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MG MGB Technical - points ignition

Over the last few weeks I have been reading quite a few posts on the B, Midget, and A boards, about electronic ignition, and all the problems people are having with these, what I find amusing is people fit these to make them more reliable or turn them into super performance cars, I run my car on points ignition, and would not have any of these units given, whats the fascination for these, I would be interested to know
Andy Tilney

"all the problems people are having with these", Well, just to confound this statement, I've been fitting electronic ignition (somewhere in the region of 15) to cars since the 80's and have NEVER had a unit fail. When you consider some of those early units must have been a touch crude compared with modern items, that's pretty good I think. The fascination, as you put it, is that you set up your ignition and the timing remains constant, whereas points close, dwell increases and timing alters pretty quickly after setting. Not to mention condenser issues and points bounce!
Allan Reeling

Thank you Allan for you reply, I have just had a count up since the 80s I have owned 6 points ignition cars, and have travelled over 500,000 miles and have also never had one fail due to ignition failure, maintaining A proper service schedule, helps, along with OE parts,as for condensers I have never had one fail, I believe the problem with these is poor diagnosis people change these and fit rubbish ones and this is where the problem lies, as there was nothing wrong with the original in the first place,

Andy Tilney

There are two very distinct camps on this. Many like Allan have fitted or know many many people who have fitted electronic ignition without issues.

On runs and other times I've witnessed failures that were all related to electronic ignition. To be fair, I was told the initial US versions of Petrronix were really borrowed from another use and really intented for our cars. Now they're onto their 3rd version. However, people with modified engines that really are into performance disliked them in favor of the more expensive ones listed below.

Since all modern cars use electronic ignition there's an obvious benefit. The question is retro fitting. With the superior points now NLA I've researched electronics pointless dizzys. Really, IMHO, there only seems to be two options where the dizzys are completely built for the electronics and not a simple add-on. The downside is they are very expensive: 123 and CSI. $400-450 USD.

As the saying goes there's those that swear by electronic dizzys and those that swear at them. Although I haven't heard owners of those two being unhappy.

For now, a good rebuilt dizzy that is recurved and running a film capacitor instead of the dodgy new condensers seems to be the best one can hope for until or if those others ever come down in price.

One note I forgot to mention. With those two you really need to figure dyno time into the cost as that will be the best way to find the best curve for your engine. This was expressed to me by a long time LBC mechanic.

Max you mentioned OE points are NLA, you can still buy these, go to your nearest Land Rover main dealer, and ask for a set of points for a Series 3 land rover which you can buy for 25D and 45D distributors, also if by any chance you ever need a condenser you can also buy an OE one there as well, you are correct about 2 camps one for and one against these two ignitions systems, rather than just fitting a new condenser make yourself one of these. and confirm if it really is faulty

Andy Tilney

Hey Andy,

Interesting test you devised there! Personally I'm good with the film cap. I discussed it in another thread.

The best points I was turned onto were Blue Streak with the lube pad. These never needed adjusting and are terrific. Not thinking they would be NLA I didn't buy a lifetime supply. Now they're just cheap versions.

I'll check out the ones you mentioned. The Lucas ones I always got always wore down even though the cam always was lubed.


Like Andy I've never had a problem with points or condenser in 50 years. Some might say that the reports of problems with electronic units are rare, but if you consider the installed base and the length of time they have been available compared to points, then the failure rate is far far higher. This is after-market devices fitted to classic cars I'm talking about, not original equipment installed by the factory.

I only have to adjust the gap occasionally on the V8 as they have a narrower tolerance, but they have an external adjuster and the distributor is on the top front of the engine so very easy to get at. The roadster usually goes significantly beyond the replacement interval before they go out, so there is little point (ho ho) in adjusting them so that is when I replace. I set them towards the upper end of the gap, so if there is wear it works through the tolerance before it goes out at the lower end. If you try and maintain it bang on the gap instead of using the tolerance, then I can see you would be fiddling frequently.

To replace I take the distributor out and do it on the bench, and adjust them there as well using an ohmmeter with an Allen key lightly clamped to the drive dog, finger twiddling is all that is needed to get a usable reading.

While I can continue to get points and condenser that work I'll stick with them. If that becomes no longer the case then I would go for one of the cheap under-cap types, and carry a second one as a spare. I'd never go for a 123 or a CSI. The early 123s with fixed original curves designed for leaded fuel in the 60s and 70s are irrelevant for today's fuels, so much so that one supplier at least recommended the generic item instead of the MGB specific saying the curves were better. The later configurable item is an improvement, don't know about the CSI. But I still wouldn't have either, if I wanted to go configurable I'd get one of the stand-alone boxes, at least if that packs up you can bypass it.

Paul - couple questions.

Several people i know do the points gap outside of the car. If a person does that don't they have to re-time the car every time?

Seems impossible not to accidentally move the body of the dizzy when reinstalling.

What ohm reading are you using?

Also I wonder if there an allen head that could replace the philips or slot head that wears out eventually inside the dizzy on the points. I don't know the thread on that screw.

Worrying about re-timing I do it in the car and check with a dwell meter. Agreed I run it at the high side so that any closing doesn't affect the performance.

Guess I've been unlucky. With all the Lucas points I'm always adjusting. If I go on a trip say 400 miles its the first thing I check and they're always closing up. Always. Only the blue streak haven't caused that issue. NLA sucks.

Don't know about the early 123. If that was the case then agreed. Only know the new style with bluetooth which has infinite curves. No experience the CSI.

Electronic iginition fitted as standard seems to have worked well. I'm helping a friend with his Alfa. The electronic ignition is from the early 80's and flawless.

Even replacing the points with the distributor in situ, you still need to check the timing.
Dave O'Neill 2

Max you can reset your dwell with the distributor still in situ, this is done by loosening the screw place a screwdriver in the adjusting slot and cranking the engine over, watching the dwell meter and adjusting at the same time as cranking the engine over.when its reads correct tighten the screw refit the rotor arm and cap job done
Andy Tilney

Dave - good point.

Andy, that's interesting! I check in situ with a dwell gun as you mentioned however its a process of snugging, checking snugging, finally tightening. Wouldn't mind being able to do it statically aside from the feeler gauge. Hence the ohm meter question. Are you using a starter switch/button to do that?

Max I am sorry but SNUGGING is a new word to me what does it mean, yes I use a remote starter button (home made from a mini reverse light switch) can you also clarify dwell gun ( do you mean meter) I find language more interesting than cars, Thanks Andy
Andy Tilney


Be aware that no screw on an MGB was a Phillips head, they were all pozidrive. Using a Phillips driver will damage the head.

H J Adler

Yes, too many years too late. :-)

I know the originals were all Pozi. Its been replaced several times and it was a straight blade for a bit. Pozi is better. I'll try to track one down.

I stand corrected. It appears the original was a slotted head which was long ago messed up. (one on the left)

Would be nice to find an original though


Couple of things. 1. I have used electronic ignitions on both my TD and my 67 BGT. TD still has the original pertronix from the 1990's. I burned up the unit in the GT when I got the coil wires on incorrectly. When looking at a new unit, I saw the cost at $120 (Moss). A set of Jeff Schlemmer (Advance Distributors) points, rotor and condenser costs me $27. A full 25d Plate with points and condenser is $30. Being something of a tightwad, I went with points. Other reasons included Jeff's recommendation to stay with points.

2. I hear of a lot of issues with new pertronix units. The company was sold some years back and the quality seems to have decreased.
Bruce Cunha

As said replacing the points and even just adjusting the gap means the timing should be checked afterwards. Especially with the steering rack shaft position on RHD cars and my ageing back it's much easier to get it out and check - adjust - repeat on the bench than do it all leaning over the wing.

No one has mentioned the notches/pip on the points and points plate that allow for fine adjustment using a flat-blade screwdriver with the screw barely nipped up, on most distributors.

Lowest ohms range but I should have added that it needs to be an analogue instrument, not a digital. If the meter has a 10v scale then even though it is switched to ohms you multiply that reading by 10 and it gives you the dwell in percent directly. If you have a 30v scale then multiply the reading by 33.3 and again you have percent. On a 4-cylinder engine divide dwell in degrees by 90 and multiply by 100 to get percent, i.e. with the 60 degree dwell on a 25D4 you end up with 64 to 70%, and with the 51 degrees of a 45D4 you end up with 51 to 62%.

Never had a problem with the screws either, but maybe that's because I rarely have to slacken/tighten them :o) And personally I think you would have to be pretty ham-fisted to damage a cross-head screw with the wrong screwdriver, especially with the level of torque that should be used in the distributor. Having said that mine all have single-slot heads, with a special screw that has a plain bit at the end to assist in getting it located correctly.


Points need replacing, ergo they deteriorate, hence performance deteriorates as the points argument for electronic. One more plus for electronic is that wear on the dizzy spindle doesn't affect their accuracy. One of my V8's has a Hall effect Land Rover dizzy with AR amp, the other has Petronix. My previous 1800's had Aldon units.
Allan Reeling

"wear on the dizzy spindle doesn't affect their accuracy"

Doubt that's true. If the wear causes the shaft to move back and fore across the face of the pickup while it is rotating it will vary the timing. But we are in 'how many angels can dance on the head of a pin' territory, unless the wear is gross I doubt anyone would notice in normal driving. What you can say is that the pressure of the points spring is continually pressing the shaft away, so has the potential to increase wear in that direction.

Similarly any deterioration in performance over the scheduled life of points is marginal in my experience. I last changed those on the roadster 9 years and 15k ago, and after similar periods there has been no noticeable change in performance with new ones. According to my records I last changed the V8 ones 22 years and 40k ago ... but may have missed one. It's been a long time though.

What many don't realise is that electronic systems pass less current through a given coil than points, so the HT spark is less compared to decent points. This is because the electric 'switch' has an internal volt-drop when closed, and typically there is also a small-value series resistance to protect the unit against short-circuits. For that reason the factory fitted lower resistance coils with their electronic systems, as low as 0.8 ohms with the 45DM4 system as that was variable dwell so the coil can pass more current without over heating, as it is passing it for a shorter time.

Not that I'm expecting anyone to say "Oh, in that case I'll go back to points ..." :o)

Fitted a Lucas Magnetronic about 25 years ago & never had to touch it since. I guess I should be touching wood as I type this!
G Britnell

A worn spindle causes it to oscillate slightly which affects dwell and therefore timing with points. Worn spindles don't cause rotational changes, which would affect timing with electronic units as it would with points. Oscillation would change the air gap on a magnetic trigger, without having any effect on triggering time. Optically triggered units are not affected at all. Like G Britnall there is a little wood touching going on, and I do carry a set of points in the boot!!
Allan Reeling

The pickup responds to the horizontal position of the shutter or magnet relative to itself, which would normally purely be from rotation passing in front of it. But if the shaft is wobbling there is a sideways movement across the face of the pickup to consider as well, just as it would if the magnet or shutter were moving past the pickup in a straight line. Points are exactly the same. Points are also sensitive to the shaft moving further away from and closer to them, but optical triggers are not as it is along the line of the shutter edge. Magnets may or may not be depending on how the magnet is orientated to the pickup. If it's sideways on i.e. a North passes before a South (or vice-versa), and the trigger point is when it changes, that will also not be sensitive to the shaft moving away or closer to. But if the air-gap is critical, then the pickup has to be sensitive to the magnet being further away from or closer to it for any reason, including wobble. But, as before, the practical effect is minimal except in a grossly worn distributor.

I said I would only use an under-cap - when I have to, but I still have a concern with these being so exposed to heat and vibration. The early factory 45DE4 Lucas Opus system had all the electronics internal to the distributor, and they had a very bad reputation for reliability, being nicknamed 'Opeless, many on MGBs being replaced under warranty. The later 45DM4 was far more reliable and used an industry-standard module mounted on the inner wing, hence in a significantly better environment.

Fascinating discussion. Nice vintage meter, Paul.

X3 on the shaft wobble issues.

Here's one I've never gotten a proper answer to even when asking Jeff at Advanced.

Looking at the timing with a proper light, the crank/harmonic balance flywheel notch will bounce. Thinking it was the distributor I was surprised to see it was the same with a newly rebuilt one by Jeff.

Everything is tight and within spec that I know of. Drive gear is tight - which is the only thing I've heard referenced. HB is rebuilt.

If you're using the pick-up clamped on number one lead it can pick up extraneous pulses from close by leads. Put it on the lead near the plug rather than near the dizzy.
Allan Reeling

when doing points on other cars, I just mark a scratch between the dizzy and it's clamp. I take out the dizzy, put in the vice and then do the points and a lube before refitting and just lining up the scratch marks again. This works a treat for a quick job, and when I check with the timing light it's usually spot on where it was before it came out. This approach also avoids difficulties if the setup has been wrongly done before (e.g. dizzy drive shaft out of position ) because I am sure I am putting the dizzy back in exactly the same orientation.
Dominic Clancy

Yes, I get the point Paul.
Allan Reeling

I think, once fitted and set and proven non faulty, an undercap electronic conversion will stay in better state than points which wear. I also get bad misfires from worn spindles on points setups. So much so that, with V8s I will not dyno them if they have points in. The exception would be competently rebuilt or new V8 ones. Points distributors in 4 cyl Bs, when new, seem to work well for a couple of years then seem better with electronic fitted. Whether points or electronic I would tend to carry spares just in case.
To be fair the most common misfire we get on points is when the cam has been greased and the grease contaminates the points and arcs out ruining the points. The old fibre heels needed greasing, the new plastic/nylon (whatever the material) survive without grease (except when using with a rusty cam!!!!)

Peter Burgess Tuning

Peter - what is your preferred electronics for the dizzy, then?

Dominic - good tip.

To be honest I like the Pertronix ones, marketed by Aldon as their Igniter over here. The Accuspark style ones work ok but we have seen a few failures over a time period.
123s are good but I am not so happy with the companies goodwill vs the cost. CSi baffles me having to count the flashes to know what curve I am on, I also find the graphs not to my brains pleasing for interpretation, I am reminded of my Psychology background and Clever Hans when the lights are flashing!
Aldon Amethyst works well and heat not a possible problem as box externally mounted.
I realise my all time favourite but pricey these days is the Lumenition optical system, many of these going strong after years and years of service, only problems we have seen regularly are wires frayed and shorting due to chopper catching and chopper sitting at wrong height and catching optic and causing a miss. What is a very useful attribute of the system is we can retard the timing on an individual cylinder for a competition engine. The holy grail of ignition systems is being able to control individual cylinders.

Peter Burgess Tuning

"What is a very useful attribute of the system is we can retard the timing on an individual cylinder for a competition engine"

How, by trimming the chopper?
Dave O'Neill 2

The problem that I have with these aftermarket electronic ignitions is that they are cheaply constructed.

They are built for the consumer electronic environment.

Though they are tasked to perform in a military type environment.
Steven Rechter

Spot on Dave, Ray Downes an ex rally driver and garage owner ended up as the eligibilty scrutineer of MGOC racing, he noticed the chopper trimmed and we had a conflab and guessed what it was then tried it on the rolling road, perfect, stopped det on no 4 cylinder whilst allowing full advance on 1, 2 and 3. One has to mark which is no 1 chopper and try and not put the chopper back in the wrong position, been there, done that!!!! We tend to lower the CR slightly on 3 and 4 cylinders with thicker sealing rings to the base of the spark plugs if we have to on race Bs these days.

Peter Burgess Tuning

Timing jitter can be caused by wear anywhere in the sequence from the crankshaft through the timing gears, cam and distributor drive gears, and distributor itself.

Cunning, Peter.

Here's a pic of myself and Ray, side by side at Mallory.

Dave O'Neill 2

Thats a nice pic Dave, I miss Ray. He used to regale us with tales of bollockings for rallying on the grass to overtake and giving rear end 'love taps' out of any marshalls sight to encourage folk to move over.
We still see Brian if he comes in with Keith Egar.

We had fun with the moggy, changed the 1 1/4" SU to cable operated throttle direct to piston damper and gained quite a few geegees removing the throttle disc and spindle. We also ended up with a Jeff Howe camshaft, we were running a 649 but it was too cammy for the little engine , the Howe cam was excellent, only lost a couple of bhp at very high revs and gained impressively around the 3-3500 mark, much better coming out of corners.


Peter Burgess Tuning

Peter, The next time I'm up you must give me a lecture on the benefits of different timing for different cylinders!!! Sounds very interesting. Is there reading matter available?
Allan Reeling

No reading matter I am aware of Allan. The lads next door use modern ecus which can change timing on each cylinder to order. Usually the rear cylinder and maybe next one forward on high CR comp 4 cyl cars can detonate earlier than front two cyls, to allow full advance to be achieved on front cyls it is good if the rear ones can be changed to suit. Something which can be done with the chopper of the optical lumention.
Peter Burgess Tuning

For me the Holy Grail of ignition systems would be knock-sensing retard - continual variation of the timing to be at or near ideal regardless of engine condition, fuel grade, driving style or anything else. Early electronic systems from BL did this, sometimes you could hear it backing off and pinking reducing. I think emissions limits put paid to that, which is why most cars these days have fixed maps tuned for 95, for which it is pointless filling with a higher grade. Performance cars often can get the benefit of the higher grade (all cars have to be able to run on 95), but AFAIK still do it by switching maps, not purely knock-sensing.

Peter, Whilst I was lying back in the steam room at the gym today, "mulling" I could only surmise that it was either down to with length of inlet tract or non standard crank.
Allan Reeling

"benefits of different timing for different cylinders!!!"

You could time cylinders separately on multi-cylinder British motorcycles from about the mid-Sixties. However, they've got one set of points per cylinder. The advantage was that it could account for any minor differences between cylinders, wear and tear etc. Before that, it was a compromise setting between cylinders.
Peter Allen

This thread was discussed between 15/05/2017 and 28/05/2017

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