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Lucas 25D4 40872 distributor users?
#1
I wanted to re-invigorate comments from threads of old, as I and some others have been looking at this unit perhaps because of the Nippyesque but narrow inlet-ed downdraft Reliant manifold which happens to have a vacuum feed. And also looking at hardy Lucas/UK made units for general use. I'd be grateful if anyone else with experience of using this unit, and particularly trialling the vacuum advance, might post here or make contact. Also of the Reliant manifold which is available reasonably cheaply but demands some work with the grinding stones. Thanks to Dave Wortley I found there was a last, festering, 40872 unit at Speedy Spares.

It is worth saying that there is a good deal of confusion in finding units which rotate the correct way as the Seven as the Lucas/Austin notation of rotation changed, probably in the 1950s. So we need CCW DK4A units (original notation, viewed from drive cogs) but now need CW units, viewed sensibly from above. The arrows on the units thus face to the left. The comments below also mention the 45D, which is a later upgrade (sic) with one bearing rather than two for the spindle.

Some quotes from earlier forum:
I have been using a Lucas 25D4 (40872) from Speedy Spares Services Ltd for the last 20 odd years on 2 A7's. They fit on without needing lathework and have vacuum advance. I fitted the first one because I couldn't get my pretend ulster with DK4 to rev over 4500rev/min without misfiring no matter what I tried.I even loctited the auto advance up solid. I think they were fitted to the Reliant Regal(Robin?) 600cc model. It's a long time since I fitted the last one and seem to remember it was a case of filing a little off the collar on the body of the distributor to obtain the correct meshing position of the skew gear.The distributor spigot dia was identical to a DK4. Except for the vacuum advance device I think they look more like an original than the Bosch (which is because they are Lucas. (Dave Wortley)

I always used the clockwise rotation Lucas 25D, advance and retard systems locked up and with new quickfit points for every race. They were fitted to early Reliant 600cc OHV engines. I’d like to use the Lucas 45D; it’s a much cleaner design with no vacuum advance/retard but so far have not managed to find a clockwise version. (Henry Harris)

Yes the Reliant distributor is a 25D4 for the Reliant 600cc. Apart from the rotation it's the same as a Mini or MM so all the consumable bits are readily available. Mine takes the quick fit one piece points GCS101, the earlier dismantled points don't fit as there's no pivot post. Good to hear it works well for others. Mine hasn't any vacuum advance - it didn't come with one - I've locked the rotating baseplate and a Glenmorangie cork sealing the body hole. (Dave Armstrong)

Re. the last comment, its interesting that the baseplates AND vacuum advances are available for peanuts from Accuspark. Whether vacuum advances are suitable generic for use on a Seven, I know not. But others might!
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#2
I use the 25D on my special, fitted with a magnetronic ignition system. The weights are welded together with a short spring to prevent movement.
Stuart Rolt and many others have used fixed timing. It seems to work particularly well with electronic ignition. Mine is a road car and there is no loss of engine flexibility.

Charles
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#3
I build a distributor using a new 24D reliant rebel advance unit and fitting it onto a non vacuum 23D body, this was 30 years ago and it has served me very well ever since. I disagree with Charles about locking a distributor it will work in a racing situation where constant high Rpm is attained so no point in having any advance mechanism and which is where Stuart Rolt and others advocated such measures, I would not suggest your humble Box would benefit.
Black Art Enthusiast
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#4
In the case of a locked distributor surely it makes no real difference which unit you use? So long as it can be persuaded to fit. To me the benefit of fitting a more modern type is generally better condition of parts, and perhaps the chance to do things with the advance curve that the DK4A doesn't really support.
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#5
Jon,
Not sure you received my pm yesterday. Anyway Series 2 Lanrovers use 25D dizzies albeit wrong rotation I think. Paddock Spares sell many Landy parts so caps condensers, points etc may be readily avaible. Parts are usually cheap from them. Cheers, Dave.

£28.91 inc VAT. "Lucas type". Just checked.That's for full dizzie inc cap etc.
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#6
(01-07-2019, 10:28 PM)Ian Williams Wrote: I build a distributor using a new 24D reliant rebel advance unit and fitting it onto a non vacuum 23D body, this was 30 years ago and it has served me very well ever since. I disagree with Charles about locking a distributor it will work in a racing situation where constant high Rpm is attained so no point in having any advance mechanism and which is where Stuart Rolt and others advocated such measures, I would not suggest your humble Box would benefit.

I’m sure Ian’s right in regard to the standard Austin Seven but I do find it interesting that my locked up  ignition timing works well with a good pull away from low revs and no problems at higher speeds. I suggest it is worth trying if you have a special and fancy a little experimenting.

Charles
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#7
I guess the 6 million dollar question Charles is where do you lock it? Stuart used to advocate about 1 1/4" BTDC I believe. How much advance your particular engine can tolerate will be determined by a number of factors (CR is the first which springs to mind).
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#8
(02-07-2019, 11:47 AM)Chris KC Wrote: I guess the 6 million dollar question Charles is where do you lock it? Stuart used to advocate about 1 1/4" BTDC I believe. How much advance your particular engine can tolerate will be determined by a number of factors (CR is the first which springs to mind).

Hi Chris, ref CR I’m using a standard 37 head which has been skimmed — I suppose about 10 thou off. So nothing too drastic. As to where it’s set relative to TDC I can’t say. Once an engine is running I play around with small changes until I can get it happy throughout a wide range of revs.
What I don’t know is the extent to which electronic ignition affects things, if at all. It certainly gives me cracking good starting and a relatively vibration free engine.

Charles
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#9
bump for an old thread. Having thought that the more efficient advance mechanism would be likely very useable, most above seemed to have welded up! I'm presuming Ian's weights are in use.
Is there any point whatsoever in trying the vacuum function for normal road use i.e. Did anyone ever experiment?
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#10
(02-07-2019, 10:38 AM)Charles Levien Wrote:
(01-07-2019, 10:28 PM)Ian Williams Wrote: I build a distributor using a new 24D reliant rebel advance unit and fitting it onto a non vacuum 23D body, this was 30 years ago and it has served me very well ever since. I disagree with Charles about locking a distributor it will work in a racing situation where constant high Rpm is attained so no point in having any advance mechanism and which is where Stuart Rolt and others advocated such measures, I would not suggest your humble Box would benefit.

I’m sure Ian’s right in regard to the standard Austin Seven but I do find it interesting that my locked up  ignition timing works well with a good pull away from low revs and no problems at higher speeds. I suggest it is worth trying if you have a special and fancy a little experimenting.

Charles

I shall be at the Shuttleworth do this Saturday and at Kop Hill in a couple of weeks time if anyone is interested in having a chat about this.   PaxtonSpecial YSV 275

Charles
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