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Adjusting magneto

Bracker1

Well Known and Active Forum Website User
VOC Member
I was reading through an old MPH and came across an article about adjusting the advance and retard by opening and closing the point gap.
Is this urban legend or is it valid. It claims up to 4 degrees either way depending on opening or closing. It is even referenced by Irving as a way to fine tune. I was under the assuption the spark was produced at the point of opening, and the size of the spark is related to the gap. Any thoughts?
 

davidd

Well Known and Active Forum Website User
VOC Member
I have not done this, but the previous owner of my Grey Flash timed it when racing by measuring the depth of the piston and made final adjustments by changing the point gap, so I think it is not an urban legend.

David
 

Peter Stokes

Well Known and Active Forum Website User
VOC Member
As I understand it - you set the points gap before doing the timing. If you then alter the points gap, within the 12 to 15 thou range, say, then if you imagine the points gap closed, then the heel of the points rocker will have moved either nearer or further away from the camring. If you then imagine the camring as a ramp which is approaching the heel of the rocker, then they will meet later if the heel is raised.

I think that if the points gap is lessened, then the heel is moved away from the camring thus retarding the ignition. Someone please tell me if this is the right way round, my brain aches!

Pete
 

Bracker1

Well Known and Active Forum Website User
VOC Member
I assume it must work because it is written, but don't know why it should work. I've tried it and don't notice much difference. I need to fine tune for the NA sprint runs, sub 20 second runs are in the forecast. Protect your Vincents, they will be the only thing worth more than gold. Thank, Dan
 

timetraveller

Well Known and Active Forum Website User
VOC Member
In the olden days altering the contact breaker gap was a recognised way of fine tuning the igition timing. I remember one Sunday morning when I was a conscipt in the RAF going up and down a road in Wiltshire trying to find the maximum speed on a 350 c Gold Star, changing the gap by one flat at a time. Increasing the gap does advance the ignition.
 

Black Flash

Well Known and Active Forum Website User
VOC Member
Sorry I am not an expert on magnetos, but from my days working with Jaguars, I know that the the points gap influences the time the coil gets current to built up the magnetic field. I am not sure but I think the English expression is dwell angle. With our poor old KVF's not being state of the art anyway, I wonder if it is a good idea to to increase the gap and thereby reducing the built up of the magnetic field.
As I say I am not an expert, it just springs to my mind.

Bernd
 

chankly bore

Well Known and Active Forum Website User
Non-VOC Member
"A good magneto will fire perfectly between the limits of .010-in. and .014-in.gap measurement. If a notable increase is gained by,say,the wider gap, check the actual timing, then reset the gap to the correct figure of .012-in. and re-time the magneto to the same figure." Tuning for Speed PEI. See the Chapter on "Ignition Topics" for the right way to time the magneto.Incidentally,increasing the gap makes the spark happen earlier,i.e. more advance.My timing equipment is one of those little probes with a 12v bulb and a lead and crocodile clip-we don't have alligators in Australia;plus some insulating tape around the contact breaker centre screw. Then a piston stop and a degree wheel. Which ever way you do it,keep the method the same every time, then you will know where you have been and where you are now.PEI says you can alter the gap one flat at a time on a "suck it and see" basis. Cheers,F5AB/2A/7945 since 1970
 

mercurycrest

Well Known and Active Forum Website User
VOC Member
The points cam locating screw/peg has an eccentric on it. You finely adjust the timing with it.. at least that's how all the AMA Pro's mechanics did it.:D
Cheers, John
 

roy the mechanic

Well Known and Active Forum Website User
VOC Member
Yes, messing with the points gap will not only alter the ignition timing, well noted Black Flash, will also alter the dwell angle . I am not sure how much it will affect a 'mag, but it will affect coil set ups , usually to the detriment.
 
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