# High Time Crankshaft

Discussion in 'Firewall Forward / Props / Fuel system' started by Kyle Boatright, Mar 25, 2015.

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1. Mar 25, 2015

### Kyle Boatright

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Assuming a Lycoming crank has been gently cared for over its life - no acro, no prop strikes, yada yada yada, at what point does one look at the logbooks and say "Whoa, that's a lot of hours, maybe I replace this crank at overhaul, regardless of condition." Or, being a steel part, are hours irrelevant?

Why do I ask? Because I'm looking at some engine cores, but the times are high, IMO...

2. Mar 25, 2015

### don january

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as a welder of over thirty years I'd be asking myself, Fatigue, can't really see it in metal at times but it's there

3. Mar 25, 2015

### Jay Kempf

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How do you intend to use the rebuilt motor? Certified? Experimental? Overhaul yourself?

4. Mar 25, 2015

### Kyle Boatright

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Not sure any of those issues change the decision making process. But the end use would be experimental. Not sure if I'll OH it or farm it out.

5. Mar 25, 2015

### Jay Kempf

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Maybe send the crank off to a certified repair station. If using it in experimental you need to decide if you will keep the engine current. That is an insurance decision. Most people that have been rebuilding cars can handle rebuilding an aircraft engine. But if you want to maintain the log you need to at least be under the watchful eye of an A&P willing to sign the engine log and he has to split the case if you are worried about the crank. Most of these engines are 40+ years old now. Haven't seen anyone saying throw any parts away. Rebuild stations do non destructive testing and either scrap or rebuild a part and put it back in service zero time. If I was worried about a crank shaft I would send it to someone that could make a real certified determination. The rest is just like any engine rebuild.

6. Mar 25, 2015

### Kyle Boatright

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Forget the minutia and regulatory issues. Legal isn't always safe and safe isn't necessarily legal.

Assume the crank gets a brand new yellow tag and a healthy bill of health from Aircraft Specialties. At what point do you say "too many hours for me"?

7. Mar 25, 2015

### Jay Kempf

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I have a 35 year old crankshaft from the factory in my 928. Been beating it for 20 years myself. I guess I don't have that worry. Take it out, assess it, grind it , put new bearings in and run it for another 40 years.

If Mattituck is happy to rebuild them every day and put them back in service I am not going to worry about it.

Most aviation engines from 40 years ago weren't exactly made of junk.

8. Mar 25, 2015

### TFF

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The flight school, at my airport, flies their 150s and 172s 2 times TBO, then check out for rebuild. Unless aerobatic, most will be undersize for certified at about 6000 hrs if well cared for. It is going to depend on how the engine was treated more than total hours.

9. Mar 25, 2015

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I would much rather fly an experienced crankshaft, regardless of hours, that has passed NDT. especially one that has been remanufactured at a reputable certified repair station, than a factory-new crank. As you noted in your original post, we are talking about steel here. Worry about the propeller that you bolt to the crankshaft.

10. Mar 26, 2015

### ekimneirbo

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What you are asking is what I consider the conundrum of using a certified or formerly certified aero engine with high time. Let me put on my chain mail armor suit before I continue to objectively point out the perils of used aero engines....... The first myth is that the log book contains everything that happened to the engine or any maintaince that was ever performed......or that something as important to the value of such an engine was just inadvertently misplaced.
The second consideration is that as these engines reach higher times, almost all of the internal components (not just the crankshaft) have been continually reused because they are so expensive). Do you really believe that the camshaft lobes are opening the valves the same amount? Is the play in the internal gears the same as new or will they affect timing events while still functioning? Have the valve guides worn or have the valves ever been replaced? Do the engine cases themselves become stressed
from so many cycles and are the mating surfaces still without fretting? Then consider the crankshaft which is generally the main concern when buying a used engine. If it ever received a minor prop strike....did the owner note it in the log? Does it have any corrosion internally which keeps it from being yellow tagged when sent for inspection and can cause failure. Did you know that magnafluxing a crankshaft still does not guarantee that it doesn't have a crack beginning due to weakening of the material
over time and stress? Attached is an excerpt from an article on crankshafts.....read it and decide if you agree/disagree. There are a lot of used aircraft engines out there that have lasted a long long long time.....a tribute to their hardiness.........but when
you buy one, its still a crapshoot in my opinion. Remember that on every rotation of the crankshaft it suffers multiple elastic moments where the combustion cycles twist the main journal. Calculate that out and you will be in the millions of elastic moments.

11. Mar 26, 2015

### cheapracer

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Been around engines all my life and the crankshaft would be the least worrying item in the engine.

Unless it is an engine with actual known crankshaft problems, which is rare, forget about being concerned about it. Crankshafts, even the poorly cast iron cousins, are amazing things, the forces they see are mind blowing and yet they are historically extremely durable.

Send it to a crank guy, get it magnafluxed (checks for cracks) especially around the boltholes, get it straightened if required, indexed, resized and lastly, balanced. It's not expensive.

The biggest killer of a 'big hour' engine is conrod bolts, followed by conrods, worry about those instead.

12. Mar 26, 2015

### ekimneirbo

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Might want to check out these websites. While I respect cheapracers opinion, in some of the aircraft crankshafts corrosion is a serious problem and there is a specific inspection process just to deal with it. If the repair does not clean up the pitting, the crankshaft is no longer considered usable in an aircraft. That doesn't mean an experimental can't use it, but they shouldn't.
The cracking that can occur can also come from other areas than the crankshaft journal as per the attached site below. While
considering a used Lyc, also try googling "Lycoming camshaft pitting pictures"............

Crankshaft Inspections

98-02-08

http://eaaforums.org/archive/index.php/t-697.html?

Hope this helps the decision making process. Did you ever wonder how Lycoming can use used engine parts and declare the
engine to be "zero time".........boggles my mind.

Last edited: Mar 26, 2015
13. Mar 27, 2015

### Kyle Boatright

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All of that is covered by having the crank re-certified by Aircraft Specialties Services (or equivalent). But a yellow tag does not turn a 6,000, 8,000, or 10,000 hour crank into a zero time crank. The hours (not a pass/fail inspection) are what I'm confounded (conflicted?) over...

14. Mar 27, 2015

### kent Ashton

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Read recently that steel is different from aluminum (cylinders, for example), in that aluminum dies a little bit every time it is stressed but steel is fine unless a certain threshold is exceeded. I have never heard of cranks being harmed just by hours in service. Aluminum cylinders develop cracks, even if they were never over-temp'd.

15. Mar 27, 2015

### TFF

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Problems you will have if doing it decertified. Stay away from prop strike crank unless you saw it happen to be just a glance with a wood prop. I put in a Continental rebuilt by Continental that had a previous propstrike crank in it. They did all sorts of NDT on it. 91 hrs we found a crack 50% around the throat it would have thrown the prop at 92 hours. You may or may not be able to get a car machine shop to work it. Airplane scares most. If they do make sure they are not lazy changing the grinding stone to the right radius; many are and dont care. Also make sure you can get bearings if it needs to be ground more than .010. You might have to have special ones made. Can blow cheap, out of the water. lots of cheap cranks that had the corrosion AD out there stay away unless you understand it. When I get to my engine, it will be a run out core with bearings and rings and exhaust valves; may or may not have the crank turned. Unless there is a retire TBO, you can run it as long as you want even certified. Continental has one of those retire on non VAR cranks. Cams on Lycoming are really the bigger problem. "0 time" and "0 time since overhaul" are two different things. You will never see "0 time" unless new.

16. Mar 27, 2015

### ekimneirbo

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Thats exactly my point. If an engine has been around long enough to accumulate that many hours, it has proven to be a good one........but I would still be concerned because it does have a functional limit somewhere, and if corrosion is a problem...the longer it was in service, the more likely to have corrosion. Can you verify the corrosion before purchasing an engine? If you give $5k for a core and it needs the crank replaced, you will be out another$4k for a crank and the cost of the inspection and possible machining costs to determine if the crank will clean up. Will the seller guarantee that the crank will meet specs after purchase? Then even if it should clean up you have the possibility of cracks that weren't picked up during inspection as TFF mentioned on the one he bought from Continental after extensive testing. If you buy a used crankshaft, even one still in an engine, its a crapshoot.

17. Mar 27, 2015

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