Re magneto

Can any member please explain this problem.
Why does a low tension magneto work perfect on the bench but is completely  dead when attached to a engine.
This one completely baffles me i have tried turning the magnet round etc.

Bad/dirty earthing points, dead short, dirty points in magneto or cylinder.

MaryAlice

Breaking down under cylinder compression.

maryalice wrote:Bad/dirty earthing points, dead short, dirty points in magneto or cylinder.

MaryAlice  

Hi thanks for your reply.
Re the magneto the mag when it has a a 6 volt bulb connected to complete a circuit it gives a bright light when on the bench .Yet when fitted to the engine still only connected as above, the bulb does not light or produce a out put yet it test out with a meter to be a circuit.Put it back on the bench its working ok.
It seems as if there is a magnetic field opposing the field of the magneto.

John.

For a magnetic field to have that effect your tools would be stuck fast to your engine.

With the magneto on the engine does to 6v lamp light if you run a wire to the lamp and you ground the lamp direct to the magneto ? ie keep the lamp circuit limited to the magneto rather than the whole engine.

blue cat wrote:With the magneto on the engine does to 6v lamp light if you run a wire to the lamp and you ground the lamp direct to the magneto ? ie keep the lamp circuit limited to the magneto rather than the whole engine.

Hi Blue cat,
The bulb is connected directly to the mag and not connected to the engine this works on the bench but not on the engine.If i put a battery in circuit it lights up, this proves there is a complete circuit.Just a complete mystery to me.
John.

ruston1942 wrote:

blue cat wrote:With the magneto on the engine does to 6v lamp light if you run a wire to the lamp and you ground the lamp direct to the magneto ? ie keep the lamp circuit limited to the magneto rather than the whole engine.

Hi Blue cat,
The bulb is connected directly to the mag  and not connected to the engine this works on the bench but not on the engine.If i put a battery in circuit it lights up, this proves there is a complete circuit.Just a complete mystery to me.
John.

This doesnt make sense, how have you connected this bulb to the magneto to create a circuit and what do you refer to a complete circuit.

Maryalice.

maryalice wrote:

ruston1942 wrote:

blue cat wrote:With the magneto on the engine does to 6v lamp light if you run a wire to the lamp and you ground the lamp direct to the magneto ? ie keep the lamp circuit limited to the magneto rather than the whole engine.

Hi Blue cat,
The bulb is connected directly to the mag  and not connected to the engine this works on the bench but not on the engine.If i put a battery in circuit it lights up, this proves there is a complete circuit.Just a complete mystery to me.
John.

This doesnt make sense, how have you connected this bulb to the magneto to create a circuit and what do you refer to a complete circuit.

Maryalice.

Hi Maryalice.
The circuit, is the magneto armature live connection wired to positive of the bulb .the negative of the bulb connected to base/earth of the mag.
1 it is driven by a battery drill and it bulb lights.
2 it is still wired as above but driven from the engine gears alas it does not light.
John.

Huge difference in speed driving with a battery drill and turing the engine over by hand. What happens if you substitute the lamp with a volt meter ?

I agree with Blue Cat, also a magneto voltage I think should be able to wreck a bulb and if your not getting it to light on the engine you have a weak and tired magneto.
Maryalice

Hi the mag in question is Low Tension and these mags in working condition will light a 6 volt bulb ok. for test purposes etc.

john.

ruston1942 wrote:Hi the mag in question is Low Tension and these mags in working condition will light a 6 volt bulb ok. for test purposes etc.

john.

Then if it works on the bench there should be no reason why it wont work on the engine.

Maryalice

Just a thought... could it have a short to the casing so when it is fitted the current is going to earth? May explain why it works on the bench but not when fitted.

mattblack wrote:Just a thought... could it have a short to the casing so when it is fitted the current is going to earth? May explain why it works on the bench but not when fitted.  

A magneto needs the circuit through the engie to work, If there was an internal short it wouldnt work on the bench either.

Maryalice

Well, I'm completely confused (no change there!)
I think we need some identification of both engine and magneto - and a few pictures would not go amiss.