500cc Dragonfly?

[Les T]

Hello,

I've recently added a single seat Steib sidecar to my Dragonfly and I'm having a rear wheel sprocket made with more teeth to lower the gearing to help haul the sidecar, but I've also been informed that it is possible to fit barrels and pistons from another manufacturer that do not require too much modification to fit (it was about 2 years ago that I was told about it and I can't remember which make and model was mentioned), which increases the cc to 500 or slightly more which will give a bit more power which would also help.

Has anyone any information about this? I have a spare crank and cases to work on so the bike would not be off the road while a modified engine was being built up. Any information anyone can give would be very much appreciated.

Les T

[eddie]

Hi Les,
           The '500' barrels you refer to were produced many years ago by a couple of LDMCC members. From memory, I think they actually increased the capacity to 475cc. The barrels were cast iron (like the 350 barrels) and required the crankcase mouths to be opened out to take them. I believe that Triumph thunderbird pistons were used with them (about 71mm bore). The whole set up replicated the bore and stroke of the 1952 factory 500 prototype.
   A couple of years ago, I was talking to one of lads who had the barrels made and he said that all were sold - so, I guess the only chance of getting a pair is if someone is just sitting on them intending to get round to doing the conversion one day!
   Regards,
                 Eddie.

[Les T]

Thanks for the reply Eddie,

I knew about the prototype 500 and the one off batch of barrels later made, but what I remember from the conversation I had with a Douglas enthusiast a couple of years ago was that a modern manufacturer's barrels and pistons could be adapted to fit on to the crankcases by machining out a bit of metal to make the skirts of the barrels fit into the crankcases, I presume the 4 bolt holes matched those of the Dragonfly as apart from turning up new little end bushes that was all that was needed to be done to make them fit. What I can't remember is the make and model of the barrels that were discussed, my memory isn't what it used to be! The info' about the Triumph pistons may be of help if I can't progress any further with the other barrels as I suppose I could get Dragonfly barrels turned out, also the crankcase mouths and then the barrels sleeved to take the Triumph pistons.

Regards  Les T

[eddie]

Les,
       The standard barrels are not thick enough to bore out for 500cc. The '500' barrels had the pattern altered to leave more meat around the bore, thus enclosing the 4 barrel studs.
  There is one full 500 Dragonfly around, but that is very much modified - including stiffened crankcases, a stroked crank and special cams.
 Regards,
              Eddie.

[Les T]

Thanks Eddie,

I'll have to give it a good dose of looking at and see if I can come up with an alternative plan

Les T

[tck]

Although we raced and spent a lot of time with George Easton when we vied for top placing inn the pre 49 class with my son Ben on his Vincent Comet I never got round to asking him how he made his 500 T35 I know I saw the inside of one side at the Grossglockner hill climb a few years ago (don't ask how) and amongst the mangled remains was a serious webbed conrod