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MG MGB Technical - dizzy difference? 45D4 and 45DE4?

Ok so this is for the real tech's out there, whats the difference between the Lucas 45D4 and 45DE4 distributors?
Cheers TJ.
T J Nicolson

TJ. The Lucas 45D distributor is a points type distributor with a four cylinder cam installed. The Lucas 45DE is an "electronic" type distributor, having no mechancial points, for a four cylinder engine. Les
Les Bengtson

The 45DE4 was the lucas 'Opus' unit with an attached electronics module, nicknamed 'Opeless' due to the many failures often whithin guarantee. These were often replaced with, and later cars fitted with, the 45DM4 with a remote electronics module. Much more reliable, the innards are still available today as they were standard across many manufacturers. The electrical connections of the two differ considerably. The suffix '4' in each case indicates it is for a 4-cylinder engine, there were variants for 6 and 8 cylinder engines with the appropriate suffix.
Paul Hunt

throw them away dig deep and get a aldon (the best)

Thanks Guys, but this leads me to ask about all the different types of 45D4 dizzy's or are the differences just to do with the curve?
Daren - I've got an Aldon on my B, just trying to learn.
T J Nicolson

TJ. The "different types" of 45D distributors are by points cam (45D4 for the four cylinder applications, 45D6 for the six cylinder applications and 45D8 for eight cylinder applications), mechanical advance curve (both rate of advance and total advance) and vacuum advance (total advance and when the advance comes on). Most of the basic interals will interchange between models. The points cam contains both the cam to open the points and the mechanical stop for the maximum mechanical advance.

As to "get an Aldon", all you are paying for is a new or rebuilt 45D distributor with the mechanical and vacuum advance set up to some predetermined specification. It may, or may not, be best suited for any particular engine application. Best way to set up a distributor is to have it tested on a rolling road, then have the dizzy custom curved to the engine's requirements. Les
Les Bengtson

Yes, the different codes for 45D4s relate to different centrifugal and vacuum 'curves'. I'm with Les as regards 'get an Aldon'. Anyone who says they have the ideal distributor for your engine without testing it on a rolling road is a charlatan simply trying to sell you what they have, at double the price from what I've heard for an Aldon over a 45D4. I'm sure that a new distibutor of almost *any* type will give better results than a knackered one, but a correctly curved distributor for your engine will be even better. All engines vary even from new, and the manufacturers specs took account of that and erred on the side of caution as well. I've had BL engines where I could advance the timing from manufacturers figures and get improved performance and economy without pinking, and another where I couldn't. And that is without changing the curve. On engine with many 10s if not 100s of miles of wear on them, odd parts replaced, and most importantly completely different fuels, if you are going to do anything other than replace with the correct original spec you have to put it on a rolling road.
Paul Hunt

Thanks and I do get my B tuned on a Rolling Road as I compete (MGCC Speed Championship) with it so it is extremley important to get it set up right. The Aldon I have was made for the cam shaft that I run. The numbers I was infact refering to ,albeit blindly, were the other numbers on a distibutor such as 41427E and such like. The 41427E is for a 62-71 B I believe but this 45D4 distibutor was also fitted to 1500 midgets but I can find no explanation for these additional numbers. Any clues?
T J Nicolson

Check this website for a table of distributor
specs including the 41427

The distributor number corresponds to a specific
advance curve and vacuum advance.

The 41427E is also sold as a replacement for
75-on low compression U.S. engines, not sure if
this indicates the "E" means a modified advance

TJ. Ron has explained it correctly. There will, normally, be a five digit specification number on the side of the distributor. The letter suffix indicates some change to the distributor which does not affect the basic specification number. The exact nature of such suffixes I have not been able to determine from the materials available to me.

The original distributor for the early Bs was a Lucas 25D4 to specification number 40897. The Lucas 45D was not introduced until about 1975. Thus, whomever is saying that the 45D4 to specification number 41427 is for the "62-71" B is claiming that it performs similar to the original 25D4 as supplied from the factory. This may, or may not, be correct.

Most, but not all, distributors will also have a three or, more commonly, four digit code below the specification number. The distributor in front of me right now has 4066 below the specification. This means it was produced in the 40th week of 1966. All of the Lucas 25D distributors I have examined have this date code. One 45D did not have this, but several others did.

The specification number, embossed at the factory, tells you where the distributor started out. However, what it actually contains can only be determined by testing. There may have been one or more rebuilds in its life and the internal parts interchange. I have seen them with wildly different internals than they left the factory with. Les
Les Bengtson

I have seen a recommendation that the 45D4 41427 is suitable for the 63 to 70 engines (and only included it on my site after some thought) but as Les points out the 45D4 wasn't fitted to the MGB until about 1974. The information I have indicates that the strobe setting for the 41427 is 13 degrees at 1500 rpm which compares to 20 degrees at 2000 for the 25D4 40897/41155 which was the factory fitted unit for the 67 to 70 engines, and 14 degrees at 600 rpm for the 40897 fitted to 62 to 67 engines. But far more concerning to me would be that the max advance of the 41427 is given as 18 degrees at 4000 rpm compared to 30 degrees at 3000 rpm and 20 degrees at 2200 rpm for the factory items. This would seem to put it way out of spec.

But for competition you should really be using a 43D4 which doesn't have vacuum advance (or a 45D4 with vacuum advance disabled) which makes setting-up significantly easier, and using the rolling road to determine the ideal curve for your specific engine and curving the distributor to that. Unless an Aldon is much easier to recurve than a Lucas 45 then there doesn't seem much point (ho ho) in spending more on one than the other.
Paul Hunt

This thread was discussed between 07/02/2005 and 12/02/2005

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