February 2007 - American Bonanza Society

BY DICK PEDERSEN, ABS TECHNICAL CONSULTANTTONY, WISCONSINBroken engine mount boltsI have found several 10-520/550-powered Bonanzas withbroken or missing mounti ng bolts on the left and right rearengine mount fittings, where these fittings bolt to the nose geartunnel sides. Those rear engine mount fitting s are the angledbrackets that are below the engine mount legs that are boltedto the engine, The square rubber Lord mount is installedbetween these two engine mount fittings.On some, the broken bolts were still in place, but the nutside of the bolt was broken off and missing inside the nosegear tunnel. These are AN4-1 OA, -II A or - 12A bolts, dependingon their location on the aft fittings. The top two bolts in thecenter of the aft fittings are usually the ones I find broken.Many times most of the rest of the bolts on the aft fittings areloose, possibly from bolt stretch.I assume the top bolts break from the weight of the enginepushing these fittings outward due to their angled design, especiallyduring turbulence or a hard landing, These bolts probablydon't get checked very often during normalmaintenance.The first time I found one of these brokenbolts in the boltom of the engine compartment,I had to look a long time before discoveringwhere it had come from because the left mufflerand manifold make the top of the fittingsomewhat difficult to see. I usually replacethese bolts at engine change time.The front engine mount fittings don'tseem to have this problem, although I havefound several slightly loose bolts in theselocations, This may be something you willwant your favorite maintenance provider tocheck from time to time.Fuel cell ventsI occasionally find a Bonanza wi th aproblem involving the fuel cell vents on theFuel vent line with small hole (orangearrow) drilled into aft side of linebottom of the wings, back by the flaps next to the fuselage,The two most common problems are the vent line beingplugged by a mud dauber nest, or the vent line is bent aft orbroken completely off.The plugged vent is easy enough to clear out with a pieceof wire or a plastic squirt tube from a WD-40 or LPS aerosolcan, assuming the nest or obstruction isn't too far up the ventline, If the obstruction is beyond the reach of your pokingstick, you will need to disconnect the vent line at a joint orsplice and blow it out with compressed air. Be sure to blow ina direction away from the bladder, as you do not want to blowthe obstruction into the bladder, nor do you want to pressurizethe bladder.A vent line being bent aft instead of in the normal 10° forwardposition is usually caused by someone accidentallybumping it while working under the aircraft or cleaning thebeUy. These vents bend aft very easily, Do be careful when tryingto bend them forward. If not properly done, the aluminumvent line will snap off just below the wing skin and ruin yourwhole day.The reason the vent line snaps off in this location is due toa small anti-icing hole that is drilled, or should be drilled, in theaft side of the vent line, fairly close to the bottom wing skin. Ifthis small hole is not drilled in the vent line or is plugged up withpaint stripper or paint and the vent line gets plugged wi th ice orsome other obstruction, the engine wi ll eventually quit from fuelstarvation as air is not being vented into the bladder to replacethe fuel the engine is drawing out of it.This can also cause the bladder to collapse and comeunsnapped from the top of the tank liner in the wing, If thisgoes unnoticed, you may not be able to put in the amount offuel that the bladder normally holds, as it may not straightenout completely on its own and it most certainly won't resnapitself back to the top skin!There is a way to detect a plugged vent inflight, before your engine quit s, if you knowwhat to watch for. I f one of your fuel gaugesstarts slowly working its way toward the fullmark for no apparent reason, we know forsure your Bonan za is not making gas! As thebladder is sucked up off the bottom of thetank liner as it is collapsing, the fuel gaugesending unit float is also being lifted up,causi ng the gauge to read a higher quantity.If you do nothing at this point, such asswitching to another tank, things could get veryquiet when fuel quits flowing to the engine, Noone has yet figured out how to keep it runningwhen you are that lean of peak IMany owners, mechanics and even FAApersonnel do not realize that these anti-icingholes are there on the aft side of the vent tube,So the ice hole sometimes doesn't get drilledPage 10047 www.bonanza.arg ABS February 2007