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Borescope Inspection of Large Reciprocating Engines

Large reciprocating internal combustion engines (RICEs) are widely employed in many industries to generate electricity or drive mechanical equipment—propeller shafts and pumps, for instance. The working principle of these engines is the same as traditional automotive combustion engines, but on a much larger scale. Here, we discuss RICE condition monitoring techniques and the uses of borescopes, along with best practice guidelines and troubleshooting tips to get the most out of these types of inspections.

Figure 1 Reciprocating internal combustion engines

To run and maintain large engines efficiently, it is necessary to understand the condition of their components. This is accomplished using various condition monitoring (CM) techniques. Each technique provides one type of information about the engine. This list summarizes the most common condition monitoring techniques used for RICE inspections:

  • Instrumentation – continuous monitoring of readings from engine sensors, such as temperature, pressure, vibration, exhaust gas composition, etc.
  • Used oil analysis – periodical collection and laboratory analysis of oil samples, which may reveal degradation of the oil or the presence of particles that can be linked to contamination, wear, or damage.
  • Borescope inspection (BSI) – visual inspection of internal parts of the engine with little or no need to disassemble parts.
  • Strip down/dismantling – disassembling parts or the whole engine for inspection, overhaul, or to replace components.

Instrumentation and used oil analysis are noninvasive techniques, which require no interruption of RICE operation and are widely seen as the first approach to condition monitoring. However, because these techniques are limited in the information they can obtain, regular borescope inspection may be required, either as part of a preventative maintenance strategy or as a tool in reactive maintenance. The focus of a borescope inspection of a reciprocating engine is the combustion chamber, which is also called the cylinder. The components surrounding the combustion chamber are subject to high pressure and temperatures and therefore need to be monitored for damage and wear. In addition to the cylinder, other parts of the engine can also be inspected using a borescope, such as the water jacket, oil galleries and sump, turbochargers, cooling and air circulation systems, and alternators, among others.

Figure 2 Representation of combustion chambers (cylinders)

Borescope Technology – A Long Legacy

Reciprocating engines have been around since the start of the 20th century and one of the initial applications of borescope technology was to inspect them. The first type of industrial endoscope to emerge was the rigid borescope, followed by the flexible fiberscopes. Today, videoscopes are state-of-the art in borescope inspection, due to their versatility, ease of use, and the ability to capture both images and video. Table 1 presents an overview of the characteristics of each of these systems. While there is still use for rigid borescopes and fiberscopes, this article focuses on videoscopes, due to their widespread application.

Table 1 Comparison of the main characteristics of rigid borescopes, fiberscopes, and videoscopes

Feature Rigid Borescope Fiberscope Videoscope
Insertion tube type Rigid, straight-line access Flexible, articulated Flexible, articulated
Light source External External Built in
Image acquisition Optical, relay lenses Optical, fiber bundle Digital, imaging sensor
Optical system Fixed Fixed or changeable Changeable
Screen, image, and video capture Require additional accessories Require additional accessories Built in
Measurement Not available Not available Possible

As seen in Table 1, videoscopes have considerable technical advantages over rigid borescopes and fiberscopes. A borescope inspection performed using a videoscope will be faster (fewer parts to attach and fewer adjustments to make to achieve a good image), and it will also produce a better output for reporting, since images and videos can be easily recorded.

Within Evident’s remote visual inspection (RVI) portfolio, the videoscopes recommended for RICE inspection are the IPLEX™ G Lite and the IPLEX GT. Both videoscopes produce high-quality images, enabling component evaluation and further reporting.

Getting the Right Configuration

  • 6.6 ft length insertion tube
  • 6 mm probe diameter
  • Two optical tips:
    • One side facing far focus tip (AT120S/FF) for an initial overview of the cylinder
    • One forward facing near focus tip (AT120D/NF) for detailed inspection

Figure 4 Rigid sleeve and articulating arm

Cylinder Inspection 101 – Best Practice

Preparing the Videoscope

  • Before inserting the videoscope probe, check if you have the correct optical tip for the inspection, and ensure that the optical tip and distal end are clean.

Inserting the Probe into the Cylinder

  • It is recommended to use the rigid sleeve when inserting the probe through the access port (as shown in Figure 3). This helps protect the probe, reducing the chance of oil contamination and probe damage. The rigid sleeve removes the need to hold the probe, improving image stability and reducing the chance of hitting the cylinder’s internal surfaces.
  • Once the probe is inside, to obtain images with a repeatable orientation, rotate the probe until the direction of 12 o’clock is at the top of the image on the screen.
  • Very often, it is possible to determine the directions of the cylinder by looking at the piston crown (top of the piston), which will have specific features or marks that are direction dependent.

Positioning the Piston

  • Cylinder inspection must be done with the piston at the very bottom of the cylinder (bottom center). This enables the inspector to visualize the largest extent of the cylinder walls.
  • To position a piston right at the bottom, observe the videoscope screen while cranking the engine manually until the piston is in the right position.
  • To increase the efficiency of the inspection, you can sequence your inspection following the firing sequence, since several pistons have their positions synchronized.
  • You can use the IPLEX Image Share app to visualize the piston position while cranking the engine.


  • Once the piston is positioned correctly, you can proceed with the inspection.
  • We advise performing a general inspection using a side view (right angle) optical tip, with which you will be able to get an overview of the cylinder walls, piston, valve deck and valves, as shown in Figure 4.
  • If additional detail is required, you can switch to a direct facing optical tip, which will enable detailed inspection closer to the target.
  • For easier management of your recorded images, save the images of each cylinder in a separated folder in your memory device – this way, each image file will be named according to the folder name, and it will be easier to manage files and prepare your post-inspection report.
  • Record images or video as required.

Removing the Probe

  • Once you have finished inspecting a cylinder, unlock the probe articulation (watch for the padlock symbol on the videoscope screen, bending section is engaged)
  • Remove the probe from cylinder.
  • Move the rigid sleeve and articulated arm to the next piston to be inspected.

Figure 5 Scheme showing how to use a side facing optical tip to obtain an overview of the cylinder


Challenge Issues Solutions
Oil Most of the inspection will be done in the presence of lubricant, which may degrade image quality
  • Have a cleaning kit (Isopropyl alcohol and cotton buds) avai- lable and clean optical tips when image gets blurry
  • Before starting the inspection, ensure that the O-ring is cor- rectly placed on the distal end, to avoid contamination inside the optical tip
  • Use IPLEX GL and GX/GX oil clearing optical tips
  • Use a rigid sleeve to avoid probe contamination duringinsertion
  • Avoid hitting cylinder surfaces with the probe
Temperature Depending how long before the inspection the engine is shutdown, the cylinders may still be hot when the inspection start
  • Observe correct cooldown period for the engine.
  • Ensure the engine temperature is at least below 80 degrees Celsius
Probe orientation Once the borescope is inserted in the cylinder, it may be difficult to determine the orientation of the images
  • Use the piston or flame deck features to locate the 12 o’clock orientation inside the cylinder and use it as reference for the inspection
  • Use a rigid sleeve to hold the probe in place
Naming image files If the user records images of different cylinders in the same folder, they will all have similar file names, and it is difficult to manage them after the inspection
  • Create one folder per cylinder and switch to the appropriate folder accordingly

Borescope Inspection of Large Reciprocating Engines


Additional Resources

Olympus IMS

Products Used for This Application

The IPLEX G Lite industrial videoscope packs powerful imaging capabilities into a small, rugged body. Lightweight and able to go almost anywhere, users working in challenging applications have a remote visual inspection tool with the image quality and ease of use to get the job done.

If you’re inspecting in the cramped quarters of a wind tower nacelle, the wind version of the IPLEX G Lite videoscope’s combination of portability and powerful imaging features can make your job easier.

With interchangeable insertion tubes and light sources, an 8 inch touch screen, and advanced imaging features, the IPLEX GX/GT videoscope delivers an optimal balance of versatility, imaging capabilities, and ease of use.

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