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To overhaul or not, that is the question...


salty

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So, I've changed my mind about overhauling at least 6 times in as many months. Here were my points of debate:

  • the engine runs great, I've never had so much as a hiccup since I've owned it, and I've put 140 hours on it this year. 
  • Oil analysis has shown no cause for alarm
  • oil pressure is good
  • Its at 2650 hours since major overhaul
  • It's NEVER had a bottom end overhaul, it's been together since 1965
  • It had a prop strike (gear up landing) over 1,000 hours and 30 years ago

But I decided to do it, and there's no going back now. I gotta say, as I was warming up the oil to drain it for the last time, it was running so smooth, I really questioned my sanity for what I was about to do. 

My IA lives across the street and we're doing a lot of the work ourselves, but we'll be sending some things out.  

Wish me luck, and any advice, especially on sourcing good parts is welcome.

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Hahaha... Either.  But I actually meant the overhaul. 

I subscribe to the school of thought that engines don't just suddenly quit, but rather give lots of warning, even if very subtle. I would not euthanize an engine giving no indication of problems from careful and regular analysis of engine monitor data, oil analysis, and borescope inspections, regardless of the hours.

8 minutes ago, M20Doc said:

Which part?  The overhaul itself or the labor?

Clarence

 

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2 minutes ago, gsxrpilot said:

Hahaha... Either.  But I actually meant the overhaul. 

I subscribe to the school of thought that engines don't just suddenly quit, but rather give lots of warning, even if very subtle. I would not euthanasia an engine giving no indication of problems from careful and regular analysis of engine monitor data, oil analysis, and borescope inspections, regardless of the hours.

 

If it ain't broke, don't fix it

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4 minutes ago, gsxrpilot said:

Hahaha... Either.  But I actually meant the overhaul. 

I subscribe to the school of thought that engines don't just suddenly quit, but rather give lots of warning, even if very subtle. I would not euthanasia an engine giving no indication of problems from careful and regular analysis of engine monitor data, oil analysis, and borescope inspections, regardless of the hours.

 

Our local flying club is disappointed if they don't get 4000 hours on an engine.  Mind you they do that in 4 years not 50.

Clarence

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Interesting question.  I doubt the hours alone would  make me do it.  But 52 years SMOH?  I wonder if there's any data on failure modes for engines this old.  Seems like too much of a voyage into the great unknown. Please tell us what you find in the case.

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Just now, salty said:

Perhaps, but if you hit a curb with the prop, I bet you wouldn't run it to 4000 hours.

It would get a prop strike inspection (like yours presumably did 30 years ago) and it would fly on until it was determined to need overhaul.

Clarence

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Just now, M20Doc said:

It would get a prop strike inspection (like yours presumably did 30 years ago) and it would fly on until it was determined to need overhaul.

Clarence

Actually, I believe that the faa has something to say about that now. 

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3 minutes ago, salty said:

Actually, I believe that the faa has something to say about that now. 

You’re 100% correct the FAA says you must comply with AD2004-10-14 and Lycoming MSB 475C.  What they don’t say is you have to overhaul it.

Clarence

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24 minutes ago, teejayevans said:

You said it’s never had a bottom job, has it had new cylinders? And if yes, did someone think to look inside? I’m at 2100 hours, so I’m an interested bystander at this point.

It has had new cylinders, but information about them s scant at best. Brief log entries with little info. 

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3 hours ago, gsxrpilot said:

Hahaha... Either.  But I actually meant the overhaul. 

I subscribe to the school of thought that engines don't just suddenly quit, but rather give lots of warning, even if very subtle. I would not euthanize an engine giving no indication of problems from careful and regular analysis of engine monitor data, oil analysis, and borescope inspections, regardless of the hours.

 

That was not my experience having had two power losses on takeoff back in my Grumman Cheetah days. When the engine quit at Kissimmee one morning, it had nothing to do TBO or whether or not the engine needed to be overhauled. 

These things tend to work right up to the point where they stop working properly. That can be sudden and without warning. Just my luck that it happened twice to me while climbing through about 250 to 300 ft on takeoff.

However, if it makes you feel more comfortable with the notion that you’ll have plenty of warning(s) before it happens to you, please go right on believing that. Those of us who know otherwise from firsthand experience don’t have the luxury of subscribing to such fantasies.

I sincerely hope that it never happens to you!

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The only way to know how long an engine will run is to run it to failure.....  Mine was at 30 years... I elected to replace early.  I think the engine would have run quite a bit more, but would rather do it on my timing.  I have seen engines that have run until the bearings wear thru.  I think it is cheaper in the long run to replace a bit early.

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17 minutes ago, BKlott said:

That was not my experience having had two power losses on takeoff back in my Grumman Cheetah days. When the engine quit at Kissimmee one morning, it had nothing to do TBO or whether or not the engine needed to be overhauled. 

These things tend to work right up to the point where they stop working properly. That can be sudden and without warning. Just my luck that it happened twice to me while climbing through about 250 to 300 ft on takeoff.

However, if it makes you feel more comfortable with the notion that you’ll have plenty of warning(s) before it happens to you, please go right on believing that. Those of us who know otherwise from firsthand experience don’t have the luxury of subscribing to such fantasies.

I sincerely hope that it never happens to you!

What was the cause of the failures?

Clarence

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34 minutes ago, BKlott said:

That was not my experience having had two power losses on takeoff back in my Grumman Cheetah days. When the engine quit at Kissimmee one morning, it had nothing to do TBO or whether or not the engine needed to be overhauled. These things tend to work right up to the point where they stop working properly. That can be sudden and without warning. Just my luck that it happened twice to me while climbing through about 250 to 300 ft on takeoff.However, if it makes you feel more comfortable with the notion that you’ll have plenty of warning(s) before it happens to you, please go right on believing that. Those of us who know otherwise from firsthand experience don’t have the luxury of subscribing to such fantasies.

What type of engine monitoring did you have and were you doing oil analysis ?

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Just now, M20Doc said:

What was the cause of the failures?

Clarence

The first one was the result of a partial blockage of airflow into the carburetor which caused an immediate power loss and rough running engine due to the resulting “too rich” mixture condition. We managed to get to about 400ft and flew a low, tight pattern back to the runway before it quit all together.

The event at Kissimmee was the result of a small piece of fuel tank sealant that broke off, passed through the two sumps of the right wing, through the fuel strainers and into the carburetor. There it managed to get itself in the perfect position needed to hang up the needle valve, causing the power loss...once again...due to a “too rich” mixture condition. The situation deteriorated quickly as the engine flooded and quit just as we set her down on the cross runway. Awfully glad they had a cross runway there. Not sure we got much higher than 300 ft on that one.

You just cannot count on getting an early warning. My advice would be to think through your options ahead of time...while you’re at home sitting on your sofa. Have a planned course or course(s) of action programmed in your mind of what you will do if it happens to you. Then every time time you pull out on a runway, be ready to respond to any anomaly that occurs. Don’t wait until it happens to start trying to figure out what to do. You will have very little time in an actual event to respond, especially if it occurs on takeoff.

I do think about this EVERY TIME. That, I guess, is the price you pay when you want to keep flying.

 

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Whats worth knowing is if this engine has 7/16" or 1/2" valves installed. The smaller has a 1200 TBO and the larger is 2000 hours.  If it has 7/16" exhaust valves, they can snap off around 1200-1300 hours and it gets interesting after that. They are hollow and sodium-filled.  A friend of mine has an exhaust valve snap and it somehow migrated to another cylinder on the opposite side and messed it up, the engine shut down at 800'. She landed, luckily, in a field right below.

The rest of this motor is bulletproof, but 7/16" exhaust valves are not predictable and are a big deal when they break.

Edited by jetdriven
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