General => Douglas Motorcycles - General Discussion => Topic started by: Dawn on 25 Nov 2010 at 07:39

Title: Dragonfly info
Post by: Dawn on 25 Nov 2010 at 07:39

I'm asking the following question on behalf of one of my section members who raised this question at the last meeting.

I have heard tales of a Lucas distributor that can be adapted to fit a Dragonfly. 

Does anyone have any knowledge of this mod?  Please advise.

Many thanks

Title: Re: Dragonfly info
Post by: eddie on 25 Nov 2010 at 11:56
Hi Dawn,
               I have never heard of a Lucas distributor being used on a Dragonfly. Most of the common Lucas distributors turn clockwise (looking at the points plate) whereas a Dragonfly turns anticlockwise, so the auto advance probably wont work - and if it did, it would actually auto retard!!
      Probably, the best solution to the Miller problems is to have a new distributor body machined up that will take a Lucas points plate. You can then use a twin points set up (as on a Norton Commando, etc.) firing twin coils if you intend to retain the 6 volt system - or just substitute a Boyer pickup assy if you want to go down the electronic route and convert to 12 volt. With the electronic setup, the advance is built into the electronics, so a fixed cam can be used. If sticking with the 6 volt points system, the main spindle will have to incorporate an advance system.
     Back in the 80's, I converted my Dragonfly to twin points and coils (still on 6 volt) using the original Miller advance bobweights attached to a custom drive shaft that runs on 2 needle roller bearings. the points cam is a copy of the profile used on a Tiger Cub, but modified to suit the new shaft. The twin points plate is from a unit Triumph which should run clockwise but seems quite happy running anticlockwise! This setup runs quite happily for in excess of 15,000 miles at a time without any attention to the points - however, I have mounted the condensers on the ignition coils where they get a good blast of fresh air (I'm convinced they get cooked in their original position under the engine cover).
     There is another option - to use a twin output coil and do away with the HT side of the distributor - but beware, these coils don't have 2 windings - they are wound with an HT lead on each end of the secondary winding, so they rely on having a full circuit from one plug to the other to operate - if there is a fault on one cylinder, it could cause both to cease operating!
      Hope this is of some help,
Title: Re: Dragonfly info
Post by: MRD on 25 Nov 2010 at 14:54
Hi Dawn
I have done similar to that on Eddies last paragraph. Mine runs with 12v using the original distributor and points but with the LV going to two six volt coils.
This means that both coils produce HT every time the points are triggered. It also means that this methood has a wasted spark on the opposite cylinder.
As Eddie stated it does do away with the troublesome HT cap on the top of the distributor, which means it is now only a dust cover
Regards       Martin