Normally one does a visual inspection on each 50hr check. I think most of them on Lyco cylinders are between the spark plug hole and the exhaust valve.
The Q is what do you do when you see what you think is one?
This came from Savvy USA. I know he is advertising his consultancy/supervision service but it is still interesting.
It is a well known technique for surface breaking cracks but limitations (from past memory) are that it isn’t so good with cracks that are under compression at rest and in structural corners/edges etc. It’s quite often used in crankshaft detection I think.
Crankshafts are normally inspected with a magnetic particle inspection.
DPI is used mainly as described above but you can also use the DPI developer to find fluid leaks and is especially good at finding the location of leaks in areas that due to airflow the fluid is quickly dispersed.
MattL wrote:
It’s quite often used in crankshaft detection I think.
For a crankshaft, I would rather perform a magnetic particle or at least a fluorescent penetrant inspection. These methods are more sensitive.
I had a cylinder crack that would not be diagnosed with a compression check (the compression on the cylinder was excellent) – it was between the exhaust port and one of the exhaust studs (basically the stud now no longer would stay screwed into the cylinder head). I think it had been cracked for some years – the stud hole had been helicoiled some time before I owned the plane – but eventually the crack grew to the size where the stud would no longer screw in securely and we started getting blowby past the exhaust gasket.
