Distributor Problem

[billlobban]

The vac advance unit on my dizzy has just gone phut. I notice that BM do a new vac unit - is it worth it? Or is the new dizzy from the same company a better buy? The dizzy is quite well worn and the 2 others I have are not any better.

[MarkyB]

You could fit one of the electronic points replacements, they are supposed to negate wear in the dizzy.
You'll still need a new vacuum advance though.

[bmcecosse]

What model dizzy is it ?

[billlobban]

25D

[bmcecosse]

They are plentiful - and uber reliable - made by LUCAS you see! Can you not pick a good used one up locally ? But the 45D is a later model - so IF getting a new one - go for that.

[billlobban]

My problem, as always, there isnt a scrapyard of any kind, within a 50 mile radius and even that one never has anything remotely related to A series engines.

[bmcecosse]

Ebay is your friend! http://cgi.ebay.co.uk/MG-LUCAS-45D-DIST ... 335ddadaa5

or for a new one which seems a bit of a bargain! - http://cgi.ebay.co.uk/LUCAS-type-45D-Po ... 1c0fba23b3

[billlobban]

There was a series of posts about this guy before and his electronic kits. The price is too good to believe. Anyone bought one before?

[Alec]

Hello Bill,

BMCE mentioned this "or for a new one which seems a bit of a bargain!"

The seller correctly states it will fit a whole series of cars, which is entirely true, but the chances of it being correct for more than one, if that, is extremely remote. Distributors are matched to specific engines, just because it fits doesn't mean it will work properly.

I would try just a new vacuum advance module, and if you wish the electronic route although I fail to see how they can compensate for worn bearings? The rotor arm will throw the shaft out of balance so it will be wobbling about anyway, even without the points pressure.

Alec

[bmcecosse]

The NEW one will be fine - if necessary it's easy to adjust the advance profile - IF it really needs doing! At that price - including a new vacuum unit etc - it is a bargain! Let's face it - the old original dizzy was 'designed' to operate the engine in the days of 2 star leaded fuel. Today's fuel is very different - no Lead tetra-ethyl and no Benzene - and burns far hotter. So the original advance curve (even imagining the springs haven't weakened in the last 40 years of use.... ) will be far from correct anyway! And in your case Bill - your engine is far from standard anyway! Go on - treat it to a new one - you know it makes sense!

[Packedup]

There was a series of posts about this guy before and his electronic kits. The price is too good to believe. Anyone bought one before?

I think it was him I bought a kit for a 25D from last year. And it was about a fiver cheaper back then, too.

After fitting, I had to adjust the timing a little to get the car running, and then a bit of tweaking to get it how I wanted, but the kit went straight on with no problems, and is still working perfectly. I'm tempted to get another, but I'm quite tight fisted and am waiting to see if the price drops or someone else does them at about £15 again..

[Alec]

Hello BMCE,

"if necessary it's easy to adjust the advance profile "

Really, just how do we do that, please enlighten us?

The fuel will not have any significant effect on the curve required, that is a characteristic of the engine not the fuel. Note, I'm referring to the curve not a specific advance at any given point.

There are companies around that will set up a distributor as it should be. Others that seek just to shift some stock without any consideration as to it's suitability are obviously there also.

Alec

[bmcecosse]

Well - since this engine is non standard - no-one will know how to set the advance curve for it anyway - because no-one know what advance is going to be best for this engine at any given revs. So may as well start with the new dizzy - and see how it goes. Ideally - it should be set on a rolling road and the best advance determined by hand for various revs up the range. The fuel is v important - advance has to be 'just not quite pinking' for best result. Modern systems do this with a knock sensor of course - cranking the advance forward until it senses pinking - then back a bit over and over many times a second. The advance curve can be tweaked by filing the bob weight where it meets the stop, to get more mechanical advance if that's what required - to allow easy starting with little/no static advance - and the springs that control the bob weights can be changed/stretched to set the point where the advance comes in. Again - to get it dead right will involve a long session on a rolling road! Generally - the A series requires about 34 degrees max advance at about 4000 revs. The dizzy is marked internally with the mechanical advance - usually something like 13 degrees - this being dizzy advance, = 26 degrees engine advance. So with say 4 degrees static advance that would give 30 degrees total. To add any more static will cause starting problems - and too much advance at low revs, so the answer is to file off the stop slightly to get say 15 degrees at the dizzy. The amount to be filed can be calculated by measuring how much the weights move to give their 13 degrees - divide that by 13, mult by the 2 degrees we want to gain = the amount to be filed away! Road testing will maybe show pinking at low revs - but none at higher revs, which suggests more mechanical advance required - and slightly less static advance, or of course -tweak the springs. There is of course the excellent '123' electronic dizzy - which comes with a whole range of built-in advance curves that can be selected at will until the 'best' is found - in combination with varying static advance settings of course. Only snag is the cost........... Electronic wizards can of course fit home built Megajolt ignition - fully mappable and eliminates the dizzy. Mini lads say it works very well - tames a wild cam nicely. I would love to do it - but it's way beyond my capabilities!!!

[billlobban]

Roy why 45D? This guy also sells 24Ds

[bmcecosse]

24 D ?? The 45 D is the later improved dizzy - so may as well get that if buying new. Or - do you have a pile of spares for the 25 D that you don't want to waste....... In which case - get a new 25D!!

[Alec]

Hello BMCE,

he didn't say it was non standard in the first post?
As you say a rolling road is the best way to set up an unknown quantity reasonable quickly and easily. There should be a fair amount of data around for 'A' series engines so that also helps. I don't agree he's worth buying one and see if it's OK. At the price it may be worth buying a 25D4 just for it's new bearings, however.
I have a book which gives the data for Lucas distributors and the variation in curves is quite bewildering, hence my saying that the chances of this new one being correct is like winning the lottery. E.g., mechanical advance start between 100 rpm and 500, maximum from 1200 to 3200 (not a misprint, ref no 41107A, 6,400 engine rpm) total advance, similar large variations. that's before going to vacuum advance specifications. (I wonder if the vendor is aware or does he honestly believe a 25D4 is the only reference required?)
The other point is that you can set low speed advance by backing off the point at which it just pinks but there is no way of telling if the high speed advance is too much (unless you fit a modern anti knock sensor) or check the plugs for cracking, which may be too late.
Even with the correct distributor that is only an approximation of the correct curve, if the diagrams are anything like accurate.
From what I remember the 123 has only 16 curves, my book has hundreds.

Alec

[MarkyB]

The 45 D is the later improved dizzy

I'm interested in what improvements were made in the 45D, superficially they seem very similar.

[Alec]

Hello MarkyB,

it lost the timing adjuster, I believe. If that's an improvement?


Alec

[bmcecosse]

Yes Alec - I have the chart showing all the possibilities for the dizzy settings! It is indeed bewildering - but else can we do ? Also - Bills engine has been 'on' here often enough for me to know it is far from standard!! The NEW dizzy seems an absolute bargain at the price quoted. I would buy a 45D - I understand it has better bearings,better points (easy change!) and better shape to the lobes on the cam block. Larger diameter to give more spacing between the HT terminals to reduce chances of spark-over, and yes - no micro adjuster for advance/retard. I don't see a problem in that......But each to their own - my own engine is running a 25D at the moment ( a nos dizzy bought a few years ago for £5) - and it's fine and a spare 25D in the on-board spares cache. But the 'new' 1275 I have in the wings has a 45D in it all ready to go - and yes - I have a spare for it too! There's no doubt - the Megajolt ignition is THE one to go for - if you know about electronics - but they just scare me to death after an attempt to build a transistor wireless set from a kit bought through the Meccano Mag some 50 years ago went sadly wrong.......... Actually - some of the Megajolt lads are free with their 'maps' - so that would be a guide to how the dizzy could best be set up. I'll ask around!

[Alec]

Hello BMCE,

I have a bit of a problem combining old cars with modern electronics. They just don't seem to go together. I can see the gains in transducer sensed timing, and modern electronics, but it's not in character with the era of the car.
Lets say I prefer to get the maximum out of the technology available when the cars were current.

Alec