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Notes on the assembly of Norton cammy engines By George Cohen This text was sent to me in 2011, when discussing the reassembly of my 1931 CS1 engine. George asked me not to share these words as they would one day be part of a manual. Alas, George died in 2016 and – as far as I know – never completed the manual. I found these notes very useful and decided to clean up the text and share it after all, assuming George would not have minded given the circumstances. Be aware this manual is far from complete and missing text is indicated by (…). John de Kruif, November 2016. Introduction The information I have provided on this CD (or in the booklet) is a collection of writings, pictures, diagrams and other information pertaining to ‘Cammy’ Nortons. I trust it will be of interest to owners of these fine machines. It is predominantly about the engines. At any meeting of enthusiasts of old motorcycles, be it at a vintage race meeting, a Sunday afternoon run or a good banter in the local pub, the term ‘Cammy’ always refers to over-head cam shaft engines or machines from Velocette, AJS and Norton and a few other makes. The ‘Cammy Velo’, ‘Cammy Ajay’ and ‘Cammy Norton’ are undoubtedly the most sporting and desirable products from their respective manufacturers. The ‘Cammy’ engine with its cams above the cylinder head is also referred to as a single or double ‘knocker’; a derivation from the German word for cam being ‘Knocken’. With a single camshaft, the engine is known as a ‘single overhead cam’ or SOHC or ‘Single knocker’ and with two or double camshafts, the terminology is ‘double overhead cam’ or DOHC or ‘double knocker’. ‘Knocker’ is a term also applied to a hinged weight on a door or as a slang description of a woman’s breasts! There are other important terms to understand when discussing these machines and these include ‘International’ and ‘Manx’. Their meaning is confusing due to Nortons infuriating habit of using the same term for different machines, which is further compounded by an illogical numbering system! I have over 30 years experience of pulling apart and putting back together these engines and in that time I have learned a few tricks. With each old motor that sits on my workbench, I continue to learn. It is quite amazing how many factory and post-factory variations, modifications and changes are to be found and consequently this should be remembered when attempting to build an engine from a ‘pile of bits’! You would be very fortunate to locate a ‘barn find’ engine that not only retains the majority of its original parts, but also is in good serviceable condition. A few years ago, while wondering around the muddy fields of the ‘Boolee’ autojumble, I spotted a scruffy old cardboard shoe box with the inscription: “Norton stuff £10”. Inside was a large pile of oily and torn documents; all originals from P.L. Garratt. He was the Service manager at Bracebridge Street and I was very lucky! A lot of the information is from this source.

www.vintagenorton.com I hope you can learn a few tips about working on Cammy engines and ensure that our children will also be able to enjoy our passion; before we wreck them all! Finally, I should acknowledge the lessons that I have learnt from Stu Rogers and Geoff Bain, who know very much more about this subject than I do. George Cohen August 2011 SOHC (single over-head cam) engines The first OHC engine, designed by Walter Moore, appeared in 1927 and brought immediate success with a win in the Senior TT that year for Alec Bennett and fastest lap with Stanley Woods. This engine did not fulfil the initial expectations and Norton was well and truly beaten on the race tracks of Europe from 1928 to 1930, predominantly by Sunbeam and Rudge. Moore left to go to NSU in Germany. Arthur Carroll, the new Chief draftsman at Norton and Joe Craig designed and developed this motor. From 1931 to 1939 Norton racing motorcycles dominated and won practically all the Isle of Man races and European Grand Prix events. Only the odd Velocette and Italian or German machine would give them a run for their money. The privateer would also enjoy numerous successes in ‘Clubmen events’ and the lucky chap who used a ‘Cammy’ Norton on the road would always show his mates the way home. Later Edgar Franks, Leo Kusmicki and Doug Hele continually developed the Cammy motors and there are a surprising number of variations, so to the builder, BEWARE! The following notes are documented to help others who have not yet learnt about rebuilding, repairing, and tuning of these engines. I do not confess to know everything and I continue to learn from the mistakes that I make. The concept of a written manual is, perhaps a little old fashioned and consequently it might be better to produce a DVD of an engine rebuild. I tried this, but after hours, days and weeks of working out what all the little knobs and switches on the camcorder did, and many hours of filming an engine rebuild, I was unable to download the footage from the bloody camera to the computer! Far more difficult than a Cammy Norton engine rebuild! So if anyone wants to be camera man, director and producer for a DVD on this subject then please get in touch. I hope this ‘manual’ is easier to follow than the one Sony produced! There are some basic principles that also apply to all of these engines. With the overhead camshafts being driven by a vertical shaft and two pairs of bevel gears it is absolutely essential to recognise the importance of parallel lines, perpendiculars and accuracy at all stages of an engine rebuild. It is equally important to acknowledge that we are playing with objects that are 50 to 75 years old and any student of metallurgy will tell you that all these parts are well past there useful life. Magnesium cases that have been exposed to hot temperatures while in a racing battle are very much colder when the treasured Manx Motorcycle is laid up in a cowshed in Scotland during the winter months. Hot means expansion and cold means contraction, which means main bearing housings, for instance, will tend to crack when in a frozen shed and then let go when hammering down the Sulby straight! Without sounding too pessimistic, the effects of dampness and consequential oxidation of surfaces also leads to impending mechanical disaster.

www.vintagenorton.com Unless you are very lucky, most of these engines have had a hard life and many are near to being totally ‘shagged out’! They have been broken in the past and repaired by poor spanner men with many replacement parts either fitted incorrectly or poorly engineered. Although the basic layout of the motors in the production run from 1931 to 1957 is the same, there are many small variations and consequently knowledge of these changes is important. For example the cambox and cylinder on the early models was held by 4 studs at a square distance of 2 1/8th inch, and from 1931 this distance was increased to 2 ¼ inch. This engine was made in numerous variations: • Model 30. 490 cc: 79 X 100 mm to ‘International’ specification • Model 40. 348 cc: 71 X 88 mm to ‘International’ specification • Model 30M. 490 cc: 79 X 100 mm to ‘Manx’ specification • Model 40M. 348cc: 71 X 88 mm to ‘Manx’ specification • Model CS1. 490 cc: 79 X 100 mm • Model CJ. 348 cc: 71 X 88 mm • Model 596-: 596 cc: 82 X 113 mm; in International, Manx, CS1 and Trials variations. The Carroll/Craig motor was first seen at the Olympia Show in November 1929 and was a hybrid of the Moore and Carroll engines which basically had the former designer’s top end and the later bottom end; the exhaust pipe exited to the left (drive-side). The cam box was redesigned and this engine made its debut at the North West 200 in April 1930 in sensational style when Tim Hunt won the junior race on the 350 version. The 500 race saw Stanley Woods come home third. These early motors (…) We will start with the workshop. Besides having a decent set of spanners, a strong vice, a big hammer, an impact wrench (preferably air power to about 150 ft.lb. but ONLY used for undoing nuts) and a few pullers; you really need a lathe, a milling machine, cylindrical and surface grinding, all types of welding equipment, a spark eroder, surface hardening equipment, and about 50 special tools, jigs and fixtures to do the job properly! Most of us do not have this equipment and have to use other workshops to help out, but I would suggest that you have access to a lathe, because there are numerous times when bolts, studs, spacers and other fittings need to be modified for proper fitting or made from scratch. You must have a good set of Whitworth spanners (ring, open ended and sockets) and be prepared to make a few special tools and jigs. (…) Remove the carburettor, exhaust pipe (if it has an aluminium cylinder head, then it is best to put some heat into the head so that the exhaust ‘nut’ will free without damage to the internal threads in the ally head). A tight nut with years of dirty carbon deposits and Castrol ‘R’ can act like an abrasive grinding paste and ruin the threads), and detach the magneto advance retard and valve lifter cables from their respective levers. Put the engine into an ‘engine stand’ on the bench so that it is securely fixed; I use one which allows me to rotate the engine through 360 degrees. Fit an accurate and solid timing disc to the drive-side main shaft and establish TDC. A really well made and solid timing disc (mine took a whole day to make!) is a dual purpose piece of equipment in that it can be used in conjunction with a stud place through one of the front crankcaseengine mounting stud holes to lock the crankshaft in any position required. For instance

www.vintagenorton.com at 37 degrees BTDC when setting the ignition timing or just to hold the crank when loosening or tightening various nuts. Remove the spark plug. Measure the tappet clearances, ignition timing and cam timing and record these in your notebook. Also have a digital camera at the ready so that you can visually record all stages of the rebuild. Tappet clearances: inlet 0.010-0.012 exhaust 0.020-0.024 inch. The tappets on the end of each rocker are designed not to come lose by the use of a taper, an adjusting nut and a locking nut. It is important to understand how the arrangement works to avoid any possible damage. The actual tappet has a taper which fits inside the internal taper of the adjusting nut and is then locked into place by the locking nut. When any adjustments are required you must first loosen the locking nut and then with a light hammer tap the end of the tappet to break the taper seal. Failure to do this will result in a breakage of the adjusting nut. The adjusting nut is 26 TPI, which means that a complete turn equates to 0.040 of an inch and hence a turn of one of the six flat equates to approximately to 0.006-0.007 inch. Ignition timing. The original manuals stated 42 degrees BTDC on full advance, but most tuners now use 37 degrees. The cam timing should be: Inlet Valve Opens 57 BTDC Inlet Valve Closes 60 ABDC Exhaust Valve Opens 85 BBDC Exhaust Valve Closes 42 ATDC This is for Megga or open pipe. With silencer fitted retard inlet by 10 degrees, ie. 47/70 Now is a good time to measure the compression ratio. Support the engine at a tilt so that the spark plug hole is facing vertically upwards. Using oil, or other liquid, pour into plug hole until the level is at the bottom of the threads; rotate the engine around your previously established TDC and make adjustments if necessary to the setting. This is, in fact the most accurate way of precisely establishing TDC. Record the amount of oil required and then compute the C.R. On a 500 cc motor; 50 cc combustion chamber, gives a C.R. of 11 to 1. (500 + 50 = 550; 550 divide by 50 equals 11. Now you can open your toolbox! The first (…) steps are only concerned with dismantling, inspecting and recording the state and settings of the engine. Step1. With the engine at TDC and the valves closed (ie. on compression) remove the four slotted screws from the cam box bevel cover and if there is a central oil feed to the camshaft then make sure you do not lose the spring and oil feed jet. NOTE: the camshaft jet has a hole approximately 0.044 inch in diameter and the jet for the timing side engine main shaft is twice as large at 0.080 inch. I have occasionally found these to have been swapped around! The timing marks on the top bevels should match. Take a photographic record. Remove the cam box oil feed pipe and the two small valve guide lubricator pipes. (Originally, the exhaust valve guide lubricator pipe had a slightly larger internal diameter; and/or the small brass union had a larger hole, so that more oil went to the hotter exhaust guide.

www.vintagenorton.com That was the theory, but I know that some tuners blank these off). Completely unscrew the bottom vertical shaft cover tube nut and loosen the four cambox holding down bolts. (It is a good idea to mark, if not already done, the bolts so that they can be replaced into the same positions). Loosen the top vertical shaft cover tube nut, but only slightly. Then rotate the engine 90 degrees forward (the camshaft top bevel will rotate in the opposite direction, so that the timing marks are now at ‘half past four’. The cam box can now be simultaneously raised about ½ inch and titled towards the timing side of the engine. Hold the cam box in your left hand, and the vertical shaft in your right and lift away from the engine. The vertical shaft may or may not stay in place. Undo the top vertical shaft cover tube nut and remove the vertical shaft tube. With a bit of luck you should now have the cam box, with the vertical shaft tube on the bench and the vertical shaft separate from it. Remove the top and bottom Oldham couplings (do not mix them up) and clean, inspect and ensure the fit to the slots in the vertical shaft is just a smooth clearance; not too tight and not too sloppy. Step 2. Remove the vertical shaft tube and refit the cam box! Torque up the cam box bolts to about 12 foot/pounds. The reason for re-fitting the cam box at this stage is so that the vertical shaft to Oldham couplings clearance can be checked and noted. It is essential that there is free play; up and down; about 10 to 30 thou is the aim. This measurement is important at an early stage because it will relate to the rebuild stage when issues such as compression plates (under the barrel), piston, squish bands, valve to piston clearances, rocker clout angles and valve stem length, and vertical shaft length and Oldham coupling dimensions come into play on the final assembly. In repairing and rebuilding these engines it will be necessary to undertake numerous trial fittings, further fettling and measurement, and final fitting until a perfect assembly is accomplished. Step3. Having established the above described vertical shaft play and recorded it in your notebook, it is time to further dismantle the engine. Remove the cam box again and undo the four cylinder bolts (mark them in the same sequence as the cam box bolts). The cylinder head can now be removed; if it is a tight fit then use a piece of soft wood as a drift into the exhaust port and/or beneath the inlet tract. Do not hit the fins! Look out for any valve caps and do not misplace the four harden washers which are found in the cylinder head nut recesses. Sometimes these washers are so well jammed in the head that it is best to just leave them in position! Put the cam box, vertical shaft assembly and cylinder head to one side, these components will be tackled later. Step 4. With the piston at TDC, lightly scribe an arrow pointing forward on the piston top (there will probably be a fair amount of carbon present), so that you know which way to replace the piston (unless a new one is required). Break the joint between the crankcase and cylinder base by very gently tapping the fins with a light rubber mallet. There may be a ‘compression plate’, usually 0.5 to 2 mm thick fitted between the cylinder base and the crankcase top and/or a paper gasket. Once the barrel is loose, turn the piston to BDC and lift the barrel up and away and place a clean piece of rag in the crankcase mouth to prevent and debris falling into the crankcase. Do not remove the piston yet. Step 5. This is the best time to dismantle the timing side because with the piston still fitted to the connecting rod, this can be used to ‘lock’ the crankshaft assembly when undoing the three nuts on this side of the engine; namely the two holding the magneto chain sprockets and the timing side main shaft nut which holds the bottom bevel and half timing pinion. Remove the magneto chain cover and undo the two nuts holding the timing sprockets; a snug fitting ring spanner and a smart tap with a mallet should loosen

www.vintagenorton.com them. Withdrawing the sprockets from their tapers is not so easy; they are usually stuck on very tight. Do not be tempted to use a big screw driver and brute force ... it will end in tears with a broken sprocket or broken inner timing cover. A high quality puller and a blow touch to warm the sprockets are required. With both sprockets and the timing chain removed, unscrew the remaining four slotted screws and the cover can be lifted away. The big end feed jet, the oil pump driving gear and the oil pump driving plate will all come off and be careful not to mislay the small spring which is behind the feed jet. Step 6. With the bottom bevels now exposed, make a note of the mesh of the bottom bevels and record if the backlash is correct or excessive. Undo the four nuts holding the bottom bevel housing and lift away; note the packing shims located beneath the housing and remove them from the four studs. Also be careful not to mislay the perforated steel cup which sits on top of the US8 self-aligning bearing in the housing (the top bevel housing has a similar part, but is shallower). Lock the crankshaft by either putting a piece of wood or aluminium plate beneath the piston skirt and crankcase top. Undo the left-hand nut from the main shaft (this should be tight; on re-assembly it is torqued to 50 ft/lb) and with a suitable puller remove the half-timing pinion. Behind the halftiming pinion is the main shaft bevel which is usually tight on the shaft and hence can be difficult to remove. It can be levered off with a good quality screwdriver or thin ‘prybar’; be careful not to damage the casing. There will be usually one or more shims behind the bevel and carefully withdraw these and store with all the other parts of the timing side and bottom bevel assembly. The woodruff key on the timing side mainshaft can remain in place. It is useful to have a number of boxes or trays (the cartons from the Chinese take away are ideal) to put all the parts from various sub assemblies into. Step 7. The piston can now be removed. Carefully price out one of the circlips and gently warm the piston with a hot air gun. Using the correct size drift (or gudgeon pin puller) withdraw the gudgeon pin and place it with the piston in one or your boxes. The Crankcase can now be split. If you have not already removed the crankcase drain plug, do so now and wipe the inevitable puddle of oil up with some old rag! Remove the timing disc previously fitted and the engine sprocket if it is still in place. Remove the remaining crankcase studs and nuts, the slotted screw situated in the timing side case at the bottom rear and finally the top rear bolt which carries the cylinder oil feed adjusting screw. The crankcase halves should now ‘fall apart’, but they are often stuck by gobs of red hermite or other gasket goop used in excess by a previous owner! The shafts may also be tight in the main bearings. The best and safest way to part the cases and avoid any damage is to support the assembly on the bench in its normal upright position with a number of blocks of wood and carefully tap the inside of either the drive side or timing side crankcase mouth with a piece of wood. One side will slide from its main shaft and then with the use of your supporting wooden blocks, lightly tap out the other main shaft from its bearing/s. Hopefully this will be straight forward, but occasionally you will find that a previous owner has either used loctite or some other poor bodge to fix the inner race of one or more of the bearings! In this case, application of heat usually does the trick, by loosening the loctite bond. I have also come across engines where the inner distance piece, located between the two drive side main bearings is a very tight fit and this is difficult to sort out. Again using good wooden supporting blocks, an aluminium ‘plug’ on the end of the main shaft, hit the plug with a heavy mallet. Removing the main bearings. The main bearings are held in place by plates with either three (International models) or four (Manx models) 3/16 whitworth slotted, countersunk screws; soldered into place. After cleaning the cases, put each case into the oven for about ten minutes to get it nice and hot (when you gob on it, the spittle should

www.vintagenorton.com form littler balls). Using a small blowtorch to melt the solder and with a snug fitting screw driver undo the screws and remove the plate. Oil pump removal. This is a tricky job, be careful not to mess things up. Remove the two screws securing the pump and carefully tap out the holes in the pump body with a 9/32 inch diameter 26 TPI tap. Screw into each hole a stud of about 3 inches long and correspondingly machined to the same thread (do not be attempted to use ¼ inch; you will break the pump body casting). I have two studs which are 9/32 in diam for (…) The body of the pump is made from a ‘Mazack’ type alloy which is brittle and does not age particularly well; it is easy to break (I know, because I have broken a couple!). The studs should stand proud of the bevel chamber joint face. Drill two holes into a sturdy piece of steel or ally and (…). You will now have a number of sub assemblies of the engine on the bench: • The cam box with top bevel housing still attached. • The cylinder head with valves, springs and guides. • The barrel and piston. • The timing side inner and outer covers with associated parts and the bottom bevel housing. • The crankcases, oil pump and crank assembly. • And probably a few other bits which you have either forgotten to catalogue or are just fit for the scrap bin! Remember, it is a very good idea to record your work with a digital camera and a pencil and note book The CamBox (sometimes referred to as the ‘Rocker Box). The single knocker cam box, as used on all the ‘cammy’ models from 1931 to 1958, is a poor design, is prone to break, is difficult to work on and it leaks oil like a primary chain case! Why Norton persisted with it for over 25 years is anybody’s guess? Most of the research and development was done on the double knockers, although in 1935 the works machines sported an enclosed cam box. The SOHC cam box is usually made from aluminium of aircraft quality RR50, but on the Manx models it is made from Magnesium. There are basically two types with three developmental changes over the years. There are at least three types of rockers. On the standard models, the oil enters by ¼ inch BSP union via the top left of the cam box, along a small passage to the centre of the cam box and is then metered into the box by a distance piece between the cam shaft ball race and the cams. This distance piece has an external keyway which mates once every revolution with the oil feed hole, and admits the correct amount of oil. On the Manx type models, this entry is not machined and the lower entry point on the lower left side is used. Oil is delivered via the exit hole and along a passage in the top bevel cover to a central jet (0.042 inch hole) which squirts a continous supply of oil along the hollow cam shaft, out through a hole in the camshaft and then out through another hole in the flank of the cam and hence directly onto the mating surfaces of the cam and its complimentary rocker pad. Very early cam boxes (1930 and early 1931) are NOT interchangeable with the later ones since the four mounting holes are at 2 1/8th inch distance in a square, whereas from mid 1931 they dimension was increased to 2 ¼ inch. Very early cam boxes incorporated a “fixed” cam, where both cams were made in one piece and hence there was no vernier adjustment. The rockers in the early cam boxes are NOT interchangeable with the later ones, because they are of a smaller diameter.

www.vintagenorton.com Rocker variations (…). The rockers are fitted with pads at the opposite end to the adjusters. These pads wear out after prolonged use, particularly if the oil supply to cam box is insufficient. They are easy to replace with new items (… thickness = related to rocker movement and fouling). Dismantling the cam box. When working on the cam box, I use a variety of special tools and jigs. The simplest ‘holding jig’, taken from Garratt, can be easily made from a six inch length of hexagonal bar and two 3/8 inch studs. It makes life very much easier. Being hexagonal, the jig can be turned round to work on both sides of the cam box, tilted at a convenient 30 degrees. Remove the vertical shaft, the cover tube and the top bevel housing cover. Turn the cam box around and then remove the two split pins from the castellated nuts on the end of each rocker shaft and then remove the rocker shafts. It is a good idea not to mix up any of the parts, so use a separate tray for the inlet and exhaust components. Remove the six slotted cheese head screws from the cam box end cover and withdraw it from the main cam box. Slacken the two oil retaining pad screws beneath the cam box (on early camboxes there were also adjusting screws at the top as well) and carefully remove each rocker and place it in the appropriate tray. With a felt tip pen mark a line across the two cams; this will help in establishing the position of each cam when rebuilding the cam box; provided the previously recording cam timing was correct! The cams are located together by means of a (…) roller fitting into holes in the butting faces of each cam. The nut which holds the bearing and the cams onto the shaft is a left-hand thread and hence is undone by turning in a clock-wise direction. It should be very tight (on the rebuild it is torqued to 70 ft/lbs) and although some manuals suggest that the square end of the camshaft is held while undoing this nut, I do not advise this method; there is a much better way. Hold the cam box in your jig, firmly held in the vice. Use a long (…). The most common fault with the cam box shell, is a broken tunnel. This is usually due to excessive wear at the rocker pad ends, which in turn means that the underside of the rocker hits the tunnel, causing the latter to break up (marked with a red line in the photograph). The purpose of the tunnel is to keep as much oil at the cam to rocker pad interface as possible and when it is broken, the oil loss from the cam box becomes so bad that most of the riders bottom half and the machines rear end are drenched in the stuff! The tunnel can also be damaged by inexperienced mechanics (bl..dy idiots) who do not know how to remove cams and replace pads. The next most common fault with the shell is a broken ‘leg’ due to someone failing to check that all four mounting points for the cam box are perfectly horizontal and square (extended head bolts on the Models 30 and 40, individual spacers on CS1 and CJ). As in all alloy (or magnesium) castings, threads are often damaged and mating surfaces scored by careless use of the wrong tool! To repair the tunnel, I machine away the broken item so that I am left with a cam box minus its tunnel. I spin this (slowly) in the lathe on a specially made mandril. I then make a new tunnel from a piece of alloy tube (2.125 inch o.d.) and use ‘J B weld or araldite’ and a 2BA countersunk screw to fix it in place (see pictures). There is more than one way to machine the cam box; spin it and hold the tool or viscera-versa! To repair a broken ‘leg’, clean the surface of the break and apply a thin layer of weld with your TIG welder. Dress the weld with a clean file. Then make a new leg from a square piece of good quality aluminium bar, hold it in the correct position and weld in place. Dress the weld and set the cam box onto the bed of a Milling machine. Mill the new leg accurately so it matches the dimension of the unbroken one and finally drill the

www.vintagenorton.com hole. In my workshop I have four different holding jigs for cam box shells alone; any decent machinist will easily work out what jigs are required. (…) It can take a very long time to do all this work and it would take me even longer to write a manual on SOHC cam box re-building! My advice is to NOT do this work unless you have someone with previous experience to show you how. There are many potential traps! The slotted cam shaft distance piece must be a good fit in the centre hole of the cam box and be of the correct length. Original items are usually satisfactory, but I have come across newly made components which are too short, (…) which means the inner face of the exhaust cam binds against the aluminium housing. It is important to check this. Top bevel housing, mesh. Correctly set up mesh, but DO NOT make a final assembly with your favorite gasket goo, because you will have to remove the top bevel housing from the cam box AFTER you have set the cam timing, to correctly tighten the two cam shaft nuts (see later) Once the cam box shell is perfect, and all the other components repaired and fettled for perfect fitting, it is time to set the cam timing. It is a good idea to try the fit of the two cams and the woodruff key onto the camshaft before fitting the camshaft into the cambox. Hold the camshaft in your left hand and place the small woodruff key into its slot, than slide on the exhaust cam along the shaft until it locates with its key; this should be a firm sliding fit. Tight or slop is not correct, so correct any problems. Then slide on the inlet cam. Once you are satisfied that the cams are a good fit onto the shaft, remove them and proceed to the next stage. Old cams and old shafts frequently have damage in the form of burrs, scrapes, chips or what ever and if any of these faults cause the cams to fit badly then you must replace them with new items. A useful trick is to make a pair ‘dummy’ cams from a piece of aluminium round bar (0.0690 inch wide and 1.075 inch O.D. and 0.0627 inch I.D.). Fit the top bevel to the cam shaft and screw on its retaining nut to finger tight, having previously checked that the locating peg is a snug fit in all the holes. Slide the camshaft into roller bearing and do not forget any shims which may be present. Fit the cam shaft distance piece, the exhaust cam, which is located onto the shaft by a small woodruff key, the ‘dummy’ cam, thin distance piece, the inner race of the roller bearing and finally the left hand thread nut to just tight (about 5ft.lb.). The use of a ‘dummy’ inlet cam enables the exhaust timing to be more accurately obtained because it eliminates the spring pressure on the ‘real’ inlet cam when the valves are at overlap. Fit the cambox onto the cylinder (…). (…) Valve timing. These timing figures can only be achieved when there is no wear to the cams, or rocker pads. For timing the cams from scratch the following procedure should be adopted: 1. Fit a degree disc to the engine main shaft, locating ‘zero’ with the piston at TDC. 2. Set both valve clearances to their respective correct figures of 0.010 for the inlet and 0.020 for the exhaust. One complete turn of the outer tappet is 0.040 inch; hence a turn of one sixth (six flats to a hexagon) is about 0.007 inch. 3. With cam box ‘loosely’ assembled on top of the engine, the vertical shaft in place (leave the shaft tube out at this stage) which locks the bevel onto the cam shaft. This will enable the peg which locates the bevel to the cam shaft to be removed.

www.vintagenorton.com 4. Rotate the engine forward to the position where the exhaust valve should commence to open ( 85 BBDC ). 5. Rotate the camshaft in an anti-clockwise direction until the exhaust cam contacts the exhaust rocker. As the locating shoulder on the camshaft has 11 holes and the bevel 12 holes, it will be found that the locating peg can be inserted through both components where the two holes coincide. 6. Replace the nut locking the bevel and tighten firmly to about 10ft.lb. (this will be later tightened to 70 ft.lb.) Check the opening and closing points the exhaust cam, repeating the procedure as required to obtain the correct timing. The most accurate way is to hold a 0.016 inch feeler in the tappet clearance and rotate the crank backwards; when the feeler is just nipped, this is the closing of the exhaust cam. Rotating the camshaft in a clock-wise direction, advances the exhaust cam. This vernier adjustment gives a crankshaft movement of approximately 3 degrees, thus allowing a reasonable accuracy. If the factory figures cannot be obtained, it is best to set the closing of the exhaust valve as this is more important than the opening. 7. Now remove the cambox, remove the end cover, undo the left hand nut and fit the inlet cam. 8. The inlet cam is located to the exhaust by means of a small roller connecting the two cam faces. The eleven and twelve holes allow a similar vernier adjustment as before. By inserting the roller in the appropriate holes, the required setting for the inlet cam can be made. The usual combination of holes is :



NOTE this diagram is wrong, there are 11 holes in the inlet cam and 12 in the exhaust!

Exh No. 5 Inlet No. 1 Exh No. 6 Inlet No. 2 Exh No. 7 Inlet No. 3 Exh No. 8 Inlet No. 4 Exh No. 9 Inlet No. 5 Note: moving down the sequence advances the Inlet timing. 9. Cam timing is made with a 0.004 inch clearance between rocker and valve; so for the exhaust timing use a 0.016 inch feeler gauge and when this nips up the setting clearance of 0.004 is obtained. For the inlet, use a 0.006 inch feeler. 10. The above process may need to be repeated until the correct figures are obtained. Once you are satisfied that the cam timing is spot on, the rocker clout angles are correct and the tappets clearances are correct, it is now time to pull the cambox to bits again! The reason for doing this is twofold; firstly to correctly tighten the two nuts on each end of the camshaft and secondly to pack the cam box with its corks and ‘felts’. 11. Remove the camshaft, noting the position of the inlet cam to the exhaust cam and hold the bevel gear firmly in soft lead jaws in a large vice. Tighten the nut to

www.vintagenorton.com 70 ft.lb. This way is preferable to holding the square end of the camshaft because it avoids putting a twisting force on the cam shaft and damaging the shaft. 12. Re-fit the camshaft, remembering to fit any shims between the bevel gear and the bearing. Fit the distance piece, the exhaust cam, the inlet cam, the thin spacer, the bearing and finally the left-hand nut. Have an assistant hold the bevel nut with a long ½ inch Whitworth ring spanner and torque the other nut to 50 ft.lb. The reason for this seemingly protracted procedure is to make sure both nuts are tight; the tightening of a right-hand nut and a left-hand nut on either end of a shaft means that as one is tightened, the other is potentially loosened! 13. Fit the corks (…). 14. Check that the underside of the cam box is not touching the top of the hairpin spring holders and also check the rocker pad adjusting screws are not touching the top of the cylinder head. It is important that the cam box sits squarely on all four cylinder head bolts. CAMBOX FITTING 1. Remove magneto cover, set engine at TDC, just after points have opened; ie. at the top of the firing stroke. 2. Remove the four allen set-screws from cambox cover and set the top bevels with red marks in alignment. Watch out for the oil-feed jet and spring. 3. Note that the rockers are stiff to move (because of new felts & corks), this is normal. The exhaust one is "stiffer" than the inlet. 4. Lift the rockers upwards to the closed position. 5. Since you need to check the oldham coupling clearances, the first assembly will be a "trial" and without the fitting of the chrome vertical tube. 6. Make sure the bottom oldham coupling is in place. 7. Put the top oldham coupling into the slot in the top-bevel shaft and take the vertical shaft and push the top into the top oldham coupling. (the vertical shaft has the circumferential ridge at the bottom.) 8. REMEMBER the small shim on cylinder bolt number 3. 9. Have the four cambox bolts ready. 10. Hold the cambox in your left hand, and the vertical shaft in your right. 11. Move the assembly adjacent to its correct position and with the cambox slightly above and towards the timing side, of its final position, fit the bottom of the vertical shaft into the oldham coupling and at the same time lower the cambox onto the cylinder head bolt tops. Remember the shim on number 3. 12. No. 11 is the tricky bit, particularly when the chrome tube is fitted, because you have to juggle your fingers to stop the vertical shaft and top oldham coupling from "falling out" of the top bevel!! 13. Fit the 4 cambox bolts and tighten. (final torque is a six inch spanner with a moderate pull). 14. Gently rotate engine back and forth to make sure all is correct. 15. Grab the vertical shaft and check that there is clearance "up and down". Anything between 0.005 to 0.050 inch is O.K. 16. Rotate engine until red marks align on top bevels, undo the four bolts and remove cambox. 17. Go for cup of tea! 18. Now for the final assembly! 19. Fit the ubiquitous carpet under lay around valve stems; its easier to do this with the cambox off.

www.vintagenorton.com 20. I have supplied two new copper/asbestos sealing rings for the vertical shaft tube nuts. Be careful not to over tighten the large nuts which tighten into the vulnerable alloy of the top and bottom housings. 21. Turn the cambox upside down. Put the smaller of the two "steel cups with holes" into the top housing. Flange against bearing. Put the oldham coupling into its slot. 22. Take the chrome vertical shaft tube (flange at top) with the top nut slid up to the top of the tube (and with new/old rubber seal in place) smear some non-hardening gasket goop onto the threads of the large nut. Push new copper washer over threads. 23. Screw large nut into housing and tighten using appropriate spanner (use the adjustable!) the copper/asbestos gasket should "flatten" down a bit. The FINAL tightening of this nut, and its lower brother is best done with a good fitting spanner (NOT the adjustable) when the engine is hot. 24. Fit the lower large nut onto the vertical shaft tube and apply goop and washer as before. 25. Hold the "cambox-housing-vertical shaft tube" assembly in your left hand and place the vertical shaft into the appropriate place, into its oldham coupling. Check that the location is good by rotating slightly the shaft and the bevels should move. 26. Place the larger of the two "steel cups with holes in" onto the bearing in the bottom bevel housing chamber. Make sure that the oldham coupling is also in place. 27. With engine at TDC (after points have opened) and red marks on top bevels aligned fit the assembly as before. This is a bit tricky since the vertical shaft and the top oldham will want to follow gravity! 28. Wriggle the cambox into place and fit the four bolts as previous and (remember shim on number 3). Check the valves are opening by rotating engine. 29. Tighten lower large nut. 30. Check tappet clearances. Since I have not disturbed the adjustment, they maybe perfect. Inlet: 0.010 to 0.012 Exh: 0.020 to 0.025 inch. 31. Connect the two small oil pipes which feed the valve guides. (that's the theory, but in practice they tend to get choked up. Particularly the exhaust side). 32. Fit the cambox oil feed and wire up. 33. Fit the cambox cover with the four NEW screws. Be careful about the oil-feed jet and spring. 34. Re-fit magneto cover. 35. Turn on oil and fire up!!! TO BE FINISHED (…) RE-BUILDING Crankcase cleaning. DO NOT sand blast, grit blast or use any type of abrasive when cleaning the crankcases. A stray grain of sand in an oil-way can cause havoc. Use plenty of your favorite cleaning fluid, fine ‘Scotchbrite’ and a lot of elbow grease. The ONLY way to make sure that all of the crap is clear of the internal oil ways is to use: extra long twist drill bits ( 3/16th & 7/32nd inch) and to turn them by hand through the oil ways. High pressure air and cleaning fluid may not clear a partly occluded oil way; I learnt this the hard way! Inspect the internal threads (there are 8 or 9 on the drive side and 24 or 25 on the timing side) and repair any damaged threads. Check that both halves of the crankcases fit together perfectly. If there is any damage to the mating surfaces, then this is a potential source for an oil leak. By removing the two locating dowels, the two halves can be lapped together with fine grinding paste; hold one half in the vice and rotate the other half back and forth. Clean off all the paste and refit the dowels.

www.vintagenorton.com With the crankcases absolutely clean and checked for any cracks, damage or stripped threads, you are now ready to start rebuilding the engine. Main bearings on the Manx and International models do vary, but essentially there is a ball on the timing side and an outer ball and inner roller on the drive side. The drive side bearings are separated by inner and outer spacers. Make sure the inner spacer is a free sliding fit on the drive side mainshaft. Using a bench grinding wheel, carefully grind two small notches, 180 degrees apart, in the outer ring of the timing side main bearing; avoid getting any metal dust into the bearing. Do the same for the outer ring of the drive side roller which is much easier to do because it is separate from the rollers. The purpose of these notches is to prevent rotation of the bearing in its housing by making a complimentary ‘notch’ in the retaining plate. Check the fit of all three new bearings on their respective main shafts. They should be a firm push fit. If the shafts are worn then you have to repair this defect. Metal spraying, electroplating are preferable to a ‘Loctite bearing fit goop’! Using three NEW 3/16th countersunk Whitworth screws, ½ inch long, tin the tops of the screws with solder. Also tin around the three (or four) holes in the retaining plate. Put the timing side crankcase into the oven for about ten minutes. With the case hot, you have to work quickly to fit the oil pump, timing side main bearing and its retaining plate, before it cools. A ¼ inch diam rod about 3 inches long and with a 26TPI thread cut on one end is screwed into one of the two threaded holes in the base of the oil pump housing. With the hot case held vertically, the oil pump is pushed over the aligning rod and into place; a light tap with a copper mallet will ensure it is home. (If the timing side case were to be horizontal on the bench, then the oil pump may drop one of its two lower most cogs as it is pushed home). Quickly screw in the two oil pump retaining screws. Now flip over the case and drop the new timing side main bearing into place; again a gentle tap with an aluminium drift will ensure it is fitted correctly. With a felt tip pen mark the positions of the two notches, so that their position can be seen when the retaining plate is in position. Working quickly so as to retain the heat in the cases, place the main bearing retaining plate over the bearing and screw in the 3 (or 4) screws and with a large soldering iron solder them into place. Clean up any excess flux. Repeat the procedure for the drive side. Examination of the big end (…) Spur gear drive for all Cammy engines. When the bottom bevel gears have been correctly shimmed to obtain perfect mesh, with even backlash of a couple of thou’ for 360 degrees; remove the bevel housing. With the spur gear in place fit the timing cover. You can now feel (by sticking your dinky in the hole!) both the axial play of the spur gear in its two bushes and the mesh with the half-timing pinion. Adjust, with spur gear shaft shims and careful cleaning and lapping of both gears so that all feels perfect. Repeated fettling, trial fitting, fettling and further trial fitting is essential at all stages of an engine rebuild. Although it takes hours to get adjacent components to fit together properly, the rewards are obvious in terms of power and reliability. Place the timing side crankcase (…) Bottom bevel housing. Important to check that the US8 bearing is held in position by the larger of the two holed dished retaining spacers. This is done by removing the vertical shaft tube from its lower nut and then tightening the nut (without the copper sealing washer) so that the bearing retainer firmly holds the US8 Bearing.

www.vintagenorton.com With the bottom end of the engine finished, it is now necessary to make a trial assembly of the top end to ensure that the following critical clearances are correct: 1. The piston to cylinder head clearance 2. Valve spring tension The tappets vary in length (…) Piston ring clearances. It is important to check the rings move easily inside their respective grooves on both old and new pistons, particularly on the top ring groove, beneath the valve pockets where the machining process occasionally closes up the groove by a tiny amount. If the barrel has had a liner fitted in the past, it is very important to secure it. A ‘cold seizure’ can result in the piston expanding onto the liner and drawing it downwards with devastating results. This happens when a very hot engine is re-started after just 5 minutes or so; the piston is still hot (and hence expanded in diameter), but the barrel is cooling (and hence shrinking); the piston the expands faster than the barrel and grips the liner and pulls it away from its bore in the barrel! By drilling a 4mm diameter hole through the barrel and liner just beneath bottom flange and at either side (not front or rear) and tapping with a 2BA thread. Counter sink the new threaded hole and fit a 0.080 inch long slotted countersunk screw. Dress the top after fitting so that it is not proud of the O.D. of the bottom.