Author Topic: Magneto bad all of a sudden, and then, only sometimes?  (Read 2257 times)

Online RichardL

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Gents,

Due to my inability to achieve a reliably starting engine, I've been embarrassed to raise head up since completing my engine rebuild a couple of months ago. Also, other life events have prevented having time and good concentration to focus on the problem. I am going to try to tell this story as foreshortened as possible, while seeking some thoughts from the group.

On first timing, no firing and spark was rare or erratic. 

Replaced wires, caps and plugs.

Retimed and kicked it over with the ATD wood peg accidentally in place (causing full advance) and she started.

Retimed and reset points gap and she started up first kick, but I noticed that the large washer (behind the horseshoe washer) was not seated properly over the two pegs. Loosened ATD bolt and set the washer. Kicked it over again to be sure this had not changed the timing. Started first kick. Now, with confidence that I was finally there, mounted the outer timing cover (using sealer and my last gasket).

Moved the bike to position in  the garage where I could run her longer while exhaust left the garage. Started first kick. Stopped the engine for some reason I cannot recall. Since then, not a single pop of ignition.  Pulled the plugs and, at first, no visible spark. Slid some paper between the points to clean them. After that I could get some visible erratic spark, but can not be sure the cleaning was the reason. Plugs back in, but no firing.

This is a very partial description of the sequence of events, but I have tried to pick details that might lead to ideas.

The thing that makes me craziest is that, when I disassembled the bike for the rebuild last year, the magneto (with its Brightspark EasyCap) seemed to be working perfectly. The bike started easily, hot or cold.  Nevertheless, this new problem seems somehow magneto related, but I cannot understand the three most recent easy starts if the magneto is shot.

Wow! I hope someone has a super-obvious answer that embarrasses the hell out of me for not catching it but, at the same time, leads to bugs in my teeth before they go dormant for the winter.

Richard L.
 
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Offline wilko

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #1 on: 07.07. 2014 00:30 »
 Try another set of plugs.

Online bsa-bill

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #2 on: 07.07. 2014 08:46 »
Quote
Try another set of plugs.

Yep - I'd would suggest also the most common cause these days.

Brought my Flash which was  in the bottom shed into the garage a distance of 30 yards for a repaint, we now need the garage for storage so had to take it back (still not painted), the normal first/second kick Flash refused to even hic - plugs - looked like a sweeps armpit, short run - sooted up and no distance to get up to heat I suppose, also maybe to rich on tickover?.
Anyway 2 new Bosch plugs - Baroom - I'm becoming a fan of these Bosch plugs, maybe Bosch haven't got around to out sourcing them too some third world nation as yet
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline duTch

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #3 on: 07.07. 2014 13:51 »

 Heya Richard- was wondering if I'd just slipped under a rock or something- been a few times when I could've used that green 'Cone of Silence' of yours.... *smile*
 Can I suggest maybe a intermittent earth 'lackage'....earth brush??

 Bill,
Quote
maybe Bosch haven't got around to out sourcing them too some third world nation as yet
you've been under my rock- I whacked in some Bosch plugs, but had to buy from two different places.
 Realised after a year that one is 'Made in Germany', the other is 'Made in India'.
Funny thing is- guess which one didn't sound right....?
  Not sure if any things wrong with it but swapped out for matching B7ES, much better, but enough of that here.
 
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Online RichardL

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #4 on: 07.07. 2014 16:34 »
During the rebuild, I replaced NGK B7ES, with 3500 miles on them, with a new pair of the same. I'll try to pick up some Bosch plugs, but my gut tells me it goes deeper (or even stupiderer *pull hair out*). Really, I hope it doesn't, go deeper, that is.

I am now wondering (among other things) if the springs behind my slip-ring pickup brushes are properly seated. Any thoughts on the right way to get the big ends into the holders? I just kept pushing with a thin screwdriver.

In case there are any questions about my new caps and plug wire: caps are Rajah-type with a screw compressing the wire directly to the plug clip; wire is Packard 440.

Richard L.
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Online bsa-bill

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #5 on: 07.07. 2014 19:18 »
Richard I don't think Bosch are so good that they will never soot up under any circumstance , just I've run with them for a year or two without problem in my other Rocket morphed Flash and it had a history of killing plugs and disappearing spark.
In the case of my ever reliable Flash sooting up and not starting any clean plug would have solved the problem
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Online beezermacc

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #6 on: 07.07. 2014 19:46 »
When fitting the Easycap it is necessary to cut wires and solder etc. My guess is something has gone wrong in the Easycap fitting process, maybe a poor solder joint or something in the low tension side tripping to earth, or something dodgy with your points. It doesn't sound like plugs. A good mag should fire through most half-decent plugs.
Priory Magnetos Ltd - A10 spares, magneto and dynamo refurbs. www.priorymagnetos.co.uk

Online RichardL

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #7 on: 15.07. 2014 00:48 »
Guys,

It sounds stupid, but I've been really thankful for a lot of bad riding weather here in Illinois. Makes me less aggravated that I haven't had enough time to get my bike on the road.

I just stoled some garage time to try to look at my problem with fresh eyes. I pulled the points out and everything looked OK there. I checked the cam to see if it was loose and, sure enough, it was. This was the first time I've had the cam out of the mag. In 3700 previous miles, two engine rebuilds and two magneto rebuilds (well, sort'a, rebuilds) it wasn't an issue.

I found this post from none other than Groily. http://www.a7a10.net/forum/index.php?topic=8393.msg59476#msg59476. Touches on my questions quite specifically about how the cam ring is held in position and held in. I looked at my bakelite cover and damned if the o-ring wasn't missing. In any case, I had started up at least once with the cover off, probably sending the cam off the pin anyway. I haven't taken care of it yet or retimed, but I still have a question: With the cam all the way in and the notch aligned with the pin, there still seems to be play in the cam between notch and pin, maybe two or three degrees. Is there a good way to snug this up?

Thanks, in advance, for your thoughts.


Richard L.


Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Offline duTch

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #8 on: 15.07. 2014 04:07 »

 I'd only be guessing if I say cable adjustment....? That is if it's manual Adv........?
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Online RichardL

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #9 on: 15.07. 2014 04:14 »
Dutch,

You have accurately pointed out that I forgot to remind the team that she has an ATD. So, no cable. Nevertheless, thanks. Any other ideas? I just don't see as how it makes sense to have the stability of timing dependent on the notch in the cam straddling less than half the diameter of the pin for holding its location. Have I described this correctly? If not, maybe there is something else going on here.

Richard L.
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Offline duTch

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #10 on: 15.07. 2014 07:49 »

 Hmmmmm- I think mine has two pins about maybe ~1/4" apart.....maybe a small blob of silicone? At least till you come up with something better.?
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

Online groily

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #11 on: 15.07. 2014 08:05 »
Hi Richard,
You don't want several degrees of float on the camring, for sure. It might be possible to eradicate it by shifting the pin's position a bit  . .  . to do that, prise the little cap off the top of the pin (it'll come without damage, v fine chisel or screwdriver), to expose the slotted head of a threaded item with an eccentric on the inner end. The eccentric is there to give fine tuning of the camring position, and will have been set to the best position for best sparks at the factory. However, chatter over the years might have worn it a bit. Because it's eccentric, you should be able to turn it a little to get the eccentric bit to fill the notch a bit better without moving the camring more than a gnat's whisker (which will be OK).
Quite often, I've made new eccentric-ended screws to eliminate this hassle.
The pin in the outer end acts as a locking device, as you'll see, by expanding the slotted outer end of the thing so it doesn't move. However, a short bit of threaded with a little locknut works just as well, and in fact you could make a bit with a file to engage exactly with the notch in the camring. Then screw it in and refit the camring. Thread is BSF, 5/16 from memory.
Also, would suggest you make up a gasket or seal thick enough for the end cover of the cb housing to pinch against the camring, to stop it fretting if it's so inclined. Often, the seals supplied or fitted don't actually engage the camring at all.

If the camring is a very loose fit in the end housing, then it might be worth using a dab of loctite on a fixed mag. The risk with loose-fitting camrings is that the firing interval between cylinders can be upset by several degrees if the ring is off centre (quite apart from there being a noticeable difference between the points gaps on the lower and upper lobe of the cam). Perfectly equal gaps are less important than 180:180 firing interval (as long as the smaller one is c. 12 thou) - but the firing interval is hard to measure. A static test can be done with a rotary table and a buzzer of the Brewington sort, but proper dynamic testing requires more serious kit with rotary spark gaps and a protractor to see what happens up the rev range, when things can look rather different from at rest
In this regard, it is also worth looking closely at the pivot for your moving cb point. Wobble on there has some of the same effects. If very worn, the pivot post can be replaced (fiddly); if not too bad, a new set of points might help.
Hope that helps a bit. Not sure that any of this will bring the sparks back however, unless there is a short on the LT side for one or other reason.  My mate KenF might chip in if I've missed anything  . . . Cheers, Bill

Just seen Dutch's  . . . only early mags have the axial screws for limit stop operation - they don't have the eccentric bit. Suspect you have the later sort Richard?
Bill

Online RichardL

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #12 on: 15.07. 2014 12:35 »
Bill,

That's a fantastic lot of knowledge and , I think, just what I needed to know. I'll know better after I implement the advice. Thanks, greatly, for taking the time to write it. By the way, The symptom in my last go-round was that, after timing, it started on the first kick three times in a row, then, wouldn't even cough. This seems to fit the moving cam-ring diagnosis.
 
Richard L.
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Online beezermacc

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #13 on: 16.07. 2014 20:22 »
In my opinion the slack cam ring isn't going to stop the mag sparking unless it has floated off the peg completely. Don't forget that a manual mag provides for about 10 degrees retard by rotating the cam ring to aid starting, so the little bit of unwanted rotation on your cam ring isn't going to make a lot of difference. The problem still sounds like an intermittent short or open circuit on the low tension side.
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Online RichardL

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Re: Magneto bad all of a sudden, and then, only sometimes?
« Reply #14 on: 16.07. 2014 23:45 »
Beezermacc (Andrew?),

Thanks for the thoughts. I believe the cam ring had floated completely off the stop pin. Until Groily shared the secret with me, I had no idea the pin was eccentric. When I first checked it, hardly any bump was available to engage the ring. In addtion to having no o-ring in the cover, I had been kicking the bike over and even started it once with the cover off. Now, I've set the pin position for no (or, bare minimum) cam ring slack. I've yet to get her back together, but I'm feeling somewhat confident that this may well have been the problem. However, it seems confidence is a setup for let down. I hope it isn't intermittance, since that is usually hard to pinpoint. I'll keep the forum posted on results.

Richard L.

Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.