Changing Oil :
Change lubricating oil after every 250 hours running.
Drain sump when engine is warm through drain plug to be found on 6/1 and 8/1 engines below the oil filter, and on 12/2 and 16/2 engines in the oil suction pipe below.
Remove crankcase door, splash plate (6/1 and 8/1) and lubricating oil strainer.
Wipe down inside of crankcase, including trough, as clean as possible.
If paraffin is used to clean out sludge, crankcase must be wiped dry before recharging with fresh oil.
Clean and replace oil strainer.
MAINTENANCE > AIR FILTER
Felt Air Filter (When supplied) :
Air filter is suitable for average operating conditions, but where very dusty conditions prevail an "oil bath" filter should be fitted.
It is important that the air filter is cleaned regularly so that the passage of air to the engine does not become partially or wholly blocked. The time interval between cleanings will vary with the amount of dust in the air, but it is recommended that this operation should be performed once a month under the cleanest of conditions.
Remove felt from cleaner and shake vigorously, then beat dust and grit out of the felt.
If the felt is damp and oily it will be necessary to wash it in paraffin and the thoroughly dry before replacing in the cleaner. Fuel oil is NOT recommended for washing the felt as it will not readily evaporate and petrol vapor may cause detonation.
Oil Bath Type Air Filter (When Supplied) :
Mount the filter in horizontal position and maintain the correct oil level as marked on the filter body. If the level is ¼ in. Too high the engine will inhale the cleaning oil, which will cause excessive carbon deposits on the valves, pistons, etc. If too little oil is used the cleaning action will not be efficient. Check the oil level weekly, and if necessary and fresh oil. Lubricating oil as used for the engine may be employed. Change the oil and clean completely every 500 hours running, or more frequently if there is any sign of the oil becoming impregnated with sand of dirt. To clean, remove from engine and dismantle. Wash in paraffin and allow to dry. Examine cork and felt washers during dismantling and change if necessary.
Air tight joints, including those between the filter and the engine are essential for efficient air cleaning.
Vacuum Breather :
The purpose of the vacuum breather on the crankcase door is to maintain a partial vacuum in the crankcase so that the lubricating oil will not work out through the bearings and joints.
If the thin metal disc should become stuck with paint or grime, remove and scrape clean on the flat surface, care being taken not to kink or distort it. Do not mislay the small distance piece which supports the cover.
MAINTENANCE > COMPRESSION C/O VALVE
To Remove Compression Change-Over Valve (6/1 and 12/2 only) Option Extra :
This is device to give a high compression for starting, and lower compression for normal running.
The Valve screwed "IN" give high compression and "OUT" gives low compression.
DO NOT run under heavy load with high compression.
For long runs at 1/3 load or less, use high compression.
Always see the valve is either Full in or Fully Out.
Keep the screw thread clean and bright.
Remove fuel pipes from injector and unscrew nut for releasing auxiliary chamber. This will withdraw the outer combustion chamber. Take note of the thin copper washer.
The main or inner combustion chamber plug may be loosened by compression in the manner described for cylinder head.
Drive a hard wooden Plug into the ¼ in. dia. hole in the center to prevent air leakage and then replace the outer portions just removed with the hand wheel in the "Out" position, and with the outer combustion chamber nut screwed into the head three or four turns which will be sufficient to prevent the inner combustion chamber from being ejected too violently when subjected to the force of compression.
Stubborn cases will have to be treated by drilling and tapping with a fine 3/8 in. thread and drawing out with a screw.
Unscrew small nut in center of hand wheel to extract valve.
Remove valve, taking care of spring, spring washer and woodruff key.
To Remove Cylinder Head :
Drain water. (If compression change-over valve is to be removed, loosen at this stage. See above).
It Remove cylinder head cover.
Detach inlet pipe, exhaust pipe, water pipe, and fan assembly if radiator cooled.
Remove valve rocket assembly, push rods and valve caps.
Undo cylinder head nuts.
Lift off cylinder head. In obstinate cases replace the injector (but not the fuel pipes), valve rockers, valve push rods and two cylinder head holding down nuts, and slacken each of these holding down bids about two turns.
Next proceed as for starting. With valve lifter engaged, turn the starting handle quickly to get up a good speed and then smartly disengage valve lifter, when the compression in the cylinder should cause the loosening of the joint between cylinder head and cylinder block.
CYLINDER HEAD (6/1 and 12/2 engines)
To Remove Valve Guides :
The inlet valve guide ran, be drive, out
The exhaust valve guide must be screwed out (turn anti-clockwise).
To Replace Cylinder Head :
Note : In the twin cylinder engine the cylinder heads are so arranged that the two inlet valves come together on the inside, the parts being connected by a common inlet manifold. The cylinder heads, therefore, most be replaced in their original positions.
Refit valve guides, inlet and exhaust valves
See that cylinder head gasket is undamaged and in place. i.e. by position of dowel.
Replace cylinder head on studs, and tighten nuts finger tight.
Note : Each cylinder head gasket must be replaced on its own cylinder If these have been changed then the head clearance must be checked as below.
Refit compression change-over valve, taking care that the copper washer between the two parts is in place.
Fit inlet manifolds on twin cylinder engines to ensure correct alignment. Failure to carry out this step will probably lead to cracked or broken manifolds.
Nuts to be tightened so that the cylinder head is pulled down flat, compressing the gasket evenly. This can be achieved by tightening the nuts in turn diagonally. Tighten each nut a little at a time and go over three or four times.
After the initial run, following the replacement of the cylinder head and while the engine is still hot, re-tighten the cylinder head nuts as described above.
Replace valve end caps, push rods and valve rocker gear and adjust valve clearances as under "Valve Adjustment".
If new heads are being fitted to multi cylinder engines they should be checked that the inlet guides are in the correct position. If they are not, as can happen if two single cylinder type heads are supplied, the guides must be changed around in one head so that the inlet guides are in the center of the engine. Regrind the valves.
Note : Inlet valve push rod is longer than exhaust valve push rod.
To Check Cylinder Head Clearance :
Place two small pieces of lead on top of piston, above the line of the gudgeon pin and not beneath the valves of transfer port. Tighten down cylinder head and turn piston slowly past T.D.C. Remove cylinder head and measure thickness of lead; this should fall between 0.045 in. (1.14 mm.) and 0.050 in. (1.27 mm.) for types 6/1 and 12/2 and between 0.0075 in. (1.9 mm.) and 0.080 in (2.03 mm.) for the 8/1 and 16/2 engines. The clearance may be adjusted by the use of paper joints, placed between the cylinder block and the crankcase.
If the clearance is much too large it my be due to worn bearings or a bent connecting rod
MAINTENANCE > PISTON & RINGS
To Remove Piston :
Remove cylinder head and cylinder block.
Remove crankcase doors.
Disconnect the big end bearing of the connecting rod.
Note : which way the dipper faces and the manner in which the big end is marked, so that it can be assembled i the same way.
Lift out piston and connecting rod. Reassemble big end loosely.
Remove either circlip, warm piston and drive out gudgeon pin.
To Remove Piston Ring :
First work them loose, then stand the piston on a flat surface, and insert thin strips of metal between the top ring and the piston at four different places. Ease the ring off over the strips of metal, and repeat the process for the other rings. Piston rings are springy hot will break if roughly handled.
To Replace Piston Rings :
Piston groove, and oil holes must be thoroughly clean. Piston rings, if new, must be wiped clean of preservative grease; used rings must have any carbon deposits removed.
To ensure that the rings will fit property when assembled on the piston, roll each one round in its own groove. Where a ring is slack, and a new one is no improvement, it will be necessary to consider changing the piston.
Place the ring in the lower part of the cylinder, square with the bore, and measure the gap between the two ends with a feeler gauge. The correct gap is not less than 0.012 in. (0.310 mm.).
Wipe all parts clean and dry and assemble the rings in their grooves by sliding them over strips of metal as in removal.
To Reassemble :
Refit piston and connecting rod, noting numbering of big end bearing and in which direction the dipper faces. The dipper fitted to 6/1 and 8/1 engines is flattened in section and should cut the oil edgeways not broadside on. The hollow dipper in twin cylinder engines is a scoop, the opening of which is turned away from the crankcase door.
Fit paper cylinder block joints equal to number removed (and 2 metal shims 0.015" 0.38 mm thick for types 8/1 and 16/2). Place a flat bar across crankcase close to connecting rod and bring piston skirt firmly down on it.
Oil piston rings and stagger the gaps. Place piston ring clamp in position and compress rings. The clamp should close quite easily. If any force is required it is better to take it off and try again.
Oil cylinder bore, lift cylinder block over starts and lower into position pushing down piston ring clamp as far as the bar underneath the piston.
Turn crankshaft to move piston up into cylinder.
Support cylinder block, remove piston ring clamp and bar and allow cylinder block to drop into position.
Assemble cylinder head.
MAINTENANCE > BEARINGS
Connecting Rod Big End Bearing :
These are steel back white metalled shells in the bottom half and lead bronze in the top half and mast not be scraped or touched up in any way. The running clearance with the crankpin should not exceed 0.003 in. (0.076 mm.).
When assembling the bearings on the connecting rod it is most important that the backs are scrupulously clean and that there is interference between the bearing and the bore of the connecting rod. This interference, or nip, is measured by placing the bearing in the connecting rod, tightening both bolts to the normal extent, then slackening one bolt only and measuring the corresponding gap in the rod at the parting line. This gap should be between 0.004 in. (0.102 mm.) and 0.006 in. (0.152 mm.).
Ensure the dipper is secure before replacing the connecting rod cap; it is screwed in place and 4 dots punched into the circumference prevent turning. Place a cork over the end of the dipper whenever working in the crankcase to avoid injury to the hands.
Tightening torque for big end nuts is 55 lb. ft. (7.6 kg. m.)
Main Bearings :
These are of the bush type and need no attention as long as they are properly lubricated. The bush is located in the housing by a locating screw through the top of the housing, to ensure that the oil holes register correctly.
MAINTENANCE > DECARBONISING
ENGINE SHOULD NOT BE RUN MORE THAN 1,000 HOURS WITHOUT DECARBONISING.
Remove cylinder head and dismantle.
Remove piston and rings.
ALL PARTS must be scraped clean of deposits of carbon and washed in paraffin before reassembly.
Special care must be take, with regard to :
Recess in bore of exhaust valve guide
Piston ring grooves.
Inside of piston.
Regrind valve seats if not in perfect condition. This applies also to the compression change-over value (6/1 and 12/2 only.)
Clean out all exhaust piping, expansion chambers, silencers, etc. Every part must be scrupulously clean before being placed in position.