So, I happened upon a really good deal on a set of Millennium cylinders for a wide deck O320. They had 1800 hours on them, and came off a Cessna in favor of a set of new Lycomings with 75089s, the owner wanted to do the 160hp upgrade. I snapped them up and it turned out to be a pretty smart move.
I had a couple of cylinders that were down on compression and a little bit of a knock at hot idle. My annual guy connected me to a retired engine guy, who still does engine work on the side. We pulled a couple cylinders and found a cracked exhaust valve seat, really tight piston pins, worn rings, and pistons are worn down to a smooth track on the top and bottom. Incidentally, my airplane has had a couple of jug replacements so it had one channel chrome, one standard chrome, one plain steel, and one steel oversize cylinder on it.......that said, the crank, cam, and bearings are in serviceable condition per the mechanic.
I had the guy take the Millennium cylinders and pistons to his shop and he overhauled them for me. He reported that they were in surprisingly good condition and needed minimal work. He did NDT on the valves, ground valve seats, did some work on the exhaust guides, replaced valve locks, and deglazed the cylinders. All good to go.
Then we get to the pistons. According to the paperwork they are 75413s. I had looked them over carefully when I got them. They appeared to be in really good condition. With the exception of the very lip of the skirts, the original machining marks are clearly visible all the way around each piston, indicating very little wear. However, my guy tells me that one of the four is measuring undersize at the skirt, and on another one of the ring lands is slightly oversize I think he said, and so he is recommending going with a new set of pistons.
Here is where it gets weird. The pistons are "Airtech" brand according to the stamp on the underside. He can't find any info on them and neither can I. I'm having a hard time grasping that a set of pistons that were in such good shape on visible inspection could be unsuitable. Thankfully, if really needed he just happens to have a set of brand new Lycoming 75413s on his shelf that belong to a buddy who changed his other mind and elected to go with all new assemblies instead of overhaul, that he'll sell me for a pretty decent price. I also think he may be a little leery of installing an unknown part on a certificated airplane, especially if it is slightly out of limits.
Has anyone ever heard of "Airtech" pistons? Is it possible that they are simply not very good quality and are undersize in excess of limits due to poor quality control?
I asked him to bring them along when he comes to the hangar this week to mic out my small end rod bushings so I can see what he is talking about. I also printed out the portion of the table of limits from the Lycoming overhaul manual that pertains to pistons so I can at least grasp the situation and try to make a good decision.
I want my engine to run smooth and quiet, and of course I would like to get as many hours as I can out of the top overhaul, which is admittedly being done to stretch my hours before I can do a major overhaul. When I do get the major done, I'm going to 75089s so whichever I go with, these pistons will only get one (likely relatively short) run in my engine.
Any mechanics have guidance they are willing to throw at me? Discuss.......
Thanks in advance!
I had a couple of cylinders that were down on compression and a little bit of a knock at hot idle. My annual guy connected me to a retired engine guy, who still does engine work on the side. We pulled a couple cylinders and found a cracked exhaust valve seat, really tight piston pins, worn rings, and pistons are worn down to a smooth track on the top and bottom. Incidentally, my airplane has had a couple of jug replacements so it had one channel chrome, one standard chrome, one plain steel, and one steel oversize cylinder on it.......that said, the crank, cam, and bearings are in serviceable condition per the mechanic.
I had the guy take the Millennium cylinders and pistons to his shop and he overhauled them for me. He reported that they were in surprisingly good condition and needed minimal work. He did NDT on the valves, ground valve seats, did some work on the exhaust guides, replaced valve locks, and deglazed the cylinders. All good to go.
Then we get to the pistons. According to the paperwork they are 75413s. I had looked them over carefully when I got them. They appeared to be in really good condition. With the exception of the very lip of the skirts, the original machining marks are clearly visible all the way around each piston, indicating very little wear. However, my guy tells me that one of the four is measuring undersize at the skirt, and on another one of the ring lands is slightly oversize I think he said, and so he is recommending going with a new set of pistons.
Here is where it gets weird. The pistons are "Airtech" brand according to the stamp on the underside. He can't find any info on them and neither can I. I'm having a hard time grasping that a set of pistons that were in such good shape on visible inspection could be unsuitable. Thankfully, if really needed he just happens to have a set of brand new Lycoming 75413s on his shelf that belong to a buddy who changed his other mind and elected to go with all new assemblies instead of overhaul, that he'll sell me for a pretty decent price. I also think he may be a little leery of installing an unknown part on a certificated airplane, especially if it is slightly out of limits.
Has anyone ever heard of "Airtech" pistons? Is it possible that they are simply not very good quality and are undersize in excess of limits due to poor quality control?
I asked him to bring them along when he comes to the hangar this week to mic out my small end rod bushings so I can see what he is talking about. I also printed out the portion of the table of limits from the Lycoming overhaul manual that pertains to pistons so I can at least grasp the situation and try to make a good decision.
I want my engine to run smooth and quiet, and of course I would like to get as many hours as I can out of the top overhaul, which is admittedly being done to stretch my hours before I can do a major overhaul. When I do get the major done, I'm going to 75089s so whichever I go with, these pistons will only get one (likely relatively short) run in my engine.
Any mechanics have guidance they are willing to throw at me? Discuss.......
Thanks in advance!
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