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Bosch FF1AL Magneto

Gary

Registered
Greetings folks,
I am about to dismantle this FF1 AL magneto to restore it. All the screws and fasteners are locked tight, so I would say its never been opened up before.
I can already see that I will need to draw the drive sprocket off and also remove the rotary contact mechanism, but before I start I thought I should ask you guys if there is any recommended dissassembly sequence or pitfalls to watch out for.
Any advice appreciated.
Thanks.
Gary
 

cobbadog

Registered
G'Day Gary.
I've never done one but the best thing to do once you start is to take a heap of pics for refference on reassembly.
It is great that you have asked before jumping in as some magnetos do have to be stripped in a certain order and if done wrong parts can break or get damaged.
Hopefully someone with all the knowledge will be along soon with some help.
Welcome to the Forum.
 

Gary

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Thanks for the good advice mate. I'm not in any hurry so I will hang fire for a while and see what comes up
 

Craig Gillingham

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Last Subscription Date
12/04/2017
I'd recommend taking the pickup brush holder out first. That way you're not likely to damage the slip-ring or brush when you come to take out the armature. I did that once to a magneto years ago, and damaged the slip ring. It is a next to impossible place to replace (still haven't) and a valuable lesson learnt.
 

Gary

Registered
Thanks for tips guys. Yes, I already took the brush mount off. Had a hell of a job cracking the screws loose after so many years, but managed it without damaging the slots. I put an endoscope through the hole and it looks clean inside. The secondary coil is around 2k ohms measured from slipring to ground. The primary coil is around 2 ohms. That could maybe be a bit low even though I presume it's few turns with heavy wire, so maybe we have a leaky capacitor. I can't find the capacitor. It must be inside somewhere. I was hoping to avoid stripping the magneto due to risk of diminishing the magnets, assuming the rotor is also the keeper so removing the rotor is unwise.
I can feel magnetic cogging when I turn the shaft by hand, and I am getting a weak spark when I rotate the magneto with a slow battery drill. Looks like I might end up having to recharge the magnets if the capacitor has to be changed. Does anybody know where the capacitor is on the Bosch FF1AL? If so, can it be accessed and removed without withdrawing the rotor?
regards to you all, Gary
 

Gary

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That was a typo. I meant to ask, can the capacitor be accessed and replaced without removing the rotor?
 

Craig Gillingham

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Last Subscription Date
12/04/2017
The condenser is located in the armature, on the breaker points end. The armature (rotor) comes apart into three pieces; drive end, the winding section and the rear section that's usually brass and the breaker point assembly bolts onto this. This is held on by two long screws, you take this off and the condenser is located in there. They're not a very easy thing to get at.
 

Craig Gillingham

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Last Subscription Date
12/04/2017
Thinking about it later on, I think there are actually four long screws that hold the three pieces of the armature together. I've had a few FF1A magnetos apart; but not for a while. I'll be able to tell you what the specifications were for the original condenser were, if you wanted to replace it with a modern equivalent.
 

Craig Gillingham

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Last Subscription Date
12/04/2017
Craig, do you use film capacitors as a replacement part for a condensor?
I've never replaced one with a modern condenser, I've always used the originals. I'd be interested to know how to go about it.
 

cobbadog

Registered
I've used film capacitors in the rotary manetos of my Victa mowers and some Villiers engines. I usually use the ceramic type ones for heat resistance. Buy them in differnt physical sizes to fit anywhere you want as well. Values from memory are 640V 2.2 Uf. You need to insulate one of the wires and I use either small shrink wrap or strip the insulation off a short length of 4-6mm wire and slip that on. Other side goes to earth. Can be bought from most electronic shops, Jaycar and online from the usual auction sites. Cost is very economical no matter where you buy them from and so far they have proven to be very reliable.
 

Gary

Registered
I removed the capacitor and tested it several different ways and it seems to be ok. Have now reassembled the armature and got it back in. I used a big cast iron g-clamp as a keeper, and a snug fitting hole-saw cutter inside the poles as an additional keeper. Trouble now is that the armature is fouling. I have tried a 0.6mm end gasket to provide some end-play, but that didn't work. Starting to look like I might have to remove the armature again and true it up in the lathe, but I hate doing that as it aint good for the magnets. That said, when I loosen the end plate a bit to free up the armature and give it a spin with my fingers, I can feel a healthy magnetic cogging, so the magnet seems to have "kept" quite well. I haven't seen any other comments on here about truing up armatures, so flying blind. Comments appreciated. Gary
 

cobbadog

Registered
Does the armature sit in bushes or bearings? Check these for wear. If a bush is slightly worn the shaft can drop and foul on another part.
There must be a reaon that this has happened right after a strip down. Keep looking and good luck.
 

Gary

Registered
Cheers mate, ball bearing races both ends and they look good.
Also, fact is that it was spinning smoothly before stripdown. I'll experiment a bit more and let you know how I get on
 

Craig Gillingham

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Last Subscription Date
12/04/2017
I've made a shim before to fit in the end plate, similar to what you've done with a gasket, but I agree, if it was OK before then it should still be OK after reassembly.

On another note, there was this excellent series a few years ago about the rebuilding of a Bosch ZEV. It's a different magneto (v-twin), but the principles are the same for a FF1A and they are both German Bosch from the same era. The only problem is the photos are from Photobucket and aren't visible anymore.

http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=446733
 

cobbadog

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Was or is there any movement in the bearings up and down, not just laterally?

Keep fine tuning the armature, you will fix it soon enough.
 

Gary

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All back together and working. Murphy's law caused me to drop the brown bakelite spark manifold which broke the end off the protruding carbon brush. I found a 4x6mm Kenwood cake mixer brush with 4mm spring online and it arrived yesterday. It only took me a few minutes to grind the square carbon brush into a 4mm circular shape, simply by rubbing it with 180 carborundum paper, and it fits perfectly. I didn't bother to solder the spring-ends together because they are in good pressure contact anyway. By flicking the armature spindle with my fingers I am getting a good spark across a gap of around 2 to 3mm which I reckon is roughly 9000 volts. I just need to adjust the contact breaker gap to spec and we are ready to roll. Next job is to restore the engine itself. Maybe not much to do as it rolls smoothly and seems to have good compression. (It's a Lister J) Thanks guys for all your generous advice. Gary
 

cobbadog

Registered
Good news, glad all is good with the magneto. Look forward to hearing that it is up and running soon.
If possible always have the HT lead earthed or near an earth so the spark can jump. It hurts them if it cannot get to ground.
 
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