The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: owain on 29.06. 2018 18:33

Title: Tightening the magneto sprocket fixing nut without the magneto spindle spinning?
Post by: owain on 29.06. 2018 18:33
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
Title: Re: Tightening the magneto sprocket fixing nut without the magneto spindle spinning?
Post by: Greybeard on 29.06. 2018 20:13
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.
Title: Re: Tightening the magneto sprocket fixing nut without the magneto spindle spinning?
Post by: muskrat on 29.06. 2018 21:21
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
Title: Re: Tightening the magneto sprocket fixing nut without the magneto spindle spinning?
Post by: coater87 on 01.07. 2018 13:32
 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
Title: Re: Tightening the magneto sprocket fixing nut without the magneto spindle spinning?
Post by: BSA_54A10 on 03.07. 2018 14:16
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.
Title: Re: Tightening the magneto sprocket fixing nut without the magneto spindle spinning?
Post by: orabanda on 04.07. 2018 01:35
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
Title: Re: Tightening the magneto sprocket fixing nut without the magneto spindle spinning?
Post by: Colsbeeza on 04.07. 2018 03:29
Hi Richard,
How long do you file the slots.? 18 degrees is quite a wide range, so must be fairly long slots.
Colin
Title: Re: Tightening the magneto sprocket fixing nut without the magneto spindle spinning?
Post by: duTch on 04.07. 2018 08:45

 I took Richards mod on board, and it may be a bit rat-tail bastard rough ,  but works for me.... *work* *beer*
Title: Re: Tightening the magneto sprocket fixing nut without the magneto spindle spinning?
Post by: muskrat on 04.07. 2018 10:31
G'day Col.
It's only 9 degrees at the mag to give 18 at the crank.
Cheers
Title: Re: Tightening the magneto sprocket fixing nut without the magneto spindle spinning?
Post by: Colsbeeza on 04.07. 2018 12:20
Hi Muskrat, Oh yes of course *good3*. So 9 degrees isn't much slot width. About 4-5mm eh???
Colin
Title: Re: Tightening the magneto sprocket fixing nut without the magneto spindle spinning?
Post by: orabanda on 04.07. 2018 15:54
Hi Colin,
I will post some useful info and pics tomorrow.
Richard
Title: Re: Tightening the magneto sprocket fixing nut without the magneto spindle spinning?
Post by: orabanda on 05.07. 2018 03:16
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!
Title: Re: Tightening the magneto sprocket fixing nut without the magneto spindle spinning?
Post by: Ted_Flash on 05.07. 2018 07:04
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.
Title: Re: Tightening the magneto sprocket fixing nut without the magneto spindle spinning?
Post by: duTch on 05.07. 2018 07:18

 (I) have a feeling someone mentioned that a while ago- maybe was you  *smiley4* ?    What thread is it ?
Title: Re: Tightening the magneto sprocket fixing nut without the magneto spindle spinning?
Post by: muskrat on 05.07. 2018 10:02
G'day Ted.
Never thought of that one.
Cheers
Title: Re: Tightening the magneto sprocket fixing nut without the magneto spindle spinning?
Post by: Colsbeeza on 06.07. 2018 11:15
Thanks Richard,
That is enough for me to go on. I see it does not leave a lot of meat at the slot ends does it.?!!
Colin
Title: Re: Tightening the magneto sprocket fixing nut without the magneto spindle spinning?
Post by: orabanda on 06.07. 2018 12:19
There is enough however.
You can choose to reduce the length of the slot.
I use heavy duty (or high tensile) 5/16"flat washer under the nut.
Post some pics when you finish
Title: Re: Tightening the magneto sprocket fixing nut without the magneto spindle spinning?
Post by: RichardL on 25.08. 2018 02:59
Where I am I can't read other posts. I use a slice of pink pencil eraser jammed between the two posts and the cam ring. This provides stability (because of the fri ction) while moving toward the points-open position and prevents running down the slope just as points open. Also, allows the pinion bolt to be loose enough make adjustments while avoiding stress on the brass locator in the points block. Finally, once in position, tap home the pinion with a socket over the bolt, then slowly sneak up on tightening the bolt. Fingers first, then light wrenching. Now recheck timing. Good? Final wrench tight and check again.

Well, that's about how I do it, at least.

Richard L.
Title: Re: Tightening the magneto sprocket fixing nut without the magneto spindle spinning?
Post by: Greybeard on 25.08. 2018 08:59
...then slowly sneak up on tightening the bolt.
I like that! Should I be tunelessly whistling?
Title: Re: Tightening the magneto sprocket fixing nut without the magneto spindle spinning?
Post by: LJ. on 25.08. 2018 10:07
Placing a screw or bolt in the earth track is a good idea, not thought of that.... BUT, I bet this is why so many earth tracks have deep grooves in them, like in photo, I've often wondered how the hell had that happened! I'd think that a brass screw or bolt would be safer than steel one. Or certainly some kind of flag or visual reminder that it is there before starting.
Title: Re: Tightening the magneto sprocket fixing nut without the magneto spindle spinning?
Post by: Triton Thrasher on 25.08. 2018 10:23
If pressing the auto advance onto the taper with your thumbs doesn’t make it stick sufficiently that you can tighten the nut without the armature turning, then the tapered faces are not in good condition.  They can be ground into each other with valve grinding paste.

Avoid straining the fibre gear teeth, by sticking a screwdriver through the auto advance yoke and pushing against the turning force of the spanner on the nut.
Title: Re: Tightening the magneto sprocket fixing nut without the magneto spindle spinning?
Post by: RichardL on 25.08. 2018 12:03
...then slowly sneak up on tightening the bolt.
I like that! Should I be tunelessly whistling?

It wouldn't hurt.