Module 2 - Basic Engine Malfunction

• Three basic causes of malfunctions:

  1. ignition malfunctions
  2. fuel system malfunctions
  3. engine part malfunctions
• Ignition Malfunctions – can be traced to defective magnetos, defective transformers in a low-tension system, improper timing, spark plugs which are burned or otherwise damaged…
• Called Floating Points – happens when the cam follower actually does not maintain contact with the cam but floats at some point between the cam lobes
• If one spark plug fails, the engine rpm will show an excessive drop when it is checked on the magneto supplying the defective plug. The bad plug may be located by the COLD-CYLINDER CHECK
• Backfiring - occurs when the flame from the combustion chamber bums back into the intake manifold and ignites the F/A mixture before the mixture enter the engine
• When an excessively lean fuel/air mixture passes into a cylinder, the mixture may not burn at all or will burn so slowly that combustion continues through the power and exhaust strokes
• Backfiring – usually caused by incorrect valve clearance, defective fuel injector nozzles, or other conditions that result in a leaner mixture entering the cylinder
• After firing - sometimes called afterburning, often results when the fuel/air mixture is too rich
• After firing – occurs when air from outside the exhaust stacks will mix with the unburned fuel, causing it to ignite and explode in the exhaust system
• After firing – occurs when air from outside the exhaust stacks will mix with the unburned fuel, causing it to ignite and explode in the exhaust system
• After firing - can be caused by cylinders that are not firing because of faulty spark plugs, defective fuel injection nozzles, or incorrect valve clearances
• Engine Part Malfunctions - Blow-by of combustion gases can lead to excessive carbon in the oil and high crankcase pressure. The high crankcase pressure can cause the nose seal to leak oil
• Crankshaft Seal - attached to the front of the engine. These seals are usually made of metal and rubber or silicone to seal the crankshaft as it turns
• Crack In Crankshaft – a problem caused by an oil leak at the nose seal within 100 hours of a prop strike may be evidence of a crack in the crankshaft
• Failing Bearing - produces heat and metal. The metal shows up in the oil filter and screen, as well as in an oil analysis. The heat causes increased oil consumption
• Metal In Oil - from a failing bearing will restrict oil flow at the sump pickup and oil screen or filter. A fluctuating oil pressure or drop in oil pressure over a few hours may be the result of metal in the oil.
• Polished Bore - a cylinder wall has many peaks and valleys to control oil. If the engine sits for long periods of time without running, the peaks begin to rust
• Stuck Valve - Exhaust valves typically stick because high temperatures have caused oil to oxidize and form carbon build up in the valve guide.
• Worn valve guides - oil that is used to lubricate the rockers can flow down the valve and into the intake or exhaust ports, causing an excessive oil consumption rate.
• Intake leak - Any change in the volume of air between the fuel control unit and the intake port results in a mixture change.
• Leaks in manifold pressure line - allows ambient air pressure to enter the line and are indicated by a higher-than-normal reading.
• Manifold pressure - a measure of the air pressure available in the engine's intake manifold
• Low cylinder compression - An engine may run normally at high power settings and appear to deliver full power. 
• Two basic types of compression testers 

  • direct-compression tester
  •  differential-pressure tester
• Cylinder Compression Testing - can be determined by measuring the static leak rate of the cylinder as compared to the leak rate through an orifice of specified size
• CAUTION - TAKE ALL NECESSARY PRECAUTIONS AGAINST ACCIDENTAL FIRING OR ROTATION OF THE ENGINE.

   
• Direct-Compression Check - This type of compression test indicates the actual pressures within the cylinder.
• fuel primer - used to draw fuel from the tanks to vaporize fuel directly into the cylinders prior to starting the engine. (helps to vaporize the fuel in the carburetor.)
• Low power - An engine that is not producing full power may not achieve the minimum static RPM
• Example Causes of Low Power:

  Carburetor ice

  Carburetor heat on

  Dirty air filter

  Intake restriction

  Ignition problem