Engine Tapping and Borescope Results
 

Hello Fellow Boxster Enthusiasts,

Earlier this year I posted this video because of a tapping noise at idle once warm: https://www.youtube.com/watch?v=HtHlYpICstI

At one point I thought it had resolved by topping off with oil but it returned. I recently switched to Castrol Edge 5W-40 and the noise seems to be louder then before. I've spent many hours researching this issue and watching youtube videos with similar sounds. I even timed the tapping at 300 taps/min which I calculated to be 5HZ and finally decided this must be a sticky lifter, rod knock would be a lower frequency I think, and that I'd live with it until I felt like taking off the cam covers to replace them. I decided to borescope the easily accessible cylinders on both banks and have attached pictures for your analysis.

The car burns very little oil (less than a quart per oil change which I perform no more than 4K miles apart), does not smoke, there is no oil in coolant and vice versa. The car runs strong besides the annoying warm idle tick. I've been running this engine in this condition for over 4K miles. Spark plugs on all cylinders look identical and all good.

While performing the borescope I found cylinder 5 to have what appears to be 3 non-linear "cracks". Cylinder 6 has at least one of these and cylinder, and cylinder 2 showed similar "crack". Cylinder 3 looked perfect (no cracks). Please review these images, I know they are not HD, and let me know what you think and what your experience is with these findings.

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Wow! Those don't appear to be cracks to me. Looks like large chunks of the piston is missing and since they are perpendicular to the wrist pin my guess would be the piston is rocking. Caused by what you ask? My guess would be detonation, but those dark spark plugs don't confirm. Interesting.

The “cracks” I’m referring to are the hair-like lines running up cylinder wall. Based on the live borescope I don’t see any chunks of piston broken off. If anything there is a good amount of carbon deposits on the piston crown. I replaced the AOS 200 miles ago after finding residual oil/sludge in intake plenum.

I don't follow why your looking at the pistons and cylinders if you think its the lifters. There is not enough definition in the pics to see what is going on. Wouldn't cracked cylinders result in coolant loss?

You could do a leak down test and see what's going on. I recently had a ticking lifter and you can see my post about that. You might get lucky like me or have to change out the lifters.

cracks or scoring?

Some frame of reference for the images would be helpful. For instance, aim of the boroscope head with respect the spark plug hole; orientation; what surface you are aiming at...these images look like the top of my two stroke engined cafe racer after a lean condition melted the exhaust port side of a piston.