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Ignition

Technical help for all early models, A, B, C, LC, D, LD, E & F models

Ignition

Postby littlejim80 » Sun Aug 19, 2018 9:18 am

Hi folks

The lambretta d is starting to play up with the “Marelli” woes, fine starting, usually second kick, runs fine until approx 5 minutes of running, then misses and pops. Mimicking timing issues.
Points, condenser, plug, ht lead, have been replaced, wiring has been checked for breaks,timing has been treble checked and is spot on.
Now I could replace with a new marelli coil from casa, but that is £60 which could be spent towards an electronic system.

I know some of you are running electronic ignition on the d’s And ld’s. But the cost for the electronic systems for d’s and ld’s is twice the price for other lambretta models so therefore the main questions are:

1. What electronic systems are you running, Ducati, casatronic? And what is the feedback?
2. Have any of you managed to make your own electronic ignition using Parts from later models, and how did you do it? As I have a working electronic stator from an early li, I would be interested if I could utilize it.

Regards

Jim
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Re: Ignition

Postby jbcollier » Sun Aug 19, 2018 2:16 pm

I went with the "Vespatronic" system. I have a modified Li crank so I went with the Li system and used the plastic fan off the D/LD system (turns the other way). It works very well indeed.
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Re: Ignition

Postby littlejim80 » Sun Aug 19, 2018 5:01 pm

Hi Jb

Thanks for the reply

However you got me intrigued now,

The li crank will fit into a later casing, but how did you marry the drive side of the crank to the clutch/ shaft drive? As the d/ld crank has a toothed spline? And the li doesn’t.

Vespatronic, didn’t think of that one either

Regards

Jim
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Re: Ignition

Postby Steve J » Tue Aug 21, 2018 10:46 am

It's not strictly necessary to run a Marelli ignition coil, later 6 Volt models (like the Li) often use a Bosch TJ/6 coil, which would be fine for testing purposes. I seem to recall that my brother used a 6 Volt car ignition coil on his cutdown Ld without any issues. For testing, I'd be inclined to lash on any 6 Volt coil before shelling out £60 for a Marelli.

I'm not sure how most people fit the Li crank into a D/Ld, but basically it's to get around the problem of the weak flywheel taper. Splitting the D/Ld crank and replacing the mag side half of the crank with an Li part maybe the easiest way, as it avoids any specialist machining on the drive side of the crank. A good time to fit a Tv175 series 2/3 type of conrod with the needle roller small end.
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Re: Ignition

Postby jbcollier » Thu Aug 23, 2018 1:27 pm

Howard Chambers supplied the modified Li crank. Basically you press in an D/LD splined stub into an Li crank.
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Re: Ignition

Postby salient » Wed Feb 06, 2019 9:10 pm

I have just managed to mate an Li mag side half crank to an original LD driveside half crank using a ten ton press. As stated above the original LD taper is way too small and I have an example of it fracturing at the thick end of the taper. To use this set up you have to either machine out the LD bearing housing or use a Series 3 mag housing and machine off the outside paraphernalia. I chose the latter and so far it seems OK but time will tell. With this set up, the stator fits without many problems. As stated above, the crank rotates the opposite way to the Series 3 and when fitting an Indian made stator and flywheel no spark is generated when rotated anti-clockwise, I have tried to reposition the LT coil the other side of the trigger/pick up unit but it still does not work. Next I will reverse the trigger/pick up wires and see if that works.

HAS ANYBODY OUT THERE ACTUALLY MANAGED TO DO THIS STATOR MODIFICATION SUCCESSFULLY?
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Re: Ignition

Postby Rob Miller » Thu Feb 07, 2019 9:50 pm

Yes me. The simple answer to the missing spark is that you must reverse the polarity of the flywheel magnets. this involves using a compass to determine which are the north and south poles and then using a remagnetising tool to swap the polarity. Howard Chambers can do this for you. I also recommend fitting a Kytronic advance box. This not only gives more torque at lower revs but also retards the timing at kickstart speeds so you don't end up with a broken foot from the engine kicking back through the short lever. Without it my model C had a misfire due to the spark moving to a different position when revved. The Kytronic also cured this. Unfortunately Casatronics don't retard at kickstart speeds which explains why people with them fitted complain that they have to run them very retarded just so they can kick them over safely!
I hope this helps.
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Re: Ignition

Postby Steve J » Fri Feb 08, 2019 8:20 pm

I was involved in building an Ld engine a few years ago, and the owner had a 6 pole SIL stator & flywheel setup from Scoot RS, complete with electronic ignition. (I've no idea if the polarity of the magnets had been reversed.) To be honest, I wasn't greatly impressed, as it used a normal weight GP flywheel with a custom made alloy fan ring and replacement flywheel boss to fit the thing to a normal Ld taper. :o (Bear in mind that a normal Ld flywheel is around 1.8kg IIRC, and the GP one with alloy fan ring is over 2.5kg, so loads of potential there for snapping the crankshaft taper without having to try very hard.) The GP stator plate fitted onto the mag flange via an adaptor/spacer plate, but the machining left a lot to be desired - the fit was sloppy, and I seem to remember having to shim things to stop the stator plate from moving off centre. It seemed to start and run OK on a test rig, but I was careful to keep the revs down for fear of being hit by an escaping flywheel. With a lightened flywheel, better machining and a thicker crank taper, it might have been a reasonable solution. I'm sure I've still got some photos somewhere....

Ld engines do have a nasty tendency to kick back - I have a theory that it's all down to the hemispherical cylinder head (with no squish), which needs far more ignition advance than the Li type due to slower burning of the mixture. I ran an Li 150 head on my Ld for a number of years, plugging the stud holes and re-drilling to suit. The only problem was that the squish clearance was enormous, due to the piston in a standard Ld barrel not getting close enough to the cylinder head to squish anything, but I don't remember it kicking back, either. Take a millimetre or so off the top of the cylinder, and that should improve matters. (Take the same amount off the bottom of the cylinder instead, and that will also reduce the overlong transfer timings, but the exhaust port will need material off the top of the port to compensate.)
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Re: Ignition

Postby Rob Miller » Sun Feb 10, 2019 10:26 am

I would not consider fitting a SIL flywheel to the standard LD crank as they will snap with the standard flywheel fitted. The point is to use a crank with an Li taper and preferably with a lightened SIL flywheel or the even lighter AF flywheel.
The kicking back problem is solved with the fitting of the Kytronic which retards the ignition at kickstart speeds as a replacement for the mechanical system fitted to many D's and LD's. Other electronic retard units may also do this but in my experience the Variotronic type ignitions are at full advance at kickstart speeds causing sore feet especially if you suffer from Gout like me!
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Re: Ignition

Postby Steve J » Tue Feb 12, 2019 11:06 pm

Rob - I agree entirely, the SIL flywheel is far too heavy for the D/Ld crank taper, but it didn't stop Scoot RS from producing a kit and going to the trouble of producing a CNC machined alloy fan ring to suit the GP flywheel (because of the opposite direction of rotation.)

My experience of playing around with mildly modified Ld engines (a very long time ago) was that the increased engine speed, coupled with careless gear changing, was easily capable of snapping the crank - at one time I was breaking crank tapers every 1,000 miles or so. I did find the problem was worse with Filso flywheels, possibly because the flywheel boss was about twice as thick as the Marelli ones, which seemed to increase stress in the crank taper. I don't recall crank fractures with a Marelli flywheel, which has a relatively thin centre boss - but I might just have been lucky with those.

The later D/Ld engines with the spring-loaded ignition advance/retard system were designed to give about 8 degrees of advance for starting, rising rapidly to full advance (about 26 degrees) by about 1,800 rpm. Even when working properly, it didn't prevent the engine kicking back from time to time. I still reckon it was down to the simplistic combustion chamber design with no squish area.
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