Forum bmwbike.com

This is for a 1954 R51/3, so it has the same headlight switch as the '55 and up BMWs.

The bike ran perfect, I parked it for 2 weeks and then she wouldn't fire up. I found that there is no power at the #2 terminal at the coil, and traced it back to the headlight switch, which also has no power at the #2 terminal (when ignition switch is down of course) The points in the headlight switch fully engage when key is inserted. I'd guess the big red wire in #51 terminal (the battery) connects the #2 terminal when key is inserted, and provides power to the coil. But upon closer inspection, there is a round space around the top of the points which doesn't allow connection between the points and the soldered wire which goes to #2 terminal. Now I am confused...

It must be something simple as the bike was running great... Any help would be much appreciated, as the sun is finally shining... Thanks, Stacey

Stacey, Have you checked the resistance of the ignition coil as well? I have the same bike with the same " no spark problem" after a couple of days..i also have 2 ignition coil to spare..as the first one was working and "malfunctioned?" and then the second one checked of its resistance was perfect but also malfunctioned after being being connected and 2 days after of idle time..disconnected / reconnected. ( final restoration work ) We have the same problemo.I really hope it is something plain and simple than coil failure..
I hope someone out there will throw in advice..

Hallo Stacey,
you have a magnetic ignition, your 51/3 don`t need any battery-power. your "2" is to make a short-circuit(Kurzschluß) ,the only way to stop a motor with magnetic ignition.It was connected to ground(31) when you pull the ignitionkey and was disconnected when you insert the key.
greetings
rolf

Hi Rolf,

You are right... I read the manual, and it says to take the #2 wire OFF the magneto and there should be permanent power...

But I am still not getting a spark (Took the sparkplug out and touched it to the head and kicked it over a few times) Maybe the coil is shot. (it is the original 50 year old coil) Do they usually fail all at once (work one day, not the next?) Is there a way to test the coil?

Thanks! stacey

Hallo Stacey,
there is away to decide if the coil is totally death.
Between the 2 connectins for the cables for the sparkplugcable must be a resistance of(I don`t know the exact data,but this is not important) of 10000 Ohm (better: something in KOhm) and between the cable(going to the Contactbreaker(?)) and Ground something about 5-15 Ohm. You have to dismantle the coil for this measurement.
Mostly the coil failes in the KOhm area.
If you are interested in more (basic) information go to the side of Kees van der Heiden(http://www.geocities.com/MotorCity/Spee ... index.html), he had a superb site and is one of the few I know who kows the the secondary ignition spool was not going to ground( in contrast to manuals coming from Bosch)
greetings
rolf

Hi Rolf,

I think the coil is shot. I get 0 resistance between the 2 posts, and 0 resistance between the post going to the contacts, and the metal base.

My second parts box coil has 10,000 resistance between the posts, and 0 resistance between the post going to the contacts, and the metal base.

I initially thought the switch would bring power to the points, so I took a spare wire and touched the battery wire to the #2 on the coil, It ended up melting the plastic between the points and the point base (basically permanently closed) Live and learn....

...with high costs

Hey Stacey, your 0 Ohm between metalbase and the post going to the points: do you have dismantled the coil?
rolf

Hi Rolf...

Yes, the coil is off the bike for the measurements.

stacey

The ohm meter should be set to 1x and the reading between the spark plug posts will be
.4 - .6 ohms, very low. For an in-depth discussion of coil problems, go to:
http://groups.yahoo.com/group/slash2/

and search on "Shorted Coil"

This was my thread, and it turned out to be a bad condenser.

Good luck,
Jim
1966 R69S