As per previous case studies, a weakness in a particular cylinder compared to others can be identified as a leak. This note discusses how to identify what the source of the leak may be.
In cases of slight leaks, it is often possible to diagnose what type of leak is present. A valve leak will generally lose pressure all the way up the compression curve as it is leaking all the time. Rings or scored liners however tend to leak more at the top of the cylinder, losing a higher percentage of air as they approach TDC.
Valve Leak on Cylinder 1 (Black Line)
Ring or Liner Leakage on Cylinders 7 and 8
When rings leak, they tend to do so at the top of the stroke. Similarly, liner scoring is most common at the top of the bore and the trace above could be either. It keeps up with other traces until about -20° then it loses pressure compared to the rest of the cylinders.
Liner Scoring – Cylinder 4
The trace highlighted in red showed an increasing loss of pressure relative to all other cylinders as it approached TDC. This was due to liner scoring as seen in the photo below.