Cylinder manufacturers offer good choices for replacement cylinder heads
By Greg Napert
aced with a multitude of choices for replacement parts today, technicians can find themselves between a rock and a hard place when trying to determine what to recommend to their customers.
The technician's recommendation to an aircraft owner is often a delicate balance between past experience, as well as Federal Regulation (government approvals) and owner's pocketbooks.
The cylinder replacement decision is not all that difficult considering there are only four companies that manufacture new cylinders, but the decision becomes more complex when faced with the option of repairing, coating, or rebarreling the old cylinder.
New cylinders today are available from both original equipment manufacturers (OEMs) Textron Lycoming and Teledyne Continental Motors, as well as from aftermarket suppliers Superior Airparts (Millennium™) and Engine Components, Inc. (Classic Cast™).
The latter two, Superior and ECI, offer "design improvements" over the OEM's cylinders with one cylinder, the Millennium by Superior, selling at a premium for the improvements.
AMT magazine interviewed several top overhaulers on their opinions related to cylinders. While most did not want to comment on their preferences on record (many are distributors and approved sales outlets for the cylinder manufacturers), the comments related to cylinders can be summarized in the following points:
• Only select improved cylinder designs if you are dealing with higher powered engines or engines that are hard-use/high-time. Smaller, low-time engines in general, do not take the punishment of a big bore engine and would not necessarily require thru-hardened barrels or beefier castings.
• Repaired cylinders are a good option for engines that are at mid-life. If you want an overhaul to go to TBO, a new cylinder is generally a better option. However, there are some exceptions.
• Consider the warranty and level of support. If you have to fight for every warranty return, it may not be worth dealing with that manufacturer. A manufacturer that has a "no-hassle" policy is worth a great deal when you replace cylinders for a living.
• Remember that each cylinder model has its own characteristics — regardless of the manufacturer. Saying that one brand is better than the other is like saying all Fords are better than all Chevys — so work with your local overhauler to determine the best choice for your circumstance.
OEMs insist on using only "New" cylindersToo many problems with heads cracking, they say
According to an article in the Lycoming Flyer Key Reprints, Textron Lycoming metallurgists argue that welding of cracks in aluminum cylinder heads is not likely to meet with long-term success. Therefore, an overhauled cylinder has little chance of being as serviceable as a new cylinder. Even if there were no cracks at the time of overhaul, metal fatigue is still a factor to be considered. But, how can you even determine metal fatigue? There is no record of time in use required for a cylinder assembly. An overhauled cylinder could have 4,000, 6,000, or 8,000 hours or more when it is put on an overhauled engine. Even a cylinder from your own engine with only one trip to TBO may not make it to TBO a second time.
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