Q: I am in the process of acquiring a Piper Seneca equipped with twin Continental TSIO-360-RB engines. Both engines have about 450 hours to go before overhaul.
The aircraft was last flown approximately three years ago. Technicians maintain that the cylinders have to be honed due to glazing as a result of the time elapsed since the last engine run.
Being an automotive engineer myself I can think of no technical reason for this requirement, apart from possible corrosion in the absence of a inhibitor. Please educate me if my assumption is incorrect.
A: Nic, as you may know, my area of expertise (if I’m allowed to stretch it that far) is in dealing with Lycoming engines, but I feel comfortable in addressing your question on the TCM TSIO-360. This particular situation could occur on either a TCM or Lycoming engine and the answer would probably be the same in either case.
There is no doubt knowing the aircraft was last flown three years ago does cause some concern with regard to the internal condition of the engine.
One of the first places to start in checking the condition of the engine would be by conducting a close inspection of the internal condition of the cylinders. A very thorough borescope inspection of each cylinder by a knowledgeable aircraft maintenance technician would provide information needed to make further decisions as to what additional work may be required.
Depending on what type cylinders are installed on the engine — chrome, plain steel or a nitride type — the borescope inspection will provide you with the information you need.
Corrosion on chrome cylinders is not a problem, but it may be on other surfaces used on engine cylinders.
If corrosion in the cylinders is observed, then the best decision would be to remove, hone and reinstall the cylinders, always using new piston rings.
On the other hand, if no corrosion is noted during the borescope inspection, I see no need to remove the cylinders for honing.
If the engines performed normally prior to the extended period of inactivity, and the oil consumption was within specification at the time it was being flown, then the cylinder walls should not be glazed.
Glazing of cylinder walls typically occurs during engine break-in and is caused by improper operation during the break-in period by operating at power settings too low to allow the piston rings to seat properly with the cylinder walls.
Glazing, to my knowledge, has never been a result of an inactive aircraft. Corrosion has always been the “Grim Reaper” for inactive aircraft!
So Nic, I agree with your assumption and hopefully, barring any unforeseen circumstances, your maintenance facility will agree with both of us.