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#11
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"Yes, but that wouldn't have sheared the bolt at..."
I agree not sheared but it would have looked like that to the OP. I would guess a tensile fatigue (probably initiated by bending) with the crack starting on the side closest to the cyl centerline for cyl 3. Assuming it is truly one of the bottom studs - they would not be thru-studs but short ones instead. My guess is a partial loss of preload of the #3 cyl assy initiated by the failure of the thru stud between 2 & 3, then causing a progressive failure at the bottom of three. There probably are also some cracks around the base of #2 also I can't explain the crack at 4. If the cyls are reused the flanges around the bottom should be subject to very careful magnaflux inspection. Maybe on general principle they should be junked. Torque to loosen will be less than torque to tighten, and less indicative. The engine history would be interesting. It certainly would have failed in a few minutes rather than hours - and it would have been a massive noisy failure too. A Bonanza friend found one of those short studs laying in the cowl while preflighting his airplane in the Bahamas. He put the family on commercial airlines & flew home on minimum power - with a life jacket on! |
#12
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It could be undertorqued too. In that case there would be a lot of
fretting under the base flange of the cylinder, and probably on the main bearing webs too. Flyers, Here is a post I found about a Cardinal RG with a similar problem. This was an interesting situation FWIW. I have pictures if you want to see them. Can they be posted here? Kobra snip You can tell from the type of cylinders, in this case the angle valve cylinders, that this is a Cardinal RG. I'll confess that I'm not certain that you can tell this from the base of the cylinders.. I think I cropped the picture some since I first asked that question. Visibly wrong in the picture are the two missing hold-down nuts and sheared stud and through-bolt. There are two more you can't see on the other side. Also visible is a long crack running down from the center of the cylinder base. This can be more clearly seen in the picture to the right. So, two items visibly wrong. What could cause this? Usually detonation causes broken pistons. This is more about looseness in the cylinder base. How could it get loose after a reputable shop worked on it? The best guess at this point is that the cylinder base or case may have been painted, or had a little bit of paint slide into the mating surface somehow. Over time this gets beaten down or squeezed out and a little looseness develops. Once loose, the power pulses at 50 HP per pulse work on the hold-down studs and bolts, eventually fatiguing them to failure. Then it's just the case and lower bolts doing their best to keep the cylinder on. This problem was first observed as a substantial oil leak enough to make oil visible outside the cowl. There was no perceptible difference in engine operation or smoothness. The pilot simply arrived at his destination and the people he was meeting commented on the oil on the cowl. With the cowl top off the pilot and a mechanic stared at the engine for about 15 minutes before one of them noticed the missing nuts. In fact one of the nuts (seen to the right) lying between the cylinders, was found and a search for where it came from ultimately led to the discovery. Before you judge these people harshly let me assure you that it was not obvious. The studs sheared off so smoothly that it looked like it was suppose to be that way. And the crack where the oil was coming from was buried behind the air filter baffling. What's the lesson here? When you have a cylinder off make sure it is reinstalled properly, with no paint in bad places, and consider talking to the shop about retourqing after a while. We're not sure what the ideal answer is, or a single thing that resolves this, but it's a possibility that should be kept in mind during cylinder work. An interesting point for discussion with your mechanic. The final result for this pilot was a series of logistics: first, a call to a friend (who happened to be me in this case) for a ride home. Next research on engine rebuilders and the selection of the best one. A fair amount of research on case half options and purchase of suitable parts to make a compete case, major overhaul, re-installation of the engine and an uneventful flight home. In all, 4 weeks and about $20,000. At least he got a freshly overhauled engine for that price. |
#13
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If the airplane was going through an annual inspection, the IA should
have generated a list of discrepancies of what didn't pass and given that to the owner. At that point the annual was complete. An ordinary A&P could then bring the aircraft back to airworthinness condition without the need for the IA. I don't believe that there is anywhere where the FSDO could have demanded anything except to do a ramp inspection after the aircraft had been flying. Denny wrote: Oh, and BTW, mechanics cannot ground airplanes ************************************************** ***** Yup, true fact... Though one local recently got into a ****ing match with his API over some annual inspection issues on a well worn TriPacer (couple of 3 year olds in adult bodies)- including the CAR 23 original equipment single mag switch that has only two positions - off and on - and the fabric passing the punch test though at the lowest allowable reading, and the mechanic refused to sign it off.. The owner (an AP but not an I) demanded the mechanic turn the plane back to him now, or else... The mechanic did, but he put an entry in the log book that the airplane was unairworthy and called the FSDO and faxed them a copy of the log entry... It took a ferry permit to get it off the field... So, the plane was shopped around to several API mechanics before he found one that would touch it... 6 months later and it is still not flying... The story I hear is that the FSDO inspector is demanding documentation that they are having problems coming up with... While an mechanic cannot "ground" an airplane he can do a fair imitation if he is determined... denny |
#14
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On 9/20/2005 12:44, nrp wrote:
[ snip ] A Bonanza friend found one of those short studs laying in the cowl while preflighting his airplane in the Bahamas. He put the family on commercial airlines & flew home on minimum power - with a life jacket on! Yea, 'cause sharks like life jackets ;-) -- Mark Hansen, PP-ASEL, Instrument Airplane Sacramento, CA |
#15
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RST Engineering wrote:
There aren't a lot of possibilities, are there? 1. The case crack set up a vibration or torque that overstressed the bolt -- and since it happened on startup when things are running less than smooth in a Lyc, I'd bet on this one. 2. The bolt was WWAAAYYY overtorqued on installation. You'll never know about this one. However, a through bolt shearing and a case crack by another through bolt leads me to check the calibration on somebody's torque wrench. 3. Something else in the engine was vibrating ... not likely as the whole AIRplane would have been vibrating to shear a through bolt. 4. Defective bolt ... not likely as throughbolts get magnafluxed or x-rayed at overhaul. 5. (Add yours here) I'd think 2 is most likely, but who knows? Oh, and BTW, mechanics cannot ground airplanes. IAs cannot ground airplanes. The FAA (unless they pull the airworthiness cert.) cannot ground airplanes. I know it is a common phrase, but the mechanic simply suggested that it would be less than wise to fly the airplane in its current condition. True, but once the pilot knows the airplane isn't airworthy, isn't he/she obligated not to fly it? At least not without a ferry permit? Matt |
#16
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wrote in message ... If the airplane was going through an annual inspection, the IA should have generated a list of discrepancies of what didn't pass and given that to the owner. At that point the annual was complete. I'm not sure what you are saying. That the airplane has a current valid annual at this point? That isn't so. THe logbook should have contained words to the effect that the aircraft was inspected on (date) and a list of unairworthy items given to the owner or operator. If the airplane is "ratty" but the mag switch(es) had been installed in accordance with the type certificate in effect as of date of manufacture and there were no subsequent ADs to change it, then the IA cannot on his own hook declare them unairworthy. Similarly, if the fabric punched "at the bottom of the airworthy scale" then the fabric is airworthy. THe IA does not get to set a higher standard than the FAA requires. An ordinary A&P could then bring the aircraft back to airworthinness condition without the need for the IA. That's true, but the aircraft still does not have a current annual inspection. I don't believe that there is anywhere where the FSDO could have demanded anything except to do a ramp inspection after the aircraft had been flying. They can demand green cheese. What they get or are entitled to get are two separate matters. Jim |
#17
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"nrp" wrote in message oups.com... "Yes, but that wouldn't have sheared the bolt at..." I agree not sheared but it would have looked like that to the OP. I would guess a tensile fatigue (probably initiated by bending) with the crack starting on the side closest to the cyl centerline for cyl 3. Hm. Most people can detect the crystallization of fatigue as opposed to the clean cut of a shear. Perhaps not. However, the OP clearly stated that it was a throughbolt, not a stud. I agree with the centerline analysis ... those pistons are slapping up and down a hell of a lot harder than left and right (we hope). Torque to loosen will be less than torque to tighten, and less indicative. Respectfully disagree. WIth torque values of these magnitudes, you will get very little movement to find the point of actual torque by tightening. However, just before the nut loosens you will generate very nearly the tight torque. The problem is to have somebody reading the reverse torque very carefully and noting the peak while you VERY SLOWLY bring the nut off. It is, as they say, an interesting (and very expensive) problem in forensic mechanics. Jim |
#18
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"Kobra" wrote in message ... Flyers, The story goes on though. As he was taking the engine off he found one other interesting item. One of the through-bolt nuts on the bottom of cylinder number 3 was sheared off completely flush the cylinder base. That's when the hair on the back of my neck stood up. I have to think that all this was related as the nut was still laying in the bottom of the engine. This was recent! Next I had a recollection of starting the engine before my flight to WWD and I remember that I heard a "snap!" just as the engine caught. It was loud enough to make me say, "...what the %$#@ was that?!" and just soft enough for me to dismiss it and ponder, "...did you really hear what you think you heard?" I'm not that knowledgeable about the internal details of the engines, so could you explain how that bolt could get sheared off? Any speculations would be understood as being such. -- Matt --------------------- Matthew W. Barrow Site-Fill Homes, LLC. Montrose, CO |
#19
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RST Engineering wrote: wrote in message ... If the airplane was going through an annual inspection, the IA should have generated a list of discrepancies of what didn't pass and given that to the owner. At that point the annual was complete. I'm not sure what you are saying. That the airplane has a current valid annual at this point? That isn't so. THe logbook should have contained words to the effect that the aircraft was inspected on (date) and a list of unairworthy items given to the owner or operator. I was saying the annual inspection was complete and current at that point and if there were any unairworthy items, they need to be attended to. The IA had completed his duties and is no longer involved. Once he signs off the annual inspection, whether airworthy or not, the inspection is complete and current. If the airplane is "ratty" but the mag switch(es) had been installed in accordance with the type certificate in effect as of date of manufacture and there were no subsequent ADs to change it, then the IA cannot on his own hook declare them unairworthy. Similarly, if the fabric punched "at the bottom of the airworthy scale" then the fabric is airworthy. THe IA does not get to set a higher standard than the FAA requires. An ordinary A&P could then bring the aircraft back to airworthinness condition without the need for the IA. That's true, but the aircraft still does not have a current annual inspection. The inspection is current and complete, but not airworthy. That inspection will be current for the next year and if it was not airworthy it can be brought into airworthiness and flown during that time period. The A&P has 0% authority with the inspection process. I don't believe that there is anywhere where the FSDO could have demanded anything except to do a ramp inspection after the aircraft had been flying. They can demand green cheese. What they get or are entitled to get are two separate matters. Jim |
#20
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wrote in message ... RST Engineering wrote: wrote in message ... If the airplane was going through an annual inspection, the IA should have generated a list of discrepancies of what didn't pass and given that to the owner. At that point the annual was complete. I'm not sure what you are saying. That the airplane has a current valid annual at this point? That isn't so. THe logbook should have contained words to the effect that the aircraft was inspected on (date) and a list of unairworthy items given to the owner or operator. I was saying the annual inspection was complete and current at that point and if there were any unairworthy items, they need to be attended to. The IA had completed his duties and is no longer involved. Once he signs off the annual inspection, whether airworthy or not, the inspection is complete and current. (S)he cannot sign off the annual inspection. 43.11 (a)(5) is quite specific as to what has to happen when the aircraft is inspected and not found airworthy. If you have another section of the regs that countermands this section, please post it. Otherwise I maintain that the inspection is neither complete nor current. The inspection is current and complete, but not airworthy. That inspection will be current for the next year and if it was not airworthy it can be brought into airworthiness and flown during that time period. The A&P has 0% authority with the inspection process. Citation from regulation, please? Otherwise I maintain as above, not current, not "in annual". Jim A&P, IA |
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