pertronix & dwell

[bus72]

i would be interested to know if any one who has fitted a pertronix kit has increased the air gap to increase the dwell.
i have fitted my kit, with the spec air gap my dwell is 57 i have read that more dwell is better, i could increase the air gap
i have some adjustment left on the pertronix. anyone played with there pertronix what results did you get?

 

[bus72]

blimey nobody fitted a pertronix kit :shock:

 

[67panel]

tbh dont think anyone will have checked the dwell "cos it aint got points"and I dont think you will notice any differance if you do alter it ,if you want veriable dwell you should have fitted a dizzy and ign box from a t25 ,its stand alone and will fit .

 

[bus72]

tbh dont think anyone will have checked the dwell "cos it aint got points"and I dont think you will notice any differance if you do alter it ,if you want veriable dwell you should have fitted a dizzy and ign box from a t25 ,its stand alone and will fit .

i had a t25 dizzy and cdi box that i got off a scrapper i fitted it timed the bus up and went for a run, pants my van ran as flat
as a pancake, on closer inspection the mechanical advance in the dizzy was shot so i put the svda back on and fitted a pertronix kit, so far really happy van starts loads better than before. i was just wondering if any one else had experimented
with the dwell on there's

 

[71Westy]

I've got a pertronix and the dwell is 48. That's within spec so I've left it as is.

Nick

 

[Geeze]

Think (being harsh ) dwell is probably beyond most folk these days, never mind those who fit pertronix given it's advertised as being fit and forget.
I check dwell but only because I was taught to set timing by my father, who's old fashioned like that. So I probably did check it when I had one but would only have been to make sure it was to spec. Never tried adjusting it.

 

[mister]

This is all a bit beyond me

However when I fitted my petronix I did have a look at this to see if the stated gap was best:

http://www.ratwell.com/technical/PertronixAdjust.html#gap" onclick="window.open(this.href);return false;

Ended up fitting as per manufactures instructions and have been really please... maybe the more learned may benefit

 

[Geeze]

Dwell angle is pretty simple really, just most folk don't seem to use it much these days.
The points need to stay closed enough of the rotation for the coil to charge up and then open long enough for the coil to discharge. The dwell angle is just a measure of this (the number of degrees of the rotation that the points are closed).
It's important because if the points aren't closed for long enough, the coil won't charge enough and the spark will be weak.

However, to check it you need a whizzy timing light that measures dwell. Which a lot of folk (and, back in the early days of motoring, garages) don't have. So clever people sit and work out the angles and do all the sums to work out how big the points gap should be for the dwell to be right (rough guide - more gap, less dwell and vica versa). And then everyone can set their points much more easily with just a set of feeler gauges.

Trouble is, as stuff wears (and replacement parts may not be exactly to spec), all the sums go out the window and things may end up slightly wrong just setting the gap. So most reliable way is to set the points (or adjust the electronic points for this post) by dwell.

All of which is lovely, but in my experience VWs are remarkably tolerant of dwell and don't seem to alter their behaviour much for quite a wide range. But some older (especially prewar) stuff with more, well, antiquated ignition systems can be really really bloody fussy about it.... :lol:

 

[67panel]

whs^^^ and of course checking the dwell is measuring the points gap with the engine running so corrects for wear in dizzy bushes ect,the gap you set static is not allways the same when its running.(motorcraft(ford)and delco(vauxhall)were the worst)I was glad when electronic ign came in

 

[KevH]

Am I the only person confused by this?

I just fitted the kit, had the dynamic timing checked by my local specialist (KraftwerkUK in Stoke) and off I went. No probs so far and with no points to set or wear out, I don't expect any either (famous last words :roll: )

 

[mister]

Geeze - cheers mate, that's the most plain English explanation of dwell I have read, it makes sense now!

 

[KevH]

Geeze - cheers mate, that's the most plain English explanation of dwell I have read, it makes sense now!

Yes, very clear. What is the relevance when there are no points though, ie the original question? I might be having a dim day... :roll:

 

[sparkywig]

Geeze - cheers mate, that's the most plain English explanation of dwell I have read, it makes sense now!

Yes, very clear. What is the relevance when there are no points though, ie the original question? I might be having a dim day... :roll:

You've still got points, which are basically just a switch, but they're miniaturised on a circuit board inside the electronic ignition module.
The downside of electronic ignition is that when it goes tits up, that's it instant failure.

 

[BJ1]

Geeze - cheers mate, that's the most plain English explanation of dwell I have read, it makes sense now!

Yes, very clear. What is the relevance when there are no points though, ie the original question? I might be having a dim day... :roll:

You've still got points, which are basically just a switch, but they're miniaturised on a circuit board inside the electronic ignition module.
The downside of electronic ignition is that when it goes tits up, that's it instant failure.

Quite right SW - so that's why you should always carry a spare set of points and a condensor, or if you are fairly rich a spare Pertronix or if you are a bit mean, carry an Accuspark.

 

[Geeze]

Geeze - cheers mate, that's the most plain English explanation of dwell I have read, it makes sense now!

Yes, very clear. What is the relevance when there are no points though, ie the original question? I might be having a dim day... :roll:

You've still got points, which are basically just a switch, but they're miniaturised on a circuit board inside the electronic ignition module.
The downside of electronic ignition is that when it goes tits up, that's it instant failure.

Aw, shucks and thank you. And at risk of ruining all my good work by confusing everyone....

As sparkywig says, it's still just a switch albeit a fancy electronic hall effect one.
To produce the hall effect in the sensor, the magnet has to pass very close to the sensor (if you think about it, it's not exactly a very strong magnet). This is why hall effect units are very sensitive to their airgap.

If you move the sensor further away from the magnet, it will only be able to generate the hall effect when the magnet and sensor are exactly aligned. As you move the sensor closer to the magnet, it will be 'in range' of the rotating magnet sooner and for a slightly longer duration, meaning that the electronic 'switch' is triggered for slightly longer which in turn affects the dwell angle.

So by moving the sensor in or out to change the airgap, you should be able to alter the dwell.

 

[KevH]

Yes, very clear. What is the relevance when there are no points though, ie the original question? I might be having a dim day... :roll:

You've still got points, which are basically just a switch, but they're miniaturised on a circuit board inside the electronic ignition module.
The downside of electronic ignition is that when it goes tits up, that's it instant failure.

Aw, shucks and thank you. And at risk of ruining all my good work by confusing everyone....

As sparkywig says, it's still just a switch albeit a fancy electronic hall effect one.
To produce the hall effect in the sensor, the magnet has to pass very close to the sensor (if you think about it, it's not exactly a very strong magnet). This is why hall effect units are very sensitive to their airgap.

If you move the sensor further away from the magnet, it will only be able to generate the hall effect when the magnet and sensor are exactly aligned. As you move the sensor closer to the magnet, it will be 'in range' of the rotating magnet sooner and for a slightly longer duration, meaning that the electronic 'switch' is triggered for slightly longer which in turn affects the dwell angle.

So by moving the sensor in or out to change the airgap, you should be able to alter the dwell.

Thanks guys, I get it now.

 

[ZedBed]

...but it won't change by much. I think the only reason for the gap (and piece of plastic to set it) is to satisfy customers that something accurate is going on and get the sensor close to the magnet without hitting it. :lol: