Coils with Dyna iii

[Stu]

Hi all. Working on a T3 and have bought an unused Dyna iii system. My bike is currently using stock points and coils. Coils are grubby looking Marellis which i assume are 76 vintage. I'm struggling to get a clean reading of the primary resistance but looks like about 4 ohms. Could be 3 plus dirty terminals!

The obvious thing to do is buy a pair of 5 ohm Dyna coils, but I don't want to... they are expensive (in UK) and are not plug and play, needing a bracket made and probably relocating to the left sidecover area. My other options are keep the originals, or buy Lucas (cheap, probably Asian built), PVL (more expensive but German) or other options from local Guzzi emporiums (more expensive and unknown provenance).

I've been digging a bit and it seems people have had problems with original coils and Dyna... although the Dyna instructions say it's designed for use with original coils. Part of me wants to put shiny new ones on with my new ignition and my other side wants to leave well alone.

Thoughts and experiences?

[moto-uno]

  You should find that if you contact Dyna directly , that they will suggest 5 ohm coils , period . Yes they'll certainly
  work with the originals , But ! That's over 50% more current draw and in time it tends to take it's toll . You might
  find quite a few old Japanese ignition coils at a bike wreckers that are 5 ohm and cheap enough , just something
  to consider  . Peter

[Frenchfrog]

Maybe you are seeing a problem when there isn't one ? From what you are saying I'm assuming that you have not tried the dyna and the coils together yet so that could just be a bad assumption ! I use the standard ones which I think are Ducati electronica....othe r wise I'd go with the PVL's without blinking an eyelid and if I go twin plug I'll be fitting those for sure.

[guzzisteve]

I have used stock coils forever or at least untill the stock ones crap out, 2 bikes of my own then got the 3 OHM Green ones. Customer bikes got same stuff and still on the road 30yrs later. I have had a few 3 OHM Dyna's crack & go bad. I have not used the black 5 OHM ones yet.

[not-fishing]

I'm using the 5 ohm Dyna with my upgrade V65 and V50.   It worked great on the V50.

My real mistake is not using the Dyna spark plug wires but I have to time he V65 resto-mod before I can say.

[ozarquebus]

Has anyone successfully used the cheap VW coils?

[moto-uno]

 ^   Could you be a bit more specific about which coils ? The major concern here has to do with the primary resistance . Peter

[groundhog105]

Get the dyna 5 ohm coils and be done with it.  I had the dyna 3 with the stock coils on my Lemans and chased a poor running, motor dying problem for a year until I finally gingered out one of the coils had gone bad.  Put on the dyna coils and a great bike is back in action.  Further research found that the stock coils will overheat and go tits up with the dyna ignition. I think I paid $125.00 USD for my pair of 5ohm coils from eBay.

[wirespokes]

Stu - The T3 came with 3 ohm coils. I had a 77 T3 that came to me with 3 ohm coils and a Dyna ignition. Was running fine when it was sold six months ago. I have an 87 LeMans with a Dyna and 3 ohm Dyna coils. Came to me that way and still rinning fine 20K late.

I wouldn't worry about it. Supposedly these ignitions won't produce a hotter spark with a hotter coil - and a 5 ohm works well. But then again, the bikes did come with 3 ohm coils. I've had Dyna ignitions on Airhead beemers running 5 ohm coils and they did just fine. They run one coil per cylinder just like the Guzzis.

VW Bosch coils are very good, however they're also very large.

The big thing is to never leave the ignition on when the engine isn't running. The coils will pass electricity, overheat and crack. Since the stock coils are 3 ohms I don't see why the Dyna would cause them to fail while 3 ohm Dyna coils work just fine.

[Stu]

Thanks, all, for your replies so far.

^   Could you be a bit more specific about which coils ? The major concern here has to do with the primary resistance . Peter

Lucas: https://www.feked.com/genuine-lucas-12v-ignition-coil-12-volt-lu47276.html (says 5 ohm here, but I've seen lower numbers elsewhere)
PVL: https://www.rexs-speedshop.com/product/pvl-12-volt-ht-coil-220601/ (4.0 ohms)
Alucoil: https://www.stein-dinse.biz/product_info.php?products_id=815#prettyPhoto (4.1 ohms?)
Dyna (best local deal I can find - 15% off!) £145 for pair delivered direct from Dynatek UK. Not much cheaper to import from US with postage and customs, and difficult return route if I have problems.

Main reason I don't want to use Dyna other than cost is that I don't have facility to make a nice bracket for them and they don't fit where the current ones are under the front end of the tank. And I don't really see the point of using expensive, high performance coils on a low compression, touring lump. 

[Triple Jim]

You can add a series resistor to each coil primary of the 3 ohm coils.  You need to add only 1 ohm, even though you'd think it would be 2 ohms. I posted about this five years ago:

"I decided that adding 1 ohm was better.  With an external resistor, some heat is generated that's outside the coil itself, rather than it all being inside.  If you work out the numbers, the heating of a 3 ohm coil with a 1 ohm resistor in the primary circuit is about 1/2 of what it is without the resistor, which is slightly better (cooler) than the 5 ohm coil with no resistor."

The 1 ohm resistors would have to dissipate 12 watts if they were on all the time, but they're not, so 10 watt resistors would be fine.  Higher power ratings are fine too, of course.

[redrider90]

Really interesting comment by Jim about 3 ohm coils with an external 1 ohm runs cooler than a 5 ohm without an external resistor.
Seeing that I have "burned" through 2 sets (that means 4 coils not a typo) of Dyna Green (3 ohm) coils in 30K miles I gotta think that adding the resistance Jim mentions
might be a help.

[bigbikerrick]

Get the dyna 5 ohm coils and be done with it.  I had the dyna 3 with the stock coils on my Lemans and chased a poor running, motor dying problem for a year until I finally gingered out one of the coils had gone bad.  Put on the dyna coils and a great bike is back in action.  Further research found that the stock coils will overheat and go tits up with the dyna ignition. I think I paid $125.00 USD for my pair of 5ohm coils from eBay.

The above was my experience exactly with my LeMans IV. I dicked around for over a year with an intermittent running issue, that was resolved 100% by adding Dyna 5 ohm black coils. I was always messing with the carbs, trying to solve my ignition issue!
Rick.

[Triple Jim]

I was always messing with the carbs, trying to solve my ignition issue!

They do say that 90% of ignition problems are the fault of carburetion, and 90% of carburetor problems are the fault of ignition.

[Testarossa]

This is true:

They do say that 90% of ignition problems are the fault of carburetion, and 90% of carburetor problems are the fault of ignition.

Dithering about coil resistance is worth the brain damage. Nominal 3ohm coils usually measure 3.3ohms, and nominal 5ohm coils are really 4.7ohms. So there's really only 1.4 ohm difference -- about 30%.

My T is still running the 3.3ohm Bosch blue coils installed at the factory in 1974, the last 15 years on a Dyna iii. I converted the Mille to Dyna this summer and kept the original coils. So far it's running fine.

Dave Richardson says all Guzzi coils up to 1993 have 3ohm coils. He points out that Dyna recommends replacement coils fall within 10% of that value -- but also says Dyna confuses the issue by telling us to use 5ohm coils with breaker points. But Guzzi points are designed for 3ohm coils. Richardson says 5ohms is excessive.

He also says that Dyna makes brackets for Japanese bikes and BMWs, and putting Dyna coils on a Guzzi is a royal PIA. On the other hand, Dyna iginitions are his favorite. See Chapter 6 of Guzziology for the full discussion.

If you don't power the ignition circuit without the engine running, of course coils (and other components) may overheat. Don't do that.

[Stu]

Thanks everyone for your input.

I cleaned up the terminals on my coils today and measured them. Clean reading of 4.0 ohms on each coil. I'm going to fit the Dyna to the existing coils and see how it goes.

If and when they give trouble I'll think about it again.

[moto-uno]

  The less current one passes through ignition points the longer they last , higher primary resistance , longer (potential) life . Peter
Good luck and many happy miles with your new Dyna ignition .