Author Topic: Post-war Mark Series - Frames Failure and Repairs  (Read 13167 times)

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Offline alwyn

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Post-war Mark Series - Frames Failure and Repairs
« on: 19 May 2008 at 02:10 »
Frames Failure and Repairs - Douglas Mark Series.

It is generally well known that a manufacturing fault occurred during the production of frames for the Post-War Mark Series Douglas which lead to the replacement of many frames by Douglas Motor Cycles Limited under warranty provisions.

Australian distributors of Douglas acting on behalf of Douglas Motorcycles Limited repaired many frames of the bikes imported to the country during this period. Presumably this also occurred in other countries about the world to where the bikes were exported. Factory made replacement frames were provided under warranty provisions to the home market in the UK.

Many non-factory repairs have been carried out by owners and restorers since those times with varying degrees of success. It is therefore not at all uncommon to find a Mark Series bike otherwise seemingly in top condition but in need of frame repair as an initial step in restoration.

Owners are well advised to keep a weathered eye on their bikes for signs of any movement in the frames during use as obvious danger to life and limb are ever present. Periodic inspections are recommended.

Breaks can occur in any tube frame member at any location but most commonly they occur at points where working stresses are most concentrated such as the forward and rear ends of the bottom horizontal tubes (which take the direct and indirect loads and torgue forces of the engine) and often at the top and bottom of the forward downtubes, particularly near the headstock connections.

The fractures in the frame tubes occur mostly near or immediately adjacent to the cast steel lugs (or knuckles) that occur at the frame intersections.

Although written essentially as a narrative about repair of the frame of my own 1948 T35 carried out late in 2006 and not intended as a 'Technical Article', the document has been deemed appropriate to this Board where it will be readily accessible and more easily located by those seeking advice about frame breakage and repairs.

There have been several discussions and accounts of repairs undertaken that have been published within this forum. The more prominent of these have been linked to the Article for convenience of reference.

...take this link to download the HTML version of  The Article, to be viewed and read in your favourite browser. 

Alwyn
« Last Edit: 19 May 2008 at 08:34 by alwyn »
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Offline Brian

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Re: Post-war Mark Series - Frames Failure and Repairs
« Reply #1 on: 19 May 2008 at 07:50 »
A bit more than an "article" methinks.A most professional step by step instruction, with such clear illustrations.
A real share and tell piece. I hope I never need to use it,but no doubt someone will. Long live the Forum.

Best Wishes to all.
Brian

Offline richson

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Re: Post-war Mark Series - Frames Failure and Repairs
« Reply #2 on: 20 May 2008 at 00:44 »
Thanks for this Alwyn, this is information that I am in need of as recently posted. I was about to effect a very different solution but this has made me think again.

Cheers, Neil

Offline alexburger

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Re: Post-war Mark Series - Frames Failure and Repairs
« Reply #3 on: 30 Oct 2012 at 07:12 »
Hi Alwyn,
Your article about repairing the T35 frame is very relevant to my current situation. With professional help I'm getting my T35 frame straightened and repaired. In particular breaks at the front of both bottom tubes and one of the joins to the steering head are being repaired. The frame has been welded previously and the cast steel lugs are quite damaged. Whilst it is feasible that the lugs could be built up with weld and machined back to their approximate original shape I'm wondering if these lugs are available for purchase anywhere. At this stage one of the tubes has been removed from the frame. I'm planning to replace both with the chromoly tubes.
I'm new to this on-line forum and in the early stages of my re-build so would appreciate any advice about frame repairs.
Cheers
Alex

« Last Edit: 13 Feb 2013 at 03:42 by Dave »

Offline eddie

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Re: Post-war Mark Series - Frames Failure and Repairs
« Reply #4 on: 30 Oct 2012 at 08:39 »
Alex,
         I have seen frames with different section bottom tubes, so I guess the early T35 frames had the thinner section bottom tubes, but with the onset of the frame breakages, Mr Douglas increased the wall thickness to about 1/8" (the thickest that would still accommodate the torsion bars). This overcame most of the problems with the bottom tubes - the remaining problems occur due to lack of lubrication of the swinging arm pivot - mainly due to the pivot pins being drilled right through, so that pumping grease in just pushes out the core plugs.
    Problems with breakages close to the steering head lug are the result of another design fault. In an attempt to strengthen the tubes, Mr Douglas fitted reinforcing sleeves inside the downtubes - these sleeves had blank ends (presumably to assist with pressing them in) which concentrated the stress at the end of the sleeve (note that the breakages usually occur about 1" from the lug). When I built my replica Comp frame (back in '78), I fitted open ended sleeves that had the lower ends taper bored in an attempt to spread the stresses. This frame was used competitively (or as competitively as you can get with a Comp!!) for over 25 years without any signs of the expected problems - not even enough flexing to crack the cellulose paint finish!
     Hope this is of some help,
     Regards,
                   Eddie.

Offline alexburger

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Re: Post-war Mark Series - Frames Failure and Repairs
« Reply #5 on: 31 Oct 2012 at 05:19 »
Thanks Eddie,
I appreciate you sharing your knowledge.
Cheers
Alex