Lycoming vs. Continental TBO

Factual Questions
1

Maybe another pilot can answer this question for me, which pops into my head from time to time.

I’ve noticed from purely casual observation that Lycoming piston engines tend to have a 2,000 hour TBO, while Continentals have a TBO of around 1,500 hours. Why is this? Both basic designs have basically been around for 70 years or so. (i.e., they’re both horizontally-opposed piston engines that have been used for decades, although there have been many improvements over the years.)

Let’s say that a light aircraft flies at an average of 100 kts. (115 mph) including take-off, landing, and taxiing. 500 hours at 100 kts. is 50,000 nm (57,500 sm). Given the high cost of overhauls, the extra flying time is desirable. (Note that I’m just using these figures as a general example. IIRC, a Continental O-200 has an 1,800-hour TBO – still less than a Lycoming.)

Is there a fundamental design difference between Lycomings and Continentals that allow a shorter TBO for the latter? Or is Continental just more conservative? If the engines are pretty much the same, wouldn’t Continental benefit from raising the TBO? Or is Lycoming overstating their engines’ reliability?

2

I have heard a lot of people say that Continental engines are not as robust as Lycomings. Not so suitable for aerobatic machines and a little more likely to get cracked cylinders, so maybe they are just not as well made.

3

I asked this question once to an astute, qualified aircraft mechanic that rebuilds his own Aircraft engines.

He told me the FAA came to their TBO conclusion based on microscopic study of the chromium cylinder wall cracks, that are normal.

Evidently, the Continental has more microscopic cracks, developing sooner, hence earlier TBO.

This is third hand info, but plauseable.

4

As I recall, TBO is determined in the field, by examining the service records of engines that have gone through a complete lifecycle. Engines have had their TBO moved up and down throughout their lifecycle. TBO can also be affected by the type of installation. What the aircraft is used for, how well the cooling system works, etc. For example, the Lycoming O-235 normally has a TBO of 2000 hours. In some aircraft, the TBO is 2400 hours.

So if Continentals typically have a lower TBO than Lycoming, I would guess that the reason is simply because the empirical evidence gathered from those engines dictates it.

5

Hm. You’d think Continental would have been able to address the microscopic cracks by now.

6

Meanwhile, eight and a half years later…

I happened to see a Cessna 162 Skycatcher on eBay today. It’s the first time I’ve seen one there. Cessna chose to use a Continental O-200D to power it. As I recall, Cessna created the 152 by replacing its Continental with a Lycoming O-235, making that aircraft cheaper to fly because it offered 500 more hours between overhauls. In the 1970s, the Lycoming was more compatible (according to Wiki, TIFWIW) with 100LL fuel. The O-200D is OK with 87 octane avgas. In the U.S., 100LL is much more common. The O-200 is up to 1,800 hours TBO now, and IIRC the O-235 has a higher TBO now as well (2,200 hours? 2,400?). It makes me wonder why they chose the Continental.

7

Cessna does not get as good a deal from one compared to the other??

8

Since you’ve been patiently waiting for an answer I’ll provide my WAG (based on various comments I’ve heard on the subject over the years);

I’d assume that changing these engines is a difficult and expensive process for Continental to conform to regulations. These engine designs are very old, and they are very reliable within the guidelines. Any change may end up requiring a lot of time and money spent satisfying the FAA, while customers would still be asking for the conventional design until data is collected about the modified engine. Being air cooled, even small changes to the cylinders could cause potential new problems.

9

Could be. I have no idea of the relative prices of these engines, let alone what kind of deal manufacturers get.

The thing of it is, the O-200 is based on the C90, which was developed in 1947; which in turn was developed from the A-65 of 1943. While it is definitely time-consuming and expensive to certify a new engine, it seems to me that whatever reasons the Continentals don’t last as long as Lycomings could be addressed by improvements that don’t require certifying a whole new engine.