In the not-too-distant past, the purchase of factory new cylinders for an engine overhaul was rare, expensive and usually reserved for those with fat wallets. It was nothing to find an $1800 price tag attached to a bag containing a factory-fresh cylinder and copious amounts of cosmoline. Because of this price gouging, cylinder overhaul companies flourished in the 1960s and 1970s. Things have changed dramatically. Now, factory new cylinders arent much more expensive than reworked jugs. Only supremely skin flinted owners wont at least consider them when overhauling or topping an engine.
Competition is such that on some engines-certainly not all-you can buy new cylinders from two or more sources. We decided to survey the field for new cylinders to get a sense of who builds the best and the worst.
In the heyday of the cylinder overhaul business, a rebuilt cylinder was half the price of new and cylinder weld repair and chrome plating became an industry standard, despite the dim view of cylinder repair advanced by Lycoming and Continental.
With the introduction of discount pricing from the likes of Air Power, Inc. and other cut-rate warehouses, new cylinder costs plummeted to a squeaky $50 over dealer invoice. Continental soon decided to purge the field of old, worn out castings by dropping its price on new cylinder kits.
Lycoming grudgingly went along, even though rebuilt Lycoming cylinders were much more dependable than weld-repaired TCM jugs. By the 1990s, everyone was buying new-even before reaching TBO-and a new standard was set for those purchasing airplanes and engines.
What was once a luxury had become a necessity of sorts, at least from a marketing standpoint. The bar has remained at the upper notch ever since. Aside from the preservation of an expensive asset, buying new cylinders improves reliability and safety.
New aluminum seldom fails catastrophically and wholesale cylinder loss in flight is virtually unheard of, thus we have generally recommended new castings at least for the past five to eight years.
But lets take a closer look at the good and the bad in new cylinders produced by the four players in this market: Teledyne Continental, Textron Lycoming, Engine Components, Inc., and Superior Air Parts, Inc.
We requested from Continental that a new O-200/O-300 cylinder kit be provided to us for a technical review. Lycoming sent us an example of its O-360 power assembly. The same request was made of Superior and ECI, both of whom sent examples of their aftermarket Continental and Lycoming replacements. Well touch on the merits of each and detail the inconsistencies we found.
A TCM Surprise
Continentals 1999 O-200/O-300 cylinder is a beefed up version of the old casting with some decidedly new changes to the cylinder as a whole. Rocker shaft towers are heavier than castings of old and the shaft itself is drilled for a bolt which locates the shaft and prevents rotation withinthetowers.This change by itself relieves the design from the burden of rocker shaft tower wear and potential tower separation-something that has plagued these jugs for years. In addition, both intake and exhaust ports are heavily walled and thicker in the valve guide grip area.
TCM has also beefed up the combustion chamber structure and the spark plug hole bosses. Cracks in these areas are common in older castings, but the effort here is more for general prudence rather than a permanent fix against heatchecking.
What surprised us is the fact that Continental ships the new O-200/O-300 cylinder with the option of the old swaged-in pushrod tubes or milled for the installation of the new pushrod tube and spring kit.
The new tube and spring kit for an entire engine sells for $537.36 and is not included with the cylinders. The old swaged tube style is sold at no additional cost. Aside from the additional cost for the upgrade, the head casting is welded in the area of the milling for the new tubes. This was done, according to Continental, because the casting design failed to support the O-ring seal needed for the new pushrod tubes.
Even though the weld is small and the area is stress relieved afterward, welding on a new cylinder strikes us as being a bit cheap. It also adds a burden to the marketing department thats hard to shake. Continental could have done better with this aspect of its upgraded cylinders.
Dimensionally, the running clearances of TCMs cylinder were by the book-at least for the most part-and the barrel measured to specifications. The ring finish was a little rough to our liking, but shop reports indicate that ring seating is predictable.
Like most of TCMs engine models, the O-200/O-300 cylinder is equipped with a moly-coated piston, which allows for closer skirt-to-barrel tolerances with less scuffing.
The intake seat is cut to 30 degrees and the exhaust is a standard 45 degrees. Neither valve nor seat is lapped, but Prussian Blue is used to ensure that a good seal is made between the two. We were impressed with the introduction of a venturi-style seat in the intake valve position.
This seat is common to some models of the normally-aspirated 520 series engines and works well to increase the flow of intake air into the combustion chamber.
Both seats were cut slightly off-center, making one side of the seating area thicker than the other. While this is common for field rebuilds, its a little annoying to see it in a new casting.
The standard exhaust studs have been replaced by a stout version of the 520 Rosan stud. This feature will help reduce cylinder removal due to broken studs and stripped-out threads. Its a small thing, but well worth the effort. In all, TCMs cylinder is of good design with thoughtful upgrades. We would like to see better valve and guide work and somebody needs to say no welding to the production crew. Overall, this cylinder ought to perform well but we werent thrilled with TCMs quality control.
Traditionally, Lycoming cylinders have been known for reliable performance with minimal attention from the maintenance department. Thisis primarily due to the engineering philosophy that an air-cooled engine should be able to withstand a lot of heat with minimal structural degradation.
Textron Lycoming has hit the jackpot here. Its cylinders are heavily constructed, sparsely finned, and can be flown by forgetful old hands and wet-behind-almost-everything students without much concern.
All Lycoming cylinders will crack eventually, but they do so in areas that generally pose no threat to normal operation. Generally speaking, the two most crack-prone areas in Lycomings straight-valve cylinder is the area around the spark plug boss and the inside radius of the exhaust port. The plug boss crack is caused by extreme heat; the exhaust port crack is caused by fatigue.
Both usually take thousands of hours to develop and often go unnoticed until the engine is disassembled for overhaul. Lycomings new cylinder castings are even more beefed up in these areas, increasing reliability.
Aside from these two changes to the casting, Lycoming has left much of its original design alone and free from the upgrades found in Continental counterparts.
Lycomings valve and guide work was slightly better than Continentals with seat-to-guide axis errors held to a minimum. The valves-like TCMs-are not lapped, but the seating faces of the valves show indications of staking.
While a lesser measure than lapping, staking at least ensures that the contact area between the valve and seat is secure and consistent.Lycoming is now using its high chrome exhaust valve guide in all of its cylinders and the sample cylinder sent to us was fitted with the new part.
Claiming that the HC guide resists wear caused by heat retained in the valve guide area, Lycoming says that repetitive inspection of the valve-to-guide fit described in several of its bulletins isnt necessary when using the high chrome part. This remains to be seen, but its encouraging that Lycoming is at least thinking about premature wear at the exhaust valve guide.
Lycomings cylinder barrel and the running clearances between new parts was fairly close to book specs. However, there was some inconsistency. None of these diversions from the book specifications would cause real operational problems. But overhaul shops are quick to point out that if you can consistently manufacture a part to the wrong dimension, you should be able to make the part to the right dimension. Good point.
Lycoming machines its cylinder barrels before assembling the barrel to the head. When the head cools, the barrel is squeezed in the thread engagement area, often resulting in warpage of the barrel. For this reason, many feel that Lycoming is cavalier with its tolerances in barrel out-of-round and choke.
Continental, Superior, and ECI all machine finish the barrel after the assembly is complete, making for a more consistent barrel in all dimensions. In recent testing conducted at Williamsport, Lycoming measured core samples of its nitrided barrel and the through-hardened barrels offered by Superior and ECI. Lycoming found that its nitrided barrel is harder than either of the aftermarket suppliers. (Or so it claims.)
Whats more, the underlying layer of steel beneath the hardened surface is also harder than the other barrels. If wear characteristics in the field mean anything, wed have to agree. Lycomings nitrided barrel is the standard in resisting wear, even though its dimensionally inconsistent from one cylinder to the next.
Finally, our Lycoming sample came to us with the choice of using a cap-style pin plug in bronze or aluminum. We wish theyd do something about this, to provide some degree of protection against pin plug wear.
Superiors integral pin plug system is obviously a better choice. Yet Lycoming has managed to circumvent the problem by eliminating the piloted cap style from the choices and hoping for the best.
Theres not much new to Lycomings cylinder-probably because theres not much to upgrade. Its a good product with better-than-average success in the field. But it comes at a hefty price, even with deep discounting by warehouse suppliers.
Classic Cast by ECI
Rogets Thesaurus lists words like model and vintage when describing the term classic. We like to call it old. ECIs casting looks like the cylinders of yore, before more precise castings and beefed up ports and walls became a standard.
The cylinders sent to us from ECI were complete in every respect. But the castings were very porous and the general areas of concern for all cylinders were left unimproved. This may not be as big a problem as one might think if youre of the opinion that new aluminum is better than old aluminum.
But the castings supplied by ECI are rough-rough and inconsistent. In fact, the fins appear to be machined by hand and the valve ports and combustion chambers are uneven. Thin areas at the rocker shaft towers, spark plug bosses and valve port walls are alarming, in our view.
On the other hand, valve seat and guide work is impeccable. Unlike ECIs valve work in its rebuilt cylinder line, its new cylinders are equipped with seats that are almost perfectly aligned with the guide and the seating area is consistent all the way around the seat face.
This work eclipses the efforts of either Lycoming or Continental even though the seats are only cut with one angle rather than the preferred three-cut seat. The valves are lapped in place to ensure a perfect seal and all dimensional data is by the book. Like Lycomings cylinders, the barrel is finished with a very fine hone, leaving a relatively smooth surface for ring seating.
We like this approach because a rougher finish has the potential to accelerate ring and ring land wear during break-in and often results in rings that cruise through the seating process only to end up feathered and worn out in a handful of hours.
ECI likes to push the advantages of its Classic cylinders, but the primary consideration here should be price. Its cylinders are on the low end of all new cylinder pricing, offering a good value to those on a budget.
We wouldnt expect to find these cylinders to be overhauled after reaching TBO because normal wear and tear will necessitate weld repair of the heads and rework of running clearances at the rocker shaft towers. But for the value-minded, ECIs cylinders arent a bad choice, if youre intent on one run only and you can get past the rough look.
Superiors Cylinders Are
When Superior Air Parts, Inc. introduced its Investment Cast cylinder head, our initial thought was that this casting, and its apparent lack of aluminum porosity, would affect the heat transfer between the head and the cooling air surrounding the fins.
This hypothesis was loosely based on some obscure observations and a general hunch or two about engines. Fortunately, the concern has come to nothing thus far and we found that Superiors Millennium cylinders in the Lycoming and Continental models to be the very best from a technical standpoint.
The Millennium cylinders are heavy, beefed up in the right areas, consistent from one casting to another and machined to a very high standard. In Superiors O-200/O-300 line, even the problematic rocker shaft towers were bushed with a bronze bushing to reduce wear and ensure towersecurity-something all the others ignored.
The valve ports are clean, the combustion chambers are heavy and the spark plug bosses are strong. Superiors valve work is almost perfect. Like ECIs valves, both intake and exhaust valves are lapped in place and the seat-to-guide axis is exact.
If anything, the seating area is slightly wide, but this is merely noise in an otherwise technically competent assembly. Guides were measured on specification, the finish was smooth and the fit was on the minimal end of the scale.
The barrel measured exactly as one might expect-on target and with minimal out-of-round. Superior prefers a moderate amount of choke, falling between Lycoming on one extreme (lots of choke) and Continental on the other (minimal choke).
Surface finish in the barrel is a little too rough for our liking. In fact, weve seen more than a few Millennium cylinders return for new rings and a less-coarse finish honing. Unlike ECI and Lycoming, Superior uses a surface finish thats even rougher than Continentals version.
Many overhaulers run a Sunnen J-85 stone through the new Superior barrel before installing the cylinder on the engine to slow the ring seating and provide a bigger margin against accelerated wear.
At a nominal $25 a hole, the added expense is minimal compared to the downtime and expense of removing the cylinders for rework later.
While operating time-in-service will tell the rest of the story, we found Superiors Millennium cylinders to be virtually perfect.
Based on our discussion with engine rebuilders in the field, the examples sent to us werent hand picked, but a true indicator of Superiors typical quality. If Superior reduced the ring finish cut in its hardened barrel, we would have no complaints at all.
As noted, in the new cylinder market, you wont always have the choice of several suppliers for the same cylinder. Overall, for those engines for which theyre available, Superiors Millenniums represent the best value in new cylinders, in our view. ECI and TCM factory jugs would be tied for second choice on Continental engines, based on our findings in examining these cylinders.For Lycomings, the factory products would be our first choice but again, ECI makes a serviceable cylinder at a good, value-conscious price, even if its cosmetically not quite as appealing as the factory jug.
-by Paul Brevard
Paul Brevard is editor of Light Plane Maintenance, whose recent issues contain more detailed reports on each cylinder assembly.