Borescopic Inspection
Rationale
Routine monitoring of ash levels on the piston crown, and some insight into the conditions in the combustion chamber, can be achieved using one of the many readily available and cheap USB type cameras. However, these usually only offer a limited view into the conditions inside the cylinder.
A professional borescope inspection is, generally, not a regular occurrence due to the time, cost and downtime required to complete it. Some companies may have access to a good quality articulated borescope, and an experienced person to operate it, but many will not and they may not fully appreciate the benefits that can be realised from such an inspection.
There are times when a professional inspection can be beneficial:
- Understand potential causes of pre-ignition or pre-combustion caused by excessive deposits or lubricant inside the combustion chamber. Such conditions will often lead to reduced power output as the engine management system tries to reduce events detected by knock sensors or similar.
- Establish the condition of the combustion chamber at the end of a warranty period or prior to changing to, or evaluating, an alternative lubricant.
- Correlate used oil analysis results to cylinder condition to understand where wear debris may, or may not, be originating.
Removal of cylinder heads can of course facilitate access to the cylinder internals, but such an intervention can be even more time consuming, expensive and much riskier than a borescope inspection.
An example of a redacted borescope inspection can be downloaded here.
Inspection Strategy
Annotation of each image taken is highly recommended, to provide clarity as to what has been captured. At times though mistakes can be made, and an annotation may clearly be incorrect. The consequences of such mistakes can be mitigated by a couple of simple strategies.
Firstly, be consistent with the sequence of examining each cylinder, especially when multiple cylinders are being inspected. If a mistake is made it should be possible to figure out what an image should be as the sequence of inspection is always the same, for example 12 o’clock top, middle and then bottom, then repeated at the 6 o’clock position. Include part of the flame deck at the top and the piston at the bottom, again so it is clear where in the cylinder you are looking.
Secondly, always take multiple images at each position, but with a slight movement of the borescope each time. This then moves reflected light and shadow slightly. When reviewing images later and you see something abnormal, it may just be the light. If you only have one image you do not know, but over 3-4 it should be apparent whether there is a problem or not.
Naming Convention
When consistently taking multiple images in each cylinder the total number of images soon becomes significant. Typically, I take around 30 – 45 images per cylinder, so 500 to 700 across a sixteen-cylinder engine.
Usually, the borescope will allocate a sequential number to each image, which is not at all helpful when trying to review or compare them. I always rename the images to something useful, and which can be filtered to compare say all the 12 o’clock top positions.
The convention I use, which is purely my own and not based on anything formal is:
C03-XXX-NNN
The first three characters indicate the cylinder number. The next characters are the part of the engine:
- 06B Bottom of the liner at the six o’clock position
- 06M Middle of the liner at the six o’clock position
- 06T Top of the liner at the six o’clock position
- 12B Bottom of the liner at the twelve o’clock position
- 12M Middle of the liner at the twelve o’clock position
- 12T Top of the liner at the twelve o’clock position
- FD Flame deck
- FDX Flame deck close-up
- PC Piston crown
- PCX Piston crown close-up
- VE Exhaust valve
- VI Inlet valve
The last three digits are a unique number for each cylinder and represent the original order the photos were taken in that cylinder.
Renaming hundreds of images is time consuming but without it the data is much more difficult, if not impossible, to manage and is far less valuable.
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