That's a "doll's head" g/box, Christian.

If you Google "inside a doll's head gearbox" you'll get lots of pics and info.

The numbers put it around 1951 although I'm not sure hat the dollshead was still used then. Perhaps someone knows?

George

The main problem with this box is the exposed clevis joints that connect the positive stop with the camplate (to be seen just to the right of the gearbox in your first picture). These wear badly especially on a trials iron and cause a lot of lost motion.

Congratulations on your purchase - looks like a nice bike and seems to have the correct fork yokes.

Another thing to check is end float on the gearbox mainshaft - that bronze washer in your second photo controls it. It can cause clutch drag as the first part of the clutch pushrod travel is used up pushing the mainshaft sideways.

As I understand it, the dollshead was still used on the 500T as there wasn't room for the laydown box.

The doll's head gearbox is the pre-WW2 item, but was fitted to the 500T, probably for easier access to the clutch lifter mechanism.

Excess lost movement is what you will have to chase.

As stated above, the doll's head and vertical boxes are prone to wear in the link between positive stop mechanism and cam plate. That on its own can cause gear engagement issues.

If you have more than a little mainshaft end float, it will affect clutch lift, cause drag, and therefore make selection difficult. If you have too much, then you need a new bronze thrust washer, or make a steel shim to reduce it.

Bu your first gear failing to engage properly sounds like insufficient movement in the first gear selector, so if it's not the external link, then the layshaft may need shimming to move the kickstart pinion to the left for better engagement.. If the box does not respond to this, then check the selector fork for wear, especially the lug where it engages the cam plate. That may be the issue.

Once you have sorted those out, you can think about losing some of the lost movement in the positive stop mechanism.....

For the REALLY keen, these early boxes can be given a special up-grade. The cam-plate is bigger in diameter than on the horizontal box, but the selector tracks are in the same place. There's lots of excess metal in the perimeter. It should be possible to grind the indent plunger profile to match the AMC cam-plate, and mate it to a long-travel indent plunger of similar design. You will then have a REALLY good Norton box, potentially as good as an AMC (with similar wide ratios) without the clutch lifter issues. I haven't done this mod (yet), as I don't have a suitable box in a bike. But I may do it for the hell of it

Paul

Previously paul_standeven wrote:

The doll's head gearbox is the pre-WW2 item, but was fitted to the 500T, probably for easier access to the clutch lifter mechanism.

Excess lost movement is what you will have to chase.

As stated above, the doll's head and vertical boxes are prone to wear in the link between positive stop mechanism and cam plate. That on its own can cause gear engagement issues.

If you have more than a little mainshaft end float, it will affect clutch lift, cause drag, and therefore make selection difficult. If you have too much, then you need a new bronze thrust washer, or make a steel shim to reduce it.

Bu your first gear failing to engage properly sounds like insufficient movement in the first gear selector, so if it's not the external link, then the layshaft may need shimming to move the kickstart pinion to the left for better engagement.. If the box does not respond to this, then check the selector fork for wear, especially the lug where it engages the cam plate. That may be the issue.

Once you have sorted those out, you can think about losing some of the lost movement in the positive stop mechanism.....

For the REALLY keen, these early boxes can be given a special up-grade. The cam-plate is bigger in diameter than on the horizontal box, but the selector tracks are in the same place. There's lots of excess metal in the perimeter. It should be possible to grind the indent plunger profile to match the AMC cam-plate, and mate it to a long-travel indent plunger of similar design. You will then have a REALLY good Norton box, potentially as good as an AMC (with similar wide ratios) without the clutch lifter issues. I haven't done this mod (yet), as I don't have a suitable box in a bike. But I may do it for the hell of it

Paul

I got to say that is onehell of gearlever nowonder yougotexcess rotation. Isthathowthey were or isita hand change mountedhorizontaly. Any play in the changemechanismwill bemagnified by that. Forsurerederess thelinkageissues but,asyoutrials boysrarelychangegear on themove wouldntashortalloy heal andtoe changerwork. PS:nice machine, very nice

Jon

I think that's a standard 500T gear lever.

An original 500T like this one would sadly be completely uncompetitive in most current pre-65 events.

The doll's head and vertical boxes are substantially 1920s Sturmey Archer boxes with a positive stop mechanism tacked on. It would be very easy to convert any early Norton box, up to the horizontal, to hand change, with a link from the cam plate sector.

Paul

Previously jonathan_newton wrote:

I got to say that is onehell of gearlever nowonder yougotexcess rotation. Isthathowthey were or isita hand change mountedhorizontaly. Any play in the changemechanismwill bemagnified by that. Forsurerederess thelinkageissues but,asyoutrials boysrarelychangegear on themove wouldntashortalloy heal andtoe changerwork. PS:nice machine, very nice

Jon

I'm not sure why anyone would want to convert to hand change?

With reference to your manual advance query, Christian, it's normal to retard for starting then move it to full advance. I usually retard it a bit when waiting at traffic lights and other hold ups or if slogging up a hill.

George

Thank you all for your replies. Like I'm French, it's going to take me some time to really understand all that, but it's part of the game.

"looks like a nice bike and seems to have the correct fork yokes"

Christian

The standard Roadholder yokes carry the fork legs well forward of the steering column stem. Someone (I believe the McCandless brothers) found that by reversing the bottom yoke it reduced the trail making the steering more suitable for trials.

Maybe you need extended steering stops?

As regards the advance / retard, if you're actually riding in a trial this is a very useful control as it can give you excellent low speed pulling. But on a road bike it's mainly used for starting.

Hi Christian,

Your 500T looks in very original condition with only a few small parts that have been changed. The 500T frame was very similar to the pre-war trials specification Model 18. This was fitted with the "doll's head" gearbox and so the easiest and cheapest way was to carry on using the same. Also if you look at the rear of the frame you will see the rear tubes are shorter to shorten the wheel base for turning tighter corners which would make the fitting of the lay-down 'box too tight to fit in..

Inside the "doll's head" section is the positive stop mechanism with a double sided ratchet with a loop spring to return the pedalto it's middle position. As Ian says the external rod linkage wears over the years so may need adjusting. If possible fit a new spring and check if the sleeve isn't missing from the pedal shaft. Remove the top and/or bottom clevis pins and pull the gear change lever up to first gear position. Nowpull the bottom cam-plate lever up to first gear position andthen set the linkage rod so it fits the length exactly. Check top gear engages fully, if not, the holes could be worn. These are .25" imperial (6.35mm) but you could carefully bore this out to 7mm if you can find 7mm clevis pins. The lever is longer and heavier than the road-going bikes as the footrests are set low down on thismodel.

The engine getting too hot is either the carburettor running too weakor the ignition running too retarded.When started the bike should run fully advanced or fully retarded, if not adjust to which ever way the engine cuts out.

Regards, Richard.

Hi Christian,

When you are happy the timing is O.K. most of your riding can be done at full advance, although retarding is good for very slow running. Yes SAE40 should be good for all conditions and is better than multi-grades as these need a fine element filter. The mono-grade oils trap the contamination in their sludge as you will probably find in the bottom of your oil tank when you clean it. SAE50 is needed for the gearbox, not EP transmission types.

The positive stop design is controlled by the ratchet teeth in the unit which means the gear lever will only move one tooth at a time. The position of the ratchet teeth is equal to the indents on the cam-plate so it stops at the right place for the selector to move each gear into place. Before this design came in (around late 1920s) it was a series of slots on the petrol tank gate to control the position of the hand lever, or you just found the gear by feel.

Hoping you get it sorted, Richard.

These are the "pawls", Christian. When you remove them check that the faces which push against the ratchet plate (with all the notches in it) are not worn. If they are then replace them along with a new spring. Both pawls should fit firmly on the ratchet plate with no free play. They are instrumental to a good gear change.

George

Christian - something pointed out elsewhere that you may not have realised. The oil supply line seems to have a (non-standard) tap in it. This will be to prevent the oil draining down from the tank into the crankcase when the bike is unused for a while (known as wet sumping). Make sure you ALWAYS check that this is turned on before you run the engine.......

Previously christian_wyss wrote:

Hi Richard,

I like the relation with the timing and my happiness. Might work with my wife also, who knows?

You said:

Your 500T looks in very original condition with only a few small parts that have been changed.

Would you please list me the parts that you see that have been changed. I think the rims and the rear spokes, seat springs, license plate, side stand and tool box looks recent. What else?

Hi Christian,

Sorry for not getting back to you earlier. Although most of the parts you list may be replacements they are very near to the original specification. The obvious new partsare all the handlebar controls have been replaced for more modern parts, also the petrol taps. The prop-stand fitted below the rear brake lever looks to be original or a good copy. The bracket (arrowed in your picture) is the prop-stand bracket from the road-going models, but this was never fitted to the 500T. Overall, your bike looks to have all the original major parts which is good after 67 years!If you can find a copy at a sensible price, the book " Norton Singles" by Roy Bacon ISBN 0-85045-485-9 has a chapter on the trials modelswith some original pictures and sometechnical information.

Regards, Richard.

The 500T fork yoke is a highly desirable part for any iron-lug frame, and consequently lots of 500Ts have been robbed of them.

When the McCandless brothers developed the 500T, they realised that it needed lots more trail. What they did was cut the platform at the rear of the lower fork yoke which supports the steering stem off, and weld it onto the other side. For standard road bikes, the rings which surround the fork stanchions are ahead of the cross yoke. The modified lower yoke has the fork stanchions further back. The upper yoke has to be bent to match the new alignment of the stanchions.

Soon after the 500T yokes were developed, the road racing team discovered that the trials yoke made the works racers handle better. So racers in-the-know bought a 500T, swapped the yokes, and sold the trials bike on to an unsuspecting buyer. Of course, it begs the question - since Norton knew that the trials yokes made a better-handling bike, why didn't they make it a standard part on all the bikes? It's a bit late to ask.

I don't know of anyone offering repro 500T yokes. So if you have one which has been pillaged, or want your rigid, plunger or s/arm iron-lug frame to handle better, then you will have to do what the McCandlesses did - take the yoke off, cut the lower platform off, and weld it onto the other side. But do make sure your welder knows what they are doing. A fracture here does not bear thinking about......

Paul

Previously christian_wyss wrote:

Thank you all for your replies. Like I'm French, it's going to take me some time to really understand all that, but it's part of the game.

"looks like a nice bike and seems to have the correct fork yokes"

How can you tell that?Asking because for me it looks like the "steering stop" on the frame doesn't touch the fork and then it's the fork which can hit the tank.

About the manual advance, is it a on/off one, just start and run position, or does it need to be adjusted "all the time"?

Christian

Another book which is well worth getting hold of if you can find one at a reasonable price is "Classic British Trials Bikes" by Don Morley. It has an excellent (though short) section on the 500T.

One here for £40 but I think that's overpriced.

https://www.ebay.co.uk/p/Don-Morley-Classic-British-Trials-Bikes-UK-1st-DJ-1984/1116275843

Hi Christian,

Your fork yokes are genuine 500T and looking closely at one of your photos I can see the 2 small lugs on the top yoke that hold the front competition number plate. These were originally made from the same malleable iron as the standard yokes but were made fromaluminium alloy on later models.I used these yokes on my 1948 Model 18 in the 1990s for short circuit vintage racing and had the same issue with tank to fork clearance so fitted longer bolts with spacers and larger diameter stops. They made the bike turn quicker into corners, not just because of the fork angle but also the shorter wheelbase. The down-side to this is less high speed corner stability which would be a problemon a public road circuit.

The standard bottom fork yoke can be modified, but be aware when welding the main section is cast in malleable iron. Modifying the standard top yoke to 500T will be quite difficult as the stanchions are a lot closer to the stem and it would be probably easier to make from aluminium plate.

Regards, Richard.

With regard to the lock stops, a lot of 500Ts had the tank dented to allow more steering lock.

The pic looks like the correct 500T lower yoke with the legs set backwards

Nortons probably had a jig specially made for the job of bending the upper yoke. Mount the upper yoke so that the stem hole is held secure and level, heat the yoke either side of the stem, and bend using a long lever (old fork stanchions?) until they are at the correct angle and in contact with a support built into the jig.

This job is also required if you have a BSA C15 Trials. The works bikes had improved yokes for increased trail, production bikes didn't. Solution is to use two blades in a hacksaw to remove the lower fork stem platform, heat the upper yoke until the gap in the lower yoke closes, and then weld it up. Been done many times

Paul

Previously christian_wyss wrote:

Thanks for the tip, but I believe this job was done already. Because how could stanchions, in a modified lower yoke, fit the standard upper yoke?

Hi Christian,

Yes you are correct, the 500T top yoke is a completely different casting to the standard top yoke which is why they are quite rare. The top yoke is made so the fork angle is the same as the headstockmaking the top and bottom yokes parallel to the fork stem and about an inch(25mm) closer when viewed from the side than the standard road yokes. The standard road yokes have a forward lead angle so the stanchions are not parallel with the headstock with the stanchion holes bored at an angle. To make a standard top yoke line up with a 500T bottom, you will need to cut out a section from each side to bring the distance back to parallel and tilt the stanchion hole sections so they are at 90 degrees to the level plane of the yoke. To maintain the 7" (178mm) centres width you will have to weld/braze slightly to each side of the "Y" arms. As you probably realise this is not as strong as a one piece casting. If you tried to fita standard top yokewith-out cutting out the sections as above this would give you a severe reverse angle and the wheel would hit the frame.

Regards, Richard.

With regard to the parts book, I don't believe the 500T was ever actually covered. However, most of the parts will be in the regular ES2 / Model 18 books from the early 1950s. Bruce Main Smith (located at the National Motorcycle Museum near Birmingham) has one which covers 1950 with additions for 1951 - 1954 - codename AURUM / 140. This is a decent quality photocopy of the original.

I think you're right in keeping it as standard as possible as so many of these bikes have been hacked about - many in an attempt to keep them competitive through the 1950s. People weren't bothered about authenticity in those days.....

You (probably) need to take the front gearbox cover off to release the parts you arrow. There is indeed a bush on the inner end of the spindle.

"KYM" was a November 1949 onwards London area registration. Have you asked the NOC records officer to look this one up ? If UK buyers returned the guarantee card, their names and addresses were usually entered in the factory ledgers.

It's not quite as simple as that, Christian. The block of numbers (probably starting at '1' but not always...) running KYM 1 to KYM 999 would have become available from November 1949. However, some licensing offices seem to have kept books for motorcycles that filled up quite slowly and batches of numbers were issued to dealers who then filled in the vehicle details when registering.

The second column in the printed list tells you which diagram and the reference - eg P.35 is diagram P, reference 35 clutch worm nut. And the first column is the part number (A2/861 in this case) - although note that some of these may have been superseded.

Also, not all parts are actually shown or referenced in diagrams.