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Misc: Ignition Lucas K1F magneto weak spark

morton90

Website User
VOC Member
My Comet mag has a very weak spark at kick start speed, I have checked the magnet strength using a compass (test as described by Ken at Brightspark in an earlier post) and found it is poor. The bike has been stood since 1982 so no surprise really. Does anyone know who offers a re magnetising service in the Leeds/Yorkshire area. Thanks Andrew Morton
 

morton90

Website User
VOC Member
Thanks Chris, I had them down to try but wasn’t sure if they would do just the re magnetising. That’s great will call them tomorrow and go down. Hope your latest project is going well, almost finished the comet, hopefully getting the mag done will let me fire it up.

Thanks Andrew
 

erik

Well Known and Active Website User
VOC Member
Have you looked at the Points while the engine is running on tickover? Best to look at in dark conditions to see if there is some contact firing.If you see sparks then the condenser is past his best time of live.Erik
 

morton90

Website User
VOC Member
Hi Eric
I have removed the original condenser from the rotor and fitted one of the Brightspark easy cap condensers. The spark is strong when I spin the mag with a drill but only just visible when I flick by hand or using the Kick start.
 

greg brillus

Well Known and Active Website User
VOC Member
I have had a few magnetos, and some that have been freshly rebuilt, that put out a week spark at low rev's......... This at kicking speeds........the culprit ended up being the main armature had been machined over its length to "True up everything" this results in the armature having a smaller OD than an original one by say 10 or 20 thou........This will loose a lot of the magnetic build strength and the magneto becomes useless for starting.
 

erik

Well Known and Active Website User
VOC Member
My experience with the easy cap condensers were not to my satisfaction.Firing Points were still visible until I changed the condenser . These Micro condensers seem to have not the same capacity than bigger ones which can mounted inside of the rotor.Erik
 

morton90

Website User
VOC Member
Thanks for sharing your experience Erik, I do also have a replacement capacitor to go in the rotor but thought I would try the Easy Cap. I am getting the body re - magnetised at Armoto this afternoon so will see how that works first. I will check the amount of arcing at the points when it is re assembled. Andrew
 

highbury731

Well Known and Active Website User
VOC Member
Magnetoman has had a lot to say about condensers for magnetos. He's studied this a lot and is unimpressed with the Brightspark Easy Cap. I can't remember where to find his postings.
Paul
 

LoneStar

Well Known and Active Website User
VOC Member
Magnetoman has had a lot to say about condensers for magnetos. He's studied this a lot and is unimpressed with the Brightspark Easy Cap. I can't remember where to find his postings.
Paul

Get comfortable, open an appropriate beverage, and settle in for a long read:

 

Magnetoman

Well Known and Active Website User
VOC Member
I do also have a replacement capacitor to go in the rotor but thought I would try the Easy Cap. I am getting the body re - magnetised at Armoto this afternoon so will see how that works first.
It's too late to affect your decision, but if you remove the armature to snip the capacitor lead you'll have wasted the money you just spent having it remagnetized. Any time you remove the armature the magnetization suffers a significant permanent -- permanent, that is, unless it is remagnetized -- drop in the magnetization.

As I've written elsewhere before, with a proper capacitor installed in the body, and it then remagnetized, the magneto will spark the engine into life even at the low end of the kickstarter speed. It will continue to do so for at least 100,000 miles with only routine maintenance of the magneto (lube the cam follower, replace pickups when they wear out, etc.). By "proper capacitor" I mean one of the two I've extensively tested and that are listed in one of the Appendices to the lengthy thread on Britbike.com.
 

timetraveller

Well Known and Active Website User
VOC Member
Clearly Magnetoman knows more about this than most of us but the magneto that I helped Nick Wingrove with was not remagnetised after fitting the BrightSpark capacitor and worked satisfactorily for several years afterwards. This was on a Comet where there is less compromise with the internal timing of the mag. The bike was an easy starter and Nick rode it for several years despite being somewhat compromised having had a stroke.
 

morton90

Website User
VOC Member
Well, clearly a lot of different views on this, I had the body re magnetised yesterday, after assembly I have a great improvement with a strong spark when I spin the mag slowly by hand. More importantly the bike started up 2nd kick after a rebuild which is a good sign. Had a look at the points while running, all looks OK.
I suppose time will tell.
Thanks for all the information provided, I now know a lot more Lucas magnetos.
Andrew
 

Magnetoman

Well Known and Active Website User
VOC Member
the magneto that I helped Nick Wingrove with was not remagnetised after fitting the BrightSpark capacitor and worked satisfactorily for several years afterwards.
The issue with remagnetizing is all about how hard you will have to kick the bike to start it. Even an extremely weak magnet will generate sufficient voltage for a spark, if the magneto spins fast enough, but that will be well past how fast someone can possibly kick it with an older "steel magnet" magneto from the pre-1930s. Alnico is more forgiving, but the effect is still present. .

A Lucas manual says 300 rpm is the low end of kick starting speeds, with 500 rpm normal. At these speeds the generated voltage will be essentially linear in speed, so if a magneto has lost half its magnetization it will require spinning it twice as fast. What this means in practical terms is that if you had a magneto that supplied sufficient voltage for starting at 300 rpm, but then remove and replace the armature for any reason resulting in it now starting at 500 rpm, someone with a good leg might still be happy that it "works satisfactorily." However, wisdom may come with age, but so do weaker legs.

Most of us, myself included, don't have tachometers attached to our kickstart levers that record the highest speed achieved when we jump on that lever. Which means most of us have no way of knowing if we have to kick them at 300 rpm, or at 500 rpm, or even higher to get them to start. However, I know that removing and replacing the armature significantly reduces the magnetization, and I also know my re-magnetized magnetos require a bit less than 300 rpm because I test them after re-magnetizing. I also know that bikes that start at 300 rpm are joys to have. Less so if 500 rpm.
 

Magnetoman

Well Known and Active Website User
VOC Member
carry a spare BrightSpark capacitor. They are so small that one wil fit into any pocket and I know that on one occassion Nick had to replace his by the side of the road.
A £13/£16/$35 (I found different prices on line) Brightspark requires the armature to be removed when the first one is installed in order to snip the lead to the existing capacitor. After that, if the magneto is re-magnetized, factory-fresh functioning will be restored, at least until/if that capacitor fails. The advantage a Brightspark has if/when it does fail is it can be replaced on the side of the road with another of the £13/£16/$35 capacitors.

To install an internal capacitor, as was used by the factory, also requires the armature to be removed, but factory-fresh functioning also is restored if it is then re-magnetized. The disadvantage of an internal capacitor is it cannot be replaced on the side of the road. However, capacitors of the type on which I conducted extensive accelerated stress tests that showed they would last at least 50 years and 150,000 miles in actual use, at a cost of $2.70 for the necessary pair.

Something that costs £26/£32/$70 for it and a spare that can be replaced on the side of the road if/when it fails. Or something that costs $2.70 and that doesn't fail. The choice is yours.
 

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