Wildgoose Chase Moto Guzzi

General Category => General Discussion => Topic started by: wymple on June 06, 2015, 08:01:44 PM

Title: I don't know why I can't find an answer
Post by: wymple on June 06, 2015, 08:01:44 PM
I thought this would be easy as a net search. What is the resistance on stock coils for a 1984 Cal II ?  I can't get an answer anywhere after searching forever. All I get is that I need a certain resistance for this or that aftermarket Dyna.
Title: Re: I don't know why I can't find an answer
Post by: Antietam Classic Cycle on June 06, 2015, 08:18:46 PM
3 ohms.
Title: Re: I don't know why I can't find an answer
Post by: wymple on June 06, 2015, 08:24:56 PM
Thank you! We found our Dyna S coils on the V65C to be defective, getting hot and running ratty, just as the boys were set to head off to Canada this morning. So I swiped the coils off the Cal II & strapped them on, which straightened everything out, so off they went. But I couldn't say they were in the proper ohms range. They are.
Title: Re: I don't know why I can't find an answer
Post by: centauro on June 07, 2015, 07:08:03 AM
So, why is it that the original Marelli coils of that era did just fine at the proper 3 ohm resistance, while  Dynatek recommends 5 ohms type coils?
One of my 3-Ohm Dyna coils cracked open some years ago, and now I have the 5-ohms type, but they actually measure at 5.8 OHms. What is the optimum primary resistance?
Title: Re: I don't know why I can't find an answer
Post by: Triple Jim on June 07, 2015, 08:26:43 AM
So, why is it that the original Marelli coils of that era did just fine at the proper 3 ohm resistance, while  Dynatek recommends 5 ohms type coils?

It's likely that the oil filled, metal housed originals dissipate heat better then the solid epoxy potted Dynatek coils.

Quote
One of my 3-Ohm Dyna coils cracked open some years ago, and now I have the 5-ohms type, but they actually measure at 5.8 OHms. What is the optimum primary resistance?

It's a tradeoff.  Lower resistance can give a hotter spark (depends on coil design), more current consumption, and depending on the system design, possibly more points wear.  Higher resistance gives lower current consumption, lower coil temperature, and again, depending on design, possibly weaker spark.

When I ran Dynatek 3Ω coils in my Mille, I didn't like their high temperature and the reports of failures, so I put 1Ω resistors in series with their primaries.  It sounds strange, but that reduces coil heating to slightly more than half the original amount, with little change in spark intensity.
Title: Re: I don't know why I can't find an answer
Post by: wymple on June 07, 2015, 08:35:00 PM
The Cal II has had the electronic Dyna S on it for at least 10 years, with the stock coils, 3 ohms. It was a set of Dyna's green coils that puked. I have heard that Dyna no longer recommends them for extended street use. I just ordered some Beru 3 ohm coils and am going to try them. I've heard good things on those, we'll see.