Modifications, Maintenance & Repairs


Note- all bold print items represent modifications from the original aircraft configuration

Mods, Repairs, and Maintenance to Twin Comanche N8121Y

Careful inspection of logbooks prior to my purchase of aircraft revealed that both engines were top-overhauled at 684 tach time in May 1979 and both prop blades on both engines were replaced in 1971 per Hartzell service bulletin. All other maintenance appeared regular and routine. Very careful inspection of this aircraft revealed no damage history or signs of repair.

Note---engine oil and oil filters are always replaced at each annual inspection and on many occasions in between.

July 19, 1989

Purchased Twin Comanche N8121Y

Tach Time and Total Time on Airframe: 789 hours

August 1989

Engine starters both rebuilt

Permanently removed 5th and 6th seats and associated seat belts for insurance purposes.

October 1989

We did a major rebuild of avionics panel as well as a general refurbishing of airplane:

We kept the King KNS-80 RNAV and KT-76A transponder, the Narco AR-500 encoder, and the KMA 20 audio panel, but almost everything else was changed out:

We added:

KR-87 ADF with KI 229 slaved ADF readout

KX-155 NAV-COM with KI 209 glide slope indicating head

KY 97A COM radio

KCS 55A HSI

S-TEC 60-2 Autopilot with altitude pre-select and new turn & bank

Astrotec clock/timer

WX 10A Stormscoope

Apollo Model 618 Loran

PS Engineering intercom dual type with rear seat isolation

Davtron pressure altitude readout

Davtron DVOR

PTT on both yokes

Westbend timer on pilot yoke

Electric trim on yoke

New 1/4 inch aluminum instrument-avionics panel (one piece)

Dual master avionics switches

Dual tachometer replaces two separate ones

Handheld radio jack in panel

Input jack for cassette player

Avionics cooling fan

Replaced flap indicator

Replaced VSI and Manifold Pressure Gauge

All 4 fuel bladders reconditioned

Rebuilt R Bendix fuel servo

Both fuel selector valves reconditioned

New copper cables from battery to starters and aux power plug to replace aluminum

Installed strobes on wingtips

Re-sealed both aux fuel pumps

Replaced one fuel level transmitter

New oil and fuel line hoses in both engine compartments

New floor insulation

New door locks- Ace tubular key type

Replaced door seal around cabin door

Airplane weighed with new wt and bal

Installed new Rosen type sunvisors

New fuel selector decals

New fuel door latch

Replaced L cowl flap cable, adjusted R one

Replaced all engine compartment hoses both engines made by Aviall

Installed loran to autopilot coupling

Installed external airswitch to Hobbs meter

Rebuilt "whiskey" compass with new gaskets

New Airspeed indicator

Rebuilt prop governor in L engine

April 1990:

Dynamic prop balance at Byam Propeller shop

New battery

Replaced mirror on L engine cowling

Replaced Southco fasteners on nose cowling with nutplates

May 1990:

Annual Inspection

Replaced generator brushes both sides

Replaced brake discs and pads

Replaced sparkplugs all 8 cylinders

Replaced Timken bearings in nose gear wheel

Replaced air filters both engines

Replaced L main gear brake line

" L main gear door hinge

" Oil and filters both sides

" scat tubing L generator

" R Lord engine mounts

Rotated L engine mounts

Cleaned and gapped plugs

Timed magnetos

Replaced Zerc fitting in nose gear (grease nipple)

Replaced L landing light bulb

November 1990

Replaced carpet, sidewalls, curtains, and upholstery of seats

Removed Apollo 618 Loran and installed Northstar M1A Loran

March 1991

Replaced generators both engines with Interav alternators, regulators, and over-voltage relays in addition to circuit breakers

Repaired (welded) exhaust stack on R engine

June 1991

Annual Inspection

Installed new fuel selector decals

Replaced ELT battery

Replaced push rod tube O rings and seals, oil return line hoses, rocker box cover silicone gaskets,

Replace fuel door latches

Replaced brake O rings

Installed Hobbs meter on Janitrol Heater

Heater AD inspection

Replaced brake discs with Flite Life black stainless discs and organic pads

Replaced nose wheel shimmy dampener with new rebuildable model made by Parker-Hannafin

Overhauled landing gear transmission

Repaired (welded) alternate air box R engine and installed new bell crank kit

Repaired (welded) exhaust stack #4 cylinder Left engine

Replaced nose gear tire

January 1992

Annual Inspection

Installed new exhaust hanger hoses

Installed new bungee cords both main landing gear

Replaced nose gear canvas tent

Replaced various bolts and bushings in landing gear per inspection for AD

Replaced boot on nose wheel steering rod

Installed Piper Kit 761-082 on nose gear

Replaced both main gear tires

Replace cylinder head temp probe on L engine

May 1992

Replaced Davtron 903 Unit with model 903 ID-Z s/n 2796

Replaced Davtron Model 630 with Model M655 s/n 3972

Purchased Kennon Heat Shields for aircraft

August 1992

Replaced all 4 magnetos with New Slick Model 4373 Magnetos and wiring harnesses

Replaced engine driven fuel pumps both engines Lycoming LW15473

Replaced all spark plugs both engines with Champion REM40E type plugs

Replaced bushing in R starter housing MZ298 bushing

March 1993

Annual Inspection

Replaced prop governor oil lines and installed steel fittings, c/o AD 90-04-06

Replaced both front crankshaft seals, prop O rings and alternator belts

Replaced air filters both engines

Replaced battery

Replaced Lord engine mounts L engine

Replaced brake pads both main gear Cleveland 66-105 pads

Installed Strike Finder Weather avoidance system and removed StormScope

Installed Northstar M2 Loran/GPS Unit, removed Northstar M1A

IFR certification for altimeter and transponder

April-May 1994

Annual Inspection

Replace Vacuum Pump R Engine

Repaired R exhaust manifold with installation of ball joint modification by A/C Exhaust Systems in W.Va

Replaced diaphragms in both fuel manifold blocks

June 1994

Replaced display in KNS 80



April 1995

Annual Inspection

Replaced R starter Bendix

Repaired Air Filter Box R Engine

Repaired Alternate Air Box L Engine

Replaced both air filters

Replaced ELT battery

Replaced L over-voltage relay

Added two standoff steel brackets for fuel injection lines per AD 93-02-05 (two per engine)

June 1995

IFR certification of altimeter and transponder

August 1995

Heater decay test to comply with AD

April 1996

Annual Inspection

Replaced Luggage Door Strut with new design by Knots 2 U

Complied with SB 518 Lycoming thermostatic valve inspection

Replaced bungee cords on both main landing gear

Replaced cushion material in pilot seat

May 1996

Overhauled Attitude Indicator

Replace existing ELT with installed Ameri-King model 450 in same location using same antenna and cable

March 1997

Replaced battery in remote Northstar GPS unit

April 1997

Annual Inspection

Replaced Vacuum Pump L Engine

Replaced EGT gauge with Alcor dual EGT gauge model 46125

October 1997

Replaced battery with new Gill G-35 Battery

December 1997

Heater decay test to comply with AD

May 1998

Annual Inspection

Re-swung “whiskey” compass

May 1999

Annual Inspection

Rebuilt Nose wheel strut with new O rings, etc.

Replaced R and L Main gear tires with 6.00X6 6 ply rated Custom Goodyear Tires

Installed new brake pads both main gear 66-10 organic Cleveland pads

Installed remote ELT switch in panel

Replaced landing gear bungee cords both main gear

Overhaul L prop due to oil leak

Replaced Vacuum pump L engine

Replace Fuel lines both engines

Replaced L alternator belt

December 1999

Update on Y2K issues with Northstar GPS

February 2000

IFR certification of transponder and static system

June 2000

Heater decay test per AD at Brodie’s Aircraft in Fort Worth

July 1, 2000

Annual Inspection

Replaced Schraeder Valve in nose gear oleo strut

Replaced EGT probe on L engine

Replaced Air Filters both engines WIX 42040

Replaced vacuum regulator filter L engine

Replaced Lord engine mounts R engine

August 1, 2000

Repaired #4 cylinder L engine, new exhaust valve, seat, guides, piston, rings. Note- on return trip from Colorado, it was noted that the compression was low on that cylinder while hand-turning the prop to circulate oil. Exhaust valve stem was noted to be corroded and tolerance was very loose in the guides. All other cylinders had good compression.

August 10, 2000

Installed exhaust extensions on both engines

Replaced internal battery in Navigator M2 Loran

August 20, 2000

Replaced #3 cylinder R engine with re-built chrome cylinder assembly in Louisville, KY after noting engine running rough on landing. The plane was then flown back to Grand Prairie, TX.

August 31, 2000

On disassembling cylinder, it was found that exhaust valve had broken off and had been ingested by cylinder, damaging the piston and cylinder head. Therefore it was elected to replace/repair the remaining cylinders on both engines. All cylinders were removed and inspected. Three cylinders were found to be in good condition and therefore those 3 were put on the L engine after replacing the rings, exhaust valves, seats, and guides.

Replaced all cylinders on R engine with rebuilt chrome cylinder assemblies

Replaced L EGT probe

October 10, 2000

Overhauled both fuel injection controller servos

June 20, 2001

Repaired left engine exhaust manifold with ball joint by A/C Exhaust Systems of Jumping Branch, W.Va.

Weld repair of left engine cowling crack which occurred when exhaust manifold broke and hit inside of cowling.

August 31, 2001

Annual Inspection- packed wheel bearings, serviced brakes, new Janitrol heater AD complied with

Repaired broken field wire to R alternator

Replaced brush block on R alternator

Replaced panel gear indicator lights with press-to-test type lights

September 5, 2002

Annual Inspection

Replaced Gill G-35 Battery

Replaced both bungee cords

Replaced both starter drives

Replaced ELT batteries (6 D cells expire March 2008)

Replaced brake pads, O rings in slave cylinders, both sides

Rebuilt brake master cylinders with new O rings, etc., both sides

Cleaned fuel strainers, replaced gaskets, and O rings in sump drains

Cleaned finger screens in fuel injector servos

Replaced Garlok seal in vacuum pump drive

Adjusted idle mixture in Left engine

Repaired both air filter box covers

Cleaned and gapped spark plugs

Repacked wheel bearings

Placarded Heater controls inoperative to avoid AD inspection (had very mild winter)

Repaired hinge on "clam shell" of right engine cowling.

October 1, 2003

Annual Inspection

Replaced all engine hoses, including flexible fuel and oil hoses.

500 hour inspection of all 4 magnetos, including lubrication, and re-setting internal timing

Flushed and pressure tested left oil cooler due to left engine running hotter than right

Replaced all cowling screws with stainless steel screw kit

Replaced both induction air filters

Replaced all spark plugs on both engines.

Rebuilt right brake master cylinder with new O rings.

Repaired another hinge on "clam shell" of right engine cowling.

Changed oil and replaced oil filters both engines.

Adjusted idle and idle mixture on left fuel injector servo.

Cleaned belly of plane and under wings behind engines with industrial grade detergent.

November 14, 2003

Replaced roll servo in S-Tec autopilot with factory rebuilt servo at Tomlinson Avionics, Gainesville, TX.

November 1, 2004

Annual Inspection

Drained and replaced engine oil and oil filters both engines.

Rebuilit left main gear brake master cylinder.

Replaced O rings in left fuel drain sump.

December 15, 2005

Annual Inspection

Changed oil and replaced oil filters both engines.

Changed bungee cords on landing gear.

Inserted spacer washers between engine and lower Lord mounts on right engine to raise engine

slightly. Recommended by Maurice Taylor to raise engine even after new Lord mounts will

not raise engine to proper position in cowling due to age of engine mounts, etc.

Replaced Garlock seal and both gaskets on vacuum pump on right engine.

Replaced no-blow gasket on left engine #2 cylinder.

Replaced O rings in both main gear slave cylinders and rebuilt left master cylinder.

Replaced brake pads on both main gear.

November 1, 2006

Annual Inspection

Due to a rough running right engine, found #4 exhaust valve stuck. Subsequently checked all valve guide

clearances and reamed three exhaust valve guides.

Replaced landing gear side brace stud (AN26-25) and main side brace stud bushing on left main gear.

Replaced both main gear tires and tubes.

Cleaned battery box and painted inside with acid resistant paint.

Removed prop governor on left engine and replaced with overhauled unit from Quality A/C Accessory in Tulsa.

Installed new cabin door hinge pins.

Installed new lug on P lead to right magneto on right engine.

Changed oil and replaced oil filters both engines.

Cleaned belly of plane and under wings behind engines with industrial grade detergent.

Replaced one spark plug on #4 cylinder on right engine which failed pressure testing.

Feb 12, 2007

Static and Transponder Check for IFR flight

March 31, 2007 Removed #3 cylinder on Right Engine for overhaul due to low compression

May 12, 2008

Annual Inspection

Changed oil and replaced oil filters both engines.

Installed new lug on right magneto of Right Engine.

Replaced D cell batteries in ELT. Next replacement due 2011.

March 12, 2010

Annual Inspection

Performed Landing Gear AD 77-13-21 totally disassembled landing gear, measured all bolts and bushings, drag link ends and bearing rod ends. Installed new AN 178-40 and AN 6-26 bolts on left side of nose gear linkage. Fabricated new steering arm roller bushings. Installed new bungees on both main gear. Performed retraction load test with torque tube adaptor and torque wrench. Found less than 95 pounds required which is well within tolerance. Greased all Zirc fittings on landing gear after reassembly. Inserted new hinge pins in main landing gear doors. Stop-drilled three small cracks in left main gear door near hinge. Fabricated and installed a 3 nut plate aluminum strip on each side to replace the three #10 nuts which attach the main gear doors to the wing. Had both nose gear doors repainted at GLO A/C Paint at Northwest Regional Airport. Performed AD 97-01-01-R1: removed both main gear side brace studs and had both magnaflux and dye tested for cracks at Apex Lab in Addison, TX. No cracks found. Repaired and reinstalled nose gear blanket.

Repainted battery box with acid resistant paint on inside and flat black enamel on the outside. Stripped and treated nose section fore of the wheel well with Alodine and painted with primer. Replaced all battery drain hoses. Removed, repaired, and reinstalled battery drain assy. Installed new Gill G-35 battery.

Installed new Rapco brake disks on both main gear, P/N RA 164-02201. Replaced brake pads and both flexible brake lines. Bled brakes.

Replaced landing gear wiring harnesses and switches. Weight and balance not affected.

Rebuilt both fuel strainers using new gaskets, O-rings, and drain hoses.

Per AD 96-09-10, on both engines, removed all accessories and rear accessory case and replaced oil pump housing assy P/N 00SL78528, gear kit P/N 00AEL18109-S, and oil pump drive shaft P/N 00AEL61174. Reinstalled all accessories with new gaskets.. Compression check Right engine: (1) 78/80 (2) 75/80 (3) 79/80 (4) 78/80. Left engine: check (1) 79/80 (2) 77/80 (3) 76/80 (4) 78/80. Replaced engine driven fuel pump on left engine P/N LW 15473 and gasket. Timing reset to 25 degrees BTC on both mags on both engines.

Heater reconnected and determined to be in airworthy condition. Performed Heater Pressure Decay Test per AD 04-21-05. Heater passed test.

ELT battery exp date 2011.