Bosch "Blue" Coils

[Red_Hen]

Greetings & Warmest Wishes for Happy Holidays & a Happy New Year!

Wondering if upgrading OEM coils on the R60/5 will show any better starting/performance?  I haven't much time on her but the few times I rode her, she started up pretty effortlessly.

But I've got the tank off and have replaced the Spark plug wires & caps.  See that Euromoto sells a new pair for under $100 but the only disappointment is they're not blue  I guess I'll get over it.

I'm assuming the coils are okay just wanting to freshen things up.

Thoughts?

[Bob_Roller]

You can always paint them !!!!!

[montmil]

If it ain't broke, don't fix it. Clean them if you wish, but then you'll notice how dull the relays are looking. And, gosh, that voltage regulator is also kinda scruffy what with those faded plastic wire connector blocks and all. Remember, Ken... No good deed goes unpunished.

BTW... There have been a few reports -on other sites- of counterfeit "blue" Bosch coils masquerading as OEM parts. Your Bosch coils are almost bulletproof. Buff up the terminals and Charlie Mike.

[Barry]

Ken

I'd have to do some digging to find you the evidence but I recall that the superiority of Bosch blue coils over the standard Bosch Black coils  is largely a myth. Bosch Black coils are no longer available so if your stock coils are still sound I'd be reluctant to change them for what might not be genuine Bosch Blues. As Monte said there are several different ones made in different parts of the world and who knows what the specs are. This is an area of interest for me so I'll go dig.

If I really did need new coils or want a better spark I'd pick a Dyna Green coil for good performance and a bit of weight saving. Then I'd fit a points amplifier.

[Barry]

As far as I can make out both Bosch Black and Bosch Blue coils have the same primary resistance but the Blue has a higher secondary resistance. The Bosch Blue coils is capable of 17.5KV output while the Black coil can only mange 13.5KV. That sounds like the Blue should be better but in practice if the plugs don't need 17.5KV to fire (and normally they don't as the voltage is determined by the plug gap) there is no benefit and possibly a disadvantage as the Black coil should have a higher spark current. You don't get something for nothing. When being switched by points both coils are limited to under 4 amps primary current so they must have similar energy input and in the end you can only get out as much energy as you put in.

Efficient design of a coil is important but in simple terms there are only 2 ways to get a stronger spark.

1. Increase the primary current - points ignition is already on the limit in this respect.
 
2. Switch the primary current cleaner and faster. A points amplifier may be an improvement particularly at idle/low revs. I believe it is but don't have the scientific evidence to back that up.


Full blown electronic ignition does both. It switches a higher primary current (for post 81 electronic ignition the current is doubled) and it switches it faster.

Going back to the original question and the comments about starting effortlessly.  If a points bike starts effortlessly then the spark must be plenty good enough when it's running because during cranking the spark is at it's very weakest due to low battery voltage (= low primary current) and relatively slow switching by the points.



Here a link to some opinions and comparative tests done on various coils. It's a bit heavy going so I'll summarise it by saying the Bosch Blue tested no better than the Black and neither of the Bosch coils were in the same league as the really hot coils tested.  That's to be expected though as they were being compared with high end expensive ignition systems.


http://www.shoptalkforums.com/viewtopic.php?f=15&t=124069&start=0

[Red_Hen]

Thanks guys.

Barry - did you study with Steven Hawkings?  You're brilliant at this electronics business!

Okay - back to orignal plan . . . clean her up and ride away.

[steve hawkins]

I would also add that the Bosch Blues are significantly longer/heavier than the originals,  My 1979 had a pair and they broke the welded mounts on the frame as well as the clamps - they are really too heavy.

I am currently using a BMW K100 dual output coil mounted that I bought second hand from Motorworks.  It did not take much adaption, it is mounted on the front right relay plate - hanging below it.  Worked for years so far.