Wyvern engine help!

[Jim CParticipant @jimc]

Hi all,

I’m looking for some much needed assistance as I come dangerously close to the completion of the build stage ! The areas that I am unsure of are:- 1. Exhaust, any advise on design would be much appreciated. 2. The ignition system, electrics has never been my strong point! so a circuit diagram would be a help together with the necessary components needed. 3. And finally? Fueling the thing, any advise on type of fuel Gas or Petrol? Here’s hoping for some tips from any engine builders out there or indeed anybody with this knowledge. I hope to get this engine finished shortly. Best regards, Jim.

[Jim CParticipant @jimc]

[MichaelRParticipant @michaelr]

Jim. You can do your own thing with the exhaust on the Wyvern, my version shown in the picture, I used a Hall sensor for my ignition by Minimag Link , however you can use points and coil ignition.

I run my Wyvern on petrol, you can use propane but I am not up on that method but it would be worth looking into.

Hope this helps.

MichaelR.

[Nick Clarke 3Participant @nickclarke3]

Jim –

PM sent to you

Nick

[Nigel McBurney 1Participant @nigelmcburney1]

I have a ollection of engines,gas with hot tube ignition,gas or petrol with low tension ignition, petrol engines with HT magneto ignition, petrol engines with low tension ignition. they range from a 3/4 ton National to a Stuart 600. If you require good runnng and starting then go for petrol, Propane gas which is the best substitute for coal gas requires a lot of fiddling to get the engine running ,plus a rubber diaphram old type gas bag/regulator,I have 2 gas Gardeners with hot tube ignition,the gas setting is critical there is no rich or lean running with a gas engine,the mixture must correct.Regarding ignition,the normal type of ignition for the small vintage open crank engine was a battery powered trembler (buzz) coil with a wipe type contact mounted on the side shaft. Stuarts on their 600 (similar in style to the Wyverne) engine used coil and battery and offered at lot extra cost a magneto ,mounting bracket, and 2:1 chain and sprocket drive from the side shaft ,the magneto was geared up to engine speed to improve the spark but of course there was a "dead" spark after two of the four strokes,quite common practice at the time, the Stuart was offered as a gas or petrol engine.The buzz or trembler coil is a Ht coil with an attached pair of contacts,when electricity is supplied to the coil contacts they "buzz"and produce a shower of sparks all the time the electric is switched on,the wipe contact mounted on the sideshaft is simply a rotary switch to supply current to the coil for a short period to fire up the spark plug. The trembler coil has adjustable contacts with a built in condenser and is usually housed in a small wooden box mounted under the engine. The trembler coil is probably the most appropriate style of ignition for the Wyverne, As for fitting a modern system,its up to the owner ,its their engine and they can do what they like,though I feel its like fitting LED lights to an Austin Seven. Replica trembler coils are available.

[Jim CParticipant @jimc]

Thanks for the replies chaps.

Michael R – Thanks for some great photos of you engine, it’s given me some ideas for exhaust and cooling methods. Presumably you exhaust is a steel tube with holes in the blanked off end. Is it willed with some sound deadening material? The ignition system is interesting and so I will have a look at the Minimag and if ok get back to you for some fitting advise ?

Nick Clarke 1 – Thanks, and I have replied to your PM.

Nigel McBurney 1 – Thanks for a great deal I’d good information on ignition systems, the bit about the 2 gas Gardner’s caught my eye as I did my apprenticeship with them in the 70’s but they wasn’t making gas engines then! I will have a look at the trembler coil that you mentioned, it may be the job.

Thanks all again. Jim.

[Henry BrownParticipant @henrybrown95529]

Jim, I have some info that may help you, drop me a message and I'll send it over….

Edited By Henry Brown on 26/05/2020 13:36:58

[JasonBModerator @jasonb]

Another option for fuel is Colmans, you can run it with the same carb as you would for petrol but it doe snot stink the place out, handy if you bring your models indoors after running, Aspen is similar. I tend to use Colmans most of the time.

A vapour tank can also work well with petrol as you don't get flooding issues or have to worry about demand valves like you may need to with propane.

Even the smallest Vietti mag would look a bit oversize on the Wyvern, not really right unless you have a big model.

For simplicity I use modern ignitions boot single spark and buzz type usually tripped by a simple contact though occasionally hall sensor. I have made trembler and low tension coils but its easy to just hook up a modern box with a couple of AA batteries.

[Jim CParticipant @jimc]

Henry, thanks have sent a PM as requested. Jim.

Jason, thanks for the advice, will definitely look into use of gas and trembler ignitions. Cheers Jim.

[MichaelRParticipant @michaelr]

Jim. My exhaust has no sound deadening just the expansion box, sounds not to bad noise wise.

MichaelR

[Jim CParticipant @jimc]

Hi all.

Having sorted out the ignition by using a Hall sensor system and fitting a basic type of exhaust, I made an attempt to run the engine on petrol today with no real success. The carburettor seems now to be the issue. I made the carb to the Westbury drawing but I know that people have had trouble in the past getting this engine to run.

Does anyone know of a more simpler carb that I might try or do I persevere with the Edgar Westbury design and try to fettle that one.

I am very close to getting the engine finished now so I would be grateful of any any advice from Wyvern builders or anybody else who has had carburettor issues. Many thanks in anticipation.

Jim.

[Roderick JenkinsParticipant @roderickjenkins93242]

JIm,

I couldn't get the ETW carb to work on mine. I had great results using the carb I made for the Matador 10cc glow engine. Very flexible running.

I tried to replicate this with a brass copy with the same internal dimensions as the Matador carb.

This runs ok but not as well as the Matador carb. I didn't put an air bleed on the brass version and I think it runs too rich at lower revs – something I intend to put right but I have now developed a leak on the inlet valve so some major work is required.

HTH,

Rod

Edited By Roderick Jenkins on 11/09/2020 19:48:00

[Jim CParticipant @jimc]

Hi Rod. Thanks for replying. Sorry to here you had problems with the original carb. Would you by any chance have some detail drawings of the two you have had success with. It would be a great help. Cheers. Jim.

[Roderick JenkinsParticipant @roderickjenkins93242]

Jim,

I'll send you a personal mail tomorrow.

[Howard LewisParticipant @howardlewis46836]

I produced a quite acceptable exhaust for a motor cycle by drilling two sets of holes, equal in total in cross sectional area to that of the pipe, and separated by a blanking plug. This allowed the gas to pass into a small expansion chamber to by pass the plug and back into the outlet pipe. It sounded quite like a post WW2 motorcycle, so the owner was well pleased.

Another silencer for a single cylinder engine was simply a 2 pint Castrol oil tin clamped by the neck to the end of the exhaust pipe, with a series of holes drilled through the base of the can.

A lot of single cylinder stationary engines seem to exhaust by a short pipe into a smaller version of two frying pans bolted together, with a series of holes drilled around the rim of the base of the outer one.

Stationary engine preservationists will no doubt be able to provide a photo of such a silencer.

For a model engine, the two parts could probably be turned from bar, and the necessary holes drilled for outlet and fixing the two halves together.

Howard

[Jim CParticipant @jimc]

Hi Howard. Thanks for your advice on the engines exhaust. I have made a very simple one but if need be I will look more closely at what you advise. Regards, Jim.

[Howard LewisParticipant @howardlewis46836]

The motor cycle exhaust was a double ended megaphone, externally.

My object was to reduce the energy in the exhaust without producing too much back pressure, which would increase pumping losses. The slower the gases can expand, the less the "bark" will be. The objective was to maintain a constant cross sectional area, and to allow expansion. But the extremely simple exhausts for the small stationary engines are unlikely to allow this, if they are to look prototypical.

These are simple exhausts., Higher frequencies can be absorbed, and lower frequencies tuned out, but these methods require space and weight which is not not always acceptable.

If you want further detail, PM me.

Howard

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