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Contact point sets problem

Culbu
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Contact point sets problem

Post by Culbu »

Good evening my dear DLOC members,

Does anyone notice anything wrong on the following picture ?
SP250 Distributor.jpg
I have no spark coming from the contact points set number 2 !! The gap between the contact points is 0.35mm for both of contact points sets.

When the number 2 contact points set is opened, I have a spark on the contact points set number 1 if I slightly and manually turn the rotor clockwise. Normal
When the number 1 contact points set is opened, I have a spark on the contact points set number 2 if I slightly and manually turn the rotor anti clockwise !!! But the rotor is supposed to only turn clockwise, isn't it ! 🤪🤪🤪

Could the problem come from the Dwell angle ? The problem is that I can not check up the Dwell angle with my Gunson lamp because the engine runs not correctly with only one contact points set efficient.

Any suggestions ?

Simon Hyslop

Re: Contact point sets problem

Post by Simon Hyslop »

Is the problem reversed if the points are swapped in their locations ? I just wondered if the contact sets can be eliminated from enquiries at this stage.

Sydsmith
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Re: Contact point sets problem

Post by Sydsmith »

Julian, not really thought this through but from what I recall there are two sets of contacts in the V8 distributor in order to increase the dwell angle of the ignition.

As the cams on the centre spindle rotate it sets both contact sets in the closed position to make the circuit, when one set opens the circuit is broken and the ignition coil produces the HT needed for ignition.

So you will only get a spark from the contacts when both sets are closed and the contacts of either set are opened. No doubt some one will put me right if I am mistaken. Syd

Ian Hastings
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Re: Contact point sets problem

Post by Ian Hastings »

Trying to remember through a red wine haze but i think the rotor turns anti-clockwise. Please correct me if I'm wrong. :roll: :?

Ian Slade
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Re: Contact point sets problem

Post by Ian Slade »

I understood that there are two sets of contacts to eliminate contact bounce, you will only get a spark when both are open, they are connected in series, a common fault in the contact ignition system is the small braided wire can short to earth intermittently due to the braid braking down and the wire inside touching earth on the base plate.
Owner since the 70's, Genghis is slightly to my left.

Culbu
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Re: Contact point sets problem

Post by Culbu »

Ian,

You’re right, the rotor turns anti-clock wise. Apologies for this mistake. But the problem is the same !

Ian (Slade),

Is a wire touched the earth permanently, it would be impossible to obtain a spark, whatever the contact points sets, which is not the case.

A friend of mine owns a SP250. I will have a look on its distributor today...

Thanks

Culbu
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Re: Contact point sets problem

Post by Culbu »

Simon,

I tried to swap the contact points sets. I also tried with another pair of contact points sets. Same result

Ian Slade
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Re: Contact point sets problem

Post by Ian Slade »

Ian (Slade),

Is a wire touched the earth permanently, it would be impossible to obtain a spark, whatever the contact points sets, which is not the case.

A friend of mine owns a SP250. I will have a look on its distributor today...

Thanks
[/quote]

The problem is that it doesn't touch permanently, it's intermittent, just ensure that wire is well clear, I had the same problem and when checking by hand it seamed OK but miss fired then cut out, follow the setting instructions for ignition timing with the lamp permanently fitted and turn the engine over by hand if there is a problem the light won't come on in the correct crankshaft position.
Owner since the 70's, Genghis is slightly to my left.

Culbu
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Re: Contact point sets problem

Post by Culbu »

Ian,
Understood. I will check that up.

Sydsmith,
Stop me if I'm wrong :
When the 2 contact points sets are closed : no spark. The coil is "double" in contact to the earth.
When the first contact points set open : still no spark because the second contact points set is sill connected to the earth.
When the second contact points set open : 2 sparks.

The fact that there are 2 contact points sets increases the Dwell angle, which means increase the period during the one the coil is in contact to the earth.

So if I'm right, it's not possible to have a spark at only one of the both contact points sets... 🤔🤔🤔

Julian

Ian Slade
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Re: Contact point sets problem

Post by Ian Slade »

Julian,
It is only possible to have a spark when the second contacts open, the action is 1. both contacts closed on the flat of the distributor cam, 2. first point opens as it comes onto the cam, 2.second point opens as it comes onto the cam, first points stay open and spark is present. Check that the points are clean and no raised points due to arcing, the setting of the gap on the first points are critical as if the gap is too small they will shut before the second points open, ie no spark. or if too large then they will close late and there will be insufficient time for the coil to recharge.
Owner since the 70's, Genghis is slightly to my left.

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