CHAPTER III
ENGINE MAINTENANCE AND FAULT TRACING

The roomy engine compartment of the Minor and the accessibility of the engine will probably encourage a practical owner to carry out much of the routine servicing and adjustments. A top overhaul, which includes decarbonizing and attention to the valves, can also be undertaken with confidence.

ENGINE MAINTENANCE
Routine maintenance comes under two headings; engine lubrication and periodical checks and adjustments.  These jobs, which call for the use only of the tools likely to be found in an enthusiastic owner's workshop, present no special difficulties. Even the novice can tackle them if the instructions given in this chapter are carefully followed. Engine Lubrication. The oil level should be checked with the car standing on level ground. A few minutes should be allowed for oil to drain back to the sump to prevent a misleadingly low reading being shown. Remove the dipstick, wipe it, return it and push it fully home before withdrawing it to check the level. It is more economical to keep the sump well topped-up than to allow the level to fall to near the danger point, at the end of the dipstick, before restoring the level.  Remember, too, that the oil consumption will be increased in hot weather and may be quite substantially increased when long, fast runs are undertaken, as compared with the figure that one becomes accustomed to when shorter runs at modest speeds are the order of the day. Tests have shown that the oil does not attain its maximum temperature until the car has been running for approximately one hour.

Choice of Engine Oil.
It should not be necessary to emphasize that "cheap" oils are the most expensive in the long run. Modern oils contain special additives which reduce corrosion of the cylinder walls, prevent the formation of sludge and gum and leave the engine in a very clean condition.  Multigrade oils, which are rather more expensive than the standard grades, have the added advantage of remaining relatively "thin" even at freezing temperature, thus reducing oil drag during starting and ensuring instant lubrication of the cylinder walls: but at the same time they maintain sufficient viscosity or "body" at high temperatures to prevent damage when an engine is heavily loaded or is driven for long periods at high speeds.

It can safely be said that the products of any reputable oil company can be used: for example, Castrol, Mobil, Esso, Duckhams, Shell and Vigzol. Normal oils are identified, in most cases, by figures that indicate their thickness or viscosity.  For engines in good condition the use of a rather thinner oil during the winter than in the summer, such as viscosity 20 or SAE SOW oils, designated in the Mobiloil range as "Arctic" and in the Castrol range as "Castrolite," will give easier starting, less engine wear and slightly better fuel consumption. For summer or in semi- tropical climates an oil having a viscosity of 30 is needed. Again, this is designated by the Wakefield company as Castrol XL and by the Mobil company as Mobiloil A. The multigrade oils just referred to are identified by figures showing their range of use: i.e.10W-30 or 20W-40. Castrolite also has multigrade properties.

When an engine is badly worn, it is an advantage to use a rather heavier grade of oil; for example, a 30 viscosity oil in winter and a 40 viscosity oil in summer. A still heavier grade (viscosity 50) may be desirable in the tropics if the oil consumption is on the high side when a 40-grade oil is used.

Changing Engine Oil.
The engine oil becomes contaminated with carbon and other products of combustion, including condensed water and fuel, and must, therefore, be drained out after, at most, 5,000 miles in service. If the engine is worn, the degree of gas leakage past the piston rings may make it advisable to change the oil more frequently—for example, at 3,000 miles.

The oil should be drained when the car has just come in from a run; being hot, the oil will be more fluid and will be holding in suspension the impurities just referred to. As the sump may contain up to six pints of oil, a sufficiently large drain pan should be provided, such as an old kitchen washing-up bowl. Sufficient time should be allowed for the oil to drain completely—at least ten minutes—before the drain plug is replaced. The sump should then be refilled until the level is up to the "full" mark on the dipstick. Normally, six pints of oil will be required, plus approximately a pint to refill the oil filter, the element of which should be changed when the oil is drained, as described below.

Oil Filter.
The felt-fabric filter, carried in a casing beside the sump (Pig. 2) is of the full-flow type; it continuously filters the whole of the oil passing through the lubrication system. As a choked filter element might cause oil-starvation, a spring-loaded valve is fitted which opens and allows circulation to continue when the element is clogged. Unfiltered oil then passes to the bearings—which is a sound reason for renewing the element at the intervals quoted on the chart or more frequently if the engine oil requires changing at shorter intervals; normally the two jobs should be done together.

It is sometimes recommended that this type of filter should be removed and cleaned in paraffin once during its life—say, after 3,000 miles of use — but experience suggests that any benefit is likely to be offset by the risk of introducing grit or dirt into the lubrication system if the filter is disturbed unnecessarily.

The filter element is renewed from beneath the car. Clean the exterior of the casing and the upper casting before removing the central retaining bolt, lower the casing and extract and discard the element.  Thoroughly clean the interior of the casing before fitting a new element and renew the circular joint washer if it does not appear to be in perfect condition, since a faulty washer can cause a serious oil leak at this point. Hold the centre bolt, with its washer in place under its head, firmly against the base of the container and prime the filter with oil before refitting the casing. After tightening the bolt firmly, start the engine and check for any signs of leakage.

Removing the Sump. 
Although the official maintenance schedule calls for removal of the sump at 12,000-mile intervals to allow the interior of the sump and crankcase and the suction oil filter to be cleaned, modern detergent oils have reduced sludge formation to negligible proportions, rendering this job virtually unnecessary nowadays—particularly if the lubrication system is thoroughly flushed out at this mileage with a special flushing oil (not paraffin) or, better still, Redex, following the instructions issued by the oil supplier. Removal of the sump, in fact, is likely to be required only when oil leakage develops at the flange joints or past the cork seals at the front and rear main bearing housings. Sump removal can be classed as an awkward rather than a difficult job to carry out single-handed; it is best done with the car over a pit or raised on a lift although it can be tackled with the front wheels raised on ramps. Two of the fourteen retaining bolts should be left loosely in place at diagonally-opposite corners to support the sump while the remaining bolts are removed.

After the sump, filter and the interior of the crankcase have been cleaned with paraffin and a lint-free rag, new gaskets and cork seals should be fitted to the sump, being held in place by a light coating of grease. It is particularly important to check that the ends of the cork packings, when pressed fully home into their grooves, stand clear of the flanges at each side by i in. This will give the correct "nip" when the sump is bolted up. If the packings are too long—which would prevent the sump seating properly—they must be trimmed with a sharp knife. To prevent distortion of the flange the sump bolts should be tightened progressively in a diagonal sequence, so that the sump is pulled up squarely.

Low Oil Pressure.
The oil-pressure switch on the crankcase normally opens when the pressure in the system exceeds 8 lb/sq. in. If an oil pressure gauge and adapter are substituted for the switch, a pressure of at least 40 lb/sq. in. should be recorded when the engine is thoroughly warmed-up and running at a fairly fast speed; about 20 lb should be shown at idling speed.

Assuming that the sump is full and that the correct grade of oil is used, low oil pressure can be caused by a choked intake filter in the sump, an air leak at the filter suction pipe unions, a faulty oil-pressure relief valve or a worn pump.

The first two points can be checked when the sump is removed, as described above. Fortunately the pump is seldom at fault (except when the engine has covered a very large mileage and is due for a major over- haul) as it can be serviced only after the engine has been removed from the car and after the clutch, flywheel and rear mounting plate have been taken off.

The oil-pressure relief valve is, however, a likely culprit. This valve, which relieves the excessive pressure that would otherwise be developed in the system when the oil is cold, is retained by a domed hexagon nut at the rear of the cylinder block, just above the starter motor. The cup should be removed and cleaned. The seating in the block should also be cleaned with a lint-free cloth wrapped around the end of a length of wood. If the length of the spring is less than 21 in. the coils have weakened and a new spring should be fitted. The valve is not adjustable. If satisfactory pressure is not restored when the above points have been attended to, the crankshaft and connecting-rod bearings are probably badly worn.

Valve Clearance Adjustment.
If a small, highly-efficient overhead-valve engine, such as that fitted to the Minor, is to be kept in good tune it is essential to check the valve clearances at 5,000-6,000-mile intervals. The correct clearance between the top of the valve and the rocker, when the valve is closed and the tappet is on the base of the cam, is 0-012 in. when the engine is cold and 0-011 in. when it is at the normal running temperature.

To make sure that each tappet is on the base of the cam, adjust No. I rocker with No. 8 valve (counting from the front of the engine) fully open. No. 3 with No. 6 fully open and continue in this manner by selecting pairs of valves that add up to 9.  To take one further example No. 7 valve would be adjusted with No. 2 fully open.

To adjust the clearance (Fig. 9), slacken off the adjusting screw lock-nut and insert an accurate feeler blade between the toe of the rocker and the valve end. The adjusting screw should now be turned with a screwdriver until the correct clearance is obtained and held in this position while the lock-nut is tightened. A firm pressure should be applied to the screwdriver in order to displace all but a thin film of oil from the cupped ends of the tappets and push rods.  A false clearance may otherwise be obtained. Then re-check the clearance.

The action of tightening the lock-nut will usually be found to change the adjustment slightly, so that one or two attempts may be necessary before an accurate clearance is obtained. It is advisable to use two feeler gauges to check the adjustment—one 0-001 in. too large, which should not enter, and one 0-001 in. too small, which should enter easily. The clearances, of course, must be re-checked again after the engine has been run and brought to normal operating temperature. Remember that if the cylinder head nuts are tightened down at this stage, the clearances will be reduced.

Before replacing the valve rocker cover inspect the cover gasket. If there is any doubt regarding its condition it should be renewed. Make sure that the cover is seating evenly on the cylinder head and is located correctly over the studs before replacing the fibre washers and tightening the securing nuts evenly.

ENGINE FAULT-TRACING
Serious mechanical trouble is comparatively rare, but minor troubles do unexpectedly crop up, although regular maintenance will go a long way towards preventing them. The accompanying fault-tracing chart illus- trates the systematic procedure which should be followed in diagnosis. Haphazard tests and tinkering are seldom very effective. A good axiom to remember is that an engine which is in sound mechanical order cannot fail to start or run efficiently provided that —

Fault Finding Chart

Of course any companies or products mentioned in the text may not exist today and any prices listed are of course no longer valid, so take company and product refernces with a grain of salt.