125 WITH NO SPARK

Lambertini era singles (125 and 250 - half v-twins)
mbmm350s
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Re: 125 WITH NO SPARK

Post by mbmm350s »

Hi Bill,

I sense your frustration from a far.

I do agree with others that the first suspicion has to be the generator winding.
I am not sure I have definitive data on 125H for the winding resistance (green to earth with ignition switch ON) as new,
for all others it is supposed to be 300 ohms, but in practice on the twins they work until the resistance
has fallen (due to shorted turns) until around 200 ohms.
The insulation breaks down due to heat, turns become shorted and layer to layer shorts occur which reduce the number of effective turns and so reduce the voltage being sent to the transducer.

Previously Paul mentioned how you can measure the a.c voltage (green to earth) which should increase linearly with rpm until it plateaus.

In order to remove any fault associated with the lighting coils you would have to disconnect the yellow and red wires from the stator- assuming your later 125 has the non direct lighting system.

Please don't let the rotor overheat, the magnetism could be damaged as well as further damage to insulation.

Mark
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Re: 125 WITH NO SPARK

Post by EVguru »

mbmm350s wrote: 21 Sep 2021 12:12 for all others it is supposed to be 300 ohms
I do wish this 300 ohm misinformation would go away.

That may be what is written in the 'blue book' and it may well have been true at the time of writing, but it's a physical imossibility for the overwhelming majority of coils (I have come across a small number of factory 300 ohm coils).

The resistance is a function of the number of turns and the resistance of the wire per turn. The resistance of the wire is in turn a function of its diameter.

I've measured the wire diameter on nearly all coils as 0.15mm (overall diamater is a little larger because of the insulation) as shown in this picture;
coil.jpg
coil.jpg (151.03 KiB) Viewed 3861 times
With wire of this diameter, there simply isn't room on the bobbin to wind enough turns to get to 300 ohm. 300 ohm coils do exist, but they use thinner wire and I suspect were more prone to breaking down, which is why the thicker wire was used.

The resistance doesn't matter very much, just the voltage ouput (within reason).

If you KNOW that a coil was wound as a 300 ohm coil, but it now measures 220 ohm, then you know it has shorted turns and is failing.

If that coil was wound as a 220, then it's proably just fine, but many a good coil has been condemned and needlessly rowound (sometimes badly) just because it read the 'wrong' resistance. People have often used thinner wire just to be able to achive the 'correct' 300 ohm value.

When I rewind a coil, I don't bother counting turns, I just use calipers to meaure the size of the coil. That will usually get me to withing +/- 4 ohm of the nominal 220. I will write that value on the coil insulation, so that in future, someone can see if the value has changed.

The value will be that of the coil at room temperature. It should increase somewhat as trmperature increases. If it drops when hot, then that is an indication that the insulation is breaking down and turns are shorting out.
Paul Compton
http://www.morini-mania.co.uk
http://www.youtube.com/user/EVguru
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Ming
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Re: 125 WITH NO SPARK

Post by Ming »

I think 300 ohms has entered into Morini folklore, Paul, despite your frequent explanations. Having rewound a coil myself (using 0.15mm wire IIRC), I seem to remember a nominal 240 ohm result and a rather bulging coil. It fitted, though, and the ignition was fine afterwards. Not a difficult job, the hardest thing was finding a suitable coil former.
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themoudie
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Re: 125 WITH NO SPARK

Post by themoudie »

Good morning Gentlemen,

Resistance between the green output cable from the low tension ignition coil and the stator ring is 478 Ohms, on my stator.

Resistance between the red output cable from the black magnetic trigger coil and the stator ring is 110 Ohms, on my stator.

Both readings are taken at an ambient temperature of ~15°C, on the 2000 Ohms scale of my Gunson multi-meter, with the stator removed from the engine.
I was getting very similar resistances when the stator was on the engine.

My conundrum at present is whether to retain the black magnetic trigger coil, original with the stator and the #323921 transducer. Or, fit a red magnetic trigger coil that apparently has a diode in its circuit, as this has proved successful for members of the German Morini Owners forum, when used with transducer #32398 112, the replacement transducer that I intend to use. The Dutch website table of transducers/pickups shows for the 125H, "125H, #323921 (green sticker), no pick-up, but a sensor in the alternator". However, my 125H engine has transducer #323921 and a black square magnetic trigger coil attached to the stator pole to the right of the low tension ignition coil. The 250T, according to the Dutch website table shows "250T (single), #323931 (?? sticker), pick-up, red". Hence my quandary, as the transducers are the same type, but the 125H trigger colour is not given and mine conflicts with the information given for the 250T!

Should I order a red trigger coil and include that in a rebuild?

I note from the circuit diagram drawn for the "self-build" transducers that there are two variables:

One, being a diode #1n4007 in the red cable from the magnetic trigger coil, if this is the black colour type. I assume that this diode is contained within the circuitry of the red colour trigger coil?

Two, the second resistor on the red wire input to the transducer has a value of "68 Ohm", I understand this is if the transducer is to be used on a 350 V-twin engine, with an advance of 34°BTDC and 2° less than recommended for the 125H (36°BTDC @6,000rpm). Whilst if the transducer is being built for a 500 V-twin engine, with an advance of 30°BTDC the resistor has a value of "270 Ohm". However, is the value of this resistor in the circuitry of my replacement transducer #32398 112 known, or will it be a case of "suck it and see" experimentation on my part on the rebuilt stator?

Thank you all for your contributions.

Bill
Attachments
Dutch Moto Morini website published self-build replacement transducer circuit diagram.
Dutch Moto Morini website published self-build replacement transducer circuit diagram.
circuit.jpg (114.08 KiB) Viewed 3838 times
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Re: 125 WITH NO SPARK

Post by EVguru »

The 125 has some unique features. The ignition is a crankshaft triggered 'wasted spark' system and the tachometer cable drive is from the right hand (timing) side.

All the other air cooled V-twin based engines equipped with Capacitive Discharge ignition, EXCEPT the 125 single have camshaft mounted pickups.
The later Kokusan ignitions are Inductive Discharge and use pickups external to the rotor. They are also wasted spark.

References to black and red pickups and the presence or not of a diode only applies to the camshaft mounted types. The 125 pickup is part of the alternator and may well be the same as a Vespa part, but I've never had an igntion probelm with a 125 and had to investigate.
Paul Compton
http://www.morini-mania.co.uk
http://www.youtube.com/user/EVguru
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themoudie
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Re: 125 WITH NO SPARK

Post by themoudie »

Thank you for your reply Paul.

Does that then mean that I don't need to concern myself with the type of Vespa/Lambretta trigger coil that I use, as they are available as both black and red units? :?:

Does your suggestion of using electrical resistance to control the advance, rather than the angle of the magnetic trigger coil in relation to the crankshaft/camshaft axis still hold true? :?:

Or, am I going to have to mechanically retard the timing by 12° beyond the factory set ignition timing point, so that I can acheive the recommended ignition advance of 36°BTDC @6,000rpm as recommended by the factory? :?:

Thank you for your time, Bill
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themoudie
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Re: 125 WITH NO SPARK

Post by themoudie »

UPDATE!

After my last flurry of correspondence here, I went and replaced the ignition power and ignition trigger coils, on the stator, with respectively, Vespa and Lambretta parts from BeedSpeed in Grimsby and recorded 524 Ohms resistance from the power coil, 110 Ohms resistance from the trigger coil.

I re-fitted the stator, with the original factory made timing marks on the stator plate and crankcase web aligned. Used the blue Ducati Electronica: 32398112 transducer, new copper cored ignition cable and NGK plug cap. The engine started and idled well, but as soon as revs were applied the engine cut out. I then repeated the test using the original black Ducati Electronica: 323921 transducer, with the same outcome.

I did use an inline timing light, rather than my Accuspark SP8000 timing light, with no difference in the result except for one heck of a "belt", whilst holding the timing light! :evil:

So, stripped all the components off the bike and despatched them and the old components to Marcus Rex at Rex's Speedshop, in the hope that their testing equipment might find something amiss. No such luck! :cry: After 10 weeks, I enquired if any progress had been made, only to receive an apology and explanation that the majority of experienced staff had either retired or jumped ship to other posts and that they would no longer be able to carry out the testing and possible replacements originally agreed, "Would I like my parts returned?" :( :( "Yes please!" and they were all returned in the packing that I had despatched them in, in good condition. Marcus had given me dire warnings, not to use the inline timing light on this ignition system, as they had found that lethal voltages were produced that were capable of breaking down the insulation of the timing light and it's leads! :shock: No wonder I had received a "belt" when last using it.

Re-fitted the stator to the original timing marks, the blue transducer, etc, and the engine started and idled happily at 1,300 to 1,400rpm, blipped the throttle once warm and the engine cut out. Same as before. Fitted the AccuSpark and at idle the 'PMS' mark on the flywheel aligns with the camshaft centreline, whilst the 'ANT' mark sits approximately 36° to the right of the clockwise rotating flywheel. Blipped the throttle and before the engine died, the 'ANT' mark moved further to the right, which I interpret as the ignition being further retarded! :evil: No wonder it cuts out and gets hot, with a glowing exhaust pipe!

I spoke with Benjy Straw, who kindly listened to my tale of woe, he suggested that I should check that I had wired the power coil with the green cable to the transducer and the red cable with the trigger coil to the transducer, which I had, and replace the blue transducer, with the original black transducer. My cables were correctly connected and I had the same result of the engine ignition appearing to retard further, as the revs were increased until it cut out.

From the 'Blue book' I understand that the 'ANT' mark should align with the centre of the camshaft at full advance 36°BTDC, at 6,000rpm.

But, with the ignition timing appearing to move in a clockwise direction, away from the camshaft centre and further retard the ignition timing, rather than anti-clockwise and aligning with the camshaft centre, I am stumped. Have I missed something fundamental in the way ignition curves move in relation to a clockwise crankshaft rotation, or are my wires crossed?

Thank you for any further advice, or do I need to borrow a complete operational 125H ignition system, fit it to my engine and see what happens?

Good health, Bill
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themoudie
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Re: 125 WITH NO SPARK

Post by themoudie »

This is embarrassing, but I managed to time the valve timing 180° out when fitting a new timing belt! :oops: :oops: :oops: :oops: :oops:

After rectifying the faux pas, the ignition did at least start to show some advance, movement anti-clockwise of the 'ANT' timing mark on the rotor towards the camshaft centre line, as the revs approached 3,000 rpm, just before the misfire starts and brings all proceedings to a halt as the engine dies.

Having run Benjy Straw's, Mark Bridger's brains ragged, Paul Compton offered to run the ignition system on his diagnosis rig. However, I had already despatched the system to a person specialising in Ducati Electronica Lambretta and Vespa ignition systems, which is what the 125H uses, for assessment and possible repair. I await his verdict and will post the outcome on this thread.

Good health, Bill
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