Robert Bosch Magneto identification - 1925

[Guest Leeroy]

Hi Guys,

I've discovered my Magneto might not be adjusted correctly, due to the fact its on a Maxwell 1925, i cant seem to find any documentation on how to set up the timing correctly.

I was hoping someone might have some information on this Magneto from Bosch

.

 

 

[Spinneyhill]

This web site has a few tech. manuals for Bosch magnetos. Maybe yours is one of them?

http://go-faster.com/BoschMagnetoVeteran.html

 

Here is a document about the MJA American Bosch magneto.

http://www.oldcroak.com/mja-1/

 

I am sure if you keep looking for magneto information on the www, rather than Mitchell stuff, you will find something.

 

[jp928]

Can you expand on the 'might not be adjusted correctly' please? What is the symptom? With my 26 Rover, with everything refurbished (according to receipts from previous owner),but not started before, it would turn over well, but no sign of any action. I set the crank at Cyl  1 firing mark (flywheel), and opened the red lower cap on the magneto (Lucas 4Jx) - the points should have been starting to open, but they were 60-70 degrees away. I removed the maggy without disturbing the crank or maggy connection on the engine side (fortunately easy - external engagement). I loosened the drive flange , turned the shaft until the points just opened, refitted the drive flange and tightened, replaced maggy  - it ran.

If your issue is failure to run, open the red lower cap (single wire), check that the points do open to the correct gap, and that they are in good condition. Problem could also be condenser failure, which is a PITA as its internal, messy to replace. REmove 1 plug lead, hold 1/4" away from any handy ground of the engine, and see if it sparks when you crank the engine - if it does, condenser is usable, but timing may be out. 

There is a lot of info out there for the Bosch units - see http://www.go-faster.com/BoschMagnetoVeteran.html  .

The serial no 279103 , from data on the above web page, appears to have been made in 1907-8 - does it look original on your Maxwell ?

See also http://www.oldengine.org/members/diesel/magnetos/Magdata6.htm

hth

jp 26 Rover 9

Edited June 29, 2017 by jp928 (see edit history)

[Alfa]

Surely the only issue is timing the mag to the engine correctly?

 

jp928 has described nicely about checking the orientation of the points. If you remove the HT cap held by the big clips, there will be a rotor arm. Set your engine to TDC on No 1, with No 4 rocking and verify that the rotor arm is pointing to the correct cylinder HT lead (it seems to have been marked already on the cap).

 

You can set up the timing in the same way that you would a distributor. I set the Scintilla Vertex magneto on my Alfa so that full retard on the steering wheel lever equates to TDC (0 degrees advance), then the range of adjustment gives me up to 40 degrees of advance for high revs. It looks as though you can adjust the position of the mag on the three studs holding the mounting plate, can`t you?

 

By the way, you can use a modern strobe timing light to check and adjust the timing with the engine running, provided that you have a suitable set of timing marks on either the crank pulley or flywheel. If not, all you really need as a TDC mark and a datum point, so you could mark up your own.

 

Hope this makes some sense.

 

Adam.. 

[Guest Leeroy]

14 hours ago, jp928 said:

Can you expand on the 'might not be adjusted correctly' please? What is the symptom? With my 26 Rover, with everything refurbished (according to receipts from previous owner),but not started before, it would turn over well, but no sign of any action. I set the crank at Cyl  1 firing mark (flywheel), and opened the red lower cap on the magneto (Lucas 4Jx) - the points should have been starting to open, but they were 60-70 degrees away. I removed the maggy without disturbing the crank or maggy connection on the engine side (fortunately easy - external engagement). I loosened the drive flange , turned the shaft until the points just opened, refitted the drive flange and tightened, replaced maggy  - it ran.

If your issue is failure to run, open the red lower cap (single wire), check that the points do open to the correct gap, and that they are in good condition. Problem could also be condenser failure, which is a PITA as its internal, messy to replace. REmove 1 plug lead, hold 1/4" away from any handy ground of the engine, and see if it sparks when you crank the engine - if it does, condenser is usable, but timing may be out. 

There is a lot of info out there for the Bosch units - see http://www.go-faster.com/BoschMagnetoVeteran.html  .

The serial no 279103 , from data on the above web page, appears to have been made in 1907-8 - does it look original on your Maxwell ?

See also http://www.oldengine.org/members/diesel/magnetos/Magdata6.htm

hth

jp 26 Rover 9

Thanks JP, yes I've found the serial number on the info page, but wasn't sure if it applied to my model as my Bosch has the "A.G." on the top, so not sure if it's a different series.

Starting up has now been sorted, but still need to be on max advance to start, it runs good, but on max advance too, slight change of performance moving 50% to full retard, but no change after that.

My Maxwell is a 1925, the exports from what I've read had the Magneto's and local ones had distributers.

[Craig Gillingham]

I'm fairly sure that's a German Bosch ZU4, the model number is usually stamped on the brass base, although it might be on the engine side so you can't see it.

[jp928]

If it needs full advance to start, sounds like the advance/retard mechanism has slipped somewhere- any sign of that occurring? Could be anywhere along the chain of linkages.

jp 26 Rover 9