Engine — Mechanical
ATA Chapter 71 — N720AK Systems Reference
Overview
N720AK is powered by a Lycoming IO-540 series engine, fuel-injected and normally aspirated, rated at 260 HP at 2700 RPM. This page covers the mechanical aspects of the engine — oil system, cooling, baffling, exhaust, and mounts. For the electronic engine management (ignition and fuel injection), see EFII System32.
Components
| Component | Part Number | Supplier | Notes |
|---|---|---|---|
| Engine | YIO-540-D4A5 | Lycoming | S/N EL-36315-48E, 260 HP at 2700 RPM |
| Engine mount | Steel tube | ||
| Oil drain plug | Magnetic Oil Drain Super Plug | Aircraft Spruce (05-12373) | 1/2“ NPT, Alnico magnet (1-1/32“ long), CAD plated, safety wire drilled. Experimental — verify sump/pickup clearance before install |
| Oil quick drain | P5000 | Saf-Air | Quick drain valve on engine oil sump |
| Oil filter | |||
| Oil cooler | |||
| Oil separator | ASA | Antisplat Aero | Installed with install kit — manual, installation guide |
| Crankcase vacuum valve | Complete kit | Antisplat Aero | Crankcase vacuum system — manual |
| Valve covers | Billet | SDS/Lycoming | O-ring #160 Viton 75 duro, torque 75–85 in-lbs — specs |
| Filtered air box | FAB-540 | Van’s Aircraft | VFR only, 1/4-20 mounts tab-locked or safety wired — installation guide. Modified alt air door — see Alt Air Door below |
| Engine mount covers | Aerosport Products | Carbon fiber covers, installed | |
| Preheat — engine | Reiff XP | Reiff Preheat Systems | Cylinder band heaters on all 6 cylinders |
| Preheat — oil sump | Reiff HotStrip | Reiff Preheat Systems | Oil sump heater; plug is inside the oil door |
| Spark plug adapters | SPA-6 | flyEFII | 18mm→14mm thread adapters, naval brass, 6 installed. Allows automotive spark plugs with EFII ignition |
| Spark plugs | NGK | Automotive 14mm plugs in EFII SPA-6 adapters |
Engine: Lycoming YIO-540-D4A5, S/N EL-36315-48E, firing order 1-4-5-2-3-6, spark plug gap 0.016“–0.022“.
How It Works
Oil System
Oil separator evacuation tube: check every oil change or 50 hrs for coking/buildup. Hose: 3/4“ (6-cyl). Pop-off valve 0.5 PSI. Oil return #4 AN. See Anti-Splat installation guide.
Cooling
Exhaust
Ball joint hardware: AN3 bolt, AN960C10 washer, MS21042-3 nut (3 places). Springs face forward toward prop. Install nut with 2–3 threads showing; do not bottom spring on bolt. See Goldberg ball joint diagram.
Exhaust hanging kit: cable assembly, anti-sway assembly, support strap bends (30° up LH, 20° down RH). See exhaust hanging kit sketch.
Alt Air Door
N720AK uses a modified alternate air door on the FAB-540 filtered air box, based on this design. Unlike the stock Van’s design (which only allows opening), this modification uses an aluminum sliding gate mechanism actuated by cable from inside the cabin, allowing the pilot to both open and close the alternate air door in flight.
Preheat System
N720AK has a Reiff XP preheat system with cylinder band heaters on all 6 cylinders, plus a Reiff HotStrip oil sump heater. The power plug is located inside the oil access door.
Engine Mount
Steel tube engine mount.
Inspection & Maintenance
Lycoming SB 634 — Cylinder Retirement
Lycoming Mandatory Service Bulletin 634 (October 2018) requires retirement of certain parallel valve cylinder and head assemblies shipped between Sep 2013 and Apr 2015, due to compression loss from head casting leakage. N720AK cylinder serial numbers were checked against Table 1 — none are listed, aircraft is not affected.
Billet Valve Covers
Replacement O-rings for billet covers: COTS Viton O-ring #160, 75 durometer. Torque: 75–85 in-lbs. Lubricate O-ring and groove before install. See SDS billet valve cover specs.
Lycoming Accessory Case Oil System
Reference: VAF thread — Lycoming accessory case oil schematic by Dan H
References
- Oil Separator / Vacuum System
- Anti-Splat Aero Oil Separator Installation Guide — evacuation tube check interval, hose sizing, pop-off valve spec
- Lycoming IO-540 Operator’s Manual (60297-10)
- Goldberg Exhaust Ball Joint Diagram (2014) — AN3/AN960C10/MS21042-3 hardware, spring orientation
- Exhaust Hanging Kit Sketch — cable assembly, anti-sway, support strap bend angles
- SDS/Lycoming Billet Valve Cover Specs — O-ring #160 Viton, torque 75–85 in-lbs
- Van’s FAB-540 Filtered Air Box Installation — VFR only, carb heat door VA-130-H
- MilSpec 4000 Series Cowling Fasteners Installation — Diamondhead quarter-turn, TSO-C-148, spacing 3.5–4.25“
- Skybolt VLoc Diamondhead Cowling Installation (Rev 22) — SK-OSG1-8 high shear grommet