Author Topic: Magneto Tming on a 1913 2 3/4  (Read 4559 times)

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Offline phil_h

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Magneto Tming on a 1913 2 3/4
« on: 06 Feb 2010 at 21:35 »
Well, I've been around the block, and even managed to run out of petrol so things must be looking up, but performance is not what it was before the rear piston exploded.
1.
It feels like it needs some more advance, but reading the little book and looking at what I have on my bike does not add up perfectly.
Rear ex valve just closed and the fibre points heel is at 9 o/c (looking from lh side).
The 'cam' is just off the heel and the fully-retarded lever position is about 1in to outside of the h'bar.
Moving it just about in line with the bar just opens the points, and the lever will move about 1 1/2 in to the inside of the bar
ie the lever is at about 25% of range for the timing point described in the little book, so I guess the mesh was made at that point.
ie I should actually have plenty of advance !
2.
What i the most likely way for oil to get onto the slip ring ?
The brush holders wernt sealed very well to the case, so is it likely to get in there ?
Or is there an internal route ?

Offline Chris

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Re: Magneto Tming on a 1913 2 3/4
« Reply #1 on: 07 Feb 2010 at 09:11 »
Hi Phil
   It does not sound from what you have said above that you are far out. I do not bother with the position of the fibre heel but concentrate purely on the point at which the contact breaker points part. This should occur at the same instant as when the exhaust valve on the rear cylinder just closes with the tappet clearance set correctly and with the advance/retard lever at the halfway position of its range of travel. However. some engines will stand for another tooth of advance on the magneto gear wheel and run very well.
     I assume also that you do have the correct clockwise (from the timing chest side) rotation magneto. In the absence of a correct magneto it is quite common to have the direction of rotation reversed on an anticlock unit. This usually leads to slack wire advance instead of tight wire advance and can cause confusion as to whether the ignition is being advanced or retarded.
    Regarding oil entering the magneto and contaminating the slip ring, it is unlikely that this is coming from the pickups (easily fixed by provision of gaskets if this is the case) but more likely to come from the timing case. I do not know what magneto you have, probably, if correct for the year a Bosch. I do have two of these but have not stripped them for many years and cannot recall what provision if any is made to prevent ingress of oil vapour. The EIC mags usually have a felt seal between the slip ring and the bearing. Chris.

Offline eddie

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Re: Magneto Tming on a 1913 2 3/4
« Reply #2 on: 07 Feb 2010 at 10:34 »
Phil,
       As Chris says, the oil is probably coming from the timing chest - if it were getting in between the pick ups and the case, the outside of the mag would have to be soaked in oil. Before investigating any problems with the mag itself, check that the drain pipe from the bottom of the timing chest is clear. If this is blocked, the oil level in the timing chest will rise to the point that the timing gears throw an excessive amount around - as well as causing a pressure build up that will add to your problems.
      With regard to the timing, as a general rule for engines that are in a mild state of tune. Bring the piston to TDC with the valves rocking, turn the engine forward exactly 1 revolution. In this position the points should be just opening with the mag fully retarded.
                             Regards,
                                           Eddie. 

Offline graeme

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Re: Magneto Tming on a 1913 2 3/4
« Reply #3 on: 07 Feb 2010 at 21:10 »
I always set the ignition timing at full advance - this eliminates any pssible variation due to handlebar lever type, arc of travel of the magneto cam ring etc etc. With Douglas machines this is easy - set up a degree disc on the flywheel (I use a blob of blue tac to hold it to the centre shaft) and set up an appropriate pointer. Then set the lever at full advance. Then turn the engine forward until you reach TDC on the firing stroke, where the magneto points should be onto the cam. I then put a 2 thou feeler gauge between the points and turn the engine backwards 180 degrees - the points will grab the feeler, and this allows any backlash in the gears to be taken up as you turn the engine forward. Then turn the engine forward until you get to 35 to 40 degrees before TDC and the points should just be opening, and you can slide the feeler gauge out.
Cheers, Graeme

Offline phil_h

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Re: Magneto Tming on a 1913 2 3/4
« Reply #4 on: 07 Feb 2010 at 21:29 »
Thanks guys,
It seems that there should not be too much wrong with the timing, and I'm not inclined to take off the carb manifold to check anything prior to the pioneer, so I've cleaned up the slip ring ready for the next outing and am hoping that could improve things.

Re feeler gauges and the mag points - where do you get any that are narrow enough to reach !
None of mine are at all useful (and I have some 'bent' ones) as they are all just far too wide to get in there.
At the moment I'm resigning myself to mullering a set by trimming them and thn bending them to suit.

phil

Offline Chris

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Re: Magneto Tming on a 1913 2 3/4
« Reply #5 on: 08 Feb 2010 at 06:50 »
Hi again Phil
   It was once put to me by a very knowledgeable and enthusiastic veteran and vintage Douglas owner that such precision as the use of feeler gauges was unnecessary on agricultural engines 80 to 100 years old. His solution was to set your contact points to the thickness of a "gentleman's visiting card". Seriously, this is not as silly as it sounds. I usually use thin "Rizla" cigarette paper cut into a thin strip and placed between the points having eased them open first and then using the feel of the drag to determine the point accurately at which they begin to open. the same system can used to set the points gap using a piece of shiny card that you know to be the correct thickness. I do have a very old set of feeler gauges that i have possessed since the 1960s that had very narrow tapered tips to each blade. I am sure that this type must still be available but modern ones do seem more often than not to be wide and useless for our old magnetos.   Chris. 

Offline eddie

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Re: Magneto Tming on a 1913 2 3/4
« Reply #6 on: 08 Feb 2010 at 07:23 »
You could always revert to a 'period' set of mag spanners - they normally incorporated a narrow 12 thou feeler for this purpose!

Offline phil_h

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Re: Magneto Tming on a 1913 2 3/4
« Reply #7 on: 09 Feb 2010 at 20:03 »
Thanks for all the info guys.
I've cleaned up the brushes, sealed the pickups with silicon, cleaned the points and achieved a first - I just managed to start it with the kickstart in the garage - hoorah  :D
If my problem is that a bit of oil is getting onto contacts and reducing the quality/reliability of the spark then that is a good lesson to learn.
The tickover is still a bit uneven and 'misfirey' at 5C, as the front inlet guide will be leaning the mixture off for me, but hopefully that will not be as bad with some warmer weather.

(If anyone has any smple suggestions to temporarily seal the guide a bit without removing the casting, I would be extremely interested !)

regards to all
phil