Cessna 172N Skyhawk

The 172N is a calculated value play. Two paths to consider:

Path A (lowest cost): Buy an original H2AD with mid-time engine, clean cam/lifter inspection, documented TCP use, and ride it carefully to TBO. Plan on a Lycoming factory reman or Airplains conversion at next overhaul. Total ownership cost is competitive with a 172M of similar avionics. Budget $50K-$65K acquisition.

Path B (best value): Buy an Airplains D2J-converted 172N. You get a 172P-equivalent airframe at a 172N price, with documented SB compliance, dual independent magnetos, and 100 lbs additional gross weight. Budget $70K-$90K acquisition.

What you should not do is buy an unconverted, run-out H2AD 172N without budget for either an overhaul or a conversion. The math does not work -- and the H2AD's metallurgy issues are not entirely solved even with all SB compliance.

See also: cessna-172-mid, cessna-172p, cessna-172-modern, cessna-r172k-hawk-xp

The 28V electrical system is the often-overlooked variant difference. Some older 14V avionics will not work in a 172N without converters, and some modern panel installs require ordering the 28V variants of LRUs.

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The 172N is identical in role to other mid-era 172s once you account for the H2AD risk:

• Flight training: 8/10 -- still an excellent platform, but the H2AD makes commercial school operators wary. Many flight schools have shifted to D2J-converted 172Ns or skipped to 172P/172R.
• First airplane: 9/10 if you find a D2J-converted example; 7/10 for an original H2AD with clean inspection history
• IFR platform: 8/10 -- 28V electrical actually advantages modern glass panel retrofits
• Cross-country: 6/10 -- 122 KTAS cruise, 440 nm standard fuel range (570+ nm with long-range tanks)
• Backcountry: 2/10 -- nosewheel, low ground clearance, marginal climb at high DA

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The 172N's 28V electrical system has practical implications for panel retrofits:

• Older 14V LRUs (some legacy Bendix/King radios, some KAP 100/140 autopilot variants) require 28V→14V step-down converters or 28V LRU variants
• Modern Garmin avionics (GTN 650/750, G5, GFC 500, GTX 345) are typically available in 28V variants out of the box
• The 60-amp alternator is adequate for typical modern panels but runs near capacity with a fully-loaded glass panel + LED lighting + transponder + autopilot. Watch alternator condition at pre-buy.

A typical "modern panel" 172N upgrade (GTN 650Xi + dual G5 + GFC 500 autopilot + GTX 345) runs $30K-$45K installed in 2026 -- and the panel may be worth more than the airframe itself on the resale market.

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Typical 2026 market range

• Run-out engine, original H2AD, basic panel: $40K-$55K
• Mid-time H2AD, well-maintained, basic IFR: $55K-$70K
• D2J converted, mid-to-low time, modern panel: $70K-$95K
• Pristine 172N with 180 HP conversion + glass panel: $95K-$120K

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The O-320-H2AD Engine Problem (CRITICAL)

[!warning] If you remember only one thing about the 172N, remember this: the original O-320-H2AD engine has a long history of cam, lifter, valve, and magneto problems. Any 172N purchase must hinge on knowing exactly which engine is installed today.

What Lycoming changed

The H2AD was a "76 series" Lycoming with three meaningful departures from the proven O-320-E2D:

1. Higher compression (8.5:1 vs 7.0:1) -- required for the 160 HP rating
2. Single Slick dual magneto instead of two independent magnetos -- a meaningful loss of redundancy
3. Wide-deck cylinders and revised valve train geometry

What went wrong

Within months of introduction, owners and shops began reporting:

• Cam and lifter spalling -- the H2AD's hydraulic lifters and camshaft lobes shed metal flakes (some engines as early as 250 hours TBO), contaminating the oil system, requiring teardown
• Stuck exhaust valves -- related to lubrication and metallurgy
• Premature cylinder wear on the wide-deck cylinders
• Single magneto vulnerability -- a failed Slick dual mag = total ignition loss in flight, unlike the redundant two-mag setup on the E2D

What Lycoming did about it

Through the early 1980s, Lycoming issued progressive service bulletins under the "Operation Blue Streak" program:

• Larger-diameter tappets with wider cam lobes
• The "T" modification (1980+) with further enlarged tappets and improved top-end lubrication
• Engines that have received the final fix carry serial numbers ending in 76A (vs the original L-XXXX-76 designation)

AD 80-04-03 required replacement of upper exhaust valve spring seats and exhaust hydraulic lifters on affected serial numbers within 50 hours.

The FAA also mandated use of TCP (tricresyl phosphate) oil additive in all 76-series engines. Owners who religiously used TCP-additized oil report dramatically fewer valve sticking events.

What this means for a buyer in 2026

[!tip] A 172N with documented Airplains STC SA2714CE conversion to the O-320-D2J is functionally a 172P at a $10K-$20K discount. This is one of the best value plays in fixed-gear GA -- you get the reliable D2J engine, dual independent magnetos, and 100 lbs additional gross weight.

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Airworthiness Directives (172N-specific)

Beyond the recurring 172-family ADs (seat rails, wing spar inspection, etc.), the 172N carries:

Pre-buy must verify all H2AD-era ADs are documented as complied with, and that any "T" modification or 76A re-serial work is reflected in the engine logs.

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Pre-Buy Inspection Priorities

A 172N pre-buy is a 172 pre-buy plus a long list of engine-specific checks:

1. Engine identification and SB compliance
   • Check engine dataplate serial number -- does it end in 76A?
   • Pull engine logs and verify all Lycoming SB compliance (especially Operation Blue Streak service bulletins)
   • Verify AD 80-04-03 was complied with on the upper exhaust valve seats and lifters
2. Cam and lifter condition
   • Borescope inspection or cylinder pull on cylinder #1 (cam lobe most accessible)
   • Oil filter cut + screen inspection for any metal particles
   • Recent oil analysis trend -- iron and aluminum levels are leading indicators
3. Magneto condition
   • Slick single dual magneto: inspect impulse coupling, check timing
   • Verify all recurring inspection AD compliance
   • Consider whether SureFly or E-MAG conversion is a near-term need
4. TCP additive use
   • Ask owner directly: have you been using TCP-additized oil (Aeroshell W100 Plus or equivalent)? Inconsistent TCP use is a yellow flag for valve sticking history.
5. Corrosion (any 172, but especially 45+ year old airframes)
   • Wing spar carry-through structure
   • Belly skins, battery box, tailcone
   • Fuel tank sealant and surrounding skin
6. Logbooks
   • Complete and continuous back to manufacture
   • Engine conversion documentation (if D2J or O-360 STC applied) -- must include FAA 337 form
7. Seat rails (recurring AD compliance)
8. Fuel system -- tank integrity, selector valve condition

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