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Workshop Manual 2017-02-03T12:36:00+00:00

Workshop Manual

My “Translation” of the workshop manual text, now including all tables and figures as provided in the original manual

The Moto Parilla 175 / 200 / 250 “High Cam” Workshop Manual

Please Note:

This is a literal translation of the Cosmopolitan Motors version of the Moto Parilla Workshop Manual based on my own experiences working on the engines & being in order confused, disappointed & amused by the information contained within. It is, as far as I know, the only workshop manual produced for the high cam engine & must have originally been written in Italian. Cosmopolitan in their wisdom chose to employ a translator who was evidently neither English nor Italian to produce the guide & the result (to one not actually trying to rebuild an engine) is endlessly amusing. Added to the language difficulties are numerical ones caused by the conversion from metric units to imperial which in some cases have been taken to 6 decimal places. Owners of 0.001968 feeler gauges may feel cheated by my decision to round this (and other 6 figure measurements) down; in this case to 0.002 – I apologise in advance.

I have made no attempt to add detail to the operations described unless they are very confusing if left as is or just plain wrong.

Any addition made by me is in italics, any original text in bold italics

Many of the operations required are glossed over or not mentioned at all.

Treat the manual as a rough guide to what needs to be done rather than the definitive publication it should have been.

Is it any wonder many of the surviving High Cam Parillas are in a terrible mechanical state when part of the instruction to set the tappet clearances advises:

“Rotate the cam in such a way that in correspondence with every plates there is the arch of rest of the cam itself”

Usual disclaimer – I cannot take responsibility for any damage to your machine you may cause by following any of the procedures advised in this manual…take it up with Cosmopolitan Motors!

All tables and figures are embedded as PDF’s.  Mouse over to highlight and click on highlighted table or figure to open in a pop-up.
Use the toolbar at the bottom to zoom etc.  Please allow 20-30 seconds for the PDF’s to load in the background before scrolling this page.

Maintenance of the Motorcycle

Maintenance of the motorcycle is comprised of checks & adjustments to eliminate wear & tear caused by use of the machine.

It is a good idea to keep the motorcycle clean & free from dirt & grit, not just for aesthetic reasons but to avoid the wear caused to the moving parts by accumulations of these contaminants.

During cleaning operations it is an ideal time to check all the systems for their correct functioning especially if when riding you have noticed some deterioration in some functions.

a) Check of the braking system.

Check that the front brake lever has about 0.4 / 1cm free play at the lever end. If not use the cable adjusters to achieve this.

Ensure the steel inner slips through the outer sheath smoothly. If not remove the inner , grease it & replace.

Check that the brake plate has no cracks where it engages with the torque lug on the front fork.

Check that the operating lever of the rear brake has free play of 0.6 / 1.5cm at the pedal end. If not use the adjuster on the end of the operating rod to achieve this.

If, due to overheating , or accidental spillage of oil onto, the brake shoes the braking performance will be affected. It will be necessary to disassemble the brakes & repair the shoes.

The operation can be limited to sanding the shoes when just the hard surface needs to be removed or may involve replacement of them if they are too worn or if the oil impregnation extends to the full depth of the lining.

Should you replace the shoes be sure to file the leading edges of the shoes – those resting on the operating cams – for a distance of 0.4 to 0.6 / 1 to 1.5cm to remove the sharp edge of the lining. Failure to do this will lead to locking of the brakes with even light pressure & may even lead to breakage of some parts.

b) Check the stability of the motorcycle.

When being ridden it should travel in a straight line even when the handlebars are not held & with no need to lean to maintain this. If this is not the case then the cause must be found:

Make sure the steering head bearings are lubricated & correctly adjusted.

Make sure the wheels are in line, that is , that the rear wheel is in the same plane as the front.

This can be checked by means of a metal or wooden straightedge held to the sides of the wheels or, as usually done, by means of a thin rope.

If they are not in line then move the rear wheel using the adjusters on the rear spindle. Take care not to over tighten the chain & follow the instructions in section f)

Make sure the tyres are not split or excessively worn, that they are inflated to the right pressure (see owners manual) & that there are no manufacturing defects or deformation caused by incorrect fitting.

Make sure there is not excessive axial play between hubs & wheel spindles. If there is ensure the spindle nuts are tight & if this does not cure it check the wheel bearings for wear.

c) Check the correct operation of the lighting equipment

Ensure the battery & dynamo are correctly maintained as described in the second part & in the Owners Manual.

d) Make sure the front suspension is operating correctly

When running on uneven surfaces or cobbled roads the front wheel should judder or move in an undamped fashion.

If the wheel fails to follow the terrain in a controlled fashion this might be due to an incorrect amount of damping oil (250cc per leg) or an incorrect grade (SAE 20w). It could also be due to worn internal parts. If this is the case they will need to be rebuilt. Normally the internals need little attention being sealed & constantly lubricated.

Change the oil after the first 1000 Km & after every subsequent 10000Km. At every oil change flush the internals with petrol to clear debris.

e) Make sure the swinging arm spindle is well lubricated.

Apply a grease gun filled with a suitable grease to the lubricating nipples regularly. Check the shock absorber mounting rubbers are not perished & the springs etc are not damaged.

Should the shock absorbers fail they can be repaired & refilled by specialists.

f) Check the rear chain tension.

It must be free to move 0.590 / 1.5cm with no one on the bike. If it requires adjustment the wheel spindle nuts will need to be loosened & the chain adjusters on the swinging arm ends can then be moved to give the correct tension.

When adjustment is completed check wheel alignment as previously described in section b)

Check that the chain tension is still correct when the wheel is rotated to the point where the chain is at its tightest & the swinging arm is moved through its full arc. There must be no point where the chain is taught.

If the chain is too tight, besides it wearing quickly, it can ruin the gearbox secondary shaft, gearbox & wheel bearings. Check the condition of the chain, rear sprocket & gearbox pinion & replace if worn. Ideally the 3 components should be changed as a unit to avoid the worn components ruining the new part quickly. Always keep the chain well lubricated as described in the Owners instruction manual.

g) Check the tightness of all nuts & bolts. Replace those with worn threads or damaged by spanners.





a) Ignition timing

b) Fuel system

c) Compression ratio setting

d) Valve timing

e) Lubrication system


a) Disassembly & checking of the cylinder head

b) Checking the piston & barrel

c) Disassembly of the left side cover & check of the internals (cam followers, crank oil injector, primary drive gears, cam drive, clutch & oil pump

d) Disassembly of the right side cover & check of the internals (generator, gear change & kickstart)

e) Splitting the crankcases & checking the internals (crankshaft, gear cluster, oil filter)


a) Check of compression ratio, ignition timing & cam timing

b) Carburation adjustment



1. – Description of the engine

The 175cc 4-stroke engine fitted to the Lusso Veloce, Sport & Sport Derivato Serie (GS / MSDS) has been designed to combine high strength, low fuel consumption & high power. The engine is a 4 stroke single cylinder, inclined forward at 5deg, with a light alloy detachable cylinder head.

The combustion chamber is hemispherical with the spark plug placed to the right side of the engine. The valves are inclined at 90deg and are operated by a high placed camshaft which itself is driven from the crankshaft at a 1:2 ratio. The cam pushes flat-faced followers which operate rockers via short pushrods.

The head & cylinder are cast with many fins to provide air cooling. This efficient cooling system & classic valve operation system, tested in numerous sporting competitions, makes it possible for the engine to operate at high thermal efficiency & consequently the fuel consumption is exceptionally low. The piston is made from a high strength, low expansion light alloy in an elliptical shape which allows the minimum piston to cylinder clearance to be used & avoids seizures. The cylinder head is made of high strength alloy, die cast. The cylinder is made of a special cast iron of a type which reduces wear to a minimum. The crankshaft is fitted with particularly sturdy bearings. The big end bearing fitted to the LV & S models is a steel bush plated with a low friction alloy lining material. On the SPORT DERIVATO SERIE engines the big end is a needle roller type with a light alloy bearing cage. Each crankshaft is statically & dynamically balanced.

The engines are equipped with automatic timing advance/retard mechanisms or a hand control.

The ignition is by battery & coil with a 6volt dynamo for charging.

The multiplate clutch is bathed in oil & is fitted with long lasting friction inserts.

The 4 speed gearbox is a constant mesh type with bushed pinions. The ratios are carefully chosen to make most efficient use of the motorcycle.

The primary transmission is by helically cut gears specially ground to provide silent operation. Lubrication is by a large capacity gear pump which supplies oil to the engine via internally cast oilways.


The types of motorcycle (LUSSO VELOCE – SPORT – SPORT DERIVATO SERIE) have characteristics which suit every owners needs:

LUSSO VELOCE – touring motorcycle with low fuel consumption & maintenance costs.

SPORT – sporting motorcycle, regularity races, motocross, etc

SPORT DERIVATO SERIE – sporting motorcycle for road racing.

The performance described can be maintained unaltered for a very long period only if correct running in procedures are adhered to & maintenance is carried out as described in the Owners manual supplied with every machine & adjustment & overhaul is carried out as described in the following chapters.



Tuning of the engine is done by a succession of checks & adjustments which will eliminate the causes of defective running. The checks must be made on the ignition, carburetion & other engine systems as described. IT IS A PROCESS OF ELIMINATION STARTING WITH THE FIRST GROUP & CONTINUING TO SUCCESSIVE ONES IF BAD RUNNING PERSISTS.

a) Checking the ignition system

Check that the sparking plug is of the correct heat range for the engine – Table No. 1

A too hot plug causes loss of power & revs and can cause overheating of the cylinder head. Too cold a plug causes difficult starting & irregular running.

Remove the plug, rest it on the cylinder head, reconnect the plug wire & with the ignition on turn the engine over with the kickstarter.

The plug should fire regularly & cleanly. If not clean the electrodes with a fine wire brush & check the plug gap is as recommended (0.61 to 0.71mm, 0.024 to 0.028) (Figure No.1)

Too large a gap may cause misfiring & power loss with very difficult starting. Too small a gap will affect the slow running as carbon forms on the electrodes.

Should the above checks & adjustments not effect a cure then change the spark plug.

Check the spark plug lead & plug cap. The lead should be in perfect condition with no cracks in the insulation, the connection to the plug cap& the coil end connection must be in perfect condition. Due to the high voltages involved even cables seemingly in good condition can break down & cause problems due to troubles not visible to the eye. This will cause misfires & problems already mentioned.

Check the contact breaker points.

The contacts, when dirty, worn out , with too small or too large a gap can cause difficult starting,  stopping after starting, irregular running & loss of power.

They must be cleaned with a fine file & if the corrosion is too great replaced

In engines with points on the left side, driven by the oil pump, ensure that the bush supporting the points cam shaft is not worn & the seal behind the points backplate is not leaking. Too much play (see table 13for limits) will affect the consistent opening of the points.

Check the lubricating felt is kept moist with a suitable grease. Running the cam dry will cause wear of the points operating heel which runs on the cam surface. This will cause the points gap to close up & affect the engines running.

Check the points gap is within limits set in figure 2.

To set the points gap loosen the fixing screw of the moveable contact & rotate the plate to achieve the correct gap. Set the points gap with the heel of the points on the highest point of the operating cam.

Setting the ignition timing

We need to ensure the spark is occurring at the correct time before TDC as set out in Table 2.

Fit a degree wheel to the generator side of the engine ( Figure 3) & fix a pointer into the cylinder fins to register zero degrees at TDC (both valves closed) (Figure 4)

Rotate the engine backwards (anticlockwise) beyond the point of maximum ignition advance. (Say 90deg) Now rotate the engine clockwise until the points just open. This should correspond with the figure given in Table 2.

The point that the contacts separate should be checked with a suitable electrical meter.

If no meter is available then a thin strip of paper may be used gripped between the points. The paper will be released on the points opening.

To adjust the points opening the backplate must be moved after loosening its fixing screws.

The degree of advance is increased if the plate is rotated against the direction of the cams rotation, decreased if the plate is rotated in the direction of rotation.

The adjustment must be made at the point of maximum advance. In the case of a manual system the lever must be in the full advance position. With an automatic advance system the advance bob weights must be jammed into the full advance position.

The minimum advance must be in the region of the figures given in Table 2.

At this point it’s worthwhile to repeat the dire warning given in the original manual:

Too high values of the advance during the starting phase may originate return shocks such as to put out of service the organs of the starter itself

In other words too much advance will cause kickbacks & poor running at low revs. Too little may cause difficult starting or stopping after an initial start.

In engines with points on the oil pump shaft the oil pump driving gear marking must line up with the reference marks on the crankshaft. (Figure 5)

Check the battery is in good condition & fully charged. A discharge battery causes difficult starting & erratic running.

Each cell of the battery can be checked with a voltmeter (Figure 6). Each should register between 1.9 & 2.7 volts. A battery with no accessible cells should read between 5.7 & 7.1 volts.

Check the condition of the terminals & clamps & brush them clean before assembling with Vaseline grease.

Check the level of electrolyte is above the plates of the battery. Check the SG of the acid with an hydrometer.

Check the condenser. If it has failed short circuit the engine will not start. If it is open circuit the engine may run but the points will spark & the engine run badly at low revs & stutter as the revs increase.

The easiest test is to replace the capacitor to see if the fault persists.

Check the ignition coil

Complex equipment is required to test the primary & secondary windings of the coil electrically & the best way to test for a fault is to swap the coil for a new or known to be good unit.

Check the dynamo

The commutator segments become blackened over time due to deposits from the carbon brushes as they wear. This can cause low output from the dynamo. Some maintenance is required to avoid this happening.

If wear to the segments is slight then a good surface can be obtained by light abrasion with a strip of emery paper to the segments. When the surface is once again bright the dust produced must be brushed away & any which has settled between the commutator segments scraped out with a suitable implement.

If the wear is too great for emery paper then the rotor must be machined in a lathe to provide a smooth surface. The insulation between the segments must be cut back with a suitable tool to a depth of 0.007-0.011.This must be done or the armature will wear out quickly.

If the above actions do not restore the dynamo operation then the help of a specialist electrical engineer should be sought.

b) Maintenance of the fuel system

First ensure the petrol is reaching the carburettor or float bowl. Remove the petrol pipe from the tap & check the flow is adequate. Clean the petrol filter in the carburettor connection with compressed air. Take out the carb jets & clean with compressed air. Check the car to head gasket is in good condition & the flange of the carb is flat & not distorted. Poor fuel flow or air leaking into the engine from the carb flange can cause poor starting, irregular running & overheating.

c) Check engine compression in the following way.

Bring the engine to working temperature, remove the spark plug & fit a suitable pressure gauge to register the pressure generated under compression. Open the throttle fully & kick the engine over several times to register a figure on the gauge. (Figure 8).

If the pressure indicated is lower than indicated in Table 4 for the engine being tested then the loss of compression must be investigated. In the first place look at the valve clearances to ensure they are not too tight then move to piston ring & piston condition.

If a suitable gauge is not available then with a hot engine depress the kickstarter. Considerable pressure should be felt & the lever will be slow to descend. If there is leakage through valves or past rings & piston there will be little, or no, resistance.

Before dismantling the engine check the valve clearances are not too tight, the head gasket is in good condition & not leaking & the spark plug is fitted with a washer & tightened correctly.

d) Check the valve clearances

The original manual brings a sinking feeling to even the most experienced mechanic at this point:

Rotate the cam in such a way that in correspondence with every plates there is the arch of rest of the cam itself

OK ……!!! Lets start our search for the plates & rest them on that arch.

Rotate the engine until the valve to be checked is in the fully closed position. This is best achieved by ensuring the other valve is just about to open or close i.e when the exhaust valve begins to open the inlet valve can be checked, when the inlet valve begins to close the exhaust valve can be checked.

The clearances should be measured with the engine cold with steel feeler gauges (Figure 9) The cold clearances for a variety of models are shown in Wear & hammering of the surfaces will change the settings & these must be returned within the limits given.

Check the cam timing

The timing is correct when at TDC on the ignition stroke (valves both fully closed) the timing marks on the cam, timing pinions & crankshaft all coincide as shown in Figure 10.

e) Check oil circulation & the oil pump.

With the engine hot remove the oil feed to the head at the top of the timing cover. Connect a pressure gauge to the timing cover. (Figure 11).

If the pressure is found to be low there could be a variety of reasons: wear in the bushed big end (if one is fitted); wear in the crank oil injector or its housing in the timing cover; leaks in the oil circuit from the pump such as the crankcase to timing cover seal; obstruction of the oil pickup filter or wear in the pump itself.

If the output from the pump is erratic it is likely to exhibit wear in the gears and shafts & must be replaced as mentioned in part c of the Engine Overhauling section of this manual.

3. – Engine Overhauling

By Engine Overhauling we mean listing all the operations which may need to be performed to restore a worn engine back to its original condition & power.

The overhauling can be total when it is desired to return the engine to as new condition or partial to rectify a particular problem

Operations for partial overhauling

a) Disassembling the head

This is necessary when one must check the valves , the head gasket , the valve guides etc

– Disconnect the spark plug cable.

– Remove the head steady.

– Remove the exhaust pipe.

– Remove the carburettor.

– Remove the rocker box covers.

– Remove the rocker gear.

– Remove the tie bolts from head to timing cover.

– Remove the clamps from the pushrod cover sleeves.

– Remove the cylinder head nuts.

During disassembly mark the valve gear, pushrods etc to ensure they are assembled back to their original positions. This will avoid noise from parts which having worn together will not be in ideal alignment if assembled with unfamiliar partners.

Checking of the head

Disassemble the valves using a suitable too (fig. 39).

If there are carbon deposits in the combustion chamber & exhaust port remove them with a suitable scraper & wire brush taking care not to damage the head, valve guides or valve seats.

Check that the valve guides are free of carbon on their bearing surfaces & well polished. This may be accomplished by means of a plug gauge (fig 12). The valve guide internal diameters must not exceed those laid down in  Table 6. Check the valve stems are not showing any signs of seizure, any marks may be lightly stoned away.

Check the valve stem OD with a micrometer against the values given in Table 6.

Check the play between valves & guides against the data in Table 6.

Check the valve seats for marks showing the valves are not seating properly. Where these are found then the valves must be ground in.

When the valves are removed the springs should be tested with a pressure tester (fig 14) & the reading compared with the data in Table 7.

Overhaul of the head

Valve heads. Grind the valve heads as shown (fig 15) & check that the seating width S is within the limits set by Table 6. If this is not possible replace the valve.

Valve seats. Cut the valve seats as shown (fig 16) to remove any deep marking & leave an even surface. The valves must be ground to their respective seats with a fine grinding paste to achieve a perfect fit. (fig 17)

Replacement of the valve seats. If the seats in the head are so worn, or damaged, that they may not be cut back then they must be replaced.

The seats must be machined out to leave a slightly oversize recess to accept the new seat. The seats must be machined from a suitable material & fitted to the interference given in Table 6.

The seats must be fitted with a suitable tool as shown in Fig 18. The head must be heated to 250deg C & the seats introduced (previously lubricated with tallow) & held in place until the head has cooled. Care must be taken that the seats are not introduced at an angle.


The heads with a bronze insert have no seats & must be machined to accept seats.

Sealing of the valves. After fitting new seats and/or new valves to the head they must be checked to ensure a perfect seal has been achieved.

Fit the sparking plug & invert the cylinder head & fill the combustion chamber with petrol. Look into the inlet & exhaust ports to observe any leakage from the valves or seats. You may blow compressed air into the ports & observe any bubbles fro either the valves or their seats. (Fig 19).

In practice some slight leakage is acceptable between head & seat – the engine will soon fill any slight gaps with carbon. On the contrary, no leakage is acceptable between valve & seat as the combustion process will soon burn the valve seat & valve in the region of the leakage. If there is a leakage then grind the valves in further.

Replacement of the valve guides.

When replacing the valve guides adhere to the tolerances given in Table 6.

Heat the head to about 250deg C before using a suitable too (Fig 20) to remove the old guide & insert the new one. After replacing the guides the valve seats must be reground & may need to be recut.

Rocker arms & pivot pins

Mark the arms & pins so as to assemble them back into the position they came from.

Check the bushings or needle roller bearings for wear against the values given in Table 8 & if necessary replace then. Likewise check the rocker pins.

Reassembly of the head components

Carefully clean the head casting, valves, springs, spring caps & collets with petrol or alcohol. Dry with compressed air.

Fit the valves with a suitable compressor (Fig 39) lubricating the valve stems with oil before assembly. Ensure the collets seat into the valves & spring caps securely. It is important to do this as if misaligned can cause the valve springs to vibrate & damage the valve stems leading to noise & failure of the components.

Ensure the valves are sealing to their seats as shown in  Fig 19.

Reassemble the rocker arms & pivots in their original positions ensuring the pins are adequately lubricated.

Reassembly of the head to the engine

Repeat, in reverse order, the sequence of operations required to dismantle the head. Pay particular attention to the jointing surfaces, ensure they are free of marks & no debris stops the joints mating perfectly. Also, make sure the gaskets are in good condition.

Place the head in position so as the rocker arms are in alignment with the valves.

(This actually refers to the alignment of the head to the pushrod tubes/cam followers & pushrods. It is impossible to alter the alignment of the rocker arms to the valves by anything done when fitting the assembled head to the engine. It is possible to alter the position of the head slightly by rotating it on the barrel. Ensure the cam followers can be viewed down through each pushrod aperture in the head & if there is any misalignment it is equalised between the exhaust & inlet side to attain the best valve gear alignment possible.)

Tighten the cylinder head nuts to 4.5Kg with a torque wrench.

We can only assume 4.5Kg means 4.5KgM. This equates to approx 32FtLb & is near the maximum possible to be applied to a 10mm stud made from 8.8 steel. As the studs are fixed into the crankcases by approx 12mm of thread care must be taken not to over tighten the cylinder head nuts & risk pulling the studs out of the cases

I would not chance 32FtLb on 50-year-old studs & cases

If fitted replace the tie rods from the rocker castings to the inner timing cover. Tighten them until they are slightly in tension with the engine cold.

b) – Disassembly of the cylinder & piston

This may be required if any of the following symptoms are observed: low compression, excessive oil burning, smoke in the exhaust

or as mentioned in the original manual:

the operation must be performed when one notices abnormal shocks (?)

Disassemble the head as described in section a

Remove the cylinder. Remove the gudgeon pin after removing the retaining circlips. If the gudgeon pin cannot be removed easily then a suitable extractor must be used. Take care not to damage the small end bearing or transmit any undue force to the big end. Remove the piston rings.

Table 10Check the cylinder surface. The surface must be checked for condition & also for ovality & wear (Fig21) . If there are deep marks or the degree of wear or ovality exceeds the limits laid down in then the cylinder must be bored out to the next oversize and a new piston & ring set fitted. The cylinder must be bored by a specialist machine shop, the factory can provide oversize pistons & ring sets.

Check the piston. Check there are no deep marks or evidence of seizing. If these are in evidence then the piston must be replaced. It is sometimes possible to eliminate light marking or seizure scores by skillful use of a fine abrasive stone.

Check the diameter B (Table 10) to determine wear to the piston. This must be added to any wear measured in the cylinder bore & be within the limits set down in the table. The measurement must be made with a micrometer (Fig.22). Check the width of the grooves in the piston rings. The play between piston rings & its groove in the piston must not exceed the values laid out in Table 10.

Check the play between gudgeon pin, small end & piston does not exceed the values given in Table 10. Ensure there is no scoring of the pin or discolouration caused by overheating. Measurement of the gudgeon pin must be made with a micrometer, the pin bore in the piston must be measured with a bore comparator gauge. This is set to zero at the measurement given by the micrometer for the pin diameter. The comparator can then be introduced into the bores of the piston & small end to measure any wear. Compare the readings with the values given in Table 10.

Check the piston rings. The ring material is very brittle so expand them only as much as is required to remove them from the piston. Check they are not stuck in their ring grooves. Check for wear & their thickness by means of a suitable gauge (Fig 23). The wear must not exceed the limits laid down in Table 10. To measure the ring gap introduce the ring into the bore squarely using the piston as a support.

Check the parallelism of the big end & small end axes.

To carry out this check  (Fig.24) a pin is required which is exactly the same diameter as the gudgeon pin. This is introduced into the small end & allowed to drop to the level of the crankcases. Both sides of the pin must touch the cases either side of the piston (This check may require the introduction of 2 slip gauges or engineers parallels either side of the piston as on 250 engines the rod will not drop down fully to crankcase level) If both sides do not touch then bend the rod slightly to achieve this. Now raise the conrod & let it the pin touch the cylinder studs near their bases. It should touch both. If it does not twist the rod slightly until this occurs. These operations are very important to ensure the piston rises squarely in the cylinder bore with no bias in any direction & subsequent frictional losses.

This next section in the manual is particularly puzzling until one realises the parts referred to are the pushrods!

Check the rocker arms rods which must not have deformations. If necessary provide for their straightening. Check the conditions of the sporic seat of the upper cup & the conditions of the ball of the lower runner

Check the straightness of the pushrods, if they are slightly bent then straighten them. Check the upper pushrod cup & lower ball end for wear.

Reassembly of the piston & cylinder

Fit the piston rings (compression & oil control) to the piston. Fit the piston to the connecting rod sliding the lubricated gudgeon pin into place, fit the two circlips to either end of the pin ensuring they snap into the grooves in the piston. When fitting the circlips cover the crankcase mouth with a cloth to prevent the clips falling into the engine should they be dropped.

When fitting the rings place their gaps evenly around the circumference of the piston so as to avoid loss of compression or excessive oil consumption. Lubricate the piston, rings & cylinder bore, lightly grease the base gasket & slide the cylinder onto the piston using a ring compressor to avoid breaking the rings.

Reassemble the head as described in part a. Refit the pushrods in their original positions.

C – Disassembly of the timing cover.

It is necessary to remove this cover to inspect the cam gear, primary transmission or gearbox.

Proceed as follows:

Drain the engine oil. Remove the lower clips from the pushrod covers. Remove all the fixing screws. Remove the cover. Mark the cam followers & pushrods for reassembly in their original positions. Check the followers & their bushes for signs of seizure. With a micrometer measure the followers & check the wear against the limits set in Table 9. Check the oil injector bushing & its seat in the cover against the limits set out in Table 13. Excessive wear in these components can ruin the con rod, big end bearing, cam & valve gear. Check the wear in the shaft driving the contact points. Check the play between the primary drive gears which should not exceed 0.004″. Measurement of the play can be made with a dial gauge as shown in Fig 42. Larger play than advised can cause knocking which can be mistaken for a worn out piston. If you need replacements then remember to quote the number engraved on the crankshaft pinion. (Fig 42)

Remove the cam, drive chain & lower drive sprocket as a unit. Remove the chain tensioner spring(s). Check the cam spindle & the other spindles for wear or signs of seizure, their measurements must be within the limits set out in Table 11. Likewise check the cam followers & cam against Table 11. If there are any signs of seizure these may be stoned away with a fine grained abrasive stone.

Remove the clutch assembly using a suitable spring compressor to avoid damaging the fine (left hand) thread on the mainshaft end (Fig 26). Check the plate thicknesses are within the limits set out in Table 12.

Check the central hub of the clutch does not bind on the mainshaft. The centre must move to allow the clutch to fully disengage.

Check the timing chain is not worn out – too slack will indicate it needs replacement.

Check the oil pump

If the oil pressure is low as measured by pressure gauge (Fig 11) then the pump may require reconditioning or replacement.

Check first that the low oil pressure is not caused by a worn crank oil feed bush, worn big end (on a bushed crank) or leaks in the seal between crankcase & timing cover. If this is not the case then wear in the pump gears or pump body may be the cause.

The oil pump components can be inspected by removing the pump cover with the pump body left in the crankcases. If the gears are obviously worn or damaged they should be replaced. If the body is damaged or worn it must be removed from the crankcase. This is easily done by replacing the cover onto the body & using the two threaded holes in the cover to lift it free of the crankcase.

To reassemble the pump in the case heat the case to 150 deg C & introduce the complete pump taking care to align it correctly with the mounting holes. Use gasket cement on the pump body to make a good seal to the crankcase.

This next bit defies translation – I have no idea what the operation consists of or how it makes a better seal.  If leaks are noticed between pump & crankcase:

you can obtain the perfect tight by effecting a rolling operation with the suitable tool. Fig 34

To check the fit of the pump in the crankcase block off the oil inlet to the pump & inject compressed air into the outlet tube where it exits the outer crankcase. With an oil can oil the edges of the pump cover & watch for bubbles forming. Some leakage is acceptable as the pump is submerged & will not suck in air.

Remove the timing gear drive pinion from the crank using the correct puller (Fig 38).

Remove the gearbox cover complete with the gear cluster. Remove the clutch backplate with a suitable puller (Fig 37). Check the individual gears & the selection mechanism for wear & replace as required. Pay particular attention to the selector forks & gear engagement dogs which can wear badly if the clutch is not employed correctly during gear changes.

Always use the clutch for gear changes as the shock loadings incurred by clutchless changes can ruin gearbox components. In particular, the keyed sleeve on the layshaft can shatter with abuse. Compare all measurements of gearbox components to the figures given in Table 16.

Reassembly of the timing cover & internal components.

Reassemble the gearbox components onto the inner cover & insert into the crankcase. Tighten the screws well & employ a locking fluid such as Loctite for security.

Reassemble the oil pump as described. Reassemble the clutch backplate & clutch by means of a suitable tool (Fig 41). Reassemble the points drive shaft, cam drive gears & chain ensuring the timing marks are lined up correctly & the shafts are lubricated.

This section applies to the very early chain tensioning system rather than the one which replaced it. This system appeared to be prone to breaking up; the bits then fell into the primary gears or oil pump/points drive gears. Not ideal. The replacement system used two tensioners which were also prone to failure of the volute tensioning springs which then fell into the primary gears or oil pump/points drive gears, still not ideal, hence the popularity of gear drive conversions today.

Reassemble the chain tensioning spring taking care to ensure the pivot is in such a position that the stop pin of the spring is placed on the centre line of the hole. If the pin is aligned so as it touches the bottom of the hole then the spring blade can break very easily. Ensure the pin cannot come out of the spring eye.

Reassemble the engine pinion using the correct tool. (Fig 25) This allows the fixing nut to be fully tightened with no risk of damaging the gear teeth. Reassemble the cam followers in their original positions Fix the cover with its screws very lightly screwed in. Check they are engaging with the cam by pushing the follower towards the cam with a pushrod and rotating the engine in the correct direction. (anti clockwise from the timing side) Observe the followers; they should turn freely & in a clockwise direction ( viewed along their axis) as the cam rotates under them. If both followers do this then the cover can be tightened up.

If the followers do not turn or turn anti-clockwise it is necessary to displace the cover slightly to make them do so. The amount of displacement is small – hundredths of a millimeter – and is within the play allowed by the covers fixing dowels.

The following conditions are likely:

Cover displaced downwards – the followers do not turn or turn anticlockwise.

Cover displaced to the right – the inlet turns more slowly than the exhaust, stops or turns anticlockwise.

Cover displaced to the left – the exhaust turns more slowly than the inlet, stops or turns anticlockwise.

Taking into account the above information displace the cover with light blows from a wooden mallet until the correct, even, clockwise rotation is achieved at which point the cover can be tightened fully.

Correct rotation of the cam followers is essential to avoid premature wear to both cam & followers.

Reassemble the head as noted in part a)

Replace the pushrods in their original positions.

Reassemble the oil injector as shown in Table 13. It is important that these items are assembled correctly or the oil supply to the crank will not be adequate & the big end bearing & cams will wear out.

d) Disassembly of the right side cover

Disassemble the generator using a suitable tool to extract the rotor (Fig27) & check it as mentioned in section a) of the chapter Adjustment of the engine.

Remove the gearbox sprocket with an extractor & check for wear.

When removing these parts avoid heavy blows to the crank or layshaft which might damage the engine internals, shafts & bearings.

Disassemble the starter gears & inspect for wear. Likewise the components of the gear selection & kickstarter mechanisms.

Total overhaul of the engine

e) After dismantling the engine to the point described in the Partial Overhaul section continue to dismantle the engine as follows:

Remove the engine from the frame. Undo the 6mm crankcase bolts. Split the cases & extract the flywheel assembly.

Check of the bushed big end assembly.

Wash out the crank assembly with petrol so as the bush & pin bearing is washed free of any oil. Inspect the big end of the conrod & side shims for any signs of overheating.

Measure the diametrical play of the big end assembly & compare to the values given in Table 14. Fig 29. Check in several positions to detect any ovality in the bearing. Measure side clearance between the thrust shims & crank cheeks with a feeler gauge & compare to the values in Table 14. To replace any of the crank components the crankshaft must be pressed apart with a suitable tool (Fig 28).

Check the crank pin.

The crankpin is bored axially & the ends are closed with aluminium plugs riveted into counter bored end sections. The pin boring tends to collect any solid debris in the oil through centrifugal action over the lifetime of the engine. This can affect oil circulation & any debris should be removed every time the crank is dismantled. Remove one of the end caps to clean out the residue & replace with a new one.

Check of the roller big end assembly.

Measure the diametrical play against the values shown in Table 15 (Measured as shown in fig.29). If the measurements exceed the values shown in Table 15 dismantle the crank as for the bushed assembly.


Inspect the crankpin for signs of seizure – if any are found the pin must be replaced. Check the pin with a micrometer for signs of wear or ovality against the values shown in Table 15.

Connecting rod

Check the big end eye with a bore gauge for ovality which must not exceed the values given in Table 15. If the degree of wear & ovalisation is less than 0.002 then the bearing surfaces of the crankpin & conrod can be ground true & reassembled with oversized rollers. This is a task for a specialised workshop. The clearances listed in Table 15 should be adhered to. If the wear exceeds 0.002 then it is better to replace the parts as further grinding of the crankpin may break through the hardened surface layer.

The following sentence makes little sense:

It is important that the differences between the diameters of the rollers used does not exceed .00787. (ovalisation)

Make of it what you will but I suspect the value given should be 0.0008″

The interference fit of the crankpin in the flywheel cheeks must be within the limits set down in Table 15. Less than this will weaken the crank assembly & render it unstable.

Assembly of the bush & roller bearing cranks.

This is a particularly badly composed & written section with no mention of the crankpin shims, the finished width of the crank or the need to align the oil delivery holes in the timing side crank cheek & the crankpin

Assemble, with a suitable hydraulic press, the crank pin into one of the crank halves having greased the pin prior to pressing into place. Put the conrod in position on the crankpin paying particular attention in the case of the roller big end that the cage assembly rotates freely. Press the other flywheel onto the crankpin keeping it in alignment with the first half. This may be accomplished with a steel rule placed cross the flywheel halves as the second half is pressed into place. The crank may be spun on centres or in a lathe (Fig 30) to check alignment, a light blow with a lead mallet will move the crank cheeks (Fig 32) until the alignment as read on the dial gauges is less than 0.001 out. Check also the bearing diameters of the crankshaft in a similar fashion. (Fig 30).

Check of the crankcases & their fitted components.

Clean the crankshaft & gearbox bearings thoroughly & check the inner rings rotate freely. Check the bearing cages are not cracked.

New bearings should have clearances similar to the following values:

Diametrical play:0.0008

Axial play:0.004

After assembly, due to the interference fit of the outer race in the crankcase, the above plays are reduced by about half. If a bearing shows signs of stiffness after assembly then it will soon wear out in service.

If the bearings have to be replaced use a press as shown in Fig 33. Press out the bearing by pressing the inner race, fit the race by pressing on the outer race. Before removing or fitting the bearings heat the crankcases to 100-150 deg C.

Check the shaft garter seals which must not be hardened or split. The edge which contacts the shaft must be in perfect condition. When fitting new seals it is essential to protect the inner sealing edge. When fitting new seals use suitable tools with a conical face as shown in Fig 40.

Check the mating faces of the crankcases which must not be marked or damaged. If they are damaged they can be refaced on an abrasive sheet placed on a surface plate.

Oil Filter

The oil, before reaching the engine, passes through a mesh filter on the intake side of the oil pump. It can be inspected from outside the engine. The oil for the engine flows through this filter & it must not be blocked. It must be removed & cleaned regularly with petrol & dried with compressed air before refitting it.

Carburettor overhaul.

It is very important for the good performance of the carburettor that the maintenance & the overhauling be effected by expert men and perfectly

Do not use needles or metallic wires to clean jets or other carb components: use only compressed air.

After a long period of operation check the various parts for damage; the jets, needle & spray tube, throttle slide etc also the efficiency of the filter & float. The carburettor is fitted with an air filter which is designed to extract any dirt or dust from the incoming air before it enters the cylinder. The longevity of the cylinder, piston, piston rings, valve guides, valve stems & the seal of the valves to the seats is dependent on the efficient working of the air filter. It is therefore, good practice to wash the filter regularly with petrol & dry it with compressed air. When it is dry oil the mesh of the filter to better pick up airborne debris.

On no account replace the filter with an open bellmouth intake. It will not increase the performance of the engine & will speed up engine wear.

f) – Reassembly of the engine

Before starting the reassembly of the engine carry out the following preparation:

Remove any gasket residue or sealant from the mating faces of all the cases & covers. Be careful not to damage the mating surfaces by using purpose built gasket scrapers.

Wash all parts in degreasing solutions (petrol, alcohol, hot water with neutral detergent) & dry with compressed air. Ensure oilways & any blind holes which may harbour debris are cleared.

Fix the centre gasket to one side of the crankcase.

Assemble the engine components in the reverse order to the dismantling operation, ensuring all parts are suitably lubricated, and having carried out carefully all the operations described in the previous chapters to the limits listed in the various tables & diagrams.

Pay particular attention to the crank end float which must be between 0.004″ & 0.008″.

The end float of the cam & drive gears must not exceed 0.006″ or the engine will be noisy.

Fill the engine with an appropriate amount of good quality oil of the correct viscosity for the prevailing conditions – SAE 50 in summer; SAE 30 in winter or during running in of an overhauled engine.

4. – Adjustment of the rebuilt engine

Check the compression ratio of the engine

After bringing the engine to TDC (with both valves closed) the engine must be inclined until the spark plug hole is vertical. Then introduce via the plughole a mixture of 50-50 oil & petrol from a graduated burette or syringe (Fig 35). The liquid should reach the bottom of the sparkplug hole & be within the limits set out in Table 5.

Check the ignition timing as laid out in section f.) of the chapter Adjustment of the engine.

Check the valve timing corresponds to the figure given in Table 18. This will only be necessary if some timing marks are missing & the job cannot be done by the method explained in section e) of the chapter Engine Adjustment.


Note: The cams are ground with quietening ramps which whilst ensuring the engine operates (relatively) silently makes checking the exact point of valve opening hard. To determine if the timing is correct it is necessary to run with a large valve clearance (0.020) to ride over the quietening ramps onto the true cam profile when the values measured should correspond to those given  in Table 18.

Fit a degree wheel to the crankshaft as described in Chapter  2a Fig. 4.

Fit a TDC piston stop into the spark plug hole.

Fit two dial gauges above the valves bearing on the rocker ends to help determine the exact opening & closing points of the valves.

Fit the degree wheel pointer (Fig 4) & set the wheel to zero at the exact point of TDC on the compression/power stroke i.e both valves fully shut.

Set the valve clearance to 0.020 taking the reading from the dial gauge.

Rotate the engine in the direction of rotation until the dial gauge on the exhaust valve moves. The angle indicated on the degree wheel at this point (with reference to the zero opposite the initial TDC zero point) is the angle of exhaust opening (AS) as shown in Table 18. If this is the case there is no need to do any further checks or adjustments – the cam timing is correct. If the difference between the angle given in Table 18 is more than 5deg either way then the meshing of the timing gears must be adjusted to give the correct timing figures.

To continue with the timing check rotate the crank further until the dial indicator on the exhaust ceases to move. The angle shown on the degree wheel (with reference to the initial TDC zero point) is the closing angle (AS) of the exhaust valve. Rotate further until the dial gauge on the inlet rocker moves. The angle shown on the degree wheel (with reference to the initial TDC zero point) is the opening angle (AA) of the inlet valve. Rotate the crank further until the dial indicator on the inlet ceases to move. The angle shown on the degree wheel (with reference to the zero opposite the initial TDC zero point) is the closing angle (CA) of the exhaust valve.

Carburetion adjustment

Tickover adjustment. If the engine runs irregularly or has a tendency to stop at tickover then after having proved it is not due to the spark plug or fuel supply move on to adjustment of the carburettor. With the engine up to working temperature & running at tickover screw in the throttle stop screw to make it run a little faster. Unscrew the mixture screw slowly until the engine begins to falter; now screw back in until the engine runs smoothly. Now unscrew the throttle stop until a slow regular tickover is obtained. If the running starts to deteriorate then move the mixture screw in slightly to regain even running.

5.- Running in the engine

Newly overhauled engines often do not turn over very easily especially when the piston & other major components have been replaced. In order to ensure the new components bed in correctly & provide smooth running surfaces, which will guarantee a long life to those components, then a running in process has to be adhered to:

Run the engine at low revolutions for 4 hours, ensure the engine is not under heavy load & good progress is being made to provide adequate engine cooling.

Change the oil to remove any metallic particles produced during this initial running in.

Refill with new oil & for the next 2000Km do not run the engine at more than 2/3 power.

Do not allow the engine to labour or work hard at low speeds or overheating & engine damage may occur.

6.- Engine maintenance

When the engine is stored for long periods it may suffer if the user does not attend to it periodically

Damage may occur from condensation which can cause rusting of the engine components such as the cylinder, piston rings, valves etc. The acid residue of burnt fuel can damage the valve stems, gudgeon pin (?) etc.

To eliminate these causes of damage the following can be done:

Squirt some engine oil into the plug hole and rotate the engine by hand to spread it over the cylinder & piston rings. Replace the spark plug & turn the piston to TDC with both valves closed. Start the engine periodically, warm it thoroughly & repeat the above operations.

For maintaining the engine during normal use follow the instructions given in the Owners Manual supplied with every machine.

Helpful??? Maybe…. :o)