750SF ignition adjustment

Points cam is an integral par of the advance mechanism if I remember rightly.
What often happens is that the felt "oiler" wears through leaving the metal blade it's mounted on against the points cam with resulting wear which is uneven because the end of the blade is 3 pronged to stop the felt wandering about.

Paul
 
Of course iis is correct "dwell" is important for coil saturation, "dwell" is the time the points are open, from one microc mini mm gap to fully open and back to the same dimension. If the max lift gap is correct your dwell should also be correct, but not neccessarrilly, adjusting the dwell with basic points as in the 750 Lav, means varying the points gap, (On old American V8's and Rover V8's after setting the points there is an external screw to adjust dwell on the distributor with the motor running, you need a "dwell meter" it microscopically changes the points gap, but once your points gap is correct, you must time the motor, preferably using a degree disc with a known accurate TDC setting (piston stop is best for this) and first check the fixed points plate side, and secondly check the moving points side, if the first is bang on, then the only way to change the moving side, is move the points set a little and get that bang on as well. My SF1 use to rev its nuts off (stock motor, and later tuned a bit for Egli)) and my SF3 did the same (also stock motor) when I had carried out this procedure.
CLEM
ps hoping I got that right as points for me are a thing of dinosaurestry, not even my mowers or chainsaws/hedge trimmers have points! (corrections welcomed by iis if appropriate)
Marxy's garage is full of archeology and might only have one of his twenty or so bikes without points!
 
Probably another incoherent post by me but some bikes have another more internal ability to clock the whole timing thing. I can remember getting more adjustment moving the whole mechanism slightly around more when running out of slot movement at the points. I can also remember filing slots bigger for more timing adjustment as well.
 
CLEMTOG said:
Of course iis is correct "dwell" is important for coil saturation, "dwell" is the time the points are open, from one microc mini mm gap to fully open and back to the same dimension. If the max lift gap is correct your dwell should also be correct, but not neccessarrilly, adjusting the dwell with basic points as in the 750 Lav, means varying the points gap, (On old American V8's and Rover V8's after setting the points there is an external screw to adjust dwell on the distributor with the motor running, you need a "dwell meter" it microscopically changes the points gap, but once your points gap is correct, you must time the motor, preferably using a degree disc with a known accurate TDC setting (piston stop is best for this) and first check the fixed points plate side, and secondly check the moving points side, if the first is bang on, then the only way to change the moving side, is move the points set a little and get that bang on as well. My SF1 use to rev its nuts off (stock motor, and later tuned a bit for Egli)) and my SF3 did the same (also stock motor) when I had carried out this procedure.
CLEM
ps hoping I got that right as points for me are a thing of dinosaurestry, not even my mowers or chainsaws/hedge trimmers have points! (corrections welcomed by iis if appropriate)
Marxy's garage is full of archeology and might only have one of his twenty or so bikes without points!
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You sometimes have to twiddle the points gap somewhat to get the timing spot on.

As for the rest Clem, to follow your gist, all Laverda are archeology.
There's not 20 bikes in the garage, I even sold one to Mr Nairn! Quite a few of those there have electronic ignition. There's Corinne's 500 and my TT2 which has an Ignitech waiting for it in an upstairs bedroom, a Chott, my 3C and my Electronica though that might make way for a motorcycle with points, and a magneto! Not to mention my cooking Aprilia.

Paul
 
Following on from Clem well described post, i hjave measured the saturation time value for various coils, 0,7ohm to 3,3ohm primary winding, BTW it is the primary winding inductance, that primarily influences saturation time, not dc resistance measurement. Impedance has more relevance.

Low resistance coils tend to have low inductance and higher inductance for increasing dc resistance as a guide. Most 3ohm coils saturate in less than 5ms ( 0,005 seconds ), higher rpm means less time for complete saturation, Laverda are not high reving motors compared to many other motors. Hard to imagine for nominal dwell settings, coils being under saturated, possible, yet not common. Time once when i was slave to an old moving coil dwell meter, or at TAFE the real deal distributor mapping dwell jig, mechanical joy to watch those jigs in action. Some electrical first principles sorted out the mystery of dwell for me...a good day that day. HTH j.
 
CLEMTOG said:
dwell" is the time the points are open, from one microc mini mm gap to fully open and back to the same dimension.
Click to expand...
I think you have it arse-about Clem. Dwell is the time the points are closed. That's when the coil is energised and trying to reach saturation.

Hey John, I'm glad you're here to answer my dumb questions about ignition.

That 5ms dwell time that you measured fore a 3 Ohm coil is interesting. I've sometimes wondered how a single coil on a multi-cylinder engine that has a distributor can keep up with the high firing frequency when it has to fire every cylinder in turn.

For example, if my arithmetic is correct, a 6-cylinder engine running at 6000 rpm has to cycle the coil 3 times per revolution, which is equivalent to 18000rpm or 300Hz. That works out (inversely) to a firing interval of 0.0033 seconds (3.3ms). If you assume the points are closed for 50% of the time, then you'd need a coil that would reach saturation in half that time, ie. 1.67ms, which is considerably less than 5ms.

My old 6-cylinder Datsun 260Z has a distributor and a single 3 Ohm coil. I don't understand how it can work if the coil needs 5ms dwell. I can only conclude that the coil doesn't need to reach full saturation. Maybe it'll reach 80% saturation in the time available, which is sufficient to make a good enough spark to ignite the fuel mixture. Am I on the right track here, or have I lost the plot entirely?
 
Pretty much spot on Cam, your math is commendable, Nicola Tesla would rate you a good engineer, one of my much respected engineer of the era, early days of electrical discoveries, oops back to topic. There is a reason that primary winding 0,7ohm or so ignition coils came into being, the rate of current rise in a primary winding ( Delta I Delta t ), to magnetize the winding, is significantly reduced.

HEI ignition types also extended the dwell to improve saturation in a hard working single coil or similar, ie real dwell is "on" time. Spark is available at less than optimized saturation, in fact once saturation is reached, wasted energy is the product of further primary current, cue current limited ignition systems for low ohmic primary winding(s) ignition coils. Can ramble further, though there are some sleepy/glazed eyes wading through this part of the topic.... grin.

Apologies to readers for the original topic/thread, am devoted to first principles as a decisive process in solving difficult faults or designs. Helps others to help themselves, as it may be of use. j.
 
iis_iis said:
Apologies to readers for the original topic/thread, am devoted to first principles as a decisive process in solving difficult faults or designs. Helps others to help themselves, as it may be of use. j.
Click to expand...
... I'm with you there 'first principles' and don't over complicate (essentially) a very simple circuit

but I do love Cam's posts 'cos there is always something to learn!
 
Most useful aspect ( of the thread ) in my view being the dwell setting, one mechanical and one electrical, the mechanical is most dominant, Electrical, providing you meet the saturation time, at higher rpm, there is no need for any extra "dwell" time.

As for the resonant function of ignition coil, points and snubber capacitor, that is a whole different topic Clem, and becomes somewhat complex. When you have the right values, a very healthy, continuous spark can be had for the fit for purpose Kettering system. j
 
iis_iis said:
Pretty much spot on Cam, your math is commendable, Nicola Tesla would rate you a good engineer, one of my much respected engineer of the era, early days of electrical discoveries ...
Click to expand...
Ha ha. High praise indeed John, but undeserved. I recently read a book entitled "The Inventions, Researches and Writings of Nicola Tesla". Approx 500 pages of very small print, only some of which I understood. The bloke was certainly a prolific inventor, but he was well beyond my intellectual capability. There were parts of the book where he lost me completely. It wasn't helped by the disappointingly poor reproductions of his diagrams and indistinct black and white photos. Interesting book but no mention of pigeons.

I'd be happy to send you the book if you haven't already read it.
 
As you read, you become, dont sell yourself short at all Cam, yas doin' good. Tah for the offer, re book, have read the 3 books that were available some decades back, on Tesla, one in particular was very good.

Not dissimilar to this thread on ignition coils, had the eye watering and literally hair raising experience of being at Woolongong University where one of the professors had constructed the biggest Tesla coil have ever witnessed in action, and i do mean action, at least for this country. The prof and undergraduates used parts from the local junkyard ( Fred Cavion, a character i delt with many times ) Fred took all manner of equipment, including military and ANSTO ( nuclear research reactor ), high grade stuff if you knew what you were looking at. The parts used in the Tesla coil had grunt potential almost unlimited. He fired up this HF coil and it pulled the electrons clean out of the atmosphere, spark lengths more than 2 metres.... the racket was like 10 Jotas pinned. Had a good conversation about the coil the uni had made, large plastic garbage containers, massive storm water pipes et al... now this was also a man of substance... the coil did let go after a few minutes, blew the snot out of the 100pf vacuum cappy, a mere rating of over 10Kamps at HF operation ( ex transmitter capy from memory ). Pulling over 30amps from the 415Vac feed...:eek:

Your average inductive discharge breaker points/coil is along the principles of Tesla coil, in a broad sense. When you have the correct inductive capacitive ratio it will ring or oscillate, heavily damped compared to a Tesla coil...j
 
Hi John, it's been a while. Tesla was such a controversial figure. Just from the Pop culture references, I peruse, he should be way up there in the public conscience but up until approx 20 years ago I had never heard of him. And sadly that firstly came from a mate who bought onto the Cult of Testa, death rays, free energy from the air etc. And apparently, a lot of that originated from Tesla's mental breakdown after years of financial struggle and eventual isolation and with his well-known rivals, some real psychos who became wealthy off his back and depicted in plenty of recent movies. Such a shame as what a world we would have with him and his work.
 
Yeah, an in depth discussion emanating from a question about how to set points on an SF. Next time someone asks about adjusting their mixture screws we can get into molecular theory of atomising hydrocarbons. Cool. I wonder if we helped Oehlin get the timing correct.
 
Should the technical aspects not be for some, no problem, skip those postings, simple things first is also a part of technical process, HTH j
 
Can see the funny aspect from the above posters. Am somewhat sensitive to the pervasive "dumb it down" all about on the WWW. Do my part in reversing that damaging trend, in deference to the usual easy going nature of folk. j.
 
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