February 2006 - American Bonanza Society

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COMPRESSION CHECKS ( BOTH USUAL & UNUSUAL)AND CRANKCASE MOISTURE REVISITEDylinder replacement at annual inspection is directly proportionalto the alimony payments or the number of children theIA has in college. Well, maybe not every time, but I thinksome cylinders are replaced before they need to be.Factory adviceBoth Continental and Lycoming have instructions for theprocedure to be used. Since 1984, with Continental's issuanceof M84-IS Service Letter (superceded by SB03-3), the old60/80 as the minimum allowable reading is a thing of the past.The main thrust of the new procedure was that there couldbe no leaks past the cylinder static seals (valves, barrel-to-headjoint, cracks in the head) while the ring set could leak anamount that, on some gauge sets, could be around the 4S-pslmark.The gauge set needs to be calibrated with a calibrated orificeto determine the actual minimum allowable reading. Thevalve no-leak requirement has been changed in later instructionsas well as adding requirements for a look inside thecylinder with a boroscope. This SB03-3 has quite a bit of usefuldetail regarding the health and inspection of the cylinderson our engines.The old gauge sets may be used after being calibrated, ora new gauge set may be purchased with the calibrated orificebuilt into the unit. The new sets run about $100 from severalsuppliers.Most mechanics will do the compression test per the serviceletter after the engine has been run and is still hot. That isthe normal routine and the figures entered into the engine logbook.However, the object of doing the compression check aspan of the engine inspection is to find out all we can aboutexactly what condition the cylinders are actually in.I have checked the compression on a few engines, whichgave very good static readings-that is with the engine notrunning-but the engine either burned excessive amounts ofoil or did not produce the expected performance. In spite of thegood compression reading, the cylinder or cylinders wereactually not up to standard.Some failed partsAs a small aside hangar war story-I was at Beckwourth,California (002) airpon to visit my pal Herb Bishop the otherday. I fly my Luscombe over there about once a week for lunchwith Herb and his crew in the little mountain town of Panola.There is usually something interesting to see going on in theshop there.That day they had just staned removing a cylinder from aC182. I asked what the problem was and Dan, one of the lAs,said, "Zero compression, and take a look at the head fins!"This was the center cylinder on an 0-470.Sighting over the front to back of the engine, it was easilyseen that the fins on that cylinder were catawarnpus WIth thefront and rear cylinders and leaking exhaust gases around thebanel-to-head joint. Not just lining up with regard to distancefrom the crankcase, but pointed off at an angle of about 5degrees. That head was about to leave the barrel. In fact, I donot know why it had not already done so when the guy flew Itin for the annual IIf the head blows off the barrel, a carbureted engine willmore than likely flat-out quit since the induction system isopen through the dislodged pipe leading to the failed cylinder.A fuel-injected engine might still run with the throttle Wideopen. I doubt you would want it to though, since there may befuel being sprayed all over the cowl from the failed or brokeninjector line to the sick cylinder! A small amount of powermight still be available, but a landing is in the very near futureof that airplane.The more I see of failed cylinders, the more J am convincedthat continued service of cylinder heads beyond oneoverhaul (tOlal time of maybe 4,000 hours or less) is not agood idea. Yes, I know that some large percentage of theengines out there may be running cylinders of some unknownaccumulated time and doing it successfully. But failure of thatold, tired aluminum head gets to be more likely beyond anunpredictable amount of time in service.I have no heartburn with first-run factory-new cylindersbeing reworked by a first-class shop and returned for anotherrun. But when one purchases a replacement exchange cylinder,there is usually no means to determine the total time it haswithstood the stress of operation.Also, the continued use of pistons beyond some reasonabletime limit can lead to disaster. The E-series engine in thephoto (on the next page) has the top of the crankcase knockedout. Usually one would think a connecting rod had broken ordisengaged from the crankshaft throw in a picture like this.However, what appears to have taken place is that the pistonbroke exactly through the center of the wrist pin hole.The piston above the wrist pin is crammed into the top ofthe cylinder. This left the wrist pin and the bottom, or skin, ofthe piston floating around on the flailing, uncontained connectingrod, resulting in the complete failure of the enginealltaking place in a matter of seconds. There was no way to
after changing (5+1- hours). High oil temperatures may resultdue to the large amount of hot gas being blown into thecrankcase. And with high crankcase pressure there may be oilblown out of various places from the engine.Remember, the allowable maximum crankcase pressure isless than one-tenth of one pound per square inch. Very lowindeed.This E-series engine has the top of the crankcose knocked out.determine the total time on this piston, but I can guarantee youIt was something other than small.In the end, the investment in new cylinder kits at engineoverhaul time is a good one.Also, I reject the notion that is !loatino around that. . 0Contmental cylmders are somehow inferior to the severalother brands available for the angle-valve engines. At this timeContinental is the only source of parallel-valve cylinders forthe E and 0-470.There may be a time when the design of any manufacturermay need some adjustment, but I know that a company likeContinental has no desire to produce anything but products ofthe highest quality. Perhaps the other brands might be of equalquality and give satisfactory service. But I believe the oriainal. 0engIne manufacturer, at this time, is building a product that isof the best possible materials and design.Those statements will no doubt lead to some hot e-mailabout failures of Continental cylinders. However, all producersof various engine pans have had their share of failed products.Things change on engine startWhen the engine is in motion, everything changes regardingthe seal the ring set makes. Although one may get a goodreading on a cylinder that has glazed walls, when the engine isrotating and the pistons are moving in the cylinder, the ringslift off the wall and allow excessive oil to migrate into thecombustion chamber as we ll as allow higher-than-normal gasblowby into the crankcase.Also, the heat and addition of oil being thrown from thecrankshaft change the fit of the parts. The high static readingswill probably not remain for too long, since the above condition(glazing) usually leads to carbon buildups in the ringgrooves, sticking the rings, resulting in low slatic compressionreadings.One of the clues about this situation, in addition to theexcessive oil consumption, is the oil turns black in short orderCrankcase pressureCrankcase pressure is one item of information that isinstantly available as a read out on a pressure gauge tappedInto the crankcase (usually an airspeed indicator). 0 need to~ait and see if the oi l turns black. The engi ne breather systemIS SIzed to allow only normal amounts of gas to be blown intothe crankcase and exit via the vent system without exceedinothe maximum allowable pressure. 0There are other causes for excessive crankcase pressurebesides piston ring blowby, but that and interpreting the pressurereadings is a separate article in itself.A margin of safetyAs with all things aviation, there is a wide maroin obetween the minimum or maximum allowable readings ofwhatever we are testing and the point where performance orsafety becomes critical. The following is quoted from theContinental publication, Tips on Engine Care:"Engine testing has shown that certification horsepowerratings will continue to be delivered even when all cylindersare at or below the minimum allowable calibrated compressionreading as established by the master orifice tool."'Cold compression checks neededSo if the compression check is done via the latest informationand the readings comply with that infornlation. allshould be well. However, there is one check of cylinder healththat most mechanics do not do and which should be done. Ihave found several cylinders-the latest one on my LuscombeLycoming 0-235 engine- that checked out just fine hot, butwould have large leaks through the valves when cold.In the case of the Luscombe, it has solid lifters asopposed to the hydraulic units in all engines used in the<strong>Bonanza</strong>s. It turned out the adjustable valve clearance was rightat zero, or thereabouts. on one cylinder and was holding thevalve not quite closed when cold. After running the engine, thevalve would close tight enough to get a normal reading. Veryeasily fixed and back to the 76/80 reading I was expecting.Morning sicknessThe principle for either solid or hydraulic lifters is thesame. That is, we are looking at all possible problems in every
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Page 9 and 10: Enter ABSThis time around. I j oine
Page 11 and 12: Stepping back in time for a moment,
Page 13 and 14: M~ WJSiC techniqueBY BILL COMPTON,
Page 15 and 16: There was a man at BAL who bought a
Page 17 and 18: autopilot had become nonfunctional.
Page 19 and 20: Perhaps the Cessna 210 owner was un
Page 21 and 22: 'Mi, 'lJi'('(·kJ'll!, 6J1/jfI(~ ~,
Page 23 and 24: with a patient and other possible c
Page 26 and 27: TECH NOTESTech Noles are from ASS T
Page 30 and 31: engine condition. There is a malady
Page 32 and 33: INTERIORSTHE INSIDE STORYPART VIIIB
Page 34 and 35: There are two problems with thearmr
Page 36 and 37: Repaired crack.Repairing a crushed
Page 38 and 39: A BRIEF HISTORY OF PILOTTRAINING IN
Page 40 and 41: My aviation daysstatted when I was2
Page 42 and 43: THE GARMIN GPSMAP 396THE "SWISS ARM
Page 44 and 45: TRANSITION TRAININGIf you are weigh
Page 46 and 47: ~ Life Membersij , '--"I~ ...-;::"~
Page 48 and 49: FEBRUA Y10-12 - BPPP Clinic. Lakela

February 2006 - American Bonanza Society

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