Differences-and Similarities Between Models
Firstly, although stated as 1931, these bikes were available from early December 1930 when the Motor Cycle Show presented them to the world, however press releases had been leaking news since the previous August. I have so far recorded about 6 machines that could be from this very early period of manufacture, when a few details were different to later, standard production bikes. These bikes are probably the remains of the initial batch of 100, that was constructed before full production got underway.
Frames: Although the frames on these bikes look identical at first sight, there are lots of differences to make interchangability quite difficult. There are 2 distinct frame sizes, let's call them large and small, the large one has a wheelbase of 54 inches, the small one 52+1/2 inches. For the 1931 season the 550sv and 500ohv used the large frame, the 350ohv and sv used the small frame. For the 1932 season, it got complicated! Some of the previous seasons production was unsold, so it carried on selling throughout the year, but a new engine configuration for the 500ohv and a new 500sv meant that it could be housed in the small frame! (see elsewhere for engine differences, but the bit you need to know to follow this is that the 1931 500 was 496cc and the 1932 500 was 493cc). Some parts of the small frame are the same on the 350s and the 493, other bits are different. The large frame, to my knowledge, had only one item changed during its entire production run (more later).
Main Frame Backbone: The large backbone has tubing of 1+1/4"and 1+1/8" diameter. The small backbone has tubing of 1+1/8"and 1" diameter. Within these sizes are other differences. The 350 backbone, ohv or sv, does not appear to have been fitted with a sidecar mounting lug underneath the headstock. Sometimes the frame number can be found on the backbone (more usually it is on the seat spring lug on the left hand side rear stay, see below), on a 350 the number usually starts with L, but a 493 with small frame (and sidecar lug) starts with H. The large frame number starts with H. I have even got records of bikes with frame numbers starting with N, but I think these must have been stamping mistakes, as there are only 1 or 2.
Front Forks: The large frame has forks with tapered tubing of 1" (larger) diameter, and has a gap in between the fork legs (measured just under the lower fork spindle) of 5+1/2". The small frame has forks with measurements of 7/8"and 4+5/8" respectively.
Front Down Tubes, both frames: The down tubes are made from tubing of 1" diameter. These tubes are very similar between models, the best way to distinguish the differences is to use the mounting holes and lugs. The 'large' tubes have a 1/2" clearance hole at each end, and 7/16" clearance holes to the inner lugs. The 'small' tubes have 3/8" holes to the inner lugs, but the top and bottom holes differ in size depending on what engine was fitted. If a 493 engine was fitted the top and bottom holes are both 1/2". If a 350 engine is fitted the top hole is 1/2", the bottom is 7/16".
Engine Tray/Channel, large frame: the internal width is 6+1/4", and matches the width of the crankcase of the 550 and heavyweight 500 (496). Small frame 500 (493): the internal width is 4+3/4", and again matches the width of the lightweight crankcase, it also has 2 slots 7/16 x 1+1/4" for mounting of the Burman gearbox. Small frame 350: the internal width is also 4+3/4", but the Moss gearbox mounting details are 1 x 7/16" hole and 1 slot 7/16 x 1+1/4".
Gearbox Top Plate, large frame: the overall length is 15", the internal width is 6+1/4", however I have yet to see a plate with such an elaborate shape as shown here, there is usually clearance for the rear mudguard and space under the toolbox for the original position of the horn, but it is more usually a simple U shape cutout. I believe the rectangular hole shown here was for the battery to be semi-recessed, yet the parts book does not identify a strap to support the base of the battery (I do have one like this, but there is no strap). I believe that this plate was further altered from the picture and the rectangular hole for the battery was omitted on later bikes. Small frame: the overall length is 12+1/4", the internal width is 6+1/4", the rear cutout is more of a simple U shape.
Rear Down Tubes (vertical, under saddle): The large frame has tubes of 1" diameter, the small frame has tubes of 7/8" diameter. The 493cc small frame has a Burman gearbox and because of this has different shaped tubes to the 350 small frame. I can supply a photo of the different types if anyone needs to know.
Rear Stays: The large frame has tubes of 1" diameter, the small frame has tubes of 7/8" diameter. The frame number is normally found on the lug that the left hand saddle spring fixes to (the bit sticking up, 1/3 of the way along from the left).
Rear Chain Stays: The large frame has tubes of 1 + 1/8" diameter, the left hand side has a sidecar lug. The small frame has tubes of 1" diameter, the 350 does not have a sidecar lug, the 493 does.
Brakes: Very early bikes have circular brake cover plates, with no rain deflector, this must have been a problem, and resulted in a factory alteration, as most bikes have the integral rain deflector. The brakes fitted to the large frame were 7+3/4" diameter (8"), whereas the brakes in the small frame were 7" diameter.
Wheel sizes: The 350 bikes were generally supplied with WM1 x 20" rims, with 300 x 20 tyres front and rear. The 500 and 550 bikes were USUALLY fitted with WM2 x 19" rims, with 325 x 19 tyres front and rear. These are the more modern (?) tyre/rim sizes, when these bikes were being sold the sizes went on the OUTSIDE DIAMETER of the tyre, ie 26 x 300. So, a 300 x 20 and a 325 x 19 BOTH have the same (or very similar) O/D. HOWEVER, you could specify a larger size as an optional extra. The late Bronze Wing in both 350 and 500 sizes was designed to have more ground clearance, and was fitted with a mixture of wheel sizes. At the front was a WM2 x 21" rim and 300 x 21 tyre (27" o/d), and at the rear was a WM2 x 20" rim and 325 x 20 tyre (also equates to 27" o/d).
Magneto: The range was publicised as having a round ML magneto fitted, the correct model is the CMA, without the normal base mount platform (it bolted direct to the steel mounting platform that bolts to the crankcase extension). This was certainly the case in 1931, but evidence is emerging that some bikes in 1932 were fitted with Lucas magnetos, type MKLC1-0 DF-0. I have two of these that came on bikes, look original fitments, and are date stamped 11-31 and 5-32. A Danish owner that recently visited me also confirmed that a couple of his bikes had the same unit fitted. Interestingly, both magnetos have a feature that makes fitment to a New Hudson possible, where most magnetos of the period would not fit. The connection for the advance and retard cable is angled backward, so that the cable does not have to exit through the top plate. Magnetos are Anticlockwise rotation viewed from the sprocket end.
Dynamo: Not absolutely certain with this one, but I think the correct model of Lucas 3 brush dynamo should be the model E3C-3, type DF-0, again I obtained one on a bike, and it is dated 10-32.
Carburettors: I am indebted to Mr B Johnston who back in 1985, worked for IMI Amal Ltd. He sent me a 1932 Settings List which is reproduced here.
| Model | Carb | Bore | Jet | Valve | Needle P. | Fl. Chamber |
| 350sv | 75/004 | 13/16" | 100 | 5/5 | 3 | 64/099 |
| 350ohv | 76/004 | 15/16" | 130 | 6/4 | 3 | 64/079 |
| 493sv | 76/014 | 1" | 140 | 6/4 | 2 | 64/099 |
| 493ohv | 6/158 | 1+1/16" | 170 | 6/4 | 2 | 14/077 |
| 550sv | 76/014 | 1" | 140 | 6/4 | 2 | 64/099 |
The one standard model missing is the 1931 496ohv. I have been given a photocopy of a page from an unidentified source which has the following information, none of which is the whole picture:
| Carb body | Float Chamber |
| 6/144 | 14/079 RH |
| 6/129 | 14/079 |
| 49/119 | 14/079 |
| 49/125 | 14/079 RH |
| 6/129 P | 14/079 P RH |
I have no idea which of these is correct, and there are no settings. All these entries were identified as 1931 500 ohv.....Since writing this, I have been in contact with Len Kelly out in Australia, who has a VERY original bike, only 2 previous owners, with almost everything as it came from the manufacturers (even down to the New Hudson tool kit, and the 1931 specification sheet-prepared on a 1931 typewriter!). Len tells me his bike is fitted with the 6/129 carburetter (but he suspects his bike is a 1931 500 Special).
I have recently bought a GENUINE Bronze Wing, and the horizontal carburetter that is with the bike is a 6/197, whether that is original I cannot say as yet. It is the same bore as the standard model fitted to the late 493cc, but I haven't stripped the jets/throttle slide out yet to check them.
ENGINES
Phew! Where to start....the easy ones! See New Hudson brochure for general specification.
346 sv
To my knowledge, there were no known engine revisions.
Bore and stroke: 70mm x 90mm
Piston: Hepworth and Grandage ref no. 3160
Covmo ref no. A1635
Flat top, 3 x 2mm plain rings, 1 + 1/8" compression height, 2 + 7/8" overall length, 3/4" diameter gudgeon pin, fully floating with brass end pads.
Valve springs: Terry ref no VS 89
Single cam to operate both valves.
547 sv
Similar to above, only 1 known engine revision, being a different form of discharge for the engine breather.
Bore and stroke: 83.5mm x 100mm.
Piston: Hepworth and Grandage ref no: 3428
Covmo ref no: A1929
Flat top, 3 x 2mm plain rings, 1+13/16" compression height, 2+13/16" overall length, 3/4" diameter gudgeon pin, fully floating with brass end pads.
Valve springs: Terry ref no VS xxxxx
Single cam to operate both valves.
496 ohv
No known changes, latest engine number known: ............
Bore and stroke: 79.5mm x 100mm.
Piston: Hepworth and Grandage ref no: 971
Covmo ref no: A1099
Domed top, 3 x 2mm plain rings, 37mm compression height, 70mm overall length, 3/4" diameter gudgeon pin, fully floating with brass end pads.
Valve springs: Terry ref no. VS xxxxx
Single cam to operate both valves.
346 ohv
Bore and stroke: 70mm x 90mm.
Piston: Hepworth and Grandage Ref no: 3700
Covmo ref no: A3078
Domed top, 2 x 2mm plain rings, xxmm compression height, xxmm overall length, 3/4" diameter gudgeon pin, fully floating with brass end pads.
Valve springs: Terry ref no: VS 90
See Page 2 for a continuation....
