Author Topic: My Mk3 Special  (Read 9466 times)

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Offline maverick65

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My Mk3 Special
« on: 16 Jul 2006 at 15:03 »
Hi,

I've had a garage load of Mark bits for years, and always meant to do something with them - well you know how it is. Recently the Club Registrar mailed me with a note saying there was an 'irregularlity' in the records of one of my Douglases, and he inadvertantly gave me the clue that solved a long-standing mystery about what I bought a dozen years ago as a rather tasty Mk1, apparently the only survivor of the three 'Land's End Trial' bikes prepared by the factory in 1948.

But it had no frame number, and there were two rear-subframe mounting points - one pair is the Mk1-type ear lugs, but the other was a pair of drilled bosses at the bottom, where the later MK4/5 sub-frame mounts were located. So I assumed it was a factory replacement frame of around 1949 - one that would do for earlier models as well as later ones.

But now I hear that it is in fact a Mk3 frame, despite the very early  T35/S/308 engine. Obviously, I need to put it back into a genuine Mk1 frame,  along with most of the rest of the original bits - my project for the next few months.

The question was, what to do with the Mk3 frame - that's a hard one, eh? So I rooted around in my workshop and built the frame up to a full bike out of my spares collection - pretty well a new Douglas. And since it's a new bike, I decided to put it together as a Special - after 50 years with standard(ish) Marks, here was the chance I'd always wanted as a lad to make something different and personal. There are several out-and-out Specials in the Club in the UK, so it's not such an outlandish reaction -  this would simply be a late addition to the efforst of a small group of odd-ball engineers and their unusual (or in Neville's case, occasionally rather weird!) machines.

So here she is!

The engine is - at the moment at least - a much modified Mk5 unit that I've been playing with for a few years. The Carbs are Amal Concentric MkIIs - 28mm diameter throats, to replace the tiny 19mm Amals fitted as standard. The inlets are bored 24mm - as large as they can go, with taper-bored aluminium spacers to match them up to the heads. The compression ratio is 9:1 - I shortened the barrels for this - and there is a pair of Suzuki GS650 62mm pistons fitted with 2-3 thou bore clearances. These are much lighter and stronger than the standard Douglas ones, and there is still plenty of room for the valves (even with the No.3 ('almost Plus') cams fitted) despite the valve head cut-out being the 'wrong way round'.

The front brake is a Plus unit that I got, already severely chopped about, from a grass-track racer. Since the Plus fork reaction link is mounted higher than that on the Marks, I've put in a new anchor bolt to keep the link parallel with the swinging arm, and used the original reaction pivot boss to convert the brake to twin - um, twin . . .  er, well, fully floating shoes! This way, there is no nodding motion on the front mudguard whenever the forks move up and down, so the stays don't break on very rough roads any more!

Oh yes - and it DOES stop, too.

Most of the non-standard fittings are in stainless (I HATE RUST!). The wheels are WM2 x 19" front and WM3 X 19" rear (stainless rims and spokes, of course!). Electrics are all 12 volt positive earth (dynamo converted for 12 v output, elctronic regulator). The seat unit/tool box is made from the door of my old fridge - recycling is supposed to be good for us, so I'm told! That tank is a 4 gallon fibreglass job I got at an autojumble for 45 quid - with an interesting hole in the side, since fixed. The Monza filler cap alone is worth the price of the whole tank!

With a rebuilt magneto she starts first time, runs like a turbine up to around 7500 rpm (maybe more, hence the rev. counter that I'm still trying to connect to the motor), and has a performance well into the 'Plus' range. And she's not a thirsty beast either - I get around 90 miles per UK gallon knocking around the district and up to 100 mpg on runs - yes, really! Those carbs make all the difference - got 'em for twenty quid from a breaker who said, "No-one wants them old things now!"

So, if you don't mind the odd Special occasionally, this one's my effort at the breed. Makes a change, anyway . . .

Cheers
Doug



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« Last Edit: 17 Jul 2006 at 01:10 by alwyn »
Doug Cross  Tel *44 1229 885420

Offline trevorp

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Re: My Mk3 Special
« Reply #1 on: 17 Jul 2006 at 09:17 »
Nice looking bike goes and stops and looks good. You would never of got a job at the douglas factory
i must admit if it turns heads and is has douglas on the tank it only raises interst in the marque
Lets call it a mk 6 sports lol

Offline KiwiJohn

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Re: My Mk3 Special
« Reply #2 on: 18 Jul 2006 at 03:26 »
Great looking bike Doug, especially that handy side stand which looks just like the one on my 80+, except mine looks more like a Triumph Herald gear lever. :lol:

Offline maverick65

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Re: My Mk3 Special
« Reply #3 on: 18 Jul 2006 at 07:52 »
Great looking bike Doug, especially that handy side stand which looks just like the one on my 80+, except mine looks more like a Triumph Herald gear lever. :lol:

Yes, I've noticed some postings about Mark sidestands. Here's a close-up of mine, in case anyone else wants to knock one up. It's based on the main lump of one of those awful mild steel clamp-on units - you know, the ones with teeth along the inside to get a better grip of your bottom frame tubes (and even more so of the paintwork!)

The critical feature is that the vertical lug (A) that takes the engine bolt MUST fit really tightly up against the frame under the lug once the engine bolt is tightened. Make it a bit oversize, then bolt up and grind away any excess until it fits but cannot move at all. Depending on what old sidestand you can find, you need to cut away anything that's in the wrong place and maybe then weld a bit of 6-8mm mild steel sheet on to make this new lug.

The leg on the main original lump (B) is cut short and a short length of stainless steel tube (C) brazed onto it. A second, smaller diameter length of tube is mig-welded and profiled  into that, to form the main leg of the stand, with an 8mm steel bolt welded to the side for the lower spring mount. The foot is a couple of bits of scrap stainless sheet, around 8mm thick, welded on and profiled. Stainless tube is MUCH stronger than mild steel - better safe than sorry!

Putting the whole thing together took around three hours, plus final finishing and polishing. Cost - a few pence for the stainless mig wire - the rest came from small off-cuts in the scrap box.



« Last Edit: 18 Jul 2006 at 11:14 by alwyn »
Doug Cross  Tel *44 1229 885420

Offline KiwiJohn

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Re: My Mk3 Special
« Reply #4 on: 18 Jul 2006 at 21:02 »
Nice piece of leg there Doug  :P,  I dont think I should post a close up of my attempt!  I have low exhausts that left me very little room for the mechanism but it eventually fitted in and is basically the same principle as yours.