Author Topic: Douglas with double pipes...  (Read 6128 times)

0 Members and 1 Guest are viewing this topic.

Offline C-Petteri

  • Member
  • *
  • Join Date: Dec 2006
  • Posts: 2
Douglas with double pipes...
« on: 26 Dec 2006 at 08:08 »
Can anyone shed a light to what are these strange "exhaust pipes", coming out from the intake side of the sylinders:



Larger view

Just out of curiosity. I have an Ural boxer myself, and maybe I could add something similar to it if it makes sense... (probably not  :D)

Regards,
From Finland
« Last Edit: 27 Dec 2006 at 00:39 by alwyn »

Offline Chris

  • Master Member
  • ****
  • Join Date: Jun 2004
  • Posts: 500
  • Location: Kent, UK.
Re: Douglas with double pipes...
« Reply #1 on: 26 Dec 2006 at 21:42 »
This is a 90 plus special built by Neville Heath some years ago. The project was started by another person and it had never worked. The engine had been modified to use ,I believe, a rotary valve system. Neville worked out what the inventor had intended and modified the basic concept until he got it working. Lubrication was a major problem and hence the additional oil pipes that can be seen at each rocker cover. The subject was written up quite extensively in New Conrod, the journal of the London Douglas Motorcycle Club, some years ago and no doubt Doug. will be able to lay his hands on it and expand upon my limited explanation above. Chris.

Offline Doug

  • Global Moderator
  • ****
  • Join Date: Mar 2004
  • Posts: 3610
  • Location: Pennsylvania, USA
Re: Douglas with double pipes...
« Reply #2 on: 27 Dec 2006 at 06:43 »
I'll look up the NCR issue reference later (I wish the NCR was indexed!) But a brief description for now:

The engine draws the mixture into the crankcase, then uses the crankcase pressure to 'blow' the mixture via the rotary valves into the cylinders. There are three rotary valves, one on top of the crankcase where the mag originally sat to distribute the mixture to the right or left cylinder, and another rotary valve directly connected to each of the the cylinders. Both original poppet valves are exhausts.

I can not remember if it is set up as a two-stroke or a four-stroke without checking the article. I think the latter, and the gain from using both pistons to charge one cylinder (super charging in effect), is offset by the tortuous route the mixture has to take to get there! There might not be enough pumping effect to set it up as a two-stroke. There seemed to be no performace gain, if anything it was down a bit on power. An interesting idea, and an engineering challenge to sort out the problems and get it to actually run, but not terribly practical.

Quote
Just out of curiosity. I have an Ural boxer myself, and maybe I could add something similar...
Only if you really despised it!  :lol:

-Doug

Offline C-Petteri

  • Member
  • *
  • Join Date: Dec 2006
  • Posts: 2
Re: Douglas with double pipes...
« Reply #3 on: 27 Dec 2006 at 12:39 »
Yep, yep. Looks like someone has really known what he has been doing :D

So, is it a 2- or 4-stroke engine ? If it takes all the juice first to the crankcase, then it sounds like it´s a 2-stroke. But, but... what a minute. Maybe I have to think about this for awhile before I start to work with my Ural.  8)

Offline KiwiJohn

  • Senior Member
  • ***
  • Join Date: May 2004
  • Posts: 163
Re: Douglas with double pipes...
« Reply #4 on: 28 Dec 2006 at 19:15 »
Hmmm, lets think a little.... pistons move inwards once per revolution and a rotary valve was required to direct the mixture to one or the other cylinder.  If it was 2 stroke this valve would not have been necessary as both cyclinders would be charging at the same time so a simple reed valve would have sufficed.  I think it is likely a 4 stroke.

 

motorcycle