Gas Needle Valve for Stuart 800 & Stuart Sandhurst

[BGH]

Thanks Jo, I intend to run mine on gas, spark provided by coil. Any thoughts as to why Stuarts suggested magneto over a coil? Out of curiosity what magneto was used, was it always the same make?

[BGH]

Thank you Dieter, yours looks great and appreciate the magneto photo. Is the stand its supported on cast iron , and bolted onto the bed?

[GRAUBELE]

A gray cast iron bracket is bolted to the motor housing.
The magnet is screwed onto this bracket.
The contact surfaces are milled at an angle.

Dieter

[Jo]

When the Sandhurst was originally designed it used a 6v Briggs and Stratton Mag. If you could find one it will probably need reconditioning at vast cost but any single cylinder mag would do.

Mini Mag do a kit for a model mag but coil ignition is very simple and much cheaper. These days electronic ignition is better.

Dieter's Mag bracket was a standard casting available with the original casting set.

Jo

[BGH]

Many thanks! 👍

[Jasonb]

The Sandhurst Drawings show that the boss at the side of the engine's base is machined vertical and the bracket fixes to that so no angled faces.

It would be quite easy to make your own bracket either adding a web to a short length of angle iron or carving it out of a block of cast iron as it is not a complex shape.

If you could find an old mag rather than get it refurbed put a modern CDI ignition inside. But don't use the mag driveshaft to trip it, finf a slower rotating part.

[Jasonb]

Should add that the outline of the mag in the drawing I posted earlier is a BTH not a B&S

[BGH]

Jo & Jason, many thanks for all of this, most interesting.
My intention is to use a small Chinese coil(?) that Graham Corry introduced me too, they seem to work fine, especially for under £10, though initially will set up using an actual buzz coil so I can hear the engine is getting a spark at the right time. But its most interesting and useful to have the magneto info in case I change my mind...this does happen LOL.
The engine has not arrived here as yet but attached is a photo of it showing the area under discussion. My thought is, and I may well be incorrect (?), the wingnut is for the earth/ground wire and the flat strip with two crosshead screws is the contact to trip the spark, what do you think please?

When the engine does arrive it will be accompanied by a Stuart 1/4hp gas engine (though currently set up for petrol). I have contacted Stuart Turner asking for copies of the drawings for both and just had a reply back, unfortunately they cannot help for either. So if you or anyone can assist me with this I would be most grateful.

Ok off to look at Minimag to confuse myself even more...
Cheers Chris.

[Jasonb]

Looks that way, I assume the washers under the two screws are not metalic as that needs insulating from the engine.

Some form of can on the black ring to push the plate down and make the circuit to the block below.

I see new BTH mags are available but rather pricy, the TT replica looks right for the job.

[BGH]

Thank you, I just had a look, crikey yes they are a bit pricey indeed!

[Alyn Foundry]

By the late 1920’s Magneto nomenclature had been pretty well established with full standardisation. As a consequence you could use any make, of which there were many at that period. BTH ( British Thompson Houston ) to name but one was very popular because of their ability to produce a spark at around 80 RPM.
A magneto is totally self contained and ready for action. No need for batteries etc. personally I’d be fitting a BTH without hesitation. 😉
I would hope that with the use of modern technology a reproduction unit would last a lifetime.

   Graham.

[BGH]

Hmmm..up until this particular Sandhurst came up I had not given them much thought, as I did not care for the look with the magneto on the front. That and I didnt know anything about magneto's!                 
I have to say though now I might be coming around to the idea given what you all have said.                                                                                                                                                                     
 I normally prefer old, but having a brand new unit that should give no trouble is slightly appealing.               
Guess I will wait and see how it looks, and if it really is as appears already set up for a buzz coil and then decide...or not LOL.

[Alyn Foundry]

The Lucas N1 also fits the bill pictorially however I could not find any historical references to its introduction date. The evolution of styles is mainly based upon the development of more powerful permanent magnets. After the invention of AlNiCo
 Most magnetos became rotating magnet machines rather than than the earlier rotating armature devices.

Anyway enough history. The Trembler box was developed to provide high tension ignition for Henry Ford’s automobile engine. It was powered by coils placed around the engine flywheel @ 90 degree spacing. A mechanical arrangement was used to advance and retard the sparks. As these boxes became mass produced more and more were being used on American Gasoline engines. A couple of 2Volt radio batteries provided the power for the Low Tension circuit. I always warn against the use of 12 volt batteries on original buzz boxes because of the risk of burning out the coils. It is, in effect an autotransformer.
I would guess that the modern reproduction units are designed to be run at higher LT voltage?

Back in the day we used to make our own trembler boxes. We used the ignition coils from many of the various single cylinder engines fitted to garden machinery. Sadly it’s not so easy now as most coils are designed around the capacitive discharge system or CDI for short.

On a humerus note to end this ramble , always make sure you ground the right side of your trembler box to the engine. 

Enough said??

   Graham.

[BGH]

Thanks for that Graham.
I'm hoping the new additions will be delivered in the next week or so, I will see how its currently set up then for a more informed decision.                                                       
 Cheers Chris.

[BGH]

Here's an update on my Stuart Sandhurst.
Looks great, runs great (-:
It did indeed arrive set up for use with a buzz coil so that made life simpler. I made an adapter for a gas/air mixer that came on my EEC and fitted that as the quickest option to see the engine run.
Second short run today as no coolant, seems to respond well to the needle valve for adjusting speed. Very happy, just need to add a nice pulley with drive dog.
Loads of compression so starting is with a drill, all good.
Cheers!