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  #51  
Old 09-24-2017, 10:33 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by ty1295 View Post
Are Lycoming counterweights bolted on?
Pendulum absorbers, not counterweights. And no, I don't care what some fool called them when they wrote the parts manual. A pendulum absorber can also be a counterweight, but it is not in this crank configuration.

There are several styles of pendulum absorbers. This type hangs on two pins. The bushing ID's are larger than the pin OD, which allows the mass to rock back and forth when the crank vibrates torsionally. The relative diameters determine the damped order. See an engine design text for the math.


Quote:
Originally Posted by BillL View Post
Looks like classic fatigue beach marks on that crank.
Yep. Good eye Bill.
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  #52  
Old 09-24-2017, 10:58 PM
PCHunt PCHunt is offline
 
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Holy Shinikees! I'd be sending those parts off to a failure analysis lab, for sure!
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  #53  
Old 09-25-2017, 05:16 AM
vic syracuse vic syracuse is offline
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I took a look at this when it failed and it was interesting to me that both of the pendulum weights had broken the pins on the crankshaft. Whether the crank broke first and then the weights sheared off, or if the weights sheared off firstl, would be nice to discover.

Vic
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  #54  
Old 09-25-2017, 05:32 AM
BillL BillL is offline
 
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Default Closer Look -

A closer look at the crank. One can see the beach marks of a progressing fatigue failure. The crack initiation appears to be in the rod bearing filet area. A high stress area due to compression/firing forces. This area is tested in a crankshaft tuning fork machine for fatigue in the lab as THE place for this kind of failure. Why it failed is a combination of weak material, or forces higher than the fatigue limit. It could be a combination of both, but even with high compression it should not have fatigued the crank. It does not appear to be torsional due to the location of the crack initiation. A metallurgical analysis of the crank would be in order to proceed to a more definitive root cause.

Overspeed events could contribute to the compressive stresses that occur at exhaust stroke on TDC, but numbers would have to be calculated based on piston and rod weight. Still more likely it was dominated by tension stresses at TDC.

One might look closely at the top of this piston to see if any preignition or detonation might have been occurring. Since fatigue is the result of accumulative overloads, 500 hrs is too many cycles for it to have accumulated loading events every rev, but only 10-20% of the time. Stuff like this is why some engines have a X minutes limit on takeoff power.

Does anyone know if all ECI cranks are certified part numbers? Are the "Y" Lycomings a certified crank, the same part number as a certified engine?

So, is there an NTSB report for this event, and would the investigator be interested in this information?

For you FAA experts out there, is there a failure reporting mechanism for this kind of thing to the FAA? or is the government best left out of these things?

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  #55  
Old 09-25-2017, 07:11 AM
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Quote:
Originally Posted by vic syracuse View Post
I took a look at this when it failed and it was interesting to me that both of the pendulum weights had broken the pins on the crankshaft. Whether the crank broke first and then the weights sheared off, or if the weights sheared off firstl, would be nice to discover.
A little logic: The very large rotating mass (the prop) is forward of the pendulums. The available rotating inertia aft of the pendulums is quite small in comparison, and anyway, a sudden stop usually pops the crank gear bolt and dowel pin, disconnecting most of it.

So, if one of the pendulum masses came adrift and jammed the crank, would the crank break forward of the jam, or aft of it?

The answer is forward of it, the end with all the inertia. Here the crank broke aft of the pendulums, the side with little rotating inertia, thus a jam is unlikely.
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Last edited by DanH : 09-25-2017 at 07:23 AM.
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  #56  
Old 09-25-2017, 10:57 AM
SportAvServ SportAvServ is offline
 
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Wow, and I thought I was unbalanced. Whew!
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  #57  
Old 09-25-2017, 03:37 PM
sblack sblack is offline
 
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Quote:
Originally Posted by jabarr View Post
Unfortunately, the mfg apparently has no interest in even looking at the pieces. They were contacted several times about the failure and the only response was that they would offer another engine at retail price.
that's the lawyers talkin'
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  #58  
Old 09-25-2017, 03:50 PM
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Seeing these photos and manufacturers response I know that I will NOT use the Titan engine in my RV-8.
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  #59  
Old 09-25-2017, 08:23 PM
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az_gila az_gila is offline
 
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Quote:
Originally Posted by BillL View Post
....

Does anyone know if all ECI cranks are certified part numbers? Are the "Y" Lycomings a certified crank, the same part number as a certified engine?

...
The UK LAA certainly seems to think so in their definition of a "certified" engine.

2. Lycoming OEM Experimental Engines
Lycoming produces a series of non-certified engines that are built in the same way as their certified engines, except those that are fuel injected use the non-certified Airflow Performance or Precision Airmotive fuel systems. These engines, known as OEM Experimental Engines, are available only through kit aircraft manufacturers and engine assembly companies that are approved by Lycoming. Although Lycoming prefix the part numbers of these engines with the letter ‘Y’, Vans Aircraft has used the letter ‘X’ to the designation prefix of the non-certified Lycoming engines that they supply. LAA Engineering has accepted the Lycoming non-certified YO-320, YIO-320, YO-360, YIO-360, YO-540 and YIO-540 engines on the basis that they are made using components identical to their certified counterparts and, in the case of the fuel injected engines, an LAA approved fuel injection system. The Lycoming Thunderbolt series of engines is not included in this general acceptance, being of a configuration that does not have a certified equivalent.

http://www.lightaircraftassociation....%20Engines.pdf
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  #60  
Old 10-06-2017, 11:43 PM
The Wizzard The Wizzard is offline
 
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Default missing the whole story

Where did theses photos come from? Your engine?
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