Author Topic: Douglas Dragonfly Blowing A Head Gasket  (Read 2794 times)

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Offline Spash

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Douglas Dragonfly Blowing A Head Gasket
« on: 29 Oct 2013 at 17:56 »
Hello all,

I am very, very new to all of this so please be patient if I ask a stupid question.  My wife is looking to buy a Douglas Dragonfly and has seen one that she likes however we have been told that the engine and bike have been totally restored however the bike has blown a head gasket.  It has been replaced but has blown again.  I have been offered a discount on the bike but I would like to know how big a job this is to pin point the problem (as it has happened twice) and how expensive would it be to fix?  Are there any good companies out there that specialise in these sorts of things?

We are both classic scooter riders and know nothing about bikes so any help would be appreciated.  I don't want to buy something that then becomes a mill stone around our necks (if that makes sense).

Cheers for the help.

Offline eddie

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Re: Douglas Dragonfly Blowing A Head Gasket
« Reply #1 on: 29 Oct 2013 at 19:47 »
Spash,
            Problems with blown head gaskets on postwar Douglases seem to be more common now we are forced to use non-asbestos gaskets. Having said that, there are also a couple of other factors that may contribute to this problem. Firstly, the head studs would benefit from a couple more threads to prevent the nuts going down thread bound on the studs. Also, there is not much room for the spanner - on my Dragonfly, I have used 5/16" nuts opened out to 3/8" so that I can get a ring spanner on the smaller hexagon. Some owners have also found that head gaskets blow after having the heads and barrels powder coated - I have put this down to the coating squeezing out from under the nuts when it gets hot, thus easing the clamping pressure. Regular checking is a must!
   If you do decide to buy the bike, replacement of the gasket is a straight forward task that shouldn't cause the average owner too many problems.
  Also, if we knew your location, there may be a fellow owner in the vicinity who could give some practical help!
  Regards,
               Eddie.

Offline Spash

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Re: Douglas Dragonfly Blowing A Head Gasket
« Reply #2 on: 29 Oct 2013 at 21:11 »
Hello Eddie,

Thanks for the reply. I am in the Worcester area so if anyone is local that would help. If it something as basic as you say then I would have thought it wouldn't be too costly to fix.

Are there any classic bike specialists in the Midlands that I could take the bike to so they can give it the once over?

Cheers

Spash

Offline David Lawrence

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Re: Douglas Dragonfly Blowing A Head Gasket
« Reply #3 on: 31 Oct 2013 at 22:38 »
Hi Spash,
Just a short addition to Eddies advice, he is quite correct replacing the head gasket is a simple enough task and has often been carried out by the roadside, even in time to continue a timed road trial! Beware two of the head nuts are hidden in counterbored holes beneath the rocker blocks, also there is a 1/4 bsf nut at the bottom of the pushrod tunnel. All his comments are correct, although the Club spares now has obtained a new supply of head gaskets with wire reinforcing, unfortunatly not with the asbestos content but we have had reports that these are much improved over those previously available. Not expensive costing just a few pounds each, only point to be aware of is the fact that The London Douglas Club only supplies Club members, however, as the subs are only 18 a year it is well worth joining for the advice, the Club magazine as well as the spares.
If you are interested the Club website is www.douglasmcc.co.uk where you will find all the details of how to join.
I am sure that someone in your area will be in contact.
Dave



[correct price of LDMCC subscription. Doug, Site Moderator, 01Nov13]
« Last Edit: 01 Nov 2013 at 14:32 by Doug »

Offline Spash

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Re: Douglas Dragonfly Blowing A Head Gasket
« Reply #4 on: 20 Nov 2013 at 13:13 »
Hello all,

Well my wife has bought the Douglas dragonfly!  It needs some work doing to it so that should keep my busy over the coming months.  I sent off the bike details yesterday so I can register to the club and hopefully I should be able to get the OK to join the Douglas Club and start getting it back on the road.

Regards

Spash