Unexpected honing pattern in cylinders

[Radioflyer]

I was borescoping nitrided cylinders on a TMX 360 engine. The engine originally had ECI cylinders which the owner replaced with overhauled Lycoming cylinders due to the ECI AD. Those Lycoming cylinders were prepped by a commercial FBO and the cylinders now have about 325 hours.
Overall, the cylinder bores, valves look quite good. However, the cross hatching looked rather course and rather flat, no where near 45 or 30 degrees. The compressions are great, engine runs fine, oil consumption normal. Has anyone seen only slightly angular cross hatching patterns in normal cylinders?

 

[airguy]

Got a picture?

 

[BoydBirchler]

In a perfect world the cross hatch should be between 35 and 40 degrees to get the result of good compressions and low oil consumption: the result, after break in. is what is of importance.

 

[Radioflyer]

Unfortunately, I did not keep the picture. There was also an A&P on site and although he thought it was an unusual pattern he had never seen before, he wasn't overly concerned given all the other positive engine operation observations. I'm just wondering if this kind of pattern may be customary in some shops or in certain types of cylinder re-work.

 

[lr172]

I was borescoping nitrided cylinders on a TMX 360 engine. The engine originally had ECI cylinders which the owner replaced with overhauled Lycoming cylinders due to the ECI AD. Those Lycoming cylinders were prepped by a commercial FBO and the cylinders now have about 325 hours.
Overall, the cylinder bores, valves look quite good. However, the cross hatching looked rather course and rather flat, no where near 45 or 30 degrees. The compressions are great, engine runs fine, oil consumption normal. Has anyone seen only slightly angular cross hatching patterns in normal cylinders?

From what I recall on auto cylinders, the angle to the piston top is typically around 20-30* and the intersection of patterns is 45. Most of the ones I have seen on lycs's are pretty shallow. My guess is that Lyc has a spec for this and it is in some obscure manual that we do not see, but the OH shops do. Have no idea what the spec is, but curious to learn. Cross hatch can affect ring rotation rate, so each ring manufacturer has their own specification, generally.

proper cross hatch requires an expensive honing matching that controls stroke relative to rotation. Highly unlikely an FBO has one. If they did the work themselves, it was probably done by hand and there is no way to control cross hatch that way. That is not necessarily bad though. I have 1000 hours on my cylinders that I honed this way. Oil consumption is still around 15 hours/qt and compression's above 74.

 

[rocketbob]

Most cylinders get worn smooth with little cross hatch left by around 750 hours depending on the type of cylinder. So they will run fine even with no cross hatch. Oil consumption obviously goes up as there is no hone to facilitate retention of oil.

 

[Radioflyer]

I received a helpful comment from a very well known cylinder overhaul shop. The flat-ish cross hatch pattern is most likely the result of a hand held ball hone done by a small local engine shop. Unlikely to cause any engine issues and should not be a concern. This pretty much is in line with what has been said here so far.

 

[BillL]

Most cylinders get worn smooth with little cross hatch left by around 750 hours depending on the type of cylinder. So they will run fine even with no cross hatch. Oil consumption obviously goes up as there is no hone to facilitate retention of oil.

AND . . . . the smooth surface can allow the oil rings to ride on a film rather than scraping it off as designed. Like grooved pavement. Wider faced oil rings are more prone to that. It is "simple" hydrodynamics.