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TD Operation Manual - Tracing Troubles

This information will provide hints on tracing engine troubles and their possible root cause.

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Tracing Troubles

Engine will not Start

Engine Misses

engine will not start

If for any reason the engine fails to start readily when the starter button is pulled out, do not keep it revolving for a long period, but return the button to the ''OFF'' position at once. One of the following things may be the cause of the trouble :—

  • The ignition switch may not have been turned on.
  • Your petrol supply may be exhausted (indicated by green light glowing).
  • The carburetter mixture control may be wrongly set, causing the mixture to be either too rich or too weak.
  • There may be condensation on the sparking plugs.
  • The sparking plugs may be fouled with oil or carbon.
  • The high-tension lead from ignition coil to distributor may be loose broken or damaged so as to leak.
  • The petrol filters of the automatic petrol pump and carburetters may be choked.
  • The automatic petrol pump may not be functioning properly.
  • The petrol pipe may be clogged or may have an air lock.
  • The ignition coil may be defective.
  • The distributor contacts may be faulty and require resetting and cleaning.
  • The low-tension wire from coil to distributor and coil to ignition switch may be broken or faulty.
  • There may be water in the petrol feed.
  • In cold weather a low-grade petrol will cause difficult starting.
  • The battery may be run down (lamps light when switched on, but gradually fade out).

ENGINE MISSES AT HIGH SPEEDS ONLY

This may be occasioned by:—

  • Faulty sparking plugs which may be fouled or gaps not properly set.
  • Shortage of fuel due to dirt or obstruction in the petrol pipe, accumulation of dirt at filters, or petrol feed not working properly.
  • Improper functioning of inlet or exhaust valves (inlet valve indicated when spitting in carburetter takes place, exhaust valve when "banging" in silencer takes place).
  • Valve clearance may be badly set.
  • One of the electrical connections may be loose, particularly in the high-tension lead between the coil and distributor.
  • Distributor contact breaker badly set or dirty.

ENGINE MISSES AT ALL SPEEDS

This may be due to:—

  • Faulty sparking plugs with an internal fault, such as oil on plug points, carbon deposit, or too wide a setting.
  • Faulty valve action due to incorrect setting of valve rocker clearance, or valve sticking in guide.

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Tracing Troubles

Engine Stops Suddenly

Engine Spits Through Carburetter

  • Warped or badly pitted valves, also arising from faulty setting of the rocker clearance.
  • Broken valve spring.
  • Insufficient fuel due to petrol filters being clogged. (See pages 50 and 52.)
  • One of the ignition wires may be loose and making intermittent connection, particularly that between coil and distributor.
  • Distributor contacts may not be functioning with regularity and in need of attention. (See page 53.)
  • A carburetter may be flooding, due to dirt on the needle valve seating, causing mixture to be too rich.

ENGINE MISSES AT LOW SPEEDS ONLY

This may be due to:—

  • Valves not seating properly, due to faulty valve tappet setting or distortion. ( See page 17.)
  • Air leaks in induction system, due to faulty joints between carburetters and induction pipe or induction pipe and cylinder block. Check joint gaskets for soundness and tighten up all nuts.
  • Carburetter setting faulty (refer to carburetter section, page 50).
  • Battery run down and thus unable to supply sufficient current for ignition purposes.

ENGINE STOPS SUDDENLY

If the engine stops suddenly without making any further attempts to run :—

  • Examine carburetters and ascertain that float-chambers are receiving sufficient petrol supply. (Shortage of fuel is usually indicated by one or two restarts before the engine finally stops, or by spitting through the carburetters.)
  • Test flow from carburetter jets.
  • Test spark at plug points by removing plug, resting on engine, and observing spark when engine is turned by hand.
  • If spark is weak or non-existent, check distributor lead connections to coil and distributor, check distributor contact breaker points, clean and reset, if necessary.
  • If the spark is still weak, test all electrical connections.
  • If the spark still remains weak, check coil as indicated in paragraph on checking ignition faults. (Page 62.)

ENGINE SPITS THROUGH CARBURETTER

This is usually an indication of a weak mixture.

  • Check fuel supply to carburetter float-chambers.
  • Remove carburetter and automatic petrol pump filters (see pages 50 and 52), clean and replace.

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Tracing Troubles

Banging in Silencer

Engine Lacks Power   •   Engine Runs Hot

  • It may be caused by air leaks in the induction system. Check over all joints in the induction manifold and tighten up nuts.
  • Faulty setting of the inlet valve rocker clearance, preventing valves from closing properly, also causes this trouble.
  • One or other of the inlet valves may be sticking in its guide.
  • Sparking plug gaps too wide ; they should not exceed .025 in. (.6 mm.).
  • Engine running too cold.

Banging in Silencer

  • This is usually an indication of a faulty exhaust valve which is not closing properly, due to a warped seating or faulty valve rocker clearance.
  • It may also be due to the exhaust valve sticking in its guide.
  • It may also be produced by faulty mixture supply, which is either much too rich or too weak.
  • If banging takes place in the silencer when proceeding downhill with the throttle closed, it is usually an indication that the throttle does not fully close when the foot is taken off the accelerator pedal.
  • The slow running position of the throttles should be checked over and the carburetter setting checked.

ENGINE LACKS POWER AND IS SLUGGISH

  • This in a new car may be caused by general tightness of the engine and will wear off after the car has been used for approximately 1,000 miles (1600 km.).
  • It may also be due to faulty setting of ignition or to a seized automatic control due to lack of lubrication.
  • Faulty setting of the carburetter mixture control is also a source of trouble of this nature.
  • In an engine which has seen some use, sluggishness is an indication of excessive carbon deposit, particularly if accompanied by "pinking" when the engine is pulling hard.
  • It may also be occasioned by faulty valves or faulty valve rocker clearances.

ENGINE RUNS HOT

  • Water supply in radiator too low. It is necessary always to have the water well covering the base of the upper tank.
  • Running with the spark too far retarded. This is accompanied by a marked loss in power, and sluggishness, and may be due to defective action of the automatic control of the distributor from lack of lubrication.
  • Carburetter mixture control maintained at "rich" position for too long a period. The carburetter mixture control should be returned to the " weak " position as quickly as possible after starting, without causing the engine to splutter and run unevenly.
  • Carburetters which are set to deliver an excessively weak mixture are also a cause of overheating.
  • Hand brake has been left partly on or foot brake adjusted too closely.

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Tracing Troubles

Engine Knocks

Importance of Early Attention

  • Hand brake incorrectly adjusted by use of nuts at base of lever instead of adjusters at brake-shoes.
  • Fan belt broken. This will be indicated by the lighting of the ignition warning light and no charge reading on the ammeter, since the dynamo is also driven by the fan belt.

ENGINE KNOCKS WHEN PULLING HARD

When an unusual sound emanates from the engine, investigate its cause immediately and do not continue running the engine in the hope that matters will right themselves. First of all ascertain that the oil gauge is registering the right pressure and that there is plenty of oil in the sump. Make sure that the noise is not due to shortage lubricant. It must be remembered, however, that the oil pump of the M.G. has a very high capacity and is capable of maintaining a reasonably high pressure even with a run bearing.

The more general causes of engine knocks are:—

1. An excessive accumulation of carbon deposit on the piston heads, valves and combustion chamber. This state of affairs is indicated by a high-pitched metallic ring or "pinking" whenever the engine is made to pull hard. This gradually develops as the engine is further used, but must not be confused with a similar noise produced by the ignition being too far advanced. When an engine is suffering from excessive carbon deposits, it will have a tendency to be sluggish, run rather hot and labour heavily on gradients.
2. Loose or worn bearings.
Loose big-end bearings: These produce a rattle usually heard at speeds of between 25 and 35 m.p.h., when the accelerator is only partly depressed and the engine is running light. If the engine is speeded up with the throttle a quarter open and the car at rest, the noise will usually develop and can then be cut out by shorting the sparking plug of the cylinder concerned. When the sparking plug is released a heavier knock will be produced. It must be remembered, however, that with modern engines with high-pressure lubrication these noises are only very light, even when a bearing has "run."
Gudgeon pin slack in piston: This is heard more readily at low speeds and is a somewhat hollow sound which is not completely cut out by shorting the sparking plug, although reduced somewhat.
The accurate diagnosis of knocks is a matter for an expert accustomed to the particular engine, and you are advised to consult your nearest M.G. Dealer as soon as any unusual noise occurs.

Remember it is bad policy to continue running a car if it is in any way faulty. If the trouble is attended to early no damage need be done and the matter may be comparatively easily rectified, but if allowed to continue, extensive damage may ensue.

  • For dynamo and lamp troubles refer to pages 63 and 65.
  • For ignition troubles see page 62.

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