World of Hurt

World of Hurt

<HTML>In an ealier thread I had gloried in having "solved" my O-200 carb heat problem by detecting and replacing a rusted-out carb heat intake tube.

Yesterday I notice on the ground beneath my airplane little one inch slivers of rusted tube coil that had apparently fell out of the rusted tube when I removed it. A subsequent inspection of tube produces all kinds of doo-doo when the tube is shaken.

Seems possible that some of that stuff was ingested over time. What do I have to do to ensure that my motor is clean of contamination and not damaged? Hopefully a mere compression check and bore scope will do it.

In addition to that mess - my carb seems totalled. During the original investigation of the carb heat problem (rough runing and 400) rpm drop, my mechanic opened the carb heat muffler manifold. We found rusty deposits inside. He then dropped the carb heat box which appeared to be clean. at that point carb cleaned was sprayed liberally up into the carb. It wa then that I discovered the rusted tube. We replaced the tube and buttoned her up. A brief runup confirmed that the carb heat was fixed.

The next day I went flying. I notice pretty quick in the flight that the EGT was 25-50 degrees higher at every throttle setting. I stayed in the pattern for an immediate precautionary landing. My mechanic fooled with the mixture control. On the next run up the motor would not exceed 1500 rpm. It turns out the screw was turned out 4 full turns. After much messing with the screw the motor seems to run ok at 1 turn out. However, when crosing from 1700 rpm to the higher ranges the motor would sometimes hestitate and even die.

The carb is now off being exchanged for a new one and I'm wondering if I need a top end. Did the carb cleaner attack the floats and seals in the carb.

Help.</HTML>

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Re: World of Hurt

<HTML>Has it occurred to you that what you really need is a mechanic who is actually competent to work on your airplane?  It's bewildering to me that any person who claims competence to work on a O-200 would even attempt to affect changes in cruise engine indications by altering an idle mixture setting on a carburetor.
It sounds like the longer you allow this person to improperly perform repairs on your airplane, the more troubles you experience.  (Carb cleaner?  While still on the aircraft?  Are you talking about automotive aerosol stuff?)
  Has it occured to you that your previously over-rich mixture settings (caused by the collapsed tube) having now been corrected, would allow your engine to run at a more proper mixture?  Has it occurred to you that a more efficient mixture would quite naturally result in better combustion and therefore higher EGT's?  Did it occur to you that your cockpit EGT is neither intended, nor capable as a flight test instrument?  And even if it were, that improper, nonstandard calibration would lead to improper diagnosis?
  The previous mis-diagnosis's and the present improper carburetor "repairs" and adjustments have probably already cost you the unnecessary expense of a new carb.  From what I've read so far, I'd suggest a different "technician".</HTML>

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Re: World of Hurt

<HTML>Thanks George. It was my first suspicion that the tube repair had modified the fuel/air mixture. I eliminated that possiblility be placing duct tape over the carb heat inlet. There was no change in engine performance implying that the carb heat valve was effectively blocking the carb heat airflow.

There is some debate as to what contribution the idle mixture port contributes to the overall mixture in the mid and high rpm ranges. In any event there must be some sort of transition from the idle port to the main fuel/air flow. I suspect it may be around 1700 rpm where the motor seems to hesitate. The hesitation seems to be affected by the idle mixture screw.

I checked with several mechanics who all seem to say that they never use carb cleaner because the typical aircraft carb is very clean, but were not alarmed that it was used. My mechanic used it because of the rust like deposits in the carb heat manifold. The stuff was in the FBO tool kit and I don't recall if the label specified aircraft use. Perhaps some of the other thread watchers can speak to the use of carb cleaner.

As for the EGT I've understood from the manufacturers specifications it is meant to be used as a relative measure of temperature.

I've found that A/P mechanics tend to be feisty and opinionated and often do not agree. Being a systems analyst I'm always very skeptical of everything I hear including a recent suggestion that a 400 rpm carb heat rpm and rough running is normal which later proved to be a serious malfunction. 

What I'm going to do is replace the carb, have the motor evaluated for ingestion damage and nail the mechanic if the carb heat cleaner is not for aircarft use and/or wrecked the carb. One possiblity is the cleaning opened up clogged defects in seals and gaskets creating a leaner mixture.</HTML>

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Re: World of Hurt

<HTML>The carb is a Marvel-Schebler 3SPA and was installed new in 1976. It does not appear to have been rebuilt during the major overhaul in 1995. The log says the assessories were not included in the overhaul. There is a chance the carb has not been touched for over 30 years.</HTML>

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Re: World of Hurt

<HTML>Quoting from the Marvel-Schebler MA-3SPA maintenance/overhaul manual:
"All fuel delivery on idle, and also at steady propeller speeds up to approx. 1000 rpm is from the idle system.  At approx 1000 rpm the suction from the increasing amount of air now passing through primary and secondary vernturi causes the main nozzle to start delivering, and the idle system delivery diminishes due to lowered suction on the idle delivery openings as the throttle fly is opened for increasing prop speeds, until at aprox 1400 rpm the idle delivery is practically nil, and most of the fuel dielivery from that point on to the highest speed is from the main nozzle...."
  (In other words, screwing around with the idle mixture is the incorrect thing to be doing with regard to your complaint.  Spraying unappproved products up the carb, and other repairs to the unit without proper equipment and tools is also incorrect.  Placing duct tape over openings is also not a correct procedure and the aircraft should certainly not be flown with that.  Imagine what would happen if that tape became dislodged and blocked the carb throat in flight.  In any case, it is an unauthorized, unapproved modification of the aircraft.)
  Unless a particular product and procedure is authorized/recommended by the equipment mfr., then it is an UN-authorized procedure/technique.  Unless the product is compatible with the materials used in the manufacture of the carburetor, then there is risk that the product will damage it and/or it's components.  (Some automotive carb cleaners will remove sealants and swell gaskets/o-rings causing failure of the carb in and by itself.  The correct repair of an internally faulty carb is removal to a certified repair station with a flow bench.)  Unless the procedure used is approved and recommended, then there is risk of damage to the unit.  Both instances would be contrary to continued airworthiness of the unit.
  Without the proper tools, manuals, and methods, no repair technician is qualified and equipped to work on any aircraft.  A person inexperienced and untrained on the particular equipment being worked upon, and using inappropriate diagnostic methods, is at a loss even if in possession of those tools and manuals. 
   I don't know how else to politely say it.</HTML>

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Re: World of Hurt

<HTML>Thanks George. No, I did not fly the airplane with duct tape blocking the carb heat intake - in fact the airplane has been grounded continually. The idea was to simulate the earlier obstruction to see if we were still working with the same mixture baseline. We were not. I found the can of carb cleaner used and it said "CarQuest" on it. It is clear to me the cleaner trashed my carb and the mechanic is through. It's funny about the cleaner - an FAA designated guy who says he's goes around helping pilots understand the maintenance of their airplanes actually sprayed the cleaner in. He had some sort of FAA ID and a hat loaded with insignias and pins. I asked him if he ever used carb cleaner on an airplane before and he said no. He says he was doing what the mechanic said.</HTML>

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Re: World of Hurt

<HTML>here's the Precision Airmotive site that now manufacturers Marvel-Schebler carbs:
http://www.precisionairmotive.com/</HTML>

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<HTML>I have a new A10-4894-1 carb and an appointment to have a very good mechanic install and then pressure test and scope my cylinders. Total hit is well over $1000. Guess the lessons here is you get what you pay for and not all licenced mechanics know what the h### their doing.</HTML>

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Re: World of Hurt

<HTML>William: Take heed to what George Horn has suggested! Being an A&P myself I find it difficult to fault another A&P, but it does seem that your man is out of his field of expertice.As for the mixture, the idle mixture, is just what it implies IDLE MIXTURE.above 1000 rpm it cuts out,and the throttle ventury takes over. As for the rust particles in the tubing.This is unusual,to say the least.That tubing must have been very old or not the proper type.The wire usedin those tubes is a very srong,and durable type.I have never seen any that was so rusted that it came apart In fact i've never seen any that was rusted.Incidentaly: when you replace that tubing it must be the single walled type. The double walled type has been known for the inside wall material to separate from the outside wall,and collaps inside the tubing,and cause blockage,such as you have been expieriencing.As to the rust getting into the carb.First it has to go to the muffler shroud.Then thrue the other tube to the carb heat box.then into the carb. It is unlikely that any pieces of any size got that far. I wouldn't think a top overhaul was needed. Do a leak check on the cylenders to see how they are holding compression. 60/80to 70/80 is pretty good for an engine with any time on it.Drain yor oil,and check the screen for metal particles(using a magnet) I don't know what to say about your carb. your man has been into it and I wouldn't care to remark on that. good luck. P.S. take Georg's advice.</HTML>

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Re: World of Hurt

<HTML>Thanks Willy. Yeah, I bit the bullet and hired another mechanic to put my motor back together. He's going to install the carb and do a top-end eval. I guess the lesson here is mechanic skills and experience vary greatly. I talked to a guy the other day who studied the freedom of information A/P exam questions and passed. The FAA considered his Navy time working on F-4's sufficent schooling and experience. Guy has no piston experience. Good thing he knows his limits.</HTML>

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Re: World of Hurt

<HTML>Good news and bad news -

The carb went on fine, but the motor still runs like doo-doo.

Two good mechanics spend 10 hour over the weekend tearing it apart. Basically the motor runs ragged and really goes to pot in the 1700-2000 range. The same for either mag. Application of primer smooths it out. Seems to be running lean. After a lengthy process of elimination it's starting to look like a leak in the induction system. We're going to probablely drop the intake manifold, and if we don't find anything there, probably pull the jugs. We checked the timing, fuel-flow rate, valve displacements, P-lines, compression, bores with a scope, idle screw settings, exterior of manifold system, etc. A pretty good going over.

We searched the carbheat box and the muff and didn't find any metal shards from the fragmented tube coil.  The compression was good on the cylinders and the bore scope didn't show any cylinder scoring or debri. There was some oil in two of the cylinders, but the cross-hatch is still very vivid. The conclusion was the motor is still breaking in. One cylinder has a compression of 75 but a hissing. I'm resigned to basically doing a full top-end tear down and inspection. My pet theory is a cracked head. My dream is a loose manifold or bad gasket.

My big concern now is if some of the metal debri could have somehow gotten into the lower end?  I can live with the top-end inspection, but I sure do not relish  paying to have the motor pulled and the cases split.

By the way, I don't so squat without a mechanic looking over my sholder.

One wag has suggested the Marvel-Shebler A10-4894-1 that was on there and the new one we installed is improperly jetted for my O-200-A. The Cessna dealers says one jet fits all. Does anyone know if perhaps my Millinium cylinders require non-standard jetting?</HTML>

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<HTML>William,

The usefull information of this story I've read is this:
1) Your engine was overhauled 7 years ago and only has 80hrs on it.

If this engine was being operated properly there'd be over 1000 hrs on it as the engine has lived 58% of recommended life of 12 years.

Whereas it's not uncommon for people to neglect their engines by letting them sit, a sitting engine is being eaten from the inside out by corrosion. 
Especially if the engine has not been "broken in".
The evidence you've supplied (a carb heat duct that's rusted to the point of deterioration) suggests that possibility of internal corrosion is high.

2) You're engine runs rough at a specific range of RPM 1700-2000.

This is not an induction leak. 

Induction leaks make the engine run rough at low RPMs.  The roughness steadily decreases as you increase RPM to almost non-existent at full throttle. 

This is because at low RPM the air pressure in the induction manifold is *much* lower than the outside air pressure (by 7.5PSI or more in some cases).  As the RPM is increased, the manifold pressure rises until you reach full throttle where the manifold pressure and the outside air pressure are essentially the same (within an 1/2PSI).

Since the pressure difference is greater at low RPM, an induction leak will allow more air to enter the induction manifold without the carb knowing it- thus making for a overly lean mixture and a rough running engine.

At high RPM the induction leak lets in relatively less air and can be initially detected by measuring all the CHTs and noting the cylinder which is running exceptionally hot.  After a while the paint just burns off the head of the hot cylinder ;-)

I suspect you have a significant amount of corrosion in youre engine.
You have already described a stuck valve situation during your compresion test.
You may have a collasped lifter or a broken valve spring. 
All of these can be brought on by corrosion.

Have the engine inspected by a reputable shop thats familiar with O-200 engines.

Cheers,
RH</HTML>

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Re: World of Hurt

<HTML>Thanks Roger. Looks like a complete tear down may be up ahead. The motor does idle rough and it gets pretty smooth at higher rpm. Also, two engine oil tests have been completely normal. One of the mechanics suggested a collapsed lifter also. Removing the mainfold and jugs is on the way to a complete tear down. Oh well, it's only money ...</HTML>

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<HTML>Roger - perhaps the motor runs smoother at lower rpms because we have compensated fore induction leak leanness with the idle mixture. When the idle mixture fades the motor goes lean from induction leakage and then gets better as you described at higher rpm. The mechanic though he saw fuel staining at the junction of the manifold and head of one of the jugs.</HTML>

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<HTML>Glenn at Brower Aviation, Ramona, got the whole story and says my C150 is prone to induction leaks, he has seen it before, and he'll have the plane running fine in 3-4 hours.</HTML>

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<HTML>I disagree somewhat, Roger.  Many times an induction leak is virtually unnoticeable at/near idle, and again at/near high power, but will show up in the mid-ranges and may be most noticeable during acceleration as either a slow acceleration or a "halting" acceleration.  This sounds like classic induction leak.  It's unfortunate that William didn't have a mechanic with more experience working this problem earlier on.
  They hissing during a cylinder compression test needs to be investigated.  It could be hissing thru the intake valve and observable at the induction leak.  But it could also be a cracked head.  I've seen cylinders show high compression in the 70's but still leak at the cylinder bore/head joint.  Soap solution should help locate the leak.</HTML>

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<HTML>My NEW mechanic tells me my number 1 cylinder has a compression of 60/80 and a bad exhaust valve (using a bore scope). He's having the cylinder rebuilt. He also says my rubber manifold couplers are cracking. This is suprising in that we had just tested the #1 cylinder cold the day before and it showed 70/80. (By the way, the guy who did my annual 3 months ago cold tested my compression to and go 72/80 on #1.) How could heating up the motor make the compression go down? Also, those couplers sure looked good to my untrained eye. In any event, how can a bad exhaust valve make the motor hesitate at 1700 rpm like an induction leak? Do I have two unelated problems - induction and valve - or did one induce the other?</HTML>

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<HTML>It's important to put to rest an old concept about compressions.  It used to be held that anything below 70/80 is bad, and that anything below 60/80 must be repaired.  Not true.  TCM has shown that compressions as low as 45/80 will still produce rated horsepower.  They issued a service bulletin regarding this matter.
Most service bulletins are available at: http://www.tcmlink.com/   under their aviator services section.  (It's free but you must register.)  Lots and lots of info about your Continental engine on that website.
  The real value of a compression test is the determination of the exact CAUSE of compression loss. If it's past rings, then it will manifest itself by an audible hissing noise at the oil filler cap.  If it's past valves then it'll be heard at the carb intake (intake valve leak) or at the exhaust tailpipe (exhaust valve leak).
 
  According to TCM, if the leak is past rings, then compression readings down to 45/80 is permissible.....but keep an eye on it.  It may be worn rings, or it could simply be that the ring end-gaps are lined up with each other.  Another 10 hours and they may shift around and good compressions return.  (Keep in mind it could also be a broken/stuck ring and that should be repaired.  An experienced mechanic is a must when interpreting compression results.)
  If the leak is past valves then a repair is called for.  The most critical condition is a leak past an exhaust valve, because those hot gases can lead to serious failure in a short while.
  Since your mechanic has found an exhaust valve problem, even tho' the compression is 60/80, he's correct in calling for a repair to be made.
  The other problems of "engine roughness" are possibly perception, possibly a problem.  It doesn't sound like it'll be solved by a discussion forum, but by an experienced mechanic on site.
  Good luck.</HTML>

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Re: World of Hurt

<HTML>Thank you sir.</HTML>

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<HTML>William;  After reading all of the correspondence concerning your airplane. It makes me wonder about the history of your plane. It would seem that you have an airplane that has sat out in the weather for a long period of time,without running,and being neglected. Tell us more about the history of your  plane. That carb heat intake hose should never have rusted the way you say it did,under normal conditions.I hope not! but you may have a white elephant, That is going to nickle,and dime you to death. Except there are no nickles invoved when it comes to airplanes,It's dollars.As you are finding out as time goes by. Best of luck, Rgds. Willy Owens.</HTML>

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<HTML>The rusted sprial support wires inside scat ducting is common especially in seacoast areas such as the San Diego area where William apparently lives.  It is not a "given" that his airplane has been neglected just because the hoses collapsed.  It is a sign, however, that closer inspections are needed during maintenance visits, and pilot attentiveness is required on all aircraft.  Grabbing hoses with your bare hands and feeling them all along their lengths is part of regular inspection maintenance.  I think William is on the right path by finding/using more qualified maintenance technicians.</HTML>

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<HTML>Thanks guys.  My airplane has 3570 TTAF of which 3400 was accumulated in the first 5 years as a trainer at John Wayne. It then became the hangar queen of a guy that fiddled much and flew little. In 1996 his daughter ran it into a ditch and got a prop strike. The motor was rebuild with new Millinium cylinders. The gentleman became gravely ill about that time and the plane was stored in a hangar for 4-5 years until I bought it. The guy was to picky not to know about pickling his beloved plane with a fresh overhaul. He was famous for grilling the mechanics about the care of his plane. I get a lot of complements about the planes overall condition.</HTML>

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<HTML>It's raining today, the boss is on jury duty, and I'm thinking ahead to the next titanic round of battle with my O-200-A.

My erstwhile mechanic just told me that a slightly burnt valve - though admittedly in need of correction - will not explain my motor's hesitancy in the mid range. He also maintains that the induction system is not leaking. He suspects a broken valve spring or mufflers without proper baffling.

In any event, the practicing mechanic who currently has the plane will preside over any further investigation.</HTML>

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