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Bloody Mary 1/8 Scale


Jo NZ

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  • 3 weeks later...

Having thought that I'd mastered at least the rudiments of Fusion, I thought I'd try the gearbox. It's a 1930s(?) Sturmey Archer  four speed motorcycle gearbox. I have loads of photos of these boxes but nothing that quite matches up to the one on BM, so this has been drawn from dealer information, photos and a very flexible scale ruler. Here's a couple of pictures  of the box:

 

gbox1a

 

 The vee  that sticks out is the clutch cable support, you can see that the clutch operating arm pushes a rod through the middle of the output shaft...

 

gbox6

 

All the brackets and linkages hiding most of the top of the box are the positive stop control, to return the gear lever to its original position after the change. An early version of a sequential gearbox?

 

Here's where I am so far....

gbox

If anyone knows any better, please let me know!

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Not an expert by any means but I have rebuilt one Sturmey-Archer 4-speed for a 1930 600cc Norton International hillclimb outfit.

 

The gearbox in your photos looks more like a 3-speed to me. There was a confusing number of variations though.

Could it be a 4-stud (racing) box rather than a 4-speed...?

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16 hours ago, Zephyr said:

Not an expert by any means but I have rebuilt one Sturmey-Archer 4-speed for a 1930 600cc Norton International hillclimb outfit.

 

The gearbox in your photos looks more like a 3-speed to me. There was a confusing number of variations though.

Could it be a 4-stud (racing) box rather than a 4-speed...?

It has got 4 studs - must add them!

 

It's definitely a four speed - if you look carefully at the vertical panel there's a gear indicator (!)  that has 2,3,4 stamped alongside the slot. 😀

 

IMG_0362

 

 

I have a section drawing of the heavyweight 4-speed which shows the bottom of the box tapering up to the output end, but no pictures of this box, and in particular no pictures of the underside of BMs box. I'm pretty sure I've got the front plate correct, and as the bottom of the box is really difficult to see from any angle I might just leave it...

 

Another reason it's a 4-speed - the parts leaflet for the positive stop control shows different pawls for the 3 and 4 speed.  Mary has the 4 speed pawl.

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I stand corrected! The gear indicator is a nice detail.

I've looked through what little material I still have from the rebuild and there's nothing quite matching that gearbox.

 

Brilliant work on the model!

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11 hours ago, Zephyr said:

I stand corrected! The gear indicator is a nice detail.

I've looked through what little material I still have from the rebuild and there's nothing quite matching that gearbox.

 

Brilliant work on the model!

Thanks for the reply, it really made me think! Looking at the gearbox next to the engine in the frame (all carefully positioned with blu-tak) it looks the right length. Next step is to finish the clutch mechanism and then draw the positive stop control. Wish me luck....

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I'm calling the gearbox finished, for the time being. It has errors, but when it's printed (it's only 20mm long) they are difficult to spot...

 

The complex bit on the top is the Positive Stop Control - I'll quote "The principle of this control is a step by step change, the control lever always returning to a central or normal position. The travel of the lever is regulated by a stop in either direction and the movement is such that only one gear-change can be made at a time."... "It has been developed to provide a quick and positive gear change for racing machines, thus enabling the the rider to keep both hands on the handlebars, giving better control of the machine."

 

gbox v2r

 

gboxv2rf gboxv2lf

 

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That looks brilliant- hard to believe it's about 1/10 of the size of the picture on my monitor...

 

Edit: More like 1/6 of the image but still really fine work!

Edited by Zephyr
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  • 1 month later...

And on to the carburettors.... There are 4 SUs, pre 1935 so not even the first"H" type, and information is very sparse. The only identifier is a stamped number on the side"1530". I had a few pictures of period carbs so started with the choke size (1 1/8") and estimated my way around the drawing.

I drew one using a picture from the car, and then realised that they are all different.

As the front engine is canted over, and the carbs need to remain upright, the manifold flanges are angled. The float chambers are fitted to either side, depending on the position of the carb, and the float chamber tops are also handed where the fuel union enters....and the float chambers appear to be bigger than standard, presumably because BM ran on Methanol.  Here's a picture of one in situ. It illustrates the relationship between the carb and manifold quite well as it's more exposed than the others.

 

Carb 2

 

 

And my random jottings...

 

Screenshot 2022-03-28 215905 Screenshot 2022-03-28 220014

 

Screenshot 2022-03-28 220045

 

 

 

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  • 5 weeks later...

There is a raised script on top of the SU float chamber - It says "S.U. Adderley Park Birmingham" and it's curved to fit the top.

Like this

 

Carb 3d

 

Fusion 360 has recently been upgraded to easily etch or raise lettering on curved surfaces. Unfortunately only on single curves, and the float chamber lid is part of a sphere. I tried a 2d engrave of the lettering but it didn't look right. I was discussing this with the guy who gave me the original 3d model and he offered to do it for me!  Said - it's my job, I do this sort of thing every day. I sent off the 3d model of the lid and it came back with the script on it - marvellous! Then I discovered that there are two different lids - they are handed with fuel inlet being effectively mirror imaged.  That isn't a problem, however the script won't mirror...

I solved it by taking a spherical cut of the lid, leaving only the script, and then joined it to the mirrored lid. It seems to work - and - it is just readable in 1/8 scale.

 

Screenshot 2022-04-20 161046

 

 

I have been printing parts as I go along, and because I've got big fingers and the parts in 1/8 scale are small, I've printed them in 1/4 scale as well. It's much easier to see where any fit problems are, and also how to split the parts for assembly and painting.

 

I've started to model the rocker gear, but I have a feeling I'm going to be making four different rockers...

 

The model so far - this a test piece, so I've only painted it for a quick look....

 

Drive side

 

IMG_3693

 

Timing side

 

IMG_3709

 

Carbs and inlet manifold (a deep breath when I fitted the manifolds - there is a gap between them - just).

 

IMG_3698

 

 

And the first valve rocker. The whole thing is split into 3 components so that it can be assembled. I still have no idea how the full size ones are fitted....

 

IMG_3697

 

 

IMG_3699

 

 

 

As you can see, there are castellated nuts! I had no idea they were standard in Fusion so I started to make my own - see the timing gear on the back of the crankcase. Then I did a search and found them  - and in Imperial sizes too.

 

Jo

 

 

 

PS - looking at the pictures I realise that I have the SU script upside down. Ho hum....

 

 

 

 

 

 

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This is top work and a great and unusual model subject.

My OCD is on form though, you have missed the second E from Adderley.

(I spent several months at SU as part of my apprenticeship!)

 

Malc.

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  • 2 weeks later...

Now I have the engines and carbs printed, it's time to start on fitting the engines into the chassis.
The engines have plates bolted to each side to allow for fixing, like this...

 

Screenshot 2022-05-11 214907

 

Except, of course, for the rear right hand mount which supports the handbrake and gear-change cross shafts and is like this🙃

 

Screenshot 2022-05-11 214700

 

The engines have a variety of supports. The rear of the rear engine is supported on hangars to the top of the chassis, and in my ignorance I supposed that all the supports were like that... no chance! There's an angle across the chassis between the engines that the front engine hangs off. Added to that the front of the rear engine hangs off the front engine by a couple of steel straps. The front engine is offset from the rear, presumably to align the chain. With me so far? more pics,,,

 

IMG_3722

 

 

IMG_3724

 

 

Making the carbs was important to align the front engine as the inlet protrudes through the bodywork, so it needs to be outside the chassis.

 

IMG_3726

 

 

Bolster had a problem with keeping the engines in sync, and originally used a jockey wheel to keep the chain taut between the two motors. A friend of his came up with an ingenious way of adjusting the front engine to keep the chain tight without the power sapping jockey wheel. There are no details... From the photos I have, I think it works like this.

 

IMG_3721

 

 

There are two adjustable rods from the front engine to the front chassis rail. When these are tightened up, the front engine pivots on it's rear mount and tightens the chain, as the sprocket moves forward.

 

 

The chain. I found that the easiest way to join a short chain was to cut down a spare jig (you get heaps) otherwise the chain has a mind of it's own

 

IMG_3717

 

I think that the chain is about right in pitch, but it's way too wide. I'm happy to live with that, when the body is on it will be difficult to see.

 

A couple more views from underneath

 

IMG_3729

 

 

IMG_3728

 

 

 

Next will be to sort out the gearbox mount and rear axle swing arm. Another voyage of discovery....

 

Edited by Jo NZ
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  • 3 weeks later...

Thanks for the praise!

 

Continuing the resinmodeller theme...

 

 I have few pictures of the gearbox bracket as it's well hidden. Here's the best view...

 

IMG_0329

 

The bracket is the black bit in the middle of the picture. Supported by 1'' by 1/4" steel bar, as is everything else!

 

I positioned the gearbox at what I hope is the correct position (measuring from photos) in Fusion360. This is how I interpreted the bracket

 

Screenshot 2022-06-01 132617

 

Screenshot 2022-06-01 133036

 

For trial purposes I've printed the bracket and gearbox as one piece - for the final version I'll print them separately to make painting easier.

 

The spring and suspension arm mount to the back axle looks like this...

 

IMG_0325

 

I drew it up to match the width of my rear spring, which is the same width as the chassis.

 

Screenshot 2022-06-01 132725

It's obviously too wide. I'm wondering if the spring tongue that slots into the bracket has been narrowed. Something to try next...

 

I also had a go at the steering wheel

 

Screenshot 2022-06-01 132814

 

 

 

It needs some more work in terms of detail. More importantly, it won't print. I had drawn the spokes at 4mm thick (which seemed reasonable) but printed in 1/8 scale they are only 0.5mm thick, and can't support the rim. I'll try double the thickness....

 

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The remodelled axle clamp. The tongue needs to be 3mm, the spring leaf is 5mm, so I'll thin down the end that fits in the slot.

 

Screenshot 2022-06-03 130737

 

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