BMW R25/3 the coil question again

Begonnen von Goahead, 04 Juli 2016, 17:50:50

« vorheriges - nächstes »

0 Mitglieder und 1 Gast betrachten dieses Thema.


Hi Everyone

Yesterday (Sunday) i took the R25/3 1954 for a motorcycle gathering, but unfortunately, bike just died 30Km after the journey was a very hot day here in PT...and engine case and gearbox were hot to the touch...(probably around 40-50C i would say)
Everything seemed right, gas, compression, etc etc but almost no spark (or none).I always thought that i had a weak spark in could, and the coil seems to be from the 50s.(wire leaving coil to spark plug is still tin soldered...old style)
After trying several things, i had to give up the ride and call for the trailer pick-up.
The beautiful journey with my 300 "friends" riding old bikes...ended. Bmw R25/3 being the worst bike in the all group :)
Next time i will catch them. question.  Since "original" ignition coils are expensive (the ones that fit inside the housing) and they will continue to suffer from heat, i was wondering if i could take the 2 wires (one from points and the other from rectifier/regulator) to the outside, and put a cheaper ignition coil bellow the gas tank.

Is this possible and reliable?
Any 6V coil will do?

I know that the bike will look a bit different from original (coil below tank), but i can maybe start to run the bike safer without coil issues.
50Km non stop would be a good goal :)

Please advise.

Kind regards


Suffer from heat....yes, of course....after 50 years ;D
Expensive? ...roundabout  50-60€ much for your coil? this really for battery-ignition?


Hi Rolf,

Thank you for your help.

Yes for battery ignition. R25/3 still all original OLD parts  ;D

60 euros plus 16€ shipping to PT is expensive for a coil...and it will suffer from heat again and again...
I would prefer buying a 20€ general one like pictures above here in PT and put the coil outside the bike.

Just need to know if its ok and what brands and references do you recommend.

thank you.


I don`t believe it.
The first seemes to be for a CDI-Ignition and the second for a magneto-ignition.
Not for batterie-ignition.

Take better a look for Bobinas  ;D like this one.

And by the way: shipping costs from germany to portugal 9 €.



Hi Cledreda.

thank you for pointing that.

Zitat von: cledrera am 04 Juli 2016, 20:35:02
And by the way: shipping costs from germany to portugal 9 €.

Usually German  shops charge 19€ or even 23€ depending on size of package for shipping. Very few only charge the real value, since they also charge for handling and for process initiation etc etc.

coils like lucas cylinders are to big to hide below gas tank.

Why do you think they look CDI coils?

can someone suggest a small ignition coil, suitable for "bellow" the gas tank option :)

i think R27 uses one.



Hi G,
I only believe it looks like an Coil for a cdi-Ignition.

To big Lucas-Coils means 62 mm diameter an the length of 152 mm ist to big?
What`s about this? (40 mm/130 mm)
A good one, the Beru ZS215, (40 mm/105 mm), isn`t cheap.

By the way: Put your old ignition coil out and under the tank. Test the west an hope the best.


Thanks again for the links Cledrera.

I also found this topic: for the Beru ZS215

For what i understood in that topic, he installed the BERU coil below the gas tank. It would be nice to see some pictures of the installation. :( to see how it looks.

I could use my old original coil, and put it outside, for fresh air, but i think its to old and spark looks a little weak, even-tough the bike runs perfectly fine..cold :)

I want to be sure to be able to make some Km in a hot day

Anyone has pictures of a "bellow gas tank coil" for share?

Kind regards


Zitat von: Goahead am 05 Juli 2016, 14:57:05
For what i understood in that topic, he installed the BERU coil below the gas tank. It would be nice to see some pictures of the installation. :( to see how it looks.

stupid of me...he already have pictures in topic :)


By the way,
don`t throw the old coil away.
For example the einzylinderforumsmember ( ;D , my english isn`t goog, but my scotch ...) Hansdampf needs an old damaged one to create a new born one (old iron-inside with new copper-wire outside).
Contact him in case of interest.


PS: I shi.. on 12V  8)

rolf is not for batteryignition


Hi Everyone,

i friend of mine offered me a Jawa CZ ignition coil.
Just like this one:

Its 44mm per +/-95mm

Should i bother to test it or is this coil not ok for BMW R25/x?



Test it.
But: You are the first Tester.  ;D


Zitat von: cledrera am 17 Juli 2016, 10:58:52
Test it.
But: You are the first Tester.  ;D

Just did some testing, battery connected directly to coil, open and close circuit by hand, but i have no spark with this coil. The only spark i have is from the DC part ;)
I believe its a thryristor coil type.

Here are some pictures of the original coil and the spark it produces after 3km ride (coil was warm)
It seems week and old...but maybe thats just me.


Well i have to find a new one.
Do you really advise to buy a new original coil and put it in original place, or should i get a different one, and put it under the gas tank.



Hi Everyone.

I end up buying this one:

Just spray it in black paint, but it was not needed...its just a extra precaution, black paint helps heat dissipation by convection, since no much of air flow under the tank.
I have spark, so i mounted it.

I couldn't test engine running yet, since i also treated the gas tank, and i am still waiting paint to dry.(POR-15)

I hope coil does not fail me soon...that is to much work to replace it, under the tank. Grrrrr


Similar topics (1)

Begonnen von Илия


Startseite Baureihe Vergleichsliste Specials Anleitungen & Bücher

Presse & Wissen

Historisches Liste der BMW Modelle Bauzeiten & Stückzahlen Prospekte & Plakate Presseberichte

Tipps & Service

Tipps Händler Dienstleister Märkte & Museen Verschleißteile & Werkzeuge

Foren & Literatur

Bildtafel-Suche Forum: Einzylinder Bildergalerie Servicedaten Handbücher

Allgemeine Infos

Kontakt Sitemap Glossar Impressum Bildtafelsuche