Thorspark magneto ignition FAQ

Thorspark magneto ignitions frequently asked questions from customers.

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To start with, a very good quote from the Real Classic magazine's article on magnetos pretty much says it all!:

"Out of my 40 years muckin' about with old motorbikes one wisdom has risen above all others. The golden rule is, unless you are convinced deep in your very soul that the mag is ticketyboo, don't waste your time fiddling with anything else. A weak yet reliable spark will mislead you through apparent poor carburation into more grief than you can possibly imagine, while a strong yet irregular spark will convince you that malevolent hobgoblins inhabit the entire power train."


This FAQ is an attempt to concisely answer questions most often put to us, we are obviously trying to sell our magneto ignition kits, but there is nothing writen here that we don't honestly believe.  We offer an electronic ignition conversion for magnetos.  It is not the solution for everyone, but if you fit one, your bike really will almost certainIy be more easy to start and run better than it ever has, be more reliable, and the ignition will require no maintenance apart from the spark plugs and a battery every few years.   I like magnetos as well as electronic, and there are plenty of people who will prefer to use them, but the Thorspark magneto ignition is an economical and practical alternative.

I have read various people on classic motorcycle forums writing how simple to get working properly and reliable magnetos are. If you honestly believe that please read these accounts of how to rewind and recondition a magneto.  It really is a precision and specialist job to do it properly, and a cheap job may not be economical in the long run.


 List of questions addressed below

1/  What are the symptoms caused by problems with the magneto

2/  Will the Thorspark ignition kit flatten my battery?

3/  If the battery stops charging, will the bike be left stranded using a Thorspark magneto ignition kit?
4/  Is electronic ignition more or less reliable than a magneto?
5/  How does the performance of electronic ignition differ from a magneto?
6/  Will the manual ignition advance retard still work with the Thorspark ignition
7/ Do I need to use suppressed spark plug caps with the Thorspark magneto ignition
8/ Can the 6v Thorspark system be run on 12 volts?
1/ What are the symptoms caused by problems with the magneto
I refer the reader first of all to the quote at the top of the page.  Problems rooted in the magneto are sometimes obvious, or can seem like all sorts of other things.
However, typical signs of magneto problems are, among others:
-- Bike hard to start.
-- Tickover, pulling away, and low-speed running erratic.
-- misfiring, particularly at higher revs and fully open throttle, or when opening the throttle.
-- engine suddenly stops when hot and difficult re-start, or is just difficult to re-start when hot (this one is a bastard as you can't stop for petrol)
-- engine only really runs ok when the manual advance is at a certain "magic" position, anywhere else and it messes about

2/ Will the Thorspark ignition kit flatten my battery?
The Thorspark system draws about a quarter of an amp in total, depending on the rpm.  That is in total, including the power used by the coil, as well as the electronics.  This equates to a total power use of about 3 watts on 12v, and less than 2 watts on 6v to produce the sparks.  The Thorspark ignition system is also quite voltage tolerant.  If the bike's battery is initially a bit flat, and the voltage low (within reason), the system will still work and the bike will still start and run as normal.
This electronic ignition is not a large extra load on the bike's electrics, the old 6 volt Lucas dynamos put out about 50 or 60 watts, so can cope with a load of 2 or 3 watts.  The ignition system is designed to use minimal power in order to work in conjunction with the Lucas dynamos and alternators, which are low power by modern standards.  As long as the battery is half decent, and it is charging to some extent, there will be enough power to run the electronic ignition many times over.


3/ If the battery stops charging, will the bike be left stranded using a Thorspark magneto ignition kit?
A magneto has the advantage of being independent of the rest of the bike's electrics, and thus is not dependent on the battery charging to work.  However, if the magneto does fail, the bike is pretty much stranded.  This is not an unheard of event, most of the bikes trailered home from our local classic bike club's French trip suffer from magneto failure in some form or other, and most of these bikes have "reconditioned" magnetos.
The Thorspark Ignition runs off the battery.  Most classic bikes nowadays actually do have a working charging system. It is not the same as years ago when we all rode around with no lights and dodgy dynamos. As long as the battery is more or less charging, the ignition will work fine as it draws very little power.  If the battery does completely stop charging, the bike will still run all day with the lights off on the remaining battery charge, and couldn't be ridden at night with no lights anyway. 
For example, as the ignition system draws about a quarter of an amp, a 7 amp hour battery will give 14 hours of running on half it's charge.  If the battery goes completely flat, a few hours on charge should get the bike home, giving many more hours of daylight running.  The bike will not be completely stranded.
We have sold many kits for trials and race bikes etc with no electrics, fitting a small battery and periodically charging it gives hours of running time.  The small extra weight is easily offset by better running and starting.

We have one (eccentric?) customer who runs his bike ignition on four AA torch batteries taped together to give 6v.  This apparently gives him a day's riding, and he can switch to four more if needed the next day...

4/ Is electronic ignition more or less reliable than a magneto?
Properly set up magnetos work extremely well, but even they do need maintenance, especially as most classic bikes are not ridden regularly, sometimes with long periods without use which is not good for a mag.  Magnetos were made in an era when people used their bikes for regular transport and had more time, and owners were expected to continually fettle their bikes.  This means that at the very least the points need cleaning and setting up at times. There are also various other brushes and wear parts in the magneto, and the infamous oil seal at the drive end.  Lucas also recommended that the magneto be removed every few thousand miles and be sent off for overhaul by the local Lucas service agent.  I quote from the book, "AJS and Matchless Twin Motorcycles" by F. Neil, regarding the Lucas K2F magneto.  I imagine the other magnetos like the Lucas MO1 magndyno were similar:
"Lubrication and adjustment is required every 3,000 miles, cleaning is required every 5,000 miles, and every 10,000 miles the complete unit should be handed to a Lucas Service Station for dismantling, replacement of worn parts, cleaning and lubrication."
It does make you wonder how many magnetos ever received that treatment! either then or now, especially as it normally takes hours of work, and some special tools to remove a magneto and then re-time it, and even then it is much easier to time it up with two people, one either side of the bike!
Coupled to this is that by now most magnetos have had to be rewound or reconditioned, and how well they work really does seem to be somewhat of a lottery, despite all the hype given out by the reconditioners about using improved modern materials, condensers, etc.

The Thorspark electronic ignition has no parts to wear out, needs no maintenance, and comes with a 5 year unlimited mileage guarantee.  It is designed to be "fit and forget", and is not effected by oil ingress. 

5/ How does the performance of electronic ignition differ from a magneto?
Once again, a good magneto is a very nice  thing!  and will do the job in spades.  However, realistically a magneto relies on mechanical components, ie a set of points and condenser to provide the spark and accurate ignition timing.  It also produces a smaller spark at low revs, such as when the engine is kicked over (this is partly why the spark plug gap is smaller on magneto ignition bikes,  to improve starting when the spark is weak).  Electronic ignition produces more accurate ignition timing, as it is not dependant on mechanical components, and produces the same size spark more or less at all engine speeds available to a classic bike. 
The result of this is that starting is easier, tickover, pulling away, and general low speed and clean running are improved, and there will almost certainly be a performance increase on both single and twin cylinder engines.  This will become more pronounced compared to a magneto if it hasn't been regularly maintained or is tired.  
For twin cylinder engines there is often the added benefit of more accurate timing between the cylinders.  Most magnetos don't accurately provide the same timing on each cylinder, so one is always running behind the other.  This is extremely difficult to correct on a Lucas magneto (most are K2Fs) or a BTH.  Even regrinding the cam ring will not necessarily fully sort the problem.  The spark occurs at just the moment when the points start to open, at which time the heel of the points is running up the slope of the cam, and It takes a very high level of precision engineering to get that point consistently exactly the same for both cams and both cylinders.  Lucas magnetos were a budget option, the major motorcycle manufacturers all wanted a cheap magneto for mass use, without the added quality of aircraft spec mags, and that is what they got! It would be interesting to know (does anyone actually know?) what was the maximum error between cylinders acceptable to Lucas when they made the magnetos?
Once again, that is not to say a good magneto is not reliable and fit for purpose, and they did work well for many years.  However that very fact is another factor.  Magnetos were produced more or less exactly the same for 40 years or more, which somewhat changed the "purpose" they were put to.  A magneto may be perfectly suited to a low compression slow revving "cooking" bike from the 1930's, but as compression ratios and revs rose in the 50's and 60's, more accurate timing was required.  I have seen fully reconditioned twin cylinder magnetos  (costing hundreds of pounds) with reground cam rings giving 2 1/2 degrees difference between the two sparks, which is 5 degrees at the crank-shaft.  That is acceptable perhaps on a really old bike, but on something like a Triumph Bonneville or Norton Commando, that will be really poor and noticeably effect performance.

As an example, we fitted an ignition kit to a customer's Norton Dominator cafe racer, this was ridden in to us, and the customer was complaining it was difficult to start.  After he left the owner rang us and accused us of interfering with his clutch, as it had started slipping in each gear...
6/ Will the manual ignition advance retard still work with the Thorspark ignition
 Yes it will continue to work as originally.
I personally really like a manual advance, it has all the benefits of simplicity, and I find it easy to use in practice.  Most of the time when riding it can be set more or less at full advance, and just retarded a little for starting, or for slogging up a hill, or with a chair attached.  While it requires a (very) little more work from the rider, it gives the rider total control of where the spark occurs, rather than with an automatic advance or if the advance is programmed electronically into the ignition system.

This can be an advantage on many bikes.  Many old bikes have a starting "procedure" which is specific to the bike, and a manual advance gives you complete control of this procedure.  If the compression ratio or other aspects of the motor have been modified from standard, the original automatic advance (or pre-programmed after-market ignition advance) is unlikely to be completely suitable for the engine.

An example is the BSA gold star, I have been told by customers that no two bikes start in quite the same way, and being able to set the ignition manually is a "boon" (well, no-one has actually used that word, obviously, but you get the drift..)


7/ Do I need to use suppressed spark plug caps with the Thorspark magneto ignition.

This is not necessary, but it is illegal in many countries to run unsuppressed spark plugs


8/ Can the 6v Thorspark system be run on 12 volts?

If you have a bike running with 6volts, and want to upgrade to 12v, we do an exchange unit for £40.

If you would like to return just the trigger unit (the rotor can be left in the magneto to keep the timing), we will flash it and return it along with a 12v coil.


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