Top End, Bottom End

[gibbons]

I'm looking at purchasing an airplane with 1700 TT (over 37 years). The engine is a Lycoming IO-320. The bottom end has been rebuilt twice as a result of prop strikes, the last time 350 hours ago (1998). The rebuild was a good one and is well documented so I'm not worried about the bottom end.

The cylinders, however, have never been done. At the last annual (about a month ago) compressions showed mid-70's. At the pre-buy compressions were done cold and were 71/66/67/72. The owner claims to put about one quart every 12 hours in the airplane.

I expect to fly this airplane about 100 to 150 hours/year and I don't mind running over TBO. My mechanic says plan on at least two new cylinders in the next year. If I do that I'll have a pretty new bottom end and a new top end, but not an overhaul.

So if I fly this airplane to, say, 2500 hours and then try to sell it, how much trouble will I have since it will be over TBO but have low-time components top and bottom?

I can work the price to compensate me for the two cylinders (I think), but if I'm going to have to do an overhaul at 2500 hours in order to sell the thing then I'll be way under water.

Any thoughts? I've got to get back to the owner soon.

Chip

 

[Stache]

Changing cylinders adding nothing to the value if the engine has not had a complete rebuilt or overhaul. I would look at the engine with new cylinder and say that nice, but the engine still needs a overhaul. Changing parts here and there does not add to engine life and having new cylinders (top overhaul) is not a full overhaul or is changing the botton end parts in the eyes of the FAA. The total engine hours continue to add up.

I would recommend if you want to keep the aircraft have the engine completely overhauled. Or if you plan on trading in or up have your mechanic perform a 100-hour inspection each 100 hours as older engines tend to wear part faster the higher time they get. Adding new cylinder may add to the faster wear on the bottom end.

Something else waiting to overhaul a high time engine will cost more as internal parts will wear more. Having a overhaul at the recommended TBO will cost less money in parts.

Just one mechanic's opinion.

Stache

 

[bbchien]

Having a overhaul at the recommended TBO will cost less money in parts. Just one mechanic's opinion.Stache

Having an overhaul at the recommended TBO will cost less money in airframe parts when you successfully execute the off field landing...or maybe not so successfully.

You CAN go beyond TBO if you have a way of monitoring all the parts. Your engine is just the sum of all its parts. But the labor cost of doing that eventually subsumes any extra hours you may get to fly.

You won't catch me beyond TBO. They are trying to tell you something based on what happens on the bench and in the field. So, when your engine talks, always listen....

 

[waldo]

The 37 years would concern me more than the 1700 hours. My Cherokee 180 has only 985 SMOH and 20 years. We had to replace the cylinders that were only rebuilt during the overhaul. While we had it down I was able to get a pretty good look at the cam lobes. What I saw wasn't pretty. Even though the cam was replaced during the last overhaul with a new one, it had minor pitts all over it (caused from sitting up). I now know that I will soon need to replace cam (pitts) and crank (because of AD).

On another note: I had a O-200 which has a 1800 TBO. The engine had 2450 SMOH but in only 10 years. The engine looked great when we did the overhaul. The case, cam, crank, gears, etc. were all able to be re-used and all within NEW limits.

Like with anything else "TIME" does take it's toll

Fly Safe,
Waldo

 

[PoAdeleted5]

A prop strike tear-down and repair does NOT equal an overhaul.

Mine had 600 hrs since a tear-down, two fresh cylinders and it coughed up a bearing.

Now it has a major overhaul, only 50 hours into my ownership. The case needed a good bit of work at Divco. So much for optimism.