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Thread: Valve Failure

  1. #1

    Valve Failure

    The Sierra broke a valve over Evansville Indiana. My partner landed in Carmi, Illinois, just West of Evansville. The cylinder was removed and the flared portion of the intake valve was missing. The piston was beat up a bit, but totally intact. We expect the valve must of failed in a couple of pieces to get past the exhaust valve. The engine has just gone past TBO with 2060 on the tach. The cylinders have never been off. If it passes inspection per Lyc SI 1193A, we will install a new tappet and reconditioned cylinder and get it home for overhaul. If the cam is lunched, I guess we will ship the engine someplace.

    Has anyone heard of a intake valve failure of this nature?

    Thanks,
    Marty Vanover
    Phoenix, Az.

  2. #2
    Not specifically but it's certainly possible. I can't remember how far up the valve the sodium chamber goes. One interesting question is did the broken valve release the liquid sodium? I'm not sure how much damage would be done venting it out the exhaust, the temps would probably have been enough to mostly vaporize the sodium. Any remaining sodium that didn't explode would have quickly oxidized to relative harmlessness.

    On the flip side if it didn't the remaining (weakened) valve stem can represent a hazard although the sodium should be solid at room temp and have a little harder time finding water before it just oxidized. So the risk is small but I don't know that I'd leave one laying around the desk drawer for "see this" value or trying to break it open in a rain storm. Intact valve or one with the chamber exposed and empty is different matter.

  3. #3
    Heard of a ton of valve (guide) issues with Lyc's. Pretty amazing to me, to hear of the ones that last 2060 hrs.

  4. #4
    I may be mistaken, because I can't recall the source, but I'm thinking that only the Lyc exhaust valves contain sodium for cooling. I'm not sure that the intakes would even get hot enough to make the sodium work. The exhaust valves are close to twice the price of the intakes, reflecting the different construction.

    Lycs don't have a fraction of the valve problems of the Continentals. It is fairly uncommon for a big-bore Continental exhaust valve to get to 800 hours without sealing face erosion and leaking. 500 hours is closer to an average failure point (leaking). When the Lycs have problems, it is usually the exhaust valve, it is usually preceded by sticking, it is usually in the straight-valve heads, and is usually related to excessively rich operation coupled with excessive cylinder temperature in the area between the intake and exhaust ports. The valve guide carbons up and causes the valve to start sticking; and for reasons not entirely understood, the valve guide sometimes wears excessively instead. Some have conjectured that this has resulted from reduced oil flow to the guides.

    I can't help but suspect that it may also be related to poor repairs or assembly, as well as maintenance and operation. There are so very many of these engines (320/360/IO360) and valves that go to 2200-2500 hours problem-free, that this can't possibly be a design issue. The difficulty is that any one of us usually have our hands on a given engine for only a fraction of its life. Bare-bones log entries (and missing entries) often tell only a portion of the story of a plane and its engine. All we can do is the best we can with our current ownership. That means proper leaning (as much as possible); managing cylinder head temperatures (lots about this on BAC); frequent oil changes (to get the lead and crud out of the engine); frequent operation; and not ignoring warning signs (for example, unexplained spells of a missing cylinder, particularly after a cold start).

    And after having said all this, I consider the breakup of an intake valve to be a rare event, on an otherwise healthy engine. That assumes that the engine is in its first run. If it is on its second or third overhaul, the story turns to the quality of the overhaul. If new cylinders were not installed, there is a high likelihood that only the exhaust valves were replaced. The intakes are often reground and re-used, on repaired cylinders. On poor quality jobs, even the exhaust valves get reground and reused. You can bet that those will not make it through a second TBO run. Technically, it cannot even be legally called a major overhaul, as the exhaust valves are on the Lycoming mandatory replacement list. At any rate, this gives you some idea of how aspects like this can lead to what seems like an inexplicable failure.

    And if the engine is first-run, and has accumulated only 2,000+ hours over 25 years or more, it is certainly due for a tear-down and inspection. I'd consider it remarkable for an engine to go with so few hours over such a long calendar time, yet have no internal corrosion anywhere inside it. Small corrosion pits are often the stress risers that trigger breakage. That includes on propellers, so keep those leading edges and thrust faces dressed, and wiped down with something like LPS-2.

  5. #5
    Thanks for the comments. I'll know more when the cylinder returns with the airplane.

    FYI according to the logs, the engine and cylinders have never been apart since installed by Beech. From the looks of the engine and cylinders, it appears to be so. The airplane did spend most of it's life based here in Phoenix at Deer Valley, although it didn't fly too much between annuals. Actually built in late 1982, the airplane was used as a factory demonstrator by Beech until sold to a Beech sales rep in 1984. It was on the East Coast for a couple of years before we bought the airplane. But it was hangered and was flown pretty frequently. My partner (also an A&P) looked in the engine after the cylinder was removed and thought it looked pretty clean.

    I agree with Mike that the intake valves are most likely not sodium filled. I haven't worked on a lot of GA engines, but even the radials I worked on in the Navy didn't have sodium intake valves. The Wright R-1820s and the R-3350s share the same cylinders. BIG intake valves.

    It's still a puzzelment to me why the valve failed. It could be our leaning techniques. We don't have a CHT (a JPI is on the shopping list for the annual in March), just an EGT. We normally fly pretty high (7000+ ft) and lean to peak EGT. The engine never missed a beat before this.

    Marty Vanover
    Phoenix, Az.

  6. #6
    Thanks Mike, you're right, brain fart. _i_n_t_a_k_e. Doh! One other post mortem would be to inspect the intake tube interior for evidence of combustion blow by - I wouldn't be surprised if the intake valve was leaking prior to failure. On a real engine monitor this would manifest (I think) as a abnormally low CHT _and_ EGT.

    You don't mention if you have a single cylinder EGT or a 4-cylinder EGT.

    Lycoming says leaning to peak EGT is safe at 75% power or less, but this is on a cylinder by cylinder basis.

    If you are running a single cylinder EGT or aren't properly leaning with a 4-cylinder EGT you run the risk of leaning one of the learner cylinders to peak EGT and leaving one of the richer cylinders in the ~50F ROP hot spot. One of the reasons a 4-cylinder EGT is "essential" for LOP operation is you need to be able to ensure you keep all the cylinders out of the 25-75F ROP range where cylinder pressures and CHT peak (CHT peaks about 50F ROP and has already fallen somewhat at peak EGT).

    EI has an excellent paper on engine trouble shooting and talks about normal operation as well as several specific tests. Problems with valves are some of the problems commonly caught early by an engine monitor. It's possible but unlikely the valve failed this catestrophically without some advance warning. You should budget an EI or JPI to go in with your overhaul. The EI (not sure about the JPI) has a 'normalized mode' where is keeps a per-cylinder baseline and "levels" out the bar graph display to normal so you instantly spot symptoms like an changed EGT or CHT.

    If you're A&P is amenable to signing off on your work the basic work of wiring in the engine monitor is pretty easy (I'm just wrapping my UBG-16 install up, mines been a bit longer because I'm doing an FP-5L some extra probes and an RPM functional module and avionics master at the same time and getting the fuel hoses and fittings takes a little longer). At the very least you and/or your A&P can get the monitor installed and wired with the probe leads to the engine compartment while the bird is down anyway. Then then it's only a few hours to install the probes, hook up and tie-down the leads.

  7. #7
    Mark,

    What you say could be true. However, if the valve was leaking prior to failure, I think the manifold presure would fluxuate or pulse. We haven't seen that. Personally I tend to operate aournd 70% power due to the normally warm temps and high altitudes out here. In the warmer months 7500 is minimum for comfortable cabin temps with the sun up. I usually get 9 gph or less depending on altitude. My partner has made two, no, make that 1 1/2 trips back East, he like to fly high, usually up at 11K going East. He was at 8K on the return trip this time when the valve let go. With the cooler weather over the Mid-West this trip, at full throttle he could have been above 75%.

    I have read up on both the EI and JPI analyzers. I don't see much difference between the two. Both have a normalized mode of operation. The guy down the hall bought the JPI from GAMI at a discount (over A/C Spruce) for his Cardinal. He loves it. Wonder if the discount is still on, we will go with the GAMI injectors during overhaul. I don't want to spark a debate, but is anyone dissatisfied with thier JPI or EI analyzer? My only critizism is the size. I would prefer a 3 1/8 instrument face for eaisier reading. Yeah, there is the JPI 900 $eries.

    Installing either system for us is no big deal, we are both A&Ps.

    Marty Vanover
    Phoenix, Az.

  8. #8
    Marty,

    Haven't got my UBG-16 installed yet (waiting for Mark to finish and post a complete installation guide for the 10 thumbed). There's another topic that already has the debate about the JPI vs EI well covered. Pretty much a coin flip.

    One thing that swayed me to EI was the remote head option which allows the placement of the body anywhere (inside the cabin - don't laugh I called and asked EI if it coudl go on the other side of the firewall) and connect via a harness to 2" deep head which will be tucked way up in the top left corner of my panel.

    On the other hand you might like the JPI which has an optional 3 1/8" head.

    Get out the coin, heads it's .....

    John Woods

  9. #9
    Agreed. I won't re-hash the UBG versus EI thread, that's well covered elsewhere. I will say I'm happy with the UBG and I went with the remote head option as well, it let me reuse the 2 1/2 hole the original EGT used, which is in the sloped lower panel - the 6+" of main box would have hung down quite a bit.

    I got a great deal on the UBG and the FP-5L togather via the fall show specials with EI, wholesale price from a dealer at AOPA Expo (special was also at Oshkosh), free Oil temp probe and a $600 rebate on top of all that (and the rebate came back in about 2 weeks direct from EI).

    I've had three contacts with EI for minor technical questions and have had excellent service on both. One I left a web inquiry and got a call back within an hour as promised, one a direct call inbound and one a web inquiry that I requested an email reply that came back in about 2 hours.

    I went with the UBG because of the remote head, the increased alarm flexibility and the better normalized mode (with historical data). I think the UBG ends up cheaper than the JPI at retail but specials vary greatly. Also I planned to do the fuel flow and EI having the STC for primary fuel pressure replacement was nice, saved me a hole and got the analog guage and fuel pressure line out of the panel.

    Note I have an IO-360 so I have a simple fuel flow setup with a single transducer between the engine fuel pump and the intake box, I don't think anyone has gotten either the EI or JPI fuel options working perfectly in all permutations on the carburated models with the split input.

  10. #10
    wojek
    Guest

    valve failure

    as humans get older, plumbing starts to plug and clog(fuel and oil lines), memory(electrical equipment and contacts) starts to malfunction, eye sight(dg and other equipment) starts to malfunction, and knees, hips and other joints(cylinders, cams, tires, bushings, etc) simply wear. what do you expect from mechanical equipment and components? I TEND TO LOOK AT REPAIRING OUR PLANE AS A MIRROR IMAGE OF MY DOCTOR TAKING CARE OF ME. Lord, please help me reach 2000 + hours on our engine before we have problems.
    XXOO N6082N

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