Bosch Lavalette magneto query

Hi,
Can anyone help me locate a company who can repair Bosch Lavalette magnetos?

I've a Bernard W13 which has a very weak spark - the spark is blueish white but not great in strength - when I compare it to the spark on my Conord F0 and Bernard W1 (both running well with basically same Bosch Lavalette mags) it's clearly very weak and despite much tweaking and cranking, there's not enough oomph to fire.

I've 130psi compression so rings and valves seem good - valve's are set at 0.4 exhaust, 0.35 inlet at TDC
Points gap is 0.55 (exactly as the other 2 running engines) and open just prior to TDC (again as the W1 and F0)
I've dropped the W13 spark plug onto the F0 and it's good, so I've eliminated that from the possible issue list.

I've cleaned the carb and jets and there's fuel vapour evident out the spark plug hole when I crank with the plug out, however even with easy start there's not an inkling of internal combustion so I can only assume the mag is just not strong enough.

Any help dearly appreciated
Cheers

Hello and welcome!

I'm no expert on magnetos but it certainly sounds like the spark is too weak to jump the plug gap under compression.

Have you tried any of the companies that advertise in 'Stationary Engine' magazine? I would think (but as I say I am no expert) that the make wouldn't matter much as they all work on the same principle?

Hi mattblack, thanks for reply.
Apparently it's all about the armature and fitting it in rewind machines- that and internal spares availability.
I've tried the obvious but no luck thus far - it's frustrating as committing to a restoration without a mag on hand is risky - it would be fun but could be rather a waste of time and effort - the engine is a peach too, so annoying!

Could you adapt another magneto as temporary measure to get it running while you look at getting the original sorted?

Do you have model/type number for mag?

Hi,
It's tricky to read but I think it's marked Lavalette Bosch AT1DS5, serial number 233392
Any assistance appreciated;)
Cheers

Hi, reading your initial post it seems your diagnosis is based on elimination of anything else being wrong. This is a good starting point but it doesn't necessarily mean that the magneto needs to be fully rebuilt. I am obviously unaware of your experience or knowledge when it comes to magnetos. So without wanting to insult your intelligence, I wondered if you had undertaken any of the basic preliminary tests on the magneto in an attempt to isolate the possible cause for a suspected weak spark. Certainly dirty or corroded points could potentially cause this situation, as would a failed or failing capacitor, both of these issues are easily identifiable and simply rectified. However the issue which could cause this and would result in a rewind being necessary would be a failing secondary winding. This is where the coil is actually open circuit but a spark is still produced by arcing across the internal gap in the winding as well as the spark plug. This mode of operating will only persist until the gap in the windings becomes too big through electrical erosion and the spark is unable to jump the gap. Again this is easily tested for, with a meter reading the resistance presented by the secondary coil. Usually a reading of a few K ohms is an indication that the coils is good, if it tests open circuit then this is a sign that the coil has failed. Even if this is the case all is not lost, as it is possible to continue to use the magneto to provide the points and capacitor function and the primary coil, which rarely fails and substitute the secondary windings with a remote coil. Details on how this may be achieved have been posted elsewhere on the forum and I also believe it has been described in The Stationary Engine Magazine. I wish you every success with your restoration, do not give up on the engine just due to your suspicions of a failed magneto.

Neil.

Hi Neil,
Fear not, you couldn't possibly insult my knowledge on the subject, my mechanical skills are pretty good but magnetos (and distributors) remain somewhat mysterious in my head
I've been lucky, I fell for the Bernard brand but thus far, all acquisitions have arrived with healthy mags.
With that in mind please forgive the long winded reply below, with no foubt incorrect terminology.
So, starting at the drive gear end, here's where we're at....
The lead pick up carbon has a good surface and the spring seems strong - I've cleaned the pick up screw so contact to the lead is good.
Through the pick up hole I can see a ring, partially exposed brass, partially coated.
The brass area is clean but does show scratches and there is a clear mark (possibly where the pick up has been stationary for years)
I've removed the horse shoe and cleaned the contact areas with the magnets in the mag body (magnets are strong)
At the back end, the points are immaculate, flat, clean and in full contact when closed. The points springs are strong. All insulating bushes and washers are present and in good condition.
Behind the points plate is an earth carbon on a spring, this is clean (as is the contact area in the body) - the carbon is healthy, as is its spring.
I suspect capacitance, the marking on the pick up ring or another break down, but I have yet to be brave enough to pull the armature out - bravery for disassembly is directly related to knowing parts availability is poor!
To be honest, long term I need to find a service provider - with 4 Bernard's here, all with Lavalette mags, inevitably one day I'm going to need it!

If you have, or can borrow, a multimeter, set to ohms, set range to 20k, connect one lead to brass slip ring an t'other to good earth. You should get a reading around 5k to 7k.
If reading is zero then either HT coil is open circuit or slip ring is not connected to HT. You would have to get the armature out to acertain which.
Came across a chap on the internet that I didn't know of. Will try to find details again.

Bob Lester in Cheshire has rewound/overhauled the two Bosch Lavalette magnetos on my Bernards.

Pete.

Thanks Woodsman, reading at your suggested test is zero - one assumes we've a mag in need of repair.
Cheers

Your testing does seem to indicate that the secondary coil is open circuit. Therefore the spark you are seeing is, as I mentioned above, jumping a gap in the failed windings before it reaches the spark plug gap. Unfortunately there is no way back from this situation, without a rewind. Luckily it looks like Foden may have identified someone who may be able to help you, with servicing your magnetos.
All the best,
Neil.

I can also suggest Bob as he did a Bosch flick mag for my Lister M.

Maryalice

Bob has been contacted and a plan is in place for magneto repair - thanks to you all for your helpful contributions - we're hopeful the W13 will live again! In time I'll drop the engine build progress on here
Cheers