screw on vacuum advance. Could be from another car that used the same dizzy, lots did.
dominic clancy

Joe. The basic Lucas distributors, of any model (DM2, 25D, 45D) were used in most Brit cars and some were exported for use by other manufacturers as I remember it.

Thus, the specification number allows us to determine what the specific application was for any distributor series. The basic distributor specification was the 40510. As Lucas made minor modifications to the distributor, without changing the basic specifications, an alphbetical suffix was added to the basic specification number. From what I have been able to accertain, these were always in sequence. Thus, a 40510A was made prior to a 40510B, etc. However, any distributor having the basic specification number should interchange with any other distributor having the same basic specification number.

There are a couple of points to remember, however. The most important is that unless it is a New Old Stock (NOS--a part that was made and never installed) any distributor you find today is, probably, not what the specification number says it is. Internal parts may have been swapped with something different and, at the very least, the mechanical advance springs will be fatigued allowing the advance to come on too soon.

My main area of interest is the Lucas 25D4 dizzy. Most of the original ones I have tested (I have a distributor test machine) have shown fatigued springs. Thus, the mechanical advance comes on too soon. If the timing is set statically, max advance comes on too soon. If timing is set dynamically, the max advance is never realized. If you set the timing at a higher rpm and at the desired max you have the same problem as when setting it statically--too much advance at lower rpm ranges.

Thus, any distributor has to be tested on either a test machine or on the car and the advance curve plotted and compared to the factory curve to see what the distributor is actually doing. John Twist, at University Motors Ltd has a distributor test machine, a wealth of knowledge about MGs, and can rebuild a distributor back to the original specifications. This is not an easy job as the original specification mechanical advance springs are not available. Considering the time spent in "tweeking" the springs, as well as the general clean up, replacement of worn parts, etc. John's price for a quality rebuild is an exceptional bargain.

I would suggest that you contact John, he has a website which can be found with a Google search for "University Motors Ltd", and discuss sending your new distributor in for inspection and, if necessary, rebuilding. By doing so, you guarantee that you will have a distributor which is capable of reproducing the original advance curve. Anything else is just a guess.

Les
Les Bengtson

Les, thanks for your input, this distributor has already been rebuilt and tested on a sun distributor tester and brought back to original curve except the mechanical advance is set to come on at 1000 rpm instead of 600 as in the factory spec.
I mainly wanted to know what the difference was with the "A" designation instead of "D" - which is on my original.
your explanation makes sense since my original DM2 was manufactured 1060 and the replacement DM2 is 1156.
so from this I'm assuming that the distributors are the same , the only difference being possibly different curve at time of manufacture. would you agree ?
thanks again
joe
joe williams

Joe. You are correct. Within the basic specification number, all distributors are the same at the user level. The alphabetical suffix may have some meaning to the rebuilder, but it has no meaning to the user. They should all work the same. If the dizzy has been rebuilt and curved properly (as you suggest it has), you should get years of excellent service from it.

Les
Les Bengtson

This thread was discussed between 27/10/2005 and 29/10/2005

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.