Ignition Coil

[Nourish]

Could I use the PVL twin output coil on my '89 R100 - The coils spec are as follows :-

Electrical specification:
Primary resistance: 0.6 ohms
Primary inductance: 1.65 mH
Secondary resistance: 8.7 Kohms
Secondary inductance: 9.2 H
High voltage supply: >21kV
Spark energy: 30mJ

Cheers

[Kurt in S.A.]

I've always thought that the resistances in the circuits were 5K ohms for each spark plug cap and 5K ohms for each coil (ie, the secondary part). Typically, the reading from one cap to the other should be 20-22K ohms. I suppose some variation is "allowed", but too much could be a problem. I didn't stay at a HIE last night, so I could be wrong!!

Kurt in S.A.

[Jean]

Primary resistance should match closely, to avoid excessive current in wiring that might not be able to handle it.
What are specs on the OEM coil for this?

[Kurt in S.A.]

Haynes says for secondaries:

Single coil - 3.7 - 5.3 Kohm
Twin coil - 7.5 - 9.15 Kohm ('87-on)

Also for '87-on, the primary resistance should be 1.15 - 1.32 ohm. Prior to '87, the singe coil primary resistance is listed as 0.67 - 0.77 ohm.

So looks like the secondary resistance of the proposed coil is spot on while the primary resistance is a bit low.

Kurt in S.A.

[Garnet]

Copied from Snobum:

(c) In 1981 to 1984, all models EXCEPT the G/S and ST, used 2 each 6 volt coils, but they are 0.7 ohm primaries, have a lightnin bolt symbol on the coils.
(d) From 1985 a single coil was used, originally gray in body color (and they cracked and were UNreliable); these were 1.5 ohm.
The Bosch number on those bad coils was 0 221 500 200 They can be upgraded with the Oilhead coil, or, BMW has an replacement for the airhead.... 12-13-1-244-426, it looks a bit different, but fits just fine.
(e) Around 1990, BMW went to a BLACK coil, the Bosch number on the coil is 0 221 500 203. These have a low primary
resistance, ~0.5 ohm, and the module was changed to handle the increased current and with some internal changes to shorten what is called the time-out period. The lettering on the module was changed to turquoise or pink. Not a great idea to use the old module with this coil, but has been done.

EDIT:

What coil are you replacing...grey or black?

EDIT 2:

To confuse the isue this is what Euromoto Electric sells for all post 80s bikes :
http://www.euromotoelectrics.com/produc ... l-r426.htm

[Jean]

So you see that Snowbum has the same warning. Since you have an "89 bike, you MIGHT have the newer parts, in which case the low primary resistance in the replacement coil is OK. If you happen to have the other older parts, the low resistance will allow more current and the possibility that the rest of the ignition system can be damaged.
The coil used from 85 on (single) or from 81-84 (2-6V coils like OLD airheads) are interchangable for all practical purposes as their primary resistance is the same since the 2-6volt coils were wired in series giving a TOTAL resistance of 1.4 ohms.
AND just to beat this topic to death, the 6volt coils were built to take a higher current than they are seeing in the series-connected mode, so they don't suffer failures nearly as often or as soon as the "potted" coils.

[Nourish]

Thanks all, I have the later black single coil (0 221 500 2030) so I have replaced it with the tiny PVL coil - its mounting holes are the same distance apart as the original, it fires up OK although I haven't taken it out for a spin as yet. Thanks again