Here is a question that was raised as of my reading an NTSB accident report in our area. Engine was about 75 hours past recommended TBO, but prior overhaul was over 15 years ago. The NTSB report stated Lycoming recommends 2000 hours or 12 years as TBO (for that engine). I can't find anything in Lycoming's website that has any reference to a year benchmark.
I am looking at an Arrow with medium engine time (850 hrs), but 20 years from last overhaul. Advice?
I would suspect that if the engine has been let go that long, then the rest of the airplane will be in sorry shape too. As soon as you start flying it, then all kinds of other problems will pop up. There will be AD's and SB's that have either not been done or are time-expired, hoses that are old and brittle, leaky seals, etc, etc.
If you factor in the cost for a complete FWF overhaul and replacement (not overhaul) of the engine, plus a healthy reserve for airframe and avionics repairs, then you might have a reasonable deal.
What part of the country and wether the aircraft has been kept in the hangar can make a big difference on the remaining life of a high calendar time engine. My 172 engine was overhauled 1-94 and accumulated only 500 hrs. It was kept in a hangar in Wisconsin. An H engine is easy to pull the lifters and check internal conditions. No problems found. On our Malibu TSIO520 engine it was installed in 1989 and flew 2700 hrs before we removed it in 2006. This airplane spent the fist 20 years in Reno. With the Lycoming engine I worry most about camshaft/ lifter problems and cylinder barrel rusting. The cylinders are easy to check, but the cam and lifters really require cylinder removals on one side. Closely checking the filter element and suction screen can help a lot. The steel shows up as small slivers. Inactivity doesn't always mean trouble if the aircraft has been taken good care of at the annual inspection.
The 12-year limit is described in Lycoming's Service Instruction 1009AQ Recommended Time Between Overhaul Periods:
"Engine deterioration in the form of corrosion (rust) and the drying out and hardening of composition materials such as gaskets, seals, flexible hoses and fuel pump diaphragms can occur if an engine is out of service for an extended period of time. Due to the loss of a protective oil film after an extended period of inactivity, abnormal wear on soft metal bearing surfaces can occur during engine start. Therefore, all engines that do not accumulate the hourly period of time between overhauls specified in this publication are recommended to be overhauled in the twelfth year."
JoeB Wrote:
-------------------------------------------------------
> The 12-year limit is described in Lycoming's
> Service Instruction 1009AQ Recommended Time
> Between Overhaul Periods:
>
> "Engine deterioration in the form of corrosion
> (rust) and the drying out and hardening of
> composition materials such as gaskets, seals,
> flexible hoses and fuel pump diaphragms can occur
> if an engine is out of service for an extended
> period of time. Due to the loss of a protective
> oil film after an extended period of inactivity,
> abnormal wear on soft metal bearing surfaces can
> occur during engine start. Therefore, all engines
> that do not accumulate the hourly period of time
> between overhauls specified in this publication
> are recommended to be overhauled in the twelfth
> year."
>
> Regards,
> Joe
> I am looking at an Arrow with medium engine time (850
> hrs), but 20 years from last overhaul. Advice?
You've been give good advice re inspection etc, but just remember that the average flight hours per year for a privately owned light aircraft is a ridiculously low number. If people stuck to the 12 year thing, a huge number of engines would never get above 1000 hours.
If most planes flew an hour a week evenly spaced for 52 hours/year, you wouldn't find many internal rust/corrosion problems. Most of those engines would happily go to TBO over many decades provided they were operated properly as well.
So yes, most believe that 12 year desire by Lycoming is too narrow in scope. One has to believe some self interest there in them seeing less liability from frequently overhauled engines, as well as their share of overhaul cash and a bigger share of parts cash from others who do some of the overhauls.
I would pull a jug and look for pitting, corrosion and spalling.
That said I would use a good anti corrosion adative such as Camguard with Phillips XC oil.
The one mechanic I have spoken to who claims to understand the reason for the twelve year limit told me that the reason for it is that the rear seal has been known to dry out after twleve years. He also said two other things: 1) It's easy to replace the seal while the engine is still on the aircraft and 2) If the plane is regularly flown, there is little risk of the seal drying out.
Corrision is really a limited risk and is more a factor of long term lack of use. The greater risk over time is related to gaskets drying out and this can be evidenced by large leaks. I would personaly not worry too much about the twleve year limit if the engine is holding oil well, thereby indicating that there is no evidence of major leaks.
