Lombardini LA75 ignition

[radou]

Hi!

Last year I got a gift from a friend, an old engine, which needed a general service (and it wasn't running for about 20 years). After that it was almost ready to start. But there is a problem if the ignition module (it can be easily separated from the engine) - spark only exists if the module isn't mounted on the engine.
I checked everything with my multimeter - every component acts as it should. Spark (secondary wind) has about 6000 V (approx. by the lenght).

Has anyone have any idea what should have gone wrong?
If it makes it easier I can upload a picture.

Thank you very much!

 

[itsmoked]

One possibility is that the insulation is failing and tracks the H.V. to the framework. Remove it and it works again.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[VEBill]

Disclaimer: this is general advice.

Perhaps something within the module itself is shorted to ground (ground in this context being the housing or chassis of the module). On the assumption that you can open the module, look for insulation under power transistors attached to the housing as a heatsink.

On big engines, such a short would draw excess current and blow a fuse. But small engines might have a low current magneto or similar power supply that provides limited current, and no fuse. So the short wouldn't be as obvioius in such circumstances. Measure power supply input current off the engine (working, running) and again mounted on the engine (trying to start). This might provide evidence for the short circuit theory.

Or just mount the module on an insulated heatsink and don't worry about it.

 

[radou]

Thanks for the advice.
I wasn't clear enough with the description, sorry for that.

It is a 70s gasoline-petroleum engine, about 400 ccm, 7 horsepower at 2600 rpm. I can't bring it to life in any case, because the engine is rare. Old mechanic few months ago said "I haven't saw that engine for at least 15 years. Throw it away." Maybe he was right, but I'm too stubborn

The module itself isn't so complicated. A rotating magnet inducts electricity to primary. One pole of the wire is grounded, the second leads to switch and a condenser (parallel). Which are at the end also grounded. So no "high tech" electronics are used, including fuses.

A couple of hours ago I was thinking about shortage. The shop where I usually buy engine parts was closed, so new sparkplug wire was out of question. So I put 4 wraps of insulation tape around the existing wire (and it's previous insulation)- so I have upgraded it for at least 20 kV of resistance. So I don't expect problems on the cable.

The next problem I'm thinking about is, that the magnet is too weak. But if it was too weak I should got a shock after rotating the module and holding the pins with moisted hands?

And maybe it helps: the ignition module is Magnetti Marelli MCR6E, rotation clockwise.

The only "valuable" hit I get is from Italy (30 miles from me ) is a guy that is selling only the coil for 200$. Which doesn't fit my wallet in any case .

Thanks.

If anyone else thinks of a clue I'm still here.

Regards.

 

[MikeHalloran]

A photo would surely help.

From here, it sounds like your module is a magneto.

If so, it must be installed with the magnet in a certain relation to the engine crank. If it's driven by a gear, both gears may be marked. Or you might have to static time it relative to TDC.

Magnetos are often equipped with nonlinear mechanical drives to provide extra voltage for starting purposes. If so equipped, turning the input shaft by hand should become more difficult at one point in its rotation, when energy is being stored, then the torque required should fall suddenly, and a spark appear, as the actual magnet shaft is propelled forward by a spring. Sometimes that spring mechanism will get jammed by corrosion; it might need cleaning.

One more thing; it's a bad idea to turn a magneto by hand without a spark plug connected. The voltage generated has to go somewhere, and if a proper air gap is not provided, it will go through its own insulation, which gets expensive.



Mike Halloran
Pembroke Pines, FL, USA

 

[VEBill]

This from a TV show about old cars: magneto magnets might weaken over the decades and need to be remagnetized.

 

[radou]

MikeHalloran, to the certain point you are right.
On the file slika0016 there is the shaft of the magneto. Only two teeth, so you cant miss anything while installing it.
Back in the engine, the magneto shaft is connected to the main shaft via helical sprocket.

No non-linear drives, mechanically, everything is pure and simple. Although you are right by saying the torque increases at some point, and decreases suddenly. But there is no spring in the module itself. (I had taken apart the module numerous times, including the whole engine once, so that isn't a problem). But if it is really necessary I can demount the engine once more, but you'll have to wait a couple of days, since my middle finger had a collision with an axe

Thanks for the warning. In most cases electrical sink was me.


I must apologize for the quality of the pictures, my cell phone is 6 years old, and I don't have anything else to take pictures.

A little bit of a comment
4, 5 and 6 - the main module, the coil is brown, secondary output is the brass "button". Magnet is the cylindrical piece under the coil. A bearing is on the shaft.
7 - condenser and switch, all mounted on the timing device,
12 - the engine we're talking about
13 - the place where the module should go.
14, 15 - module mounted together (the front cover is missing, but I hope you get the point)

Thanks!

 

[MikeHalloran]

>>> taken apart the module numerous times, including the whole engine once<<<

That may be your problem. If you didn't 'phase' the helical gear that drives the magneto with respect to the crankshaft, your ignition timing will always be wrong. That would also leave your valve timing off, if I'm guessing correctly about the function of that gear and its shaft.

You can check both by static timing the points.

While you have the plug out to find TDC, replace it with a brand new one.

Replace the plug wire with a new one also.

Do you have the shop manual for that engine? This would be a good time to find one.


Mike Halloran
Pembroke Pines, FL, USA

 

[radou]

The gears are phased, I'm always careful about that. On most engines nowadays there's a little dot, on this one there is a dot too.
Well, the real problem is, that I don't have a spark. A "friend" on the other forum also suggested to remagnetise the magnet.
The ignition start is timed 7° above TDC. The sparkplug is brand new NGK ab-6.

Yeah, the shop manual would be really a light in the tunnel, but no clues yet.
On monday I'll go shopping for a wire and call a guy that may have some of the parts I need.
Wish me luck.

 

[radou]

Today we had rain all day, so I had time to sit down and have a chat with my engine.
In the corner of my workshop I found a old coil and mounted in on.
And guess what happens. Half an inch spark.

So the motor now gives a bit of smoke, now there is a cylinder gasket to replace, but mechanical things were never a problem.

Thank you very much for the help and advice provided.

Regards.