After measuring compression we took a borescope and looked inside of all cylinders. Cylinder #3 has a mark at about 10 o'clock. We are puzzled what could cause it? Compression for the particular cylinder is 74/80 and the engine is nearing 3,000 hours of trouble free time. Take a look at the pictures below.
Looking at the piston. There are some swirls visible on top of the piston and against the most visible one there is a wear mark.
![](/proxy.php?image=http%3A%2F%2Fi447.photobucket.com%2Falbums%2Fqq197%2FN666BK%2FEngine%2520Hoist%2FSat%2520Nov%252026%252015-00-35.jpg&hash=1b44e25cd983dae8ea6495403a107e27)
That's where the mark is located. About 10 o'clock if it matters.
![](/proxy.php?image=http%3A%2F%2Fi447.photobucket.com%2Falbums%2Fqq197%2FN666BK%2FEngine%2520Hoist%2FSat%2520Nov%252026%252015-02-32.jpg&hash=5012b3b7a765b05ea7b2403ecd9e6216)
Closer look at the wear mark.
![](/proxy.php?image=http%3A%2F%2Fi447.photobucket.com%2Falbums%2Fqq197%2FN666BK%2FEngine%2520Hoist%2FSat%2520Nov%252026%252015-08-56.jpg&hash=90a526d3b2cbcbe011b3795777c8a763)
What could be the cause? RocketBob are you around?![Smile :) :)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
Looking at the piston. There are some swirls visible on top of the piston and against the most visible one there is a wear mark.
![](/proxy.php?image=http%3A%2F%2Fi447.photobucket.com%2Falbums%2Fqq197%2FN666BK%2FEngine%2520Hoist%2FSat%2520Nov%252026%252015-00-35.jpg&hash=1b44e25cd983dae8ea6495403a107e27)
That's where the mark is located. About 10 o'clock if it matters.
![](/proxy.php?image=http%3A%2F%2Fi447.photobucket.com%2Falbums%2Fqq197%2FN666BK%2FEngine%2520Hoist%2FSat%2520Nov%252026%252015-02-32.jpg&hash=5012b3b7a765b05ea7b2403ecd9e6216)
Closer look at the wear mark.
![](/proxy.php?image=http%3A%2F%2Fi447.photobucket.com%2Falbums%2Fqq197%2FN666BK%2FEngine%2520Hoist%2FSat%2520Nov%252026%252015-08-56.jpg&hash=90a526d3b2cbcbe011b3795777c8a763)
What could be the cause? RocketBob are you around?