General => Douglas Motorcycles - General Discussion => Topic started by: tck on 17 May 2019 at 13:06

Title: Mk4 sports
Post by: tck on 17 May 2019 at 13:06
I have a 1950 Mk4 sports engine it has a rev counter housing on the front and two flange fitting carburetors
It was dispatched originally to Mcandless in NI (the feather bed guys)
I must admit I think I knew there must have been a MK4 before the Mk5 (and a 1-2-3?) but it is rarely mentioned anywhere and the designation 'sports' is new to me
What was different in the Mk4 sports engine from the T35 or the Mk5 and was there ever a MK4 non sports? or was the 'sports' a forerunner of the 80 or 90 plus?
Title: Re: Mk4 sports
Post by: eddie on 19 May 2019 at 11:08
       The postwar series started with the T35 (it never assumed the title 'Mk1' until later versions appeared). Concurrent with the T35, Mr Douglas was experimenting with other models, including one with shaft drive - but nothing became of them. Somehow, a Mark 2 never reached the marketplace - the T35 being replaced by the Mark 3 and it's sportier sibling - the Mark 3 Sports, this being given another 3 BHP by fitting the sports cam (stamped with an 'S')(the standard cam was stamped 'T' for touring). Both the touring and sports models continued into 1950 being labelled Mark 4 and Mark 4 Sports. Later in 1950, the sports version was dropped when the bikes developed into the Mark 5's. In the period spanning late Mark 3 production to the early Mark 5's, Douglas were also producing the even sportier 80 & 90Plus models. Early development of the Plus series was not without it's problems and on a Mark 3 Sports, Don Chapman beat the 'Pluses' to win the 1950 350 Clubman's race at Silverstone.

  Hope this helps,
Title: Re: Mk4 sports
Post by: tck on 21 May 2019 at 07:45
Thats a lot clearer Eddie so basically the camshafts were the main engine difference. I think that the cast iron head finning looks more extensive than on the MK5 and T35 I  I had previously but thats only an impression  the rocker covers are plain and as I say it has a rev counter mounted on the front of the timing chest and flanged horizontal car manifolds carrying larger  amal carbs. The fact that it went to Mcandlass Bros of NI is interesting they were a hot bed of development around 1950. its fitted in a 48 T35 frame