Gas Needle Valve for Stuart 800 & Stuart Sandhurst

[BGH]

I would like to make a finely adjustable gas needle valve and would value some pointers as to the design. Its for a small gas engine, Stuart 800.
The mixer shown seems to work OK on another engine, even if its lacking in its visual refinement.
I need a fine thread, BA, BSB or ME no problem.
Now should the threaded brass part be bottoming out when screwed fully in, or more likely the needle itself??
In this example the needle is 1.8mm dia, so drill a hole that diameter with a standard drill bit ?, or should the tip of the needle seat into a matching tapered hole?
Should the needle have a longer taper? Ideal material for this?
Is this a good basic design, or are there published designs/ sketches available?
Any help gratefully received.

[pirmin]

hy, a sharp needle would do the trick, just like model aero engine carb needles i would say.

[BGH]

Thank you Pirmin, I will look into those .

[Jo]

A size 15 Darning needle will provide what you need.

Jo

[BGH]

Thank you Jo, I will look into those (-:

[Jasonb]

You can also rough out the taper on say a bit of 1/16" rod and then finish with a needle file. Put a bit of wood or MDF in the toolpost with a tapered Vee filed into it to support the delicate end.

Or if you want something a bit thicker turn the taper and make a reamer at the same topslide setting, these are for the fuel and burner on my Allman

[BGH]

Thank you Jason thats most helpfull.
Is there an o ring within the nut?
It looks neater without the spring (as on my example)
But think its the o ring in the Wade valves that causes fluctuation in the gas flow.

[Jasonb]

I just used a bit of Graphite Yarn gland packing.

[BGH]

Ah yes great, thank you! 😊👍

[Jasonb]

Section for you. It also makes the needle captive so no chance of screwing it out too far and making a flame thrower.

[BGH]

Great thank you, well that explains some more of the mystery, at least in my head! 😅
I suspect I will try the simple option first but may come back to this if I want to refine it.
That's all a great help, much appreciated 😊👍

[BGH]

A quick update on the needle valve project..well its stalled, for now.
I bought some darning needles as suggested by Jo, but have progressed no further. The engine stopped when I stepped outside to hear how loud or not it was, and has not run again since.
Its currently got me stumped and I am waiting on some expert in person help to try and locate the issue. I know its lost all compression but cannot locate why. With the gas hose removed air from the cylinder is being pushed out of the gas inlet when I turn the engine over by hand. The timing I don't see as being out as everything is keyed in place. Ive had the valve chest off and ground in the gas and air valve. However I cannot see that its the valves that are leaking if I follow the possible path of the gas.
I have just bought a Stuart Sandhurst, so will need a needle valve for that and also the air intake section. So no doubt I shall be back here in due course in the hope of more expert help!
Cheers Chris.

[Jo]

Good Luck, it should be possible to find the leak.

The Sandhurst uses a standard Amal carb.

Jo

[GRAUBELE]

This is the carburetor of my STUART Sandhurst.

Dieter


Edit: Supplemented with picture of Lucas SR Magneto.

[Jo]

That is very pretty 

Jo

[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!

[GRAUBELE]

Hi BGH

Can you take a photo of your Sandhurst that shows the same section as my photo?
I might want to replace the connecting rod, and I think the connecting rod on my engine wasn't made according to the drawing.
It's probably the previous owner's own creation.

Dieter

[BGH]

Hope these photos come through.

[Jasonb]

like this

[GRAUBELE]

Thank you both for the pictures and drawings.
They're something to work with.

Dieter

[Alyn Foundry]

Hi BGH

Can  ;)you take a photo of your Sandhurst that shows the same section as my photo?
I might  want to replace the connecting rod, and I think the connecting rod on my engine wasn't made according to the drawing.
It's probably the previous owner's own creation.

Dieter

Hi Dieter.

The builder of your engine has made an interesting conrod, effectively allowing for variable compression. Although not pretty to look at quite a practical idea!  😉 When first launched in the early 30’s it would provide power to drive anything that would now use an electric motor.  There was a bewildering array of fuels ( liquid) with an even wider range of quality so this might be the reason for the adaptation.
Most of the collectors of small power IC engines these days like to see them running as slowly as they can. A low compression ratio can really tame a beast.

Speaking personally I would leave the engine in its original ( as found ) condition however a new taper turned conrod would certainly look a lot nicer.

   Graham.

[GRAUBELE]

Hi Graham

Basically, I'm concerned about a worn connecting rod bearing on the crankshaft.
There's quite a bit of play, and the engine rattles slightly.
I think I'll just focus on the rear part with the bearing bore. 

Dieter

[Jo]

Don't discount the idea of fitting a pair of shell bearings inside the original big end bearings 

Jo

[GRAUBELE]

Hi Jo

When restoring a steam engine, I once made a missing eccentric bearing of my own design.
That would also be my approach for the Sandhurst.
Then, if necessary (due to wear), the bearing shells can be replaced separately.
Attached is the history of the bearing in one of my steam engine.

Dieter

[Dave Otto]

Nice repair!

Dave

[Michael S.]

A successful repair, Dieter.

Many large original steam engines had cast steel eccentrics and a strip of white metal as the bearing metal.

What model is this?


Michael

[GRAUBELE]

What model is this?

Michael

After about 10 years in my possession, it's still the "great unknown" steam engine.
I haven't been able to identify a manufacturer to this day.

Dieter