Author Topic: Tightening the magneto sprocket fixing nut without the magneto spindle spinning?  (Read 893 times)

Offline owain

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I'm wondering if anyone has any tips about how to tighten the magneto sprocket fixing nut (that double threaded nut!) to the magneto spindle without the spindle moving out of place. It seems like a bit silly to set the piston 11/32" before TDC and set the magneto so that the contact breaker is just about to seperate, only for the magneto spindle to rotate out of position when tightening the magneto sprocket fixing nut. I have the auto-advance sprocket btw.

The only thing I can think of doing is trying my best to hold the contact breaker as best as I can in my hand whilst tightening the nut, but it still moves slightly out of position and I'm not super thrilled about all the torque being applied to the contact break when grasping it and tightening the nut. Has anyone got any tips for setting the timing in a more efficient and precise manner?

Cheers
Sweden & North Wales
'50 BSA A10
'69 BSA A75R

Online Greybeard

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Try loosely tightening the ATD. You may be able to tap the points plate to the correct, (fag paper release) position using a blunt screwdriver as a drift and then go round and fully tighten the ATD. Recheck the timing after that, of course.

By the way, clean and adjust the points BEFORE timing.

Online muskrat

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G'day owain.
I get the points to the right position and use a small timber wedge between the post and cam ring to hold it. Then bring the motor to firing position and gently place the AA unit on the shaft and start the thread. I the use a large socket to give the AA unit a short sharp tap (not belt or whack just a tap) then tighten the nut. Even doing this it may move a tad so I fudge the timing this tad to be correct when tight.
I love my Boyer  *smile*
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
Australia
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Offline coater87

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 Hi Owain,

 I think this is a real common problem.

 I found out that every time I did this, I was off 7-8 degrees when done. I started to cheat the system 7-8 degrees. After that I hit it second try.

 I think its just important to be gentle and patient no matter which way you try to do this.

 Lee
Central Wisconsin in the U.S.

Online BSA_54A10

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Interesting.
I have always used a piston stop once the correct position has been determined.
You can still be out by the backlash in the gear train.
But I use a timing disc so I can determine if there is any great difference.
Engines with timing set by piston drop are not all that fussy unless you are running 11:1's on 85 octane.
Bike Beesa
Trevor

Offline orabanda

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I have had a couple of fibre (timing) gear failures through the years, and in hindsight have probably contributed to them, by tightening the magneto nut against the gear train. I now realise that side loading on the fibre teeth from a spanner, is not going to do their mechanical integrity any good.

So, these days I use a similar procedure to Mighty Musky, to ensure there is no loading against the fibre teeth when tightening the nut.

If you are re-fitting the magneto drive gear, then it's not much more effort required to remove the K2F and slot the three mounting holes. This will give you approx 18 degrees of rotation (9 degrees advance, 9 degrees retard if you fit the gear onto the taper in the middle of the arc of rotation.

Carefully offer up the gear and follow Musky's procedure of a sharp tap to seat the taper, before tightening the nut against the ATD body (not the fibre gears). Time with strobe light, and rotate K2F body until you have 30 degrees BTDC for iron heads, and 32 for alloy.

Then brumble down the lane!

Richard

Offline Colsbeeza

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Hi Richard,
How long do you file the slots.? 18 degrees is quite a wide range, so must be fairly long slots.
Colin
Colsbeeza
Australia

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 I took Richards mod on board, and it may be a bit rat-tail bastard rough ,  but works for me.... *work* *beer*
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
Australia

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G'day Col.
It's only 9 degrees at the mag to give 18 at the crank.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
Australia
Muskys Plunger A7

Offline Colsbeeza

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Hi Muskrat, Oh yes of course *good3*. So 9 degrees isn't much slot width. About 4-5mm eh???
Colin
Colsbeeza
Australia

Offline orabanda

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Hi Colin,
I will post some useful info and pics tomorrow.
Richard

Offline orabanda

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The hole(s) are arced to a length of 0.7" I initially used a file, but now use a drill press and dividing head.

The magneto casing fits over the mandrell (see pics & drawing) - remove the shaft end bearing & insulating washer first.

Then dividing head is mounted to drill (or mill) table, and mandrell / K2F casing clasped vertically. After centering any one of the three mounting holes under the drill arbor, use an end mill to slot the hole say 8 degrees each side of the mounting hole centre.

After slotting all three, remove from the mandrell, clean up the slots with a file, and trial fit on the RH crankcase.

File off any high spots, until the casing can swing fully in each direction.
Reassemble Magneto

Happy trails!

Online Ted_Flash

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No one has mentioned the trick of replacing the earth brush housing temporarily with a bolt to hand tighten against the armature to prevent it moving during tightening of the magneto/ATD nut.  It's always worked for me but I accept that there may be a downside I'm not aware of.
Ted Wilkinson, Ramsbottom, Lancashire
1950 Golden Flash

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 (I) have a feeling someone mentioned that a while ago- maybe was you  *smiley4* ?    What thread is it ?
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
Australia

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G'day Ted.
Never thought of that one.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
Australia
Muskys Plunger A7