Mysterious parts, 
not so visible failures, special tools, home made spares and other stuff

Other parts are prone to failure but their failure is not always obvious. Additionally it is helpful to have some dimensions of parts not so readily available anymore like friction discs for front fork and steering damper.

The engineering of the bike is lovely crude. Any superfluous oil is just discarded on the road through multiple copper pipes. Length and routing of those pipes hardly ever are original nowadays. They tend to break off or have been cut short after kinking. If you have to make new ones, some guidance is given on how to get the original look again. When building up a bike from parts, some of them are difficult to find as they are not clearly visible in the illustrated parts list.

Also some special tool are given which can be made to ease tinkering on the bike.

I hope my experiences can be of help. I expect this to become a small list in the end. It is not always to be taken as advice. It is always your own decision and responsibility if you follow what I did/do. 

MYSTERIOUS PARTS

Crankcase breather valve.
To alleviate the pressure differences which develop in the crankcase when the piston is going up and down, a pressure relieve system is usually utilized. On the 16H and Big 4 engine, this consists of two supplementary systems, one timed version breathing through the driving side flywheel into a cavity in the crankcase blowing out of a hole underneath the driving shaft behind the primary chain case and one ball valve type breather on the left hand side of the crankcase onto which a copper pipe is mounted spitting excess oil onto the rear chain and relieving pressure at the same time.  The ball assures that the oily mist is going one way only.

 This copper breather tube, steel ball valve and the brass nipples are not very obvious in the spare parts list.  It is listed under Transmission as "Crankcase breather, complete with Pipe" part no. 9531.  It would be more appropriate in the Engine section!
The Maintenance and Instruction manuals do refer to a valve, without any further description of the configuration.

Over time when engines wear and more pressure develops due to gasses bypassing the piston this breathing system becomes more important.
At the same time wear occurs on the screw in the valve reducing the available aperture for the air to blow through. The steel ball hammers into the brass and deforms the screw end, which will therefore reduce the possibility for breathing while you actually would need more. This will likely result in a leaking engine at all kinds of places.
Pictures below show the valve construction and the wear on the central screw.

           
      Bottom view crankcase breather valve                                Top view crankcase breather valve        wear on breather bolt, new, medium, severe

Strangely enough, Norton never described this wear nor an inspection of the valve and similarly no information on the play the ball should have in the valve.
I assume the ball should lift just enough to have the same aperture surface as the the hole surface in the screw which is obtained around at 1-1,5 turn from fully seating.

One note of caution, some people block-off the timed breathing aperture in the crankcase behind the primary case because there will be some oil dripping from it, especially when the engine is prone to wet-sumping due to worn oil pump gears and/or prolonged storage.
This is not correct and may lead to more oil consumption/leakage as it halves the breather capacity.

Felt and leather washers
 Many bikes have lost their felt and leather washers over the years. Many people don't even know there should be any at all. The M&I manual does sometimes mention them, but although mentioned in the spares lists, they are relatively mysterious.
Between the primary chaincase and the engine crankcase a leather washer is used. Between the primary chaincase and the gearbox a felt washers is used. I added a felt washer between the magneto and the timing chain case. Felt washers were further used for: clutch nut, gear change pawl carrier, wheel hub bearings (both sides), inside primary chaincase between footrest tube and outer casing, and sheets of packing felt between the top frame tube and the petrol tank on "later" bikes. Up to 1940  rubber sheets appear to have been used. 

Gearbox main axle dished spring washer
The exploded view drawings of the gearbox in the M&I manual as well as various books, show a dished steel spring washer at the end of the main axle. I personally have never found such a washer in a gearbox, and wonder if they were actually used on all boxes, or only the later ones. Its not given in the spare parts list of either old or newer contracts or postwar civilian lists. The dimensions are I.D. 5/8", O.D. 1 7/16", steel thickness 1/64" and dished height 1/16" as measured on an original sample.

Clutch Roller Cage with Rollers
The number and dimension of the rollers is not given in either spares list or maintenance manual. From the M&I manual it can almost be deduced how many with a small margin of error. In actual fact, 20 rollers are used 1/4" x 1/4".  Post war AMC clutches used 15 rollers of the same dimension.  Not quite sure why the more powerful postwar machines had less rollers. Only thing I can assume it was an overkill to use 20 or the material properties had been improved.

Clutch Back Plate
The original military WD16H and Big 4 backplate was a sheetmetal stamping with a thickness of approx 3 mm. Post war, the early AMC backplates were machined and have a greater tickness. Later AMC backplates (post 1957?) with incorporated friction parts may work as well but with the correctly associated plain Clutch Sprocket. Drawback of using AMC backplate is that the clutch becomes wider and will interfere with the inner chaincase more easily. A lot of tweeking may be required to get the parts into such position that they do not rub against each other.

Kickstarter Axle cork oil retainer washer (3810)
To prevent the oil leaving the gearbox along the kickstarter axle there is a cork washer fitting in a recess in the gearbox cover.
The washer p/n 3810 is not shown on the M&I manual exploded views. People have replaced the cork with a proper size O ring.
If you do, make sure it is chemical resistant to the oil. NBR or Viton will do the job.

Driving Side Main Bearing Distance Piece (4155)
On early 16H and Big4 spare parts lists, this metal ring is not mentioned despite the fact that they are mounted in all engines after 1935. It is placed between the two main bearings at the drive side of the engine. It is a flat ring with an oil channel at the outer circumference and 4 recesses on one side, or 6 holes around the circumference. These recesses are to face the crankshaft when mounting the bearings in the drive side crankcase half. This position is taken from the Big 4 exploded engine view in the M&I manual, a schematic also used for civilian engines between 1938 and 1948.  The 16H M&I manual exploded engine view does not show this part.

  Click picture to enlarge

Carburetter needle jet
The Needle jet in the 276 carburetter  has been described in the original AMAL specification sheets for WD16H and B4 as "standard". The Spare parts lists and the VAOS lists describe it just as Needle Jet with part number AM/4/061.
The Burlen Ltd company, (present official AMAL manufacturer, see links page) stated that the "standard" part was actually the 1065. These were not marked. For reason of optimisation, there are alternative needle jets available numbered, 105, 106, 107, 108 and 109. The number signifies the internal diameter in 1/1000th of an inch.

Carburetter needle clip position
Something that crops up all the time is whether you count the needle clip slot from the top down or bottom up. With all Amal carburettors the clip position is top down. (ref The Burlen Ltd website).

Fork Spindle Knurled Adjusting Washers (3184)
The drawing of the front fork as given in the Maintenance & Instruction manual is not completely correct. The drawing only shows 4 knurled washers (10) but it have to be 6 as stated by the spare parts lists and logic. I adapted the drawing to show the two additional washers (10) on the bottom rear spindle.

   Click picture to enlarge

Wheel distance bushes and wheel bearing spacer
Dimensions of wheel distance bushes and bearing spacers can be found on the Part sketches for manufacture or reference.
 

UNEXPECTED DIFFERENCES

NOT SO VISIBLE FAILURES (AND SPARES)

Main Gear Wheel Sleeve Bearing Roller Retainer Washer.
Pictures of the "exploded view" gearbox show that the rollers in the main gear wheel are neatly housed. What it does not show is that the rollers are closed into the main gear wheel by a steel washer, against which the bronze clutch thrust washer rotates when activating the clutch. Look at the picture given in the gearbox and transmission page where I added the washer for clarity.
This hardened steel washer has the tendency to fracture. Two of the 3 gearboxes I have showed this to be the case. The washer is given in the spare parts lists (all) under no 3598 (Main Gear Wheel Sleeve Bearing Roller Retainer Washer).  I have however not been able to find original replacements for them, and had them made from a cold work tool steel (AISI D2 or UNS T30402) and hardened to 59 Rc. Remains of the original were measured to be 60 Rc so I think I am close enough. See Parts sketches for manufacture or reference  page for dimensions.

 Loosening clutch nuts
On some bikes, you see an additional disc in the large depression produced in the primary chain case to house the clutch. This is usually the result of adjustment of the clutch disengagement while actually the clutch nut has come loose.
So if you ever have the urge to adjust the clutch disengagement stroke, first check the central nut on the clutch. Despite the spring washer behind it, it loosens on occasion.

OIL AND GREASE STUFF (See alo the running a 16H or Big 4 page)

Oil non-return valves.
Anybody not having used his bike for some time will have experienced the blubbering noises and heavy kickstarter actuation when trying to start his machine.  I know, everybody has a perfect oil pump, but me?
The oil tank has drained itself into the engine crankcase after finding its way past the gears of the oil pump.
A safe solution is to add a non-return valve into the oil line. Although I made one myself, you can also buy them on the market.
An oil tap works but with rising age is not the best solution, unfortunate experience! 

Valve grease nipples.
One of the most amazing features on the 16H engine are its valves. There are grease nipples on the valve guides as a token addition to subdue valve stem wear. Initially I used to give them a squirt of high temp molybdenum based grease. This usually resulted in a fairly sizable smoke curtain at the beginning of a trip.
I stopped greasing them as I don't think it has any use. I am now about 15.000 miles further since I stoppped greasing and it still works. I know I don't have the maximum compression, and I don't go faster than 50 MPH anyhow because that is a very uncomfortable speed on a dinosaur suspension. But what the heck, put in a new set of valves and guides and I will ride into my old age pension!
These bikes are rugged!!!!    I love it!

Latest tip I got was the use of : "(air) gun grease". This apparently has a very high temperature resistance, and would therefore be able to withstand the temperatures of the cylinder head. I will try to get some and have a go at it myself. Keep you posted. I will first try to do some temperature measurements on the barrel using a non contact gauge as used by modellers. Then see if it is useful.

Oil regulating grub screw on top of timing cover
An often asked question reaching me is about the setting of the grub screw valve on top of the timing cover.
The setting of this grub screw regulates the amount of oil being fed to the rear of the piston/cylinder.
It is not properly described in the military Maintenance and Instruction manuals people usually use as guide.
The setting of this was done at the factory and should normally not need to be touched. After 60 odd years however some cleaning of the insides may be required or the workmanship of previous owners needs to be checked.
The standard setting of this screw is one turn from the fully closed position. (According to WC Haycraft in 1936 and EM Franks in 1952).
 Its difficult to say if this is still correct for all engines, but depending on the state of the engine it may need some adjustment.
It should be adjusted such that there is a minimal amount of smoke coming from the exhaust. As the smoke from the exhaust does not only come from this setting, its a setting with lots of possible positions.
The standard setting is therefore the most likely correct one.

Oil drain pipes all over the motorcycle
The M/C has a number of pipes added to direct oil coming from various positions to be discarded at the underside of the M/C in an probably vain attempt to keep the Gentlemen's trousers clean.
They are: "Tappet guide oil pipe", "Magneto chain cover oil pipe", "Crankcase breather pipe" and not on engine but oil tank the "Oil tank air release pipe"
The routing and lengths of these pipes are usually not as original anymore after 70 years of tinkering by professionals and hobbyists alike.
Based on contemporary pictures I come to the following routing (dotted lines). Lengths to suit. Both Tappet guide oil pipe and Magneto chain cover oil pipe were routed between the oil feed and return lines and the crankcase and ended approximately below the footrest.

    Click picture to enlarge, note:  lines on my bike as shown are not fully "original".

A comprehensive description of all oil and petrol lines, sizes and means of fixing is given in  pdf file "Oil and petrol lines".

 

THREADS ON NUTS AND BOLTS.

Attached list (pdf file) shows all nuts and bolt sizes on the Norton 16H. Most of these are also used on the Big 4.
The list can be useful if you are searching what taps and dies you might need to clean up threads or recreate fasteners.