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General => General Douglas Discussion => Topic started by: Ed Byrne on 24 Dec 2013 at 13:58

Title: What Type of Douglas is this?
Post by: Ed Byrne on 24 Dec 2013 at 13:58

Hello,

Ed Byrne here from Dublin, Ireland.

This Douglas below was raced in Ireland during the 30's and 40's, before getting the "Burt Monroe" treatment over the years. Dispite its looks it was a fearsome sprinter up until the 70's, running on dope.

Can anyone tell me what it might once have been? I know it came from one of the Thorpe brothers who raced and tuned Douglas's pre-war.

All info welcome.


Regards,

Ed

Title: Re: What Type of Douglas is this?
Post by: Doug on 24 Dec 2013 at 23:22

Ed,

It looks to be one of the Thorpe single cam engines. This is a slightly different one than appeared in the 1995 Mar/Apr issue of the New ConRod magazine, in that this has the later valve enclosure patterned upon the JAP ohv engines, and as used on the final Thorpe twin-cam engine. The earlier mentioned engine had Thorpe's alloy heads with slightly down-facing exhaust ports and hairpin valve springs like this, but used the detachable rocker perches from the 1931-35 Douglas ohv models, all exposed. While there was a Thorpe outfit racing from 1936 onward, casting of special heads and barrels date immediately postwar.   

This is not however the Thorpe outfit but a highly modified Dougie (unknown) using a secondhand Thorpe engine. If it was sprinting into the seventies, someone out there will know more details about its history, and who constructed it.

-Doug

Title: Re: What Type of Douglas is this?
Post by: Ed Byrne on 25 Dec 2013 at 08:54

Quote from: Doug on 24 Dec 2013 at 23:22

Ed,

It looks to be one of the Thorpe single cam engines. This is a slightly different one than appeared in the 1995 Mar/Apr issue of the New ConRod magazine, in that this has the later valve enclosure patterned upon the JAP ohv engines, and as used on the final Thorpe twin-cam engine. The earlier mentioned engine had Thorpe's alloy heads with slightly down-facing exhaust ports and hairpin valve springs like this, but used the detachable rocker perches from the 1931-35 Douglas ohv models, all exposed. While there was a Thorpe outfit racing from 1936 onward, casting of special heads and barrels date immediately postwar.   

This is not however the Thorpe outfit but a highly modified Dougie (unknown) using a secondhand Thorpe engine. If it was sprinting into the seventies, someone out there will know more details about its history, and who constructed it.

-Doug

Thanks for the Info, very interesting! The bike is in a shed about 1km from my house. I will ask if i can dig it out and take some more pictures of it.

Have a great Christmas everyone!

Title: Re: What Type of Douglas is this?
Post by: Ed Byrne on 19 Feb 2019 at 16:36

It's still around amazingly!!!

Where could I get more info on the motor? Does another one exist like this That is running?

Title: Re: What Type of Douglas is this?
Post by: Ed Byrne on 14 Mar 2019 at 18:42

Picture 2

Title: Re: What Type of Douglas is this?
Post by: Ed Byrne on 14 Mar 2019 at 18:43

More pics

Title: Re: What Type of Douglas is this?
Post by: Ed Byrne on 14 Mar 2019 at 18:44

Pic three

Title: Re: What Type of Douglas is this?
Post by: Doug on 15 Mar 2019 at 05:20

Here are some pictures of the Thorpe twin-cam cylinder heads. I believe these were the same as used on the later iterations of the Thorpe single-cam.

The have the same angled downward ports (the cylinder on the left is inverted) as the Works 1932 machines had. Unfinished casting on the right. Note the fins around the ports are filled in. These were finished by roughing out with a hacksaw and finishing with a file. For a bit of manual labor it greatly simplified the pattern work; a very pragmatic approach.

(https://www.douglasmotorcycles.net/aa-files/images/doug/2019/thorpe/thorpe-1.jpg)

Here can be seen the JAP inspired rocker gear. Except for the cover plate, it might well be JAP components.

(https://www.douglasmotorcycles.net/aa-files/images/doug/2019/thorpe/thorpe-2.jpg)

And a view propped in place.

(https://www.douglasmotorcycles.net/aa-files/images/doug/2019/thorpe/thorpe-3.jpg)

The cylinder barrel. Alloy with iron liner. The distinctive fin shape is a reconcilable feature.

(https://www.douglasmotorcycles.net/aa-files/images/doug/2019/thorpe/thorpe-4.jpg)

An period photo of the Thorpe single cam outfit in an earlier guise. Here it still has the Douglas valve gear (rocker arms and oil reservoirs recognisable), exposed pushrods, and no sump. The sump and side mounted oil pump looks very much like the style used by the Works on their 1930-33 racing models.

(https://www.douglasmotorcycles.net/aa-files/images/doug/2019/thorpe/thorpe-single-cam.jpg)

-Doug

Title: Re: What Type of Douglas is this?
Post by: cardan on 21 Nov 2020 at 04:09

The story of the bike is here: https://www.douglasmotorcycles.net/index.php?topic=5444.msg33020#msg33020

Leon