TBO

flyingmoose said:
You also had the luxury of trending the engines. That is not always the case. Those are all good reasons, but if you didn't know what the oil pressure has been in the past then its hard to come to the conclusion to keep running without other indications as you also mentioned.

Its a great idea to keep a flight log of engine parameters so you know if things are changing.
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That's true, and one must work with what one has and look at other factors. Although we hadn't trended the engines since new, we got the plane with the engines at TBO. They may have degraded since new (probably did). What I do know is we had no issues with oil blowing overboard when we first got the plane.
 
wabower said:
It means the closer to the number that your engine has achieved hours in service, the lower the offer you can expect to receive.
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wabower said:
And so? What do we know now that makes any difference compared
to what we knew before?
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Not everyone is an expert like you Wayne and the discussion Tom is creating has value to them. I'm sorry you can't see that.
 
An EAA study seemed to conclude that engine failure rates don't significantly increase if flown beyond TBO. However they also mentioned that there is far less data above the published TBO, as many engines are simply removed around that number. Still, the data was comforting. An old engine is much more reliable than a new one.
 
cujet said:
Still, the data was comforting. An old engine is much more reliable than a new one.
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This may be true, BUT , there is a far greater chance of the new parts list being a lot longer, and IF it does have a catastrophic failure it will ruin a lot more parts than you might have re-used at TBO.
 
Tom-D said:
This may be true, BUT , there is a far greater chance of the new parts list being a lot longer, and IF it does have a catastrophic failure it will ruin a lot more parts than you might have re-used at TBO.
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This is one of the reasons I have noticed why alot of warbird operators will pull engines at TBO or before rather than wait for indications of the need. I have been told by many that it is cheaper that way.
 
Fearless Tower said:
This is one of the reasons I have noticed why alot of warbird operators will pull engines at TBO or before rather than wait for indications of the need. I have been told by many that it is cheaper that way.
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And those TBOs are a lot shorter because we can't allow the engine to fail.

the Warner recommended tear down cycle is 400 hours, simply because there is no filtration, the engine depends upon the sludge traps to catch the heavy debris. once they fill there is a great possibility that you will ruin the crank.

and there are no replacements
 
TBO is that point where overhauling will result in the lowest allover cost of running the engine over a long period of time.
 
Tom-D said:
TBO is a number of hours that the manufacturer has determined that a new engine can be run and all parts in that engine will meet service limits.
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Which begs the question: How are "service limits" defined/determined?
 
kgruber said:
TBO is that point where overhauling will result in the lowest allover cost of running the engine over a long period of time.
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Not necessarily true. Too many variables to say that for certain.
 
TBO isn't set in stone for Part 91 operations. I used to co-own a Cessna 150 with a Lycoming O-320 conversion that we took all the way to TBO+1000 before selling. The key is to overhaul when the engine needs to be overhauled, not at some arbitrary number.
 
Henning said:
LOL, I always loved ventilating engine blocks, everytime I exploded one though it was when I lifted my foot past the traps.
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Yup.... For the non motorheads here.... Most rod failures happen with partial or closed butterflies... Connecting rods are surprising strong under compression, but when you get a motor spinning at high RPM's and get off the throttle ,the vacuum in the cylinder, or less down pressure on the rods turns into stretching the rod and it actually fails from tension, ie, pulls apart.... :eek:

Henning has been there, done that ,,, and to heck with the Tee shirt, he got the firesuit to wear too....
 
N801BH said:
Yup.... For the non motorheads here.... Most rod failures happen with partial or closed butterflies... Connecting rods are surprising strong under compression, but when you get a motor spinning at high RPM's and get off the throttle ,the vacuum in the cylinder, or less down pressure on the rods turns into stretching the rod and it actually fails from tension, ie, pulls apart.... :eek:

Henning has been there, done that ,,, and to heck with the Tee shirt, he got the firesuit to wear too....
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It's why I replace rod bolts on every engine rebuild even if the crank and rod are still in spec, the most common point of failure on a bottom end is from stretched rod bolts.
 
Henning said:
It's why I replace rod bolts on every engine rebuild even if the crank and rod are still in spec, the most common point of failure on a bottom end is from stretched rod bolts.
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Me too............ Rod bolts are CHEAP insurance..:yes:
 
Henning said:
It's why I replace rod bolts on every engine rebuild even if the crank and rod are still in spec, the most common point of failure on a bottom end is from stretched rod bolts.
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When you comply with the Maintenance manuals of both major brands, they are required to be replaced.

did you think you had the option?
 
Henning said:
Go to the library, there's a hundred different engine manuals there.
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Not buying that.. Show me any other overhaul manual for either major manufacturer's aircraft engine that doesn't require the rod bolts to be replaced.
 
Tom-D said:
Not buying that.. Show me any other overhaul manual for either major manufacturer's aircraft engine that doesn't require the rod bolts to be replaced.
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I never limited my statement to aircraft engines.
 
N801BH said:
He didn't Tom.........:nonod::no:..

Especially motors that "went through the traps " :rolleyes:;)
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We are an aviation page are we not?

Are we not true to the OP?

There are only one true way to overhaul any aircraft engine. FAR 43.2
 
Tom-D said:
We are an aviation page are we not?

Are we not true to the OP?

There are only one true way to overhaul any aircraft engine. FAR 43.2
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We're on post 68 Tom, in case you've never encountered thread creep before, this is a minimalist example. However, an intelligent person may extend the information to understand that the rod bolts are the real victims of having 'the prop drive the engine and over speeds resulting from it may cause catastrophic issues down the road leading to failures beyond TBO.
 
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Tom-D said:
This may be true, BUT , there is a far greater chance of the new parts list being a lot longer, and IF it does have a catastrophic failure it will ruin a lot more parts than you might have re-used at TBO.
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Really? How so? I'm not sure I follow that reasoning. A modern overhaul won't generally re-use pistons, valves, pins, camshaft, lifters, bearings rings, etc.

Unless you expect the crankshaft, connecting rods or cases to fail during that extended run, I suspect the overhaul cost won't be significantly different.

For the sake of argument, extending the operation of a healthy engine by 400 hours (not unusual) could save more money than the hypothetical "ruined" parts.

With all of that in mind, I pulled my 2000 hour TBO engine at 1700+ hours and I'm glad I did. It was making metal, so the signs were there.

DSC00149_resize_with_arrow.jpg
 
cujet said:
Really? How so? I'm not sure I follow that reasoning. A modern overhaul won't generally re-use pistons, valves, pins, camshaft, lifters, bearings rings, etc.

Unless you expect the crankshaft, connecting rods or cases to fail during that extended run, I suspect the overhaul cost won't be significantly different.

For the sake of argument, extending the operation of a healthy engine by 400 hours (not unusual) could save more money than the hypothetical "ruined" parts.

With all of that in mind, I pulled my 2000 hour TBO engine at 1700+ hours and I'm glad I did. It was making metal, so the signs were there.
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What was the total time on the engine?
Was it a factory re-man, where you get a new log book but old reworked parts.?

With normal care the factory new engine will go to TBO and all the parts will pass inspection with in service limits.

I will admit most overhaulers won't do a service limits, but with a new engine at TBO you will not be worried about buying a new crank because the last overhauler ground it to limits.

It's all about how many parts in the engine will be used again.
 
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Ok, on a related note. I have been chasing a running rough issue. The engine was last rebuilt in 1988 (24 years). It is an O-320 Lycoming. It has about 800 hours since overhaul. It accumulated about 500 hours from '88 until '99 and then about 50 hours until 2010, when I bought it (10 hour pilot in training). I have since put about 260 hours on it.
-it only runs rough between 2300 and 2450 RPM.
-It has been doing this for at least 200 hours (I was a new pilot, now I am less comfortable with this issue).
-I have rebuilt the carb, rebuilt and bench tested again, installed loaner carb.
-checked thoroughly for induction leaks (found a small one; didn't fix the problem).
-Checked mags, reversed ignition harness (per SB)
-EGT climbs during the rough running area. This is pronounced when throttling back for cruise. It smooths out at about 2300 and the EGT drops again. Runs smooth at 2,500 with no issues.
-Problem manifests equally on both Mags.
-I just had to put a new cylinder on it. (Compression drop). This did not affect the problem.
-Compressions are now good and I change oil regularly with oil analysis.

My A&P is out of ideas on how to fix the issue (a very respected local shop). Should I be looking at an overhaul, since this is a 24 year old engine?
 
John221us said:
Ok, on a related note. I have been chasing a running rough issue. The engine was last rebuilt in 1988 (24 years). It is an O-320 Lycoming. It has about 800 hours since overhaul. It accumulated about 500 hours from '88 until '99 and then about 50 hours until 2010, when I bought it (10 hour pilot in training). I have since put about 260 hours on it.
-it only runs rough between 2300 and 2450 RPM.
-It has been doing this for at least 200 hours (I was a new pilot, now I am less comfortable with this issue).
-I have rebuilt the carb, rebuilt and bench tested again, installed loaner carb.
-checked thoroughly for induction leaks (found a small one; didn't fix the problem).
-Checked mags, reversed ignition harness (per SB)
-EGT climbs during the rough running area. This is pronounced when throttling back for cruise. It smooths out at about 2300 and the EGT drops again. Runs smooth at 2,500 with no issues.
-Problem manifests equally on both Mags.
-I just had to put a new cylinder on it. (Compression drop). This did not affect the problem.
-Compressions are now good and I change oil regularly with oil analysis.

My A&P is out of ideas on how to fix the issue (a very respected local shop). Should I be looking at an overhaul, since this is a 24 year old engine?
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TRy to re-index the prop.

24 years ??? probably wouldn't hurt.

Has your A&P, inspected the valve springs for proper tension?
 
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Tom-D said:
TRy to re-index the prop.

24 years ??? probably wouldn't hurt.

Has your A&P, inspected the valve springs for proper tension?
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1- Re -indexing the prop is a great idea.. Try it,, it is cheap to do.

2 - Check cam lift with dial indicator,,, Try it, it is cheap to do.

3- Weak valve springs will NOT get better the higher you rev the motor..



Carry On. ;)
 
I'm in agreement with the cost savings.

We ran the 310s engines 400 over TBO. That equates to about a $15k savings. Even if both cranks and both cases needed to be replaced as a result of running longer, we'd about break even.
 
Ted DuPuis said:
We ran the 310s engines 400 over TBO. That equates to about a $15k savings. Even if both cranks and both cases needed to be replaced as a result of running longer, we'd about break even.
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Is that because you are talking about running LOP, or simply going past TBO?
 
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