Wyvern Engine

[Dave CParticipant @davec87625]

Hi all, Would anybody be able to offer any experience / knowledge or advice regarding the Wyvern Engine.

I have never built this kind of engine before and so it will be a learning curve regarding electrics / ignition etc. I was interested in a redwing hit and miss engine but the wyvern appears to be considerably cheaper.

Due to health issues I now how limited dexterity and so smaller engines such as Stuarts are far too fiddly for me.

I have just completed a PM research 6CI engine which I found very enjoyable and a good size for me to handle now.

Any experience or advice would be very much appreciated. I am not short of equipment of any kind just energy and slight loss of dexterity.

Many thanks

Dave C

[Roderick JenkinsParticipant @roderickjenkins93242]

I don’t think there is anything particularly difficult about the Wyvern.  3 points you might like to consider come to mind:

Wyvern was designed to made in cast iron but the Hemingway castings, apart from the fly wheels, are aluminium.  The design for the exhaust valve seats directly in the casting which most builders seem to think isn’t a good idea in aluminium so use an insert similar to the inlet valve.

You might want to consider using an O ring rather than cast iron piston rings for better compression.

Cheap and readily available ball bearings can be used for the cam followers.

HTH,

Rod

Edit P.S.  ETW’s design calls for 2:1 skew gears of the same diameter.  These are not easy to come by and, I believe, Hemingway supply 45 degree gears of different diameters which don’t fit in with the design as drawn.

[DurhambuilderParticipant @durhambuilder]

I’m 95% of the way through a Wyvern, it’s been quite tricky and there are a few errors in the drawings which you can find in the drawing error section of this forum. Having also built a Jerry Howell Farmboy I would say that this a significantly more straight forward Engine to build and also in my opinion a much more interesting engine to run with the simple hit and miss governor. Andrew Whale has done an excellent video series on YouTube for the farmboy. Swap all the American unc / unf fixings for the nearest equivalent metric ones, much much cheaper and huge availability of heads and lengths etc.

[JasonBModerator @jasonb]

Compared to a #6CI even a Wyvern will have a lot of small parts. The valves, carb and governor if fitted are on a par with typical Stuart 10 type size parts. I’ve just done what would effectively be a half scale #6 so know it is quite a chunky engine.

This is probably true of a lot of other open crank designs of around the 1 -1 1/2″ bore size range.

The original Westbury build series for the Wyvern can be found online, have a look through that and see if you feel happy with some of the small parts.

 

[MichaelRParticipant @michaelr]

Rod mentioned in his post about the valve seats for the Wyvern, I modified the cylinder head valve arrangement by using valve pockets and making the exhaust valve the same as the inlet valve.

Hope the pictures help.

[Dave CParticipant @davec87625]

Thank you all for taking the time to reply, I am very grateful for all the advice. It looks like I have some more thinking to do before taking the plunge. Maybe back to the redwing consideration would be a better if not more expensive option.

I would be interested in any other options for similar larger sized models for consideration. The PM research just completed comes in at 18 inches long x 8 high and 8 wide. I think this will be my maximum manageable to be honest. I have sadly had to stop my 3″ scale Maclaren traction engine build which is possibly 50% complete due to the weight issues.

many thanks again to all, Much appreciated.

Dave C

 

[MichaelRParticipant @michaelr]

Dave, Build thread on forum for Redwing may give you a idea what’s involved.

https://www.model-engineer.co.uk/forums/topic/building-1-4scale-redwing-hit-and-miss-engine/

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