Why dual bits in a wasted spark system?

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grandpaul

grandpaul

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Can anyone give me a good reason for the dual pickup coils on the stators, and dual magnet triggers on the rotors, of modern wasted spark igntion systems?

It doesn't appear to be for failure redundancy, as the systems die when one of the coils suffers a malady anyway.

I would think manufacturers could save some money and/or lower their prices by going to single-circuit bits...
 
grandpaul said:
Can anyone give me a good reason for the dual pickup coils on the stators, and dual magnet triggers on the rotors, of modern wasted spark igntion systems?

It doesn't appear to be for failure redundancy, as the systems die when one of the coils suffers a malady anyway.

I would think manufacturers could save some money and/or lower their prices by going to single-circuit bits...
Click to expand...

As you know the position and stability of the cam in the points box is not exactly precise.

Dual pickups are not sensitive to position or the gap. Jim
 
So you are getting an averaged/overlap spark instead of a precise one.

I wonder how much better or worse that actually is than using a single unit?
 
grandpaul said:
So you are getting an averaged/overlap spark instead of a precise one.

I wonder how much better or worse that actually is than using a single unit?
Click to expand...

If your looking at an analogue ignition with dual pickups -The spark timing is determined by the voltage from the pickup coil. The ignition fires when the pulse reaches a preset voltage. This is not a very accurate way of doing it but it is close enough for the average low compression engine.

If you only had one pickup, the timing would very a lot as the cam flexed and the gap changed. With dual pickups -as one gap gets larger the other gap gets smaller -so the end result is more accurate.

Even with a digital ignition I would suspect that the averaged zero crossing point using two pickups would be more accurate than the output of one sensor on a wiggling shaft. Jim
 
Great and simple explanation Jim. I've wondered about this too.

A simple further question though. Do spark plugs tend erode twice as fast with wasted spark, or does normal plug wear only occur when an A/F mix is actually ignited?
 
Biscuit said:
Great and simple explanation Jim. I've wondered about this too.

A simple further question though. Do spark plugs tend erode twice as fast with wasted spark, or does normal plug wear only occur when an A/F mix is actually ignited?
Click to expand...

Yes, spark erosion will happen twice as fast with wasted spark. But generally spark erosion is not the limit to the life of a spark plug in a Norton.

Usually it's the buildup from rich mixtures, fuel additives and oil consumption that kills a plug before the gap wears out.

That is not considering possible damage from incorrect timing or the wrong heat range plug -which will round off the center electrode pretty quickly. Jim
 
or the 4 iridium for the Ducati .... about $75 CAD ...
Craig
 
truth is on a year to year basis I spend about as much time on Commando as Ducati .... other than the first time I did belts and valves ( on Duc ) .... that did take a bit of time and hair loss .... and the iridium do seem to improve running and they last life of belts .... when I tried them in Norton it was a disaster , so some $ saved there ....
Craig
 
Craig said:
truth is on a year to year basis I spend about as much time on Commando as Ducati .... other than the first time I did belts and valves ( on Duc ) .... that did take a bit of time and hair loss .... and the iridium do seem to improve running and they last life of belts .... when I tried them in Norton it was a disaster , so some $ saved there ....
Craig
Click to expand...

In what way was it a disaster?

I run iridium plugs in my Commando and am convinced it runs better in them.

They definitely last longer too.

A spark plug breaking down can creep up on you, causing loss of performance and poor running that you either don't notice, or don't imagine is linked to spark plugs. For me, running iridiums eliminates this.

Because I run the bike on track days, and its a high CR, the plugs do get a harder life than steady road use.

I change them every year as part of 'standard' maintenance, this is wasteful of course as they would happily run far longer, but I figure that as part of annual running costs, its kinda insignificant.
 
the iridium plugs were fouling at same card jetting as the ngk bp7 were run at with good results .... so not disaster really .... just my time wasted .... I had hoped for similar results to what I had with the Duc but after a couple of cleanings went back to ngk
Craig
 
Brooking 850 said:
Nigel what iridium plugs you running
Denso or NGK also what heat range?
Regards Mike
Click to expand...

NGK. Number 8s as a rule but also tried 9s for Dyno days and track days. Seems to run fine on both. I tend to stick to 8s.
 
grandpaul said:
I would think manufacturers could save some money and/or lower their prices by going to single-circuit bits...
Click to expand...

Yes, but they'd need to be crank triggered as opposed to cam triggered.


Tim
 
grandpaul said:
Can anyone give me a good reason for the dual pickup coils on the stators, and dual magnet triggers on the rotors, of modern wasted spark igntion systems?

It doesn't appear to be for failure redundancy, as the systems die when one of the coils suffers a malady anyway.

I would think manufacturers could save some money and/or lower their prices by going to single-circuit bits...
Click to expand...


Wasted spark pickups generally are "single circuit". The Lucas Rita (a camshaft-driven wasted spark system) has a single pickup coil.
 
Tintin said:
grandpaul said:
I would think manufacturers could save some money and/or lower their prices by going to single-circuit bits...
Click to expand...

Yes, but they'd need to be crank triggered as opposed to cam triggered.

Tim
Click to expand...

Yep, I overlooked the critical aspect of cam turning half speed relative to crank!

In the immortal words of 'Emily Latella' (Gilda, Radner, SNL / R.I.P.):

"Never mind!"
 
The first ever electronic ignition I fitted to a Norton was a break the beam job, it had 2 sensors on the stator and a black plastic shield that fitted to the original AAU, the shield broke the light beam on the 2 sensors. One of the sensors was fixed to the stator and the second was on a additional plate that could be moved in a short arc on the stator. So it was single sensor per spark plug and to account for cam chain tension variation you could move one sensor slightly to synchronise full advance. Downside was the AAU was still in use providing the advance and sticking on full advance. The next system I plan to go to once the next Boyer goes caput will be the Ignitech system which on a twin uses 2 sensors one per plug with a programmable advance curve, so you can add idle stabilisation to your curve plus use inlet depression sensor or a switch to choose one of two advance curves to stop pinking at lower revs.
 
Tintin said:
grandpaul said:
I would think manufacturers could save some money and/or lower their prices by going to single-circuit bits...
Click to expand...

Yes, but they'd need to be crank triggered as opposed to cam triggered.


Tim
Click to expand...

Not if you have two magnets on the rotor -as Boyers do.

You can actually remove one pickup coil on a boyer plate and jump the connectors and the bike will run fine except it will be hard to start.
I did that one time many years ago to get home after one pickup coil died [fell apart]. I had to roll the bike down a hill to start it. Jim
 
Isn't there a wasted spark with dual points? The timing gear is the same and the points are 180 degrees to each other.
 
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