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MG MGB Technical - points ignition

Anyone heard of a gadget that closes the points electronically, before they close mechanically, thus eliminating pitting and extending points life. I believe its called a dwell extender, where do I get one? I've heard of a company called Jaycal in USA but can't locate them. Any help from accross the pond would be appreciated
Cheers
Graham
Graham Cherry

I've heard tell of, and seen references to, a simple electronic circuit involving not much more than a resistor, diode and capacitor, but no details of the circuit otherwise I'd have tried it just to see what differeence it makes. But like much stuff that seems to be available in the USA no references in the UK, possibly because it is just snake oil. But you don't need a dwell extender anyway (nor dual points ignition which does much the same thing) on a standard MGB, it just doesn't rev high enough to warrant it. The V8 has half the dwell time of the 4-cylinder (Jag V12's even less) for much the same max rpm, and they don't need it, so there's no way the 4-cylinder will. Pitting occurs from day one, but if you check the points using dwell rather than gap you should find you can ignore this anyway. I've been running sets of points in both my roadster and V8 for well over 10k miles now and the dwell is still within spec. I carry a spare in both cars, but I'm going to leave them in untouched just to see how far they will go before going out of spec.
Paul Hunt

In addition to Paul's comments, I would like to add something that was told to me many years ago and I have found to be true. Capacitors (condensers) normally have a large tolerance range and the value can vary by 20% or more between capacitors that are marked as a given vlaue. Before arbitrarily changing capacitors every time the points are changed, look at the old points and only change the capacitor if large amounts of metal has been deposited from one contact to the other. If there has been little metal migration on the contacts, it means the capacitor is very close to the nominal value for the system it is operating in and should be left in. Capacitors are not a high failure rate item and it is pretty safe to leave them in place for long periods of time (in over 30 years, I have never changed the capacitor in our TD and have never experienced a problem with it). Of course, one always wants to have a spare at hand just in case. Cheers - Dave
David DuBois

Hello Graham,

I have installed a Capacitivre discharge ignition 20 years ago and it worked fine with my B-GT and after my TR6. I have to replace my point set after 10 years as the spring broke but points were not pitted. The idea in that concept is: point doesn't give current to coil but only trigger the electronical device for the right time to work.


A theorotical example of how its works and and circuit example, is:

http://www.beyond-designs.com/pspice_CD.htm

I bought mine for Tri-star corp for $19,95 and it still works. That company vanished with the arrival of electronic ignition in all cars.

Cheers,

JGC
Jean Guy Catford

Still me,

I forgot that it is not snake oil as I remember that my B with its 2 6Volts weak battery was unable to start at -20F( I ruined that car with salts widespreaded in Canada during winter, what a shame). Starter was draining most of current to crank engine, but with CDI it started despite the low current avaliable. The only drawback of this system: If points flutter at 5,ooo RPM and over, the system could not correct that. This means that points are not the best thing around. Let think that in conjunction with a pertronix trigger device, it must be nice. I think MSD sells something similar in modern version to this old CDI system.
Jean Guy Catford

Hi Graham,
Have a search for Sparkrite on ebay. It's the same sort of thing and Maplins do a DIY kit that may be easy to site invisibly. The Sparkrite does the job but might look a bit out of place in your rather smart engine bay. My experience of it is that it stops any burning of the points. I'm not sure about any other benefits (many were claimed) and I take Paul's comments on board. I bought it on the say so of a friend who does a lot of competition driving, so didn't much question the thinking behind it. The one thing I can say is that with the plug gaps opened wide the car will not run if you switch it out - you can bypass the circuit and run as stock using a switch on the box. I'm not sure if this is a sign of the quality of the device or an indication that it's masking a problem in my HT set up! Any ideas Paul?
Steve Postins

Graham,

I found this item that appears similar to mine from a different company
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33691&item=7967587356&rd=1&ssPageName=WDVW

It must be easier to find one in UK
JGC
Jean Guy Catford

A capacitive ignition is a completly different animal. It produces a hi voltage spark whether the engine needs it or not. The result is, that your engine ignition system must be in perfect condition or it will fail. If the voltage is hi enough, a stock system will fail and not operate even if in good condition.

The regular systems - even with transistor switching put a charge to the coil until it gets hi enough to spark. Even a very hi performance coil will only produce the same voltage a stock coil makes, as needed to fire the plug. The extra ignition dwell time and the hot coil is to enable a higher voltage spark if and when needed. Hi rpm and hi compression both put additional stresses on an ignition system. Widening the sparkplug gap or a worn plug can also increase the voltage necessary to bridge the gap and spark.

The basic transistor system increases the reiliability by eliminating point adjustment and failures. It also provides a quicker on off, resulting in more time for the coil to charge and the postential of a hotter spark.

On a stock or near stock engine the original ignition system is very adequate. The goal is to get rid of the hassle of adjusting and replacing points.

A supercharged v8 running at very hi rpms may very well benefit from a capacitive discharge engine. An MGB?

Barry
Barry Parkinson

Thanks everyone for your comments, very interesting site JGC, at Beyond-Designs.
I will have a look at Maplins to see what they have, Steve, thanks.
Graham
Graham Cherry

I still have a Sparkrite system in a drawer in the garage that I built (the Sparkrite that is, not the garage ...) in the early 70s, that you can switch between normal points and points triggered capacitive discharge. I did use it on a couple of cars, but found it made no detectable difference to anything on a properly set up system, although it quite possibly would on one with voltage and/or tuning problems and adverse weather conditions. It does prevent arcing and pitting/spliking of the points, but since I started checking dwell at intermediate service points instead of gap I have never had to adjust them between replacements, indeed both cars have currently done more than 10k on their points. When checking gap the spike that appears after just a short time means you have to get them off, face them up, and readjust, which is a pfaff, not to say a waste of time.

On my first car when still learning about electrics and tuning I did have a couple of occasions when our ageing Mini parked outside (when we got colder winters than we do now) wouldn't start, but one of the first wrinkles I learned was to pull the HT lead out of the coil a fraction whilst the wife cranked it, and that got it going. By retaining the points it would still suffer from the mechanical degradation that some complain about, although I have never had any problem with Lucas points (nor a condenser failure) in 40 years.

Opening out the plug gap simulates worn plugs of course, and is one of the wear factors than contributes to poor starting. A bigger gap also causes the HT voltage to reach a higher peak, which can break down other HT components. But in the case of the Sparkrite working where straight points didn't was probably just due to the greater energy spark that was available with it switched in.

Systems like the factory 45DE4 basically use an electronic switch for the current in the coil, other than that the voltage and current parameters are much the same as evidenced by the same dwell,as for points. The 45DM4 HEI system *may* be a bit different, it doesn't have a dwell quoted, but given its age and small physical size I can't imagine it has much inside by way of electronics. I'd be interested to know what the dwell is on Pertronix, Aldon Ignitor, and Lumenition sytems. The factory adopted electronic systems for North American spoec cars as they were required to go 50k miles without any adjustments, and stay within the increasingly tight emisions limits. With the best will (and points) in the world I can't imagine points lasting that long, much less stay in spec. But changing the points every 10k (or longer) is no big deal, I *like* fiddling with my cars :o). The biggest improvement in adverse condition starting is on the rubber bumper cars with their 6v coils and ballast resistors, which are bypassed during cranking, usually resulting in a *higher* than normal coil voltage for starting.

But Graham's question was about dwell extenders, which haven't been mentioned.
Paul Hunt

Thanks Paul, I put the thread on to find out if dwell extenders were still available, as I believe it is a simple bit of electronics, probably using SCR's or Triacs to close the circuit immediately and certainly well before the points do, thus preventing arcing and pitting. I do not want to go to electronic ignition, as we rally the car and can not afford to have complete ign failure, as I have experienced twice with Ignitor units. I merely wanted to extend points life, but as you say, setting using dwell, which I do, overcomes the odd lumps and bumps.
Cheers
Graham
Graham Cherry

This thread was discussed between 15/04/2005 and 19/04/2005

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