Do Lycoming or Continental engines have any specific failure mechanism after X hours, and how was the TBO determined?

Also, there is an advantage in reusing your own first or even second-run parts (case, rods, crank…) when you are overhauling your engine rather than doing an exchange. When you exchange you may be getting third or fourth OH parts.

So if you are sticking to your own parts, you don’t want to damage them by running them too far beyond TBO or else you may limit reusability, partially voiding the economic case for the longer run

The o-360 is about as bullet proof as you can get for a conti/Lycoming used in a school environment. Rollar tappets also address it’s weak spot. I’ve also heard they good for 3000 hours but it’s all a bit mute as in the UK they have to overhauled at TBO.

I’m not sure there is any advantage of overhauling an engine with respect to reusing parts. An o-235 camshaft will need replacing at its TBO regardless and that’s if it’s made TBO in the first place

Decent crankcases are a problem. There just isn’t a good stock kicking around in the overhaul market. Ones from divco have welds on welds. And a new crankcase from Luci/conti are just silly money.

Now the 4 stroke rotax. They are class 4000 hours is the norm.

My O360 was overhauled at 2550 hat approx. It ran fine but then we got a bent pushed which we could not explain so we but the bullet. But without such things I am convinced they can run up to 3k or beyond if proper taken care of.

Peter wrote:

So what led to the (say) 2000h TBO number?

Statistics.
And what you can get away with from the market.

Arne wrote:

Peter wrote:
So what led to the (say) 2000h TBO number?
Statistics.
And what you can get away with from the market.

Hi Arne. That is the theory and how modern aircraft maintenance programs are done, but for the OP, I think historical reasons weigh as much as actual statistical data.

In practice, once the TBO target has been set, if there are relevant items failing with statistical significance in advance of TBO, both Lyco and Conti have issued SB’s or changes ( roller tappets, mag inspections, heavy cases, 7th stud, etc ) or component retirement/inspection requirements to more reliably achieve the same target TBO, rather than adjusting TBO.

Mike Busch reports every now and then about his Cessna 310 which he seems to have brought way past TBO, don’t know the exact number but was double the TBO and still running.

He also holds to the opinion that any engine properly maintained and not abused in operation (“baby your engine” is one of his articles) will make this, too.

I have 1600 hours on my engine left till TBO, so don’t know if I may ever contribute here with own experience.

Antonio wrote:

n practice, once the TBO target has been set, if there are relevant items failing with statistical significance in advance of TBO, both Lyco and Conti have issued SB’s or changes ( roller tappets, mag inspections, heavy cases, 7th stud, etc ) or component retirement/inspection requirements to more reliably achieve the same target TBO, rather than adjusting TBO.

According to this

Mike Kraft reminded me that when Lycoming certifies an engine, they test it not just to the 150-hour mandatory minimum. Instead they run a 400-hour pressure cooker test defined by AC 33.19-1, most of which is conducted at red line conditions on everything.