SD 102

[seagull101]

Do you have a pic of the crated one that shows a cowl Jacob? I think you maybe correct. The 'D' and 'C' adverts show the cowl and we know BS have a gradual change so it is unlikely the SD range finished with the trumpet.

Here, you can see it under the paper:

[Hugz]

Hi Jacob,

Indeed it does look like a cowl and definitely does not have a trumpet attached. Maybe an optical illusion but it seems to be further over towards the float chamber than the carb body. Maybe Keith might be the chap to cast his eye over it and give an analytical view point. Thanks.

[Keith.P]

I have seen another one original wartime with a cowl and living in the crate, it would make more sense having a cowl.

[Hugz]

Yes, all four of mine had the cowl before I changed two of them to the trumpet. Be interesting if we can find out when the trumpet was discontinued. I would hazard a guess around the time tank saddle became brass.... but not a shred of evidence. Need to keep an eye out for photos to see if we can spot the cowl on pre '45 motors. We don't have a parts list printed during the war do we?

[Charles uk]

Why would it make more sense, Keith?

Was the trumpet not suitable for purpose, was the trumpet difficult to manufacture, was it made from restricted material?

I.E. was it broke & needed fixing?

Nudge (as our resident casting expert) can you comment on how the cowl was manufactured & what tooling & fixtures would be required.

[Keith.P]

As per painted cylinder, the picture of the cylinder before it got cleaned up, the cylinder was plated, but it came off really easy, that's why I painted it.
As far as the cowl, if it was fitted at the time or replaced, I don't know.

[headdownarseup]

As far as float bowl positioning goes, it's largely down to which type of fuel pipe is fitted to the motor at the time.
With what we call a proper SD fuel pipe there's only way the bowl will fit together and that's closest to the spark plug. I have a couple of slightly later post war 102's with a similar type of copper fuel pipe but with fewer bends in it, and due to the constraints of this pipe the bowl will only fit in one position, only this time the bowl is closest to the crankcase.
With any other type of flexible fuel line the bowl can be fitted either way to suit the owners needs.

Hugz
According to the wartime spares list i have (62 version with revisions) there's mention of 2 types of tank support brackets listed as

BRACKET ,supporting,petrol tank (old type tank) .....i reckon this was the steel bayonet tank

or

BRACKET ,br (presumably brass) supporting,petrol tank,( now listed as new type tank) ....... i think this was probably brass and with a screw type fuel cap.... rh and lh. 1 pr (which suggests to me that at some point during production there was indeed a slight change to the format)

If that's anything to go by i'd take a guess at saying maybe half-way through the SD production there might have been a noticeable change from cast ally tank mounts to pressed brass and possibly a change at a similar point with inlet cowls from brass trumpets to cast ally.
Why? Who knows, but i bet the more data you can collect the more this will become apparent.
If the previous pictures are correct we can see that the engine's serial number is in the 9000's, which to me is getting towards the end of SD production, and looking closer i can see pressed brass tank mounts on it too. Ties in somewhere with what i'm looking at in the wartime spares list.
Similar sort of thing with the inlet cowl
listed as
INTAKE,carburettor,vertical.... which sounds suspiciously like a cast aluminium type of cowl to me! Pictures look exactly the same too but without SEAGULL cast into them??? (probably the artist forgot to add that into the drawing perhaps!!)

I wouldn't say this was a case of "if it aint broke don't fix it", more a case of how readily available certain materials were at the time of production.I think it's fair to assume that as ww2 progressed there probably were some shortages in raw materials that were probably ear marked somewhere else in the war effort. What we're seeing with some of these motors is the direct result of making do with whatever other materials were available at the time. I'm fairly sure that BS would have faced the same shortages during this period of production. A small tweek to production like this was to be expected i guess.Some of the motors we see today that have lived in a box all of its life are probably testament to this slight alteration to the original format.


Jon

[Hugz]

Your '62 wartime spare list is irrelevant, unfortunately, as it includes later spares that fit, the mk1 magneto comes to mind. All SD's had the rolled sheet steel tank with bayonet cap and had the copper fuel line that was shaped to preheat the fuel next to the barrel and attached to the high amal bowl on the sparkplug side of the carb.

[Charles uk]

If you'd done any research Jon, you would have discovered that British Seagull during the war years (42 to 45) only appeared to be an assembly shop not a manufacturing facility!

[Nudge]

Im going to say the trumpet would a LOT easier, faster and cheaper to make!

Nudge (as our resident casting expert) can you comment on how the cowl was manufactured & what tooling & fixtures would be required.

I was lucky to have a cowl to use to make a master pattern. I had to make a patttern to make a core box... to make core (the void on the inside of the cowl)

I used plaster of paris (the white bit) to start making the master pattern

then the same plaster part was remaved and used to make the core box

The grey part is the core box, this is used to make the core.
The core is made out of sand and sodium silicate and is gased with CO2 untill it is hard.

The master pattern would be rammed up in sand, the part that hangs out of the cowl it used to support the core.
....
Once you have the raw casting it needs to be cleaned up and put in a lathe to cut the thread to fit it to the carb.

Not a very quick thing to make!
I would be guessing they would have die cast the cowl, but still a lot more work and effort to make than the trumpet.

[Collector Inspector]

Im going to say the trumpet would a LOT easier, faster and cheaper to make!

Nudge (as our resident casting expert) can you comment on how the cowl was manufactured & what tooling & fixtures would be required.

I was licky to have a cowl to use to make a master pattern. I had to make a patttern to make a core box... to make core (the void on the inside of the cowl)
IMG_2521.JPG
I used plaster of paris (the white bit) to start making the master pattern
IMG_2523.JPG
then the same plaster part was remaved and used to make the core box
IMG_2526.JPG
The grey part is the core box, this is used to make the core.
The core is made out of sand and sodium silicate and is gased with CO2 untill it is hard.

The master pattern would be rammed up in sand, the part that hangs out of the cowl it used to support the core.
....
Once you have the raw casting it needs to be cleaned up and put in a lathe to cut the thread to fit it to the carb.

Not a very quick thing to make!
I would be guessing they would have die cast the cowl, but still a lot more work and effort to make than the trumpet.

Obvious trumpet.

Thanks mate.

BnC

[headdownarseup]

Charles

That was a bit harsh wasn't it accusing me of not doing any research in the first place?

No more input from me any more.


see ya

[seagull101]

Is it possible that the carbs turned from part brass part aluminium to full aluminium and thats when the cowls changed?

Just an idea.

[Oyster 49]

Those brass bodied carbs have always been a bit of a mystery. I wonder why some were brass bodied and some were not. Material availability perhaps? I doubt we will ever know!

I agree with hugz, that 1962 parts book ( I have one in vgc) shows the parts available as alternatives at the time. Alloy cowls replacing the inlet trumpet, different magnetos etc.

What I’m still looking for is that elusive photo of an SD in use!

[Hugz]

Is it possible that the carbs turned from part brass part aluminium to full aluminium and thats when the cowls changed?

Just an idea.

Good point Jacob. I hadn't noticed that the top of the float chamber changed from brass to ali at around the 6000# mark.

Charles That was a bit harsh wasn't it accusing me of not doing any research in the first place? No more input from me any more. see ya

Well, you have let the Seagull community down with the limited data collection in your three years of administrating the SD register including not inspecting the crated SD and I recall seeing a few HSD surfacing in your time. Notwithstanding, I wish you well on your Seagull journey and may see you on one of the other associated forums.