Borescope Inspections

         The majority of General Aviation aircraft are single engine piston powered. In-flight engine failure therefore has severe, sometimes fatal, consequences. Preventive maintenance is a vital part of managing this risk. The traditional Compression test is highly unreliable and has issues around repeatability. It can detect issues such as worn piston rings, leaking valves, etc. There is no substitute for a visual inspection of the cylinder walls, valves, cylinder head etc but to do this requires removing the cylinder(s) from the crankcase. Due to the design of typical GA engines like Continental and Lycoming, which use a mixture of studs and through-bolts to secure the cylinder to the crankcase, un-necessary cylinder removal should be avoided as it carries with it the risk of bearing shells being rotated, blocking oil holes and there is also the difficulty of ensuring that adequate clamping forces are achieved when torque controlled tightening of cylinder nuts is used.

      The Borescope allows a visual inspection with no disturbance to the engine. It allows early identification of problems such as:

  • Valve overheating (burning) due to leakage of hot gases (especially exhaust valves).
  • Deposits on valves and valve seats.
  • Cylinder head cracks which may develop in the vicinity of spark plug holes and valve seats.
  • Excessive wear of valve guides- e.g. if you have high oil consumption the oil may be entering the combustion chamber from the rocker box via a worn valve guide. Which cylinder is to blame can be seen from the borescope inspection.
  • Damage to piston crowns – e.g. strike marks caused by impact with valves – indicating past engine over-speed events or incorrect timing.
  • Wear and corrosion (pitting) of cylinder walls.

In these current COVID-19 times with GA operators prevented from flying as frequently as normal (which may be far too infrequent to start with!), corrosion of cylinders due to condensation is a big problem. However other parts, not visible, can corrode just as easily (e.g. the camshaft).

Burnt valves will not be picked up by a Compression or Leak-down test but are easily seen during a borescope inspection. 

A borescope inspection therefore provides an effective and inexpensive means of reassuring yourself about your engine’s health and condition.

We can carry out the borescope inspection at your aircraft’s normal place of residence and provide a report with photos of the interior of the cylinders and our observations and recommendations.

The borescope can also be used to inspect inaccessible areas of the wing structure etc and fuel tank walls for corrosion.

                        First Photo -   Valve Guide      Second Photo - Exhaust Valve (Closed) Third Photo - Valve open - all from a Lycoming O235 L2C engine - compare to Fourth Photo from recent Top Overhaul on the same engine - i.e. new cylinder.

Exhaust Valve Lycoming O235 L2C