Author Topic: Magneto woes  (Read 1499 times)

Offline BSA500

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Magneto woes
« on: 12.03. 2017 20:14 »
Well getting the bike ready after skimming the drum etc. Been difficult to start for a while, now no go. Intermittent sparking timing side and none drive side. She has been stuttering at higher revs for while so any guesses on what has gone home on the mag. Best wait to see what bonus I get. BTW Bezzermac is a good looking guy who is brilliant with mags(and my discount is???)

Offline trevinoz

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Re: Magneto woes
« Reply #1 on: 12.03. 2017 20:19 »
I'd have a look at the pick-up brushes and the slip ring and see if there is carbon build up and whether the brushes are too soft.

Offline BSA500

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Re: Magneto woes
« Reply #2 on: 12.03. 2017 20:36 »
Done that all fine. Swopped the leads around no change and Andrew supplied the pick up brushes so are correct (I have had some before that were too hard and they put a nasty groove around the slip ring  *eek* ).
 She has been getting more cankerous over the last 6 months over the starting.

Online Triton Thrasher

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Re: Magneto woes
« Reply #3 on: 12.03. 2017 20:52 »
Plugs first. Are they sooted or oiled up?

Points second. Are they clean, dry and gapped?

Offline BSA500

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Re: Magneto woes
« Reply #4 on: 13.03. 2017 08:51 »
I had popped the leads off so when I am talking about sparks -or the lack of- I am talking pre plug. Like I said she has been giving me issues before this. Strange how either side is firing differently could be leads/pick ups but the sparks are intermittent or not at all.
 

Offline BSA500

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Re: Magneto woes
« Reply #5 on: 14.03. 2017 20:33 »
So tonight tried again to trouble shot. 1. Tested the leads both now spark. 2. Put them back on the plugs kick x 30 no firing up. 3. Cleaned now wet plugs 4. Tested plugs-sparking back into head. 5 Kick x 30 starts. 6. run for 5 mins turn off. 7. Restart-nope. 8. Keep trying starts again now knackered. 9. Retire suspect mag is having issues 10. Beg wife for money  :!

Online bsa-bill

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Re: Magneto woes
« Reply #6 on: 14.03. 2017 21:47 »
Modern plugs once wet cannot be dried in any useful time and once wetted they just short out, if you can find a pair of really old plugs (but decent) try them they will stand getting wet better.
All the best - Bill
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Offline BSA500

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Re: Magneto woes
« Reply #7 on: 15.03. 2017 09:21 »
Plugs have been an issue before but these are sparking just fine. The bike seems to need alot of kicks these days so I feel the mag is getting a bit tired. It used to be a 1/2 kick starter  *sad2*

Offline BSA500

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Re: Magneto woes
« Reply #8 on: 04.04. 2017 16:55 »
Well bit the bullet and sent it to Priory Magneto's. What was wrong with it I hear you ask. Everything is the reply.... The points I can remember 1 slip ring fuburred 2 cam rough 3 armature sparking all over the place 4 chipped bearing-how?? 5 pick up brushes poor quality and some other stuff. Waiting for it to come home now so I can stroke it. If it's anything like the work that has been done to my dynamo in the past I will be well happy. How the hell did the mag manage to run as well as it did?????

Online KiwiGF

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Re: Magneto woes
« Reply #9 on: 05.04. 2017 02:38 »
Out of interest.....a guy in nz who has built up many BSA's , mainly singles, reckons that in almost all cases replacing the capacitor with the "brightspark" (external) version has stopped him having to send the mags off for rewind etc, or in other words, in his experience the original windings are not usually duff on old mags, it's just the (internal) capacitors have failed through age etc.
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Online RichardL

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Re: Magneto woes
« Reply #10 on: 05.04. 2017 04:19 »
Out of interest.....a guy in nz who has built up many BSA's , mainly singles, reckons that in almost all cases replacing the capacitor with the "brightspark" (external) version has stopped him having to send the mags off for rewind etc, or in other words, in his experience the original windings are not usually duff on old mags, it's just the (internal) capacitors have failed through age etc.

A rousing round of applause for our member and friend Groily, and his friend and business partner Ken, who is sadly gone.

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Online groily

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Re: Magneto woes
« Reply #11 on: 05.04. 2017 06:53 »
Oftentimes the 'guy in NZ who  . . . etc  . . .' is right and his words of support are much appreciated. But replacing a capacitor won't  get anyone round a defective coil problem.

Sometimes, a coil with a small break inside will keep working for a good while as the spark will jump it until it gets too big, and a replacement condenser (of any sort) will have the effect of bringing things back to life if the original has started to fail. But it is unwise not to try to establish the state of the HT winding. Some originals are still , rather surprisingly, OK - but the twin risks of an internal break (which can usually be established by simple resistance measurements) and of failing insulation (which can't), should never be overlooked. Being perfectly honest, I'd say 8 out of 10 original coils I see fail to match the Lucas specs on test, often showing problems when heated to the Lucas test temperature of 50°C.

By contrast, 90% of 'modern' rewinds test good for continuity and insulation, although there are variations in performance depending on the exact recipe used by the particular winder. The basic Lucas performance spec is that you want a K2F to produce 90%+ of all sparks, across 5.5mm test gaps with three points, at 130rpm of the magneto. A good one will produce them all at 110rpm, and exceptionally down to 100rpm. A good MO1, as per B series machines etc, should do slightly better than a K series mag.

Many of the modern condensers fitted don't do as well as the originals and are the the reason for premature failure of rebuilt instruments. The choice of condenser is important and many mains suppressor types are not good at resisting voltage spikes in the low tension circuit (which can be surprisingly high). Although many rolled paper items are 'self-healing', ie if the insulation inside them is perforated, it self-seals, but they can't do it indefinitely. In many cases, their voltage rating is marginal, or inadequate. That's when a capacitor on the points is most likely to be a handy solution, and in the event of any future worries, easy to replace.

On my own machines, I've run our widgets for more than 6 years on three machines, and for less time/miles on 2 others. All the mags have modern windings - and no problems in a total of over 60K miles between them. Of around 10,000 widgets sold, the failure rate has been negligible (unless people aren't complaining and asking for their money back!) I think we have seen fewer than 10 returns, of which several were actually OK.

So confidence isn't misplaced, but there are no medium- or long-term get-rounds for faulty HT coils, and it's a lot of work to have to take a mag apart again because a short-cut didn't do the trick!

Bill

Online beezermacc

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Re: Magneto woes
« Reply #12 on: 05.04. 2017 07:28 »
I agree entirely with Groily. I was typing a similar post whilst he was typing so I'll drop my tuppence worth in as well.......

The vast majority of K2F's passing through my workshop need new oil seals which, in turn, means the main bearing has to be removed and replaced with a new insulator so that the oil seal is trapped at the end of the magneto. If the tricky procedure for fitting the insulator is not carried out effectively the insulator will tear or it will not be tight enough to grip the oil seal. Furthermore, because the machining of the main bearing housing is not always consistent or has been damaged it is necessary to stock insulators in a variety of thicknesses to achieve a good, tight, fit. If the oil seal comes loose when the magneto gets hot the magneto floods with oil and the earth side stops working and bike stutters and bangs like a machine gun. Whilst I have no wish to dispute the experience of others (guy in NZ) I find that about 6 out of 10 magneto coils are not fit to be reused, not always due to continuity problems. Other problems I often encounter are imbalance of points gap and firing interval, cracked / arcing slip rings, poor quality / arcing pickup brushes, worn points pins, incorrectly assembled points, incorrect endfloat on armatures, loose driveshafts in capacitor housings, damaged keyways, damaged threads on armature shafts, rough bearings due to earth brush and insulation failure (very common).  As with any forum we have to be able to filter the good advice from that which is well intentioned but perhaps a little inaccurate. I accept that the guy in NZ deals mainly with singles (which don't have oil seals) but I find that the MO1 magnetos quite often suffer from coils which have overheated plus the many other problems associated with MO1's. My previous references are to K2F magnetos because this is an A10 forum!
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Offline duTch

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Re: Magneto woes
« Reply #13 on: 05.04. 2017 10:54 »

 My two bits worth is that when I had my Auto advance K2F redone by Les McKittrick, he told me the internal windings had corrosion in the joins of the wires, shorting between windings, and the condenser was shot; basically farqued....rebuilt and reckons it will outlast me  *eek*......having said that, there was still a 0.00?" (Few thou) difference between L/R in the points gap.
   I still reckon I should aaahhmm- arm myself with a ready to go spare, set up with the (dangerous) knowledge I've garnered here.. *wink2* *wink2*
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Offline JulianS

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Re: Magneto woes
« Reply #14 on: 05.04. 2017 12:00 »
Dont worry too much about a difference in points gap. Lucas put a tolerence of 3 thou...

The main thing is that the timing is the same on both lobes. 1 degree out at the mag is 2 degrees out at the crank.

I bought a complete K2F from Priory just over 2 years ago - the points gaps were the same and the timig spot on between cylinders. No easy to achieve that.