Model 77 gearbox

According to my notes, the 1956 Model 77 started life with an AMC gearbox.

The earlier 500cc Model 77, from 1950 to 52, would have used the laydown box.

The Model 7 was 500cc. It started in a plunger frame, and got a swing fork conversion circa 1953, still iron lug. Model 77 600cc

The 77 came out after the AMC box. This box had unusual ratios. Sleeve gear and second same ratio as earlier boxes, third is 21 to 21, and it got the slightly higher first gear.

Ratios were much improved in 1960 (closer sleeve and 3rd gear pairs), this was a popular move

FWIW the horizontal box came out on the first Model 7, in a plunger frame. It was much better than the 'upright' box brought out just after WW2, because it eliminated the external link between positive stop mechanism and cam plate. Gear shift is much better. It fitted between engine plates at the top, eliminating the divided top lug which was a source of fractures.

Norton never made a gear box. Up to 1932 they bought Sturmey Archer's boxes, then bought the design rights and paid Burman to make a slightly improved version which had several stepwise developments (pre WW2 'doll's head', post WW2 'upright' and 'horizontal'). After the AMC takeover of Norton they developed an improved Norton box to be used by all the conglomerate's heavyweight machines.

Hi George,

GB8 is a featherbed gearbox. Your bike if it's a pre featherbed swing arm machineshould have one starting G102 or things may not line up as they should.

Jim

Attached advert shows the forgotten Model 77 as produced between 1950 and 1952. Most being exported towards Australia.

Note the iron head on the early500cc engine and the laydown gearbox. As pointed out by Jim, 'G' letters were used as identifiers on pre AMC gearbox bikes.

People rebuilding these early boxes need to be aware of the variety of components that were used in them depending on which model bike they were being fitted to. Most being interchangeable. The box for any Dominator engined bikes need the longer GT 176 mainshaft fitted for example.

Barry Stickland and Bob Proudman have the knowledge and produced useful gearbox articles in Roadholders 187 (pages 42/3) and 212 (also pages 42/3).

Some of us have been members for a long time. Check out attached. More to follow if needed.

The "later" , or 600cc Dominator Model 77 started life in 1956 with a Laydown gearbox, the switched to the AMC box in the 1957 model year. Here are some good pics of a Model 77 manufactured in 1956:

http://www.barkshire.co.uk/bikes/images/Norton77_1958/index.htm

Keep in mind, the AMC box wasnt made available until 1957.

Skip

Previously George Phillips wrote:

Hi Jim Thanks for that info. My bike is a pre-featherbed ES2 (1955) but is definitely fitted with a gearbox stamped BG8 xxx. I'm told that the top width of the box is the same as the ES2 box but the bottom width is narrower (3 3/6" rather than3 1/2" so some extra washers needed) but it appears to fit OK if a bit tight at the top. I'll try and check out those references that Phil gave. George

The reason for the differences between gearboxes for featherbed and iron-lug s/arm frames is in the lower mounting lug. Featherbeds clamp the box between engine plates which are the same width top and bottom. On a 'pre-featherbed', the lower lug bolt pivots in lugs brazed into the lower frame rails. It's wider. This lower gearbox lug is the same arrangement as with plunger frames, which have the divided top lug and a slotted lug on the seat tube. If the top bolt gets loose, the gearbox starts to chatter, causes wear, and so there develops clearance between lugs and frame. So when it gets clamped up, the lugs have to bend inwards, they don't grip so well, it comes loose again, more wear, and eventually the lugs fracture.

Another point worth bearing in mind is that there are lots of differences between 'Norton' boxes and 'AMC' ones, despite the later one being a close derivative of the Norton box, and has many common parts.. For example, the sleeve gear pair have the same tooth numbers as Norton box up to 1960, but the 4th gear engagement dogs are closer in on AMC gears. They don't have to fit round the bronze thrust washer as fitted to the Norton boxes. You can not fit AMC sleeve or 3rd gear pairs into a Norton box. If you get a full set, you can put Norton 3rd and 4th mainshaft gears into an AMC box AS A PAIR

I do like the cam plate indent profile on AMC, it has a fully round index profile and long travel index plunger. It's one of the reasons the AMC give such a good gearchange. Unfortunately these big index ramps make the AMC camplate too large to fit into a horizontal box. I tried, it don't go. But if you want a reversed cam-plate (reversed gear-lever for rear-sets,anyone?) there is enough metal to grind that nice round index profile onto the back of the cam-plate.....

The earlier vertical and doll's head boxes have a larger diameter cam-plate - so it may be possible to use it, but I haven't tried. Well, if you have one of these, make sure the shift linkages have no slop, and the pivot bushingss for the positive stop mechanism are good before worrying about that.

A useful improvement in gearshifting for horizontal boxes is to reduce lost movement before the postive stop mechanism starts to bite. I got a pair of ratchet pawls built up with wear-braze. No idea if it will last, I haven;t tried it on the road yet.