Author Topic: ignition timing on a K2F  (Read 2148 times)

Offline BSAlien

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ignition timing on a K2F
« on: 27.10. 2017 20:59 »
Dear all,
this is my first post in this forum.

As I have read a lot of things over all 4 years now and got really helpful informations,
I would like to give something back.

(Sorry for my English at all)


The camring of the K2F is locked by an excentric screw, which is not visible from the outside
and it is not listed in any documents of the K2F magnetos.
This invisible excentric screw again, is locked by a small rivet on the camring-housing.

If you drill this rivet (2,5 – 3,0mm drill) out, you can see a slotted screw.

This screw can be easily replaced by a longer one, which can be made of a stud bold (rockerbox cover of an A10)

So you can adjust the timing of the Magneto very, very easily without dismantling the timing-side-cover again.
Also during a test drive with just some little tools!!! 

You can easily adjust the timing while you use a stroboscope lamp.

Hope the pictures can give you more informations, than I can right down here .

Cheers
Hubse

How can I post the pictures in here???

adm edit:  If the picture question refers to pictures inside post \ text: until the new version of forum software is released (no date yet) pictures are added below the post. Just refer to them in the text (example: see pic1, see pic 2, or ref. attachment 1, ref attachment 2, or whatever that makes sense).




Online Triton Thrasher

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Re: ignition timing on a K2F
« Reply #1 on: 27.10. 2017 21:26 »
Why did you drill the cap when it can be lifted out with knife blades?

Do not adjust ignition timing with that eccentric screw. It is for timing points opening to be correct in relation to magnetic flux.  That is: the magneto’s internal timing.  You are weakening the spark by wiggling it around to set your ignition timing.

Online muskrat

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Re: ignition timing on a K2F
« Reply #2 on: 27.10. 2017 22:15 »
G'day BSAlien,  *welcome*
Thanks for your insight to the timing of our K2F's but as TT said your mod will change the intensity of the spark. Now that you have "adjusted" it, it may be hard to get it back to maximum flux.
Beezermacc or Groily may be able to shed further light on the subject.
The best quick "fix" for timing I've seen is Orabanda's slotted magneto mounting holes.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
Australia
Muskys Plunger A7

Online beezermacc

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Re: ignition timing on a K2F
« Reply #3 on: 27.10. 2017 22:54 »
Thanks for the invitation Musky!..........   mmmmm, interesting one! Strangely I'm in agreement with everything above, even though there are two sides to the debate. The eccentric screw is to make sure that the points open at the optimum moment relative to the magneto's internal flux. This occurs just after the cheeks of the armature pass the faces of the magnets in the body. If the points open too early you get no spark at all. The later the points open relative to 'peak flux' the weaker the spark gets, so the bike gets increasingly difficult to start. A good magneto will tolerate an inaccurately set cam ring as its surplus performance compensates for the weakening spark. However a poor magneto, i.e one with a weak spark already, will not tolerate late opening points as this makes the spark even weaker and the bike becomes impossible to start. I would guess that the eccentric screw is capable of moving the cam ring less than 10 degrees so, provided the magneto is good and the points don't open early, the magneto should perform OK. To test the effect of moving the eccentric screw you need to set the magneto up on a rig, run it at slow speed and turn the screw whilst adjusting the spark gap. A Vincent is a 50 degree V twin and uses a K2F, just like an A10, except that the cam ring is asymmetrical to ensure the points open at the right time for each cylinder. In fact the points open at 155 degree and 205 degree intervals. Remember that the points can't open early so the second cylinder is firing 25 degrees late, yet it still fires. Agreed, starting a Vincent takes a bit of practice but, with a good magneto, Vincent owners say they have no problems starting them. There is no way the eccentric screw on a K2F makes an adjustment anything like 25 degrees; and I'll bet the vast majority of magnetos on our A10's have not had the eccentric screw checked for flux strength. So, my conclusion is that you can adjust the timing with the eccentric screw but you might weaken the spark. If you weaken the spark sufficiently so that you notice the bike being more difficult to start (or any other dip in performance) you'll have to go back to the 'by the book' method. There are other reasons, fuel economy etc., why it is best to make sure the magneto is performing as effectively as possible so it is best to use the eccentric screw for peak flux adjustment rather then timing, but a 'slight nudge' one way or the other is not likely to make a lot of difference.
Priory Magnetos Ltd - A10 spares, magneto and dynamo refurbs. www.priorymagnetos.co.uk

Online groily

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Re: ignition timing on a K2F
« Reply #4 on: 28.10. 2017 08:09 »
As ever, all that B'macc says I agree with.

It's maybe worth just adding that with wear on the heel of the opening point and on the camring (or pushrod and camplate on a face-cam thing like a magdyno) you'll get some internal timing 'error' over time (compared to the maker's setting) so tweaking to get a fraction more internal advance isn't necessarily a bad thing sometimes.
Fitting new points or a new or different camring changes things again though. You can only really see the differences on a dynamic rig.

The difference in low speed spark performance between full advance and retard of the ecccentric can be more than you'd think although as B'macc says there aren't many degrees of movement here.
It is often possible, where a K2F won't spark the Lucas spec test gaps at the rpm specified by the makers, to gain significant improvement. Typically, there is an upside of maybe 30 or 40 rpm on the mag between 'late' and 'spot-on' on this screw, which makes a useful difference when trying to start, say, a Velocette with its low-geared kickstart, not to mention the problem with the late spark on the second cylinder of a V twin. That problem is compounded by the use of a manual camring on a V, where you can be asking the second spark to occur at 45° of retard compared to optimum (and it still works, albeit not below maybe 250+ rpm). Only the use of twin mags, or conversion to coil igniton with a distributor, will get round the unsuitability of using a device not designed to work asymmetrically.

The best I have ever seen a K2F do is 'all sparks across 3 point 5.5mm gaps' at 90rpm of the mag. Standard spec is almost all sparks at130rpm, excellent (to me anyway) is about 110rpm, a bit sad is 150rpm (double these numbers for engine speed). In all cases the beast will start, and the mag will make good sparks at the flick of a wrist. (When you think that some mags for commercial vehicles in the vintage period would produce their sparks at THIRTY rpm, it shows how effective these things can be at low speed!)

In the context of minor departures from performance specs, other things are just as likely to be relevant too, however. The magnetism, the state of the cb points, whether there is wiggle on the opening point's pivot, whether there is wear on the opening ramps of the camring (which denies the points a snappy opening)  . . . and maybe above all the air gap between armature ad magnet on a several-times rebuilt instrument. All of which can have a worse effect than a minor maladjustment of the eccentric pin.

So yes, a modest tweak of the eccentric screw won't probably have much visible effect  . . . but all the same, best to try to set it right and leave it there, I'd say.

Bill

Offline BSAlien

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Re: ignition timing on a K2F
« Reply #5 on: 28.10. 2017 09:05 »
Dear all.

If somebody is using a manual controlled K2F magneto, you turn the camring to get the right ignition points
to start and drive on higher RPMs.

With the excentric screw it is possible to turn the camring over a range of about 5° at all.

Where is the difference in adjusting the timing between the "advance/retard control" and the excentric screw
by using an auto advance unit?

I can not see a difference in these mechanisms.

Cheers
Hubse

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Re: ignition timing on a K2F
« Reply #6 on: 28.10. 2017 09:31 »
You are right, in that retarding the spark with the hand trigger also weakens the spark.

Online Greybeard

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Re: ignition timing on a K2F
« Reply #7 on: 28.10. 2017 09:36 »
Well Hubse you certainly dropped a pebble in the pond with your very first post!


Welcome to the forum. *welcome*

Online JulianS

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Re: ignition timing on a K2F
« Reply #8 on: 28.10. 2017 11:22 »
Lucas sought to improve the performance of the KVF magneto by fitting platinum points, rather than tungsten, as standard.

And BSA fitted platinum points to the 1961 Super Rocket, according tothis USA market service sheet, although I woild not order parts using those numbers which I think are for clockwise mags!

Online beezermacc

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Re: ignition timing on a K2F
« Reply #9 on: 28.10. 2017 14:00 »
Dear all.

If somebody is using a manual controlled K2F magneto, you turn the camring to get the right ignition points
to start and drive on higher RPMs.

With the excentric screw it is possible to turn the camring over a range of about 5° at all.

Where is the difference in adjusting the timing between the "advance/retard control" and the excentric screw
by using an auto advance unit?

I can not see a difference in these mechanisms.

Cheers
Hubse

You are quite right, there is no difference... they both cause weakening of the spark as they delay the moment when the points open relative to the position of the armature. If you set the A/R lever to full retard most bikes won't start at all because the spark intensity is almost completely lost (depends how far the lever can move, of course). The fact that the eccentric screw only moves about 5 degrees emphasises my point that it is possible to adjust the timing with the eccentric screw because the little difference it makes is likely to be unnoticeable to the rider.  Even with manual advance you can set the eccentric screw to achieve points opening at peak flux. As groily said with reference to Vincents, they are 25 degrees late and even worse when you retard the ignition on the lever, but they still start (just about!). However, the best set of circumstances will give you the best spark at startup, and this is with the eccentric screw adjusted to peak flux and the timing set properly with the drive gear.
Priory Magnetos Ltd - A10 spares, magneto and dynamo refurbs. www.priorymagnetos.co.uk

Online groily

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Re: ignition timing on a K2F
« Reply #10 on: 28.10. 2017 17:45 »
Amen to that B'macc.
The only other thing I would say is that it is so worth checking the basic timing setting properly again after doing any playing.
Even a spoke down the plug 'ole 'n a bit of fag paper is good enough to show up small changes which, when doubled up at the crank,  may amount to several degrees.
Bill

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Re: ignition timing on a K2F
« Reply #11 on: 28.10. 2017 18:33 »
Definitely. You always have to check the timing after you think you’ve set it!

Offline orabanda

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Re: ignition timing on a K2F
« Reply #12 on: 29.10. 2017 09:21 »
As some of the good family of the forum might recall, I advocate slotting the three mounting holes in the K2F body. If you are careful with a round file, it can be nearly as tidy a job as if it were done in a mill. You will end up with between 15 -18 degrees total movement, depending how close you take the end of the slots to the edge of the triangular mounting flange (ie how much "meat" you leave). So, if you end up with 16 degrees total arc, then set the timing (locking the magneto pinion on the shaft) when the magneto is in the middle of the slot. Therefore you will have 8 degrees of advance or retard available from that position).

Richard

Online duTch

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Re: ignition timing on a K2F
« Reply #13 on: 29.10. 2017 09:33 »

 I quite readily did that as soon as I had the opportunity- works for me *smile*.....but
Quote
If you are careful with a round file, it can be nearly as tidy a job ..........
oh yeah... *eek* *eek*
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Offline orabanda

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Re: ignition timing on a K2F
« Reply #14 on: 29.10. 2017 09:36 »
Tsk Tsk Dutch, you didn't warm up properly; Three beers before the first hole would have steadied your hand.