Airone Magneti Marelli Magneto

[Barry Wilson]

Hi all,  At last I have finished the Airone Sport and tried to start it with no success, having checked all the settings were okay I discovered that the mag was only producing a spark every 8 ish  engine revolutions. I was driving the engine by the crankshaft nut with a cordless drill, it runs at about kick-start speed.  The one spark is good and the mag was rebuilt with a new coil and condensor.  Could it be that the condensor is the wrong value, I assumed any old type motorcycle ignition condensor would work. Would a genuine replacement make such a big difference ?  Any suggestions ??

Barry

[Rick Yamane]

“About” kick start speed sounds questionable. Use the kick starter. Try bump starting.

 

Rick

--
You received this message because you are subscribed to the Google Groups "Guzzi Singles" group.
To unsubscribe from this group and stop receiving emails from it, send an email to guzzi-single...@googlegroups.com.
To post to this group, send email to guzzi-...@googlegroups.com.
Visit this group at https://groups.google.com/group/guzzi-singles.
For more options, visit https://groups.google.com/d/optout.

[wea...@yahoo.co.uk]

Try as I might I have never been able to understand or fix mags but I have had a few done by experts. They all say the condenser is critical, any old one will not do. Also New old stock ones are no good as they have a limited shelf life. That's everything I know.

[Rick Yamane]

My understanding is that all automotive type condensers are essentially the same. Someone here probably knows more about capacitors than I, but I believe the newer style are not prone to age deterioration. The older and probably original ones used mica and I think they would break down with age. Other factors affecting the magneto are demagnetization which can be common on +50 year old ignitions and the timing of the maximum flux to the opening/closing of the points. My experience with standard flywheel magneto ignitions has shown that a bad condenser normally manifests itself by giving a very large spark but one without the “oomph” to fire a plug under a compressed air/fuel mixture.

Weak magnets will require a higher turning speed to produce a spark although I think if the magneto was just rebuilt, they would have taken the time to remagnetize the unit. You might want to check on that if possible.

[SED Sci]

There was a essay on the Britbike forum from an electrical engineer who rebuilt some mags for his and his friends use.  He put a ton of work into it including building a lot of his own equipment to rewind, remagnetize and test mags.  He also dissected mags supposedly "rebuilt" by others and pointed out faults.  He said what was said above - that capacitors have a shelf life because starting in the 1930s (I think) manufacturers used waxed paper as the insulating layer between the conducting layers.  The wax paper degraded over time.  The older mica capacitors did not have the same decay problems.  There are some solid state modern capacitors (e.g. Brightspark Easy Cap) that don't have the decay problem, but apparently their construction is not as robust and so have a shorter working life.  My perception is that virtually all capacitors produced for the auto/moto industry are still the basic wax paper design.

[SED Sci]

Like someone else said, kick it!  I wouldn't trust the cordless drill test.  I'd think if you have a rebuilt mag giving good spark the problem is more likely timing.   A friend just purchased a "restored" Airone and the timing was set for an auto-advance mag instead of the manual advance mag.  The difference is about 60mm on the flywheel circumference if I recall.   Took a while to figure out because it looks correct in the manual.

Might also check the bolt holding the points on - I left mine loose and it definitely looses sparks!!! 

Let us know what you find!

[Barry Wilson]

I wish I could Rick, it is on the workbench so bumping is not possible, in any case at 78 not easy,  The 18v Dewalt runs at least kick-start speed more like 400 rpm.  There is no spark at all for up to 10 revolutions i.e. 5 cycles, and then there is one good spark, then nothing for many more revs.  The bike has not been run yet since a rebuild, I have triple checked the timing, both valves and ignition which is auto and they appear fine.  It won't even give a kick with Easystart.as I cannot tell when the spark will occur, not much use when the second spark won't be there to keep it going anyway. Does anyone have any suggestions as to the source and rating ( Ohms ? )  of a suitable condensor ?

[Barry Wilson]

Thanks for your input,   I have two 2 strokes with kick-starts which I have been using lately, there is nothing more tiring that fruitlessly kicking knowing there is little or no chance of it starting, As I explained to Rick at 78 I don't have alot of kicks in my dodgy ( bike injuries many years ago, don't ask ! )  right leg.  I need the left one to stand on.  I built the mag myself and the magnets are good and the coil is newly rewound, new bearings etc.It is timed at the maximum flux point so should be fine.  My mag is auto and timed accordingly, I will check out the points screw but as it's only just been built I can only blame myself if it is.  However it wouldn't be the first time I forgot to tighten a nut.  I still suspect the condensor ....

Thanks again Barry

[James Francis]

Barry,

 

There are a number of Youtube videos on how to test a condenser.  There are also some good written pieces on the subject if you do the internet search.. 

 

Wicker

[Mac Dennis]

Bad condenser will give large spark at points. If you see lots of carbon on points it's a good idea to change out condenser.

--

  Mac Dennis

  capr...@fastmail.fm

[Don West]

Barry

Try North Leicester motorcycles for a new condensor.  There has been a batch of bad ones going around.  I have heard of a few v twin owners having troubles with their bikes and curing them by putting the old condensor back on.  Try temporarily removing it and see if it sparks reliably then. 

I've not had a bike with a mag for many years, but what do you mean by it having had a new coil?  A mag doesn't usually have a coil in the normal sense of the word?

Don 

[Rick Yamane]

I was assuming he was talking about the armature windings. Speaking of armature, Barry, did you check the condition of the brush and commutator? Maybe the brush spring has lost tension or the brush just worn beyond serviceability?

From everything I’m hearing, it sounds like the condenser could be the only likely suspect left. There isn’t much that would lend itself to an intermittent spark.  Capacitors, which a condenser is, are measured by microfarads. While a was working in an autoparts store a mechanic showed me, probably 40 years ago how to check them. Remembering is another story.

I’ll confess, I’ve never dealt with a Marelli mag but have a fair amount of experience with Lucas and Bosch. We do have a spare on the shelf for Chris’ Falcone. I should dig into it sometime.

 

Rick

[Andrew Nahum]

I agree its worth changing the condenser. Even new ones can be no
good. It does need to be an automotive one. Radio spares or general
electronics capacitors to the same microfarad number are not robust
enough.

I agree too about the carbon brushes. There will be one spring-loaded
carbon brush and maybe two in the magneto. Magnetos are complicated
animals and there are a lot of places for the electricity to get lost
even if the magnet and windings are good. The brushes need to be clean
and long enough, the brass tracks they bear on need to be bright, and,
agreed, the springs should be firm. I can't remember the Marelli
arrangement but there is often a low-tension brush or earthing brush
as well as and a high tension one that feeds from the secondary
winding to where the HT lead screws in.

That plastic moulding for the HT take-off should be lined with a close
fitting brass tube that the carbon brush slides in and it is that
brass tube that carries the high tension - ie the spark - up from the
slip ring to the HT cable connector. I have seen (had) some modern HT
mouldings for vintage magneto that looked good but whoever reproduced
them did not know about that bit, so there was no brass liner and the
HT travelled up the spring. This works usually for a bit but is bad
because A) the spring gets hot and loses its springiness, and B)
spring steel is not a particularly good conductor compared to brass.
(Where are you located? I could suggest someone with good expertise
and all the testing gear in UK).

Good luck

Andrew

[Barry Wilson]

Thanks Don, The Magneti Marelli has a field coil like a dynamo, my coil was scrap so I bought one from Italy which had been rewound.  I have to admit the electrical side of vehicles sometimes baffle me, give me a problem to be solvedby removing half a thou from a component any day ............I have decided to remove the mag and thoroughly bench test it before refitting,  I was hoping to get it running for the Moto Guzzi club Singles ( cylinders ! ) Rally next weekend.  Not very hopefull though.  Regards    Barry

[Jerome Kimberlin]

I've had several mags rebuilt by Savage Magneto.  When bench tested, the
rebuilt mags put out 3/8"  sparks at 100 rpm and were run for an hour or
so for the test.  You can't use a spark plug for this test since the
electrodes are too close.  Spark length can deteriorate with heat.  We
also have found that the spark plug wire can leak if routed next to the
cylinder, so make the wire go out around the frame instead.

JerryK

[Alan Comfort]

When you bench test your magneto, be sure to get it up to operating temperature. I would say very warm to the touch, but not so hot to cause a burn. I use a heat gun for this purpose. I find that a tired magneto can sometimes work perfectly when cold, but the spark will become weak and  intermittent when hot.

I think that is because the coating on the wires in the windings tend to break down with heat and/or the condenser breaks down after a few minutes of running.

Alan in Roberts Creek

To unsubscribe from this group and stop receiving emails from it, send an email to guzzi-singles+unsubscribe@googlegroups.com.

[Barry Wilson]

Thanks Alan,   We are having silly temeratures here in the U.K. which is not normal so everything is warm, I do take your point but the problem is when it is cold, I havent had chance to run it at all.as the bike won't start.  A fellow club member here in sunny Lincolnshire had exactly the problem you describe on a 50's Triumph.  2 miles and then nothing.   Many thanks, ( I understand its very hot your side of the pond as well, it seems worldwide,  does it mean the sun is going to finally burn our little planet to bits ?  )   regards   Barry

[Barry Wilson]

Good advice Jerome, I will bear it in mind, thanks.  Barry

[Rick Yamane]

Resistance increases with heat. Old marginal windings will become apparent. Combine that with weak magnets and “poof”

Get Outlook for iOS

 

---

From: 30451060520n behalf of
Sent: Sunday, July 29, 2018 7:52 AM
To: Guzzi Singles
Subject: Re: [guzzi-singles] Airone Magneti Marelli Magneto

 

[SED Sci]

Barry (and everyone else),

My GTV mag has suddenly lost it's spark.  Where did you find information for working on yours?  Did you find Marelli specific info?  Where did you get your parts?  

Thanks,

Shawn

[Barry Wilson]

Hi Shaun,  It was a long job,  I stripped it down and found the coil was burnt out. I found another new/rewound coil from Italy  ( ebay,it )  I rebuild it but is didn't work so fitted a new modern capacitor and now it works, however it doesn't produce massive 1/2" sparks and not big fat blue ones.  Having said that it starts first 2 kicks and I did a 60 mile trip without a sparking problem, don't get me started on the other things that went wrong !!   I finished the run amongst Falcones, GTV's etc at the Guzzi Singles Rally at Rampton, Notts U.K.   30+ single cylinder motorcycles sounded great.

The coil was over £100 and the capacitors about £5 for 3 from RS Componenets.  It seems I was lucky as most folks opt for sending them off to " experts"  I would think twice about doing it again.

Finding info on Marelli mags is very difficult as they don't appear to support old stuff.  This site is the best bet by miles. I do have a full workshop with lathe/miller/5 ton press etc so had all the right tackle,  I found no information from Marelli at all.

Its not cheap to get them repaired.  before you get into removing it I would check the HT lead,  mag pick up, plug cap and plug.    I hope this helps.

Regards   Barry

[SED Sci]

Thanks Barry,

I've let this sit on the back burner while doing other things, but it will be a winter project.  I've got a small lathe and various pullers and pushers.  Did you happen to take any photos you could post here?

Wow, you guys in the UK must have a lot of Guzzi singles!  Sounds like a great run.  Congratulations.

Shawn

[Rick Yamane]

Barry, the big fat blue sparks are an indication of a bad condenser.

I believe I said earlier that condensers are very reliable but after conversations on a Henderson list and doing a bit more research, I need to retract that. The early condensers were made of wax paper, then went to mica. The paper ones especially were susceptible to damage from moisture. Reading notes from a local “scholar” on the subject he says he will usually find the condenser to be bad on malfunctioning mags. At least on the common Bosch mags used on most American bikes of the pre-30’s he had a number for Panasonic condensers which he uses in pairs to achieve the correct capacity.

Get Outlook for iOS

 

---

From: 30441044360n behalf of
Sent: Monday, September 3, 2018 9:12 AM

[SED Sci]

I think he meant the spark at the plug, not the points...

Lots of useful info on Magnetos here: http://www.themagnetoguys.co.uk/condensers-theory

[Jerome Kimberlin]

Mareli, Miller, Bosch, and Lucas all use the Lucas patents.  Lucas licenced their patents to the other three

JerryK

[SED Sci]

Does it mean that Lucas parts fit Marelli?  

I've read (internet) that Bosch magneto patents were turned over to the allies (includes Italy) as reparations after WWI which explains why all the designs are similar.  Indeed the diagrams for Bosch magnetos look very similar to Marelli's fixed magnet design.  But don't know if early Bosch parts fit Marellis.

[Jerome Kimberlin]

Doubtful, but it does give an alternate source of circuit diagrams or keywords to find patents, etc.  Mags are so simple that none of them are much different than the other.

JerryK

[Rick Yamane]

Yes huge spark at the spark plug is indicative of a bad condenser.

Get Outlook for iOS

---

From: guzzi-...@googlegroups.com <guzzi-...@googlegroups.com> on behalf of Jerome Kimberlin <kimb...@comcast.net>
Sent: Monday, September 3, 2018 5:50:01 PM
To: guzzi-...@googlegroups.com