Engine Paint & Coatings

From Practical Street Builds to Aerospace-Inspired Preservation

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Why “Paint” Is an Oversimplification

In engineering terms, there’s a critical distinction between decorative or protective paint systems, chemical conversion coatings, and thin-film functional coatings. Understanding this distinction is essential when discussing magnesium case preservation in air-cooled VW and Porsche engines.

Volkswagen never applied any of these at the factory—not because they were harmful, but because they were unnecessary for the intended service life. Today, we apply coatings as preservation tools, and the appropriate technology depends entirely on the engine tier and intended lifespan.

Street-Focused Builds: Thin Protective Paint Systems

For engines that will be driven regularly, maintained by the owner, and built with cost consciousness in mind, the engineering goal is straightforward: slow surface oxidation without altering thermal behavior, while keeping labor and materials reasonable.

Appropriate Paint Technology

At this level, thin, heat-tolerant organic coatings are appropriate—not structural or insulating coatings. 

The chemical families that work well include:

• Silicone-modified alkyds

• Ceramic-reinforced engine enamels

• Inorganic resin high-temperature paints

These coatings cure thin, resist oil and fuel, withstand normal engine case temperatures, and crucially, do not create a thermal barrier when applied lightly.

What to Avoid: 

Certain products are incompatible with magnesium or inappropriate for this application:

• Acid-etch primers

• Zinc-rich or sacrificial primers

• Heavy epoxy chassis paints

• Powder coating

• Rubberized or textured coatings

These products either chemically attack magnesium & sometimes Aluminum, trap heat due to thickness, or fail under repeated heat cycling.

Application Characteristics

The key is restraint:

• One light primer pass (adhesion only)

• One to two light topcoats maximum

• Total dry film thickness kept extremely low

• Fully cured before assembly

Engineering Reality:

At this thickness, the coating’s thermal resistance is insignificant compared to oil temperature variation or head temperature changes. Street engines fail from tuning errors and oil control issues, not from case surface conditions.

This approach protects against corrosion, keeps costs realistic, preserves serviceability, and avoids unwarranted performance claims

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Premium, Platinum & Heritage Engine Builds at VF4. (Great example)

Magnesium Conversion and Aerospace-Influenced Coatings

For engines intended to survive decades, be rebuilt multiple times, retain structural integrity, and preserve irreplaceable castings, a different approach is warranted—one that shifts from “paint” to surface chemistry.

Understanding Conversion Coatings

A conversion coating chemically alters the surface of magnesium, forming a stable, bonded layer that:

• Inhibits oxidation

• Improves paint adhesion (if topcoating is used)

• Does not build measurable thickness

• Does not insulate

This technology comes from aerospace, aircraft piston engines, and military magnesium components.

Common Conversion Chemistries

The industry has established several proven systems:

Chromate Conversion Coatings

• Historically used in aircraft engines and gearboxes

• Extremely effective corrosion protection

• Environmentally restricted today

Modern Chromate-Free Systems

• Zirconium-based

• Phosphate-based

• Rare-earth metal systems

These form a microscopic protective layer, measured in microns—not mils.

Learning from Aircraft Engine Practice

Air-cooled aircraft engines (Lycoming, Continental, etc.) operate at sustained high loads with magnesium and aluminum components in harsh environments.

They rely heavily on:

• Conversion coatings

• Controlled thin-film finishes

• Chemical compatibility over appearance

They do not use thick paint for protection.

High-End Application Process

For High End Aircooled Engine Builds ( premium , platinum & heritage builds at VF4) , the appropriate process includes:

• Extensive mechanical cleaning

• Magnesium-safe chemical pretreatment

• Conversion coating application

• Optional ultra-thin topcoat (where appropriate)

This process stabilizes the Magnesium & Aluminum dramatically slows oxidation, preserves thread integrity, improves long-term machinability, and does not alter thermal behavior.

Why Not Apply This to Every Build?

Because it is labor-intensive, expensive, and unnecessary for many street engines. Just as not every build needs a forged crankshaft or dry sump system, not every case requires aerospace-level preservation.

Engineering Summary

The evidence supports several key conclusions:

• Thin paint systems are appropriate for street builds when applied correctly

• Conversion coatings offer superior long-term magnesium & aluminum's preservation

• Aircraft practice confirms thin, chemical protection—not insulation

• The engine case is not a primary heat rejection surface

• Coating thickness matters more than coating type

Core Philosophy: 

Preserve the casting. Respect the engineering. Match the process to the purpose.

Every coating decision should be made with longevity, physics, and honesty as the guiding principles. 

The air-cooled community benefits when we distinguish between what’s necessary, what’s optimal, and what’s marketing.

Dale Hansen

Owner / Sr. Engine Builder

  A Technical Rebuttal to the "Don't Paint Magnesium" Myth

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EXECUTIVE SUMMARY

The vintage VW/Porsche air-cooled community has perpetuated a dangerous myth: "Never paint magnesium engine cases - it traps heat and prevents the engine from breathing."

This statement is engineering nonsense, contradicted by 80+ years of aircraft engine manufacturing, FAA certification standards, and basic thermal physics.

The Truth: Aircraft engine overhaul facilities - the gold standard for air-cooled engine rebuilding - ALWAYS coat magnesium cases with multi-layer protective systems. These engines operate under far more demanding conditions than any VW Type 1, yet suffer zero heat-related issues from proper coating.

This document presents the engineering case for coating vintage flat-4 magnesium cases using aircraft industry best practices.

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PART 1: THE AIRCRAFT ENGINE PARALLEL

Air-Cooled Engines: The Common DNA

Your VW Type 1 and a Lycoming O-320 share fundamental design principles:

Common Elements:

• Horizontally-opposed cylinder configuration (boxer/flat design)

• Air-cooled via forced convection (fan-driven airflow)

• Magnesium alloy crankcases for weight reduction

• Aluminum cylinders with cooling fins

• Splash/pressure lubrication systems

• Direct-drive or reduction-geared output

The Critical Difference:

• VW Type 1: Intermittent duty, STOCK 60 HP up to HP 200 HP, ~280-350°F case temps

• Lycoming O-320: Continuous duty, 150-160 HP, ~350-450°F case temps

If coating causes heat retention problems, aircraft engines running 100°F HOTTER should be catastrophically affected. They are not.

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The 2,000-Hour TBO: What It Really Means

Aircraft engines are certified for Time Between Overhaul (TBO) intervals:

• Lycoming O-320: 2,000 hours TBO

• Continental O-200: 1,800 hours TBO

• Rotax 912: 2,000 hours TBO

Translating to automotive terms:

• 2,000 flight hours at cruise (120-150 mph average) = 240,000-300,000 miles

• But aircraft engines run at 65-75% continuous power (imagine highway driving at 4,500 RPM constantly)

• Equivalent stress = 400,000+ "hard" automotive miles

Your VW typically sees rebuild at 60,000-100,000 mixed-duty miles.

Aircraft engines operate under far more severe thermal stress, yet maintain reliability WITH coated magnesium cases.

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PART 2: AIRCRAFT ENGINE OVERHAUL - THE PROCESS

What Happens at 2,000 Hours

When a Lycoming or Continental reaches TBO, it undergoes complete teardown and rebuild. Current costs: $27,000-$70,000 (compared to $2,000-$5,000 for VW).

Why so expensive? The process is exhaustive:

1. Non-Destructive Testing (NDT) - MANDATORY

Every critical steel component undergoes:

Magnaflux Inspection (Magnetic Particle Inspection):

• Crankshaft is magnetized using high-amperage electrical current

• Ferromagnetic particles applied to surface

• Cracks as small as 0.001" become visible under UV light

• Can detect subsurface defects invisible to human eye

• Equipment cost: $15,000-$50,000

• Technician requirement: FAA Level II or III NDT certification

Liquid Fluorescent Penetrant (for aluminum/magnesium):

• Magnesium crankcase halves are cleaned and inspected

• Fluorescent dye penetrates surface cracks

• UV light reveals defects

• Rejection criteria: ANY crack = case replacement ($8,000-$15,000)

Parts tested:

• Crankshaft (most critical)

• Camshaft

• Connecting rods

• Crankcase halves

• All gears and shafts

• Rocker arms

VW / PORSCHE average builder equivalent: Visual inspection with flashlight, "looks good to me"

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2. Dimensional Precision - Aerospace Standards

Aircraft overhaul shops measure EVERYTHING to tolerances that would shock most VW builders:

Crankshaft main journals:

• Must be round within 0.0005" (half a thousandth)

• Surface finish: 10-16 microinch Ra

• Taper: less than 0.0002" per inch

• Measured with precision micrometers (±0.0001" accuracy)

Connecting rods:

• Length tolerance: ±0.005" maximum variation in set

• Weight matched within 2 grams per set

• Straightness: 0.002" maximum deviation

• Big-end bore: ±0.0005"

Camshaft lobes:

• Lift measured to 0.001"

• Lobe taper measured and compared to service limits

• Heat-treated surface depth verified (often requires NEW cam vs. regrind)

Why this matters: These tolerances ensure perfect balance, minimal vibration, and maximum component life under continuous high-power operation.

VW / PORSCHE average builder equivalent: "Measures within a few thousandths, send it"

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3. Mandatory Parts Replacement - No Exceptions

FAA Service Bulletins require specific parts be replaced regardless of condition:

Always replaced:

• All connecting rod bolts and nuts (fatigue life limit)

• All case through-bolts

• All exhaust valves and guides

• Hydraulic tappets/lifters (wear limit = zero)

• All bearings (main, rod, cam)

• Complete gasket and seal kit

• All hoses and flexible lines

• Spark plugs and ignition harness

Magnetos: Overhauled to zero-time or replaced Cost for mag overhaul: $800-$1,500 EACH (aircraft has two)

Why no reuse? Fatigue life, liability, and zero-tolerance for failure. One broken connecting rod bolt at 8,000 feet = engine failure = potential fatalities.

VW / PORSCHE average builder equivalent: "Bolts look OK, I'll reuse them"

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4. Crankcase Preparation - The Foundation

Magnesium crankcases receive exhaustive treatment:

Inspection sequence:

1. Complete disassembly and cleaning

2. Liquid Fluorescent Penetrant inspection (finds cracks)

3. Ultrasonic testing (finds hidden voids/defects)

4. Dimensional checking of all bearing saddle bores

5. Threaded insert inspection and replacement

6. Case face milling for perfect flatness (within 0.002")

If cracks found: Case is REJECTED and scrapped. No repairs allowed on structural magnesium.

Align boring: If bearing saddles are out of spec, case halves are align-bored together (expensive machining operation requiring specialized fixtures).

Case face preparation:

• Mating surfaces must be dead-flat for oil-tight seal

• Surface finish: 32-63 microinch Ra

• No scratches, gouges, or irregularities allowed

VW / PORSCHE average builder equivalent: Wire wheel, ScotchBrite pad, maybe a file on the high spots

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5. Test Cell Validation - Proving Airworthiness

After assembly, every aircraft engine undergoes 3-5 hours of test cell operation:

Test protocol:

• Break-in at varying RPM (30 minutes)

• Full-power run at 100% rated output

• Oil pressure verification at all RPM ranges

• Compression testing on all cylinders

• Ignition timing and magneto drop testing

• Leak testing (oil, fuel, intake, exhaust)

• Temperature stabilization verification

Test cell equipment: $50,000-$150,000 investment Fuel consumed: 15-25 gallons at $6-8/gallon Technician time: 8-12 hours (setup, run, teardown, analysis)

Data recorded:

• Oil pressure vs. RPM curves

• Cylinder head temperatures (all cylinders)

• Exhaust gas temperatures

• Vibration analysis

• Power output verification

VW / PORSCHE average builder equivalent: "Started it in the driveway, sounds good!"

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PART 3: THE COATING STANDARD

Aircraft Industry Practice: ALWAYS Coat Magnesium

After $30,000-$60,000 of precision overhaul, aircraft shops don't leave expensive magnesium cases bare and unprotected.

Standard aircraft engine coating system:

1. Chemical cleaning: Solvent degreasing, alkaline wash

2. Conversion coating: Alodine/Iridite treatment (chromate or non-chromate) 

o Creates molecular bond with magnesium

o Gold/iridescent protective layer

o Corrosion resistance even if topcoat chips

3. Epoxy primer: 2-3 mils thick 

o Excellent adhesion to conversion coating

o Fuel, oil, and chemical resistant

4. High-temperature topcoat: 2-3 mils thick 

o Lycoming grey, Continental gold, or custom colors

o Heat-resistant to 500°F+

o UV and weathering resistant

Total coating thickness: 4-6 mils (0.004-0.006 inches)

Why coat?

• Corrosion protection (magnesium corrodes aggressively)

• Fuel/oil resistance (prevents surface degradation)

• Professional appearance (customer confidence)

• Case longevity (protection = longer service life)

What about heat retention? Aircraft engineers aren't concerned because the physics prove it's a non-issue.

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4. Crankcase Preparation - The Foundation

Magnesium crankcases receive exhaustive treatment:

Inspection sequence:

1. Complete disassembly and cleaning

2. Liquid Fluorescent Penetrant inspection (finds cracks)

3. Ultrasonic testing (finds hidden voids/defects)

4. Dimensional checking of all bearing saddle bores

5. Threaded insert inspection and replacement

6. Case face milling for perfect flatness (within 0.002")

If cracks found: Case is REJECTED and scrapped. No repairs allowed on structural magnesium.

Align boring: If bearing saddles are out of spec, case halves are align-bored together (expensive machining operation requiring specialized fixtures).

Case face preparation:

• Mating surfaces must be dead-flat for oil-tight seal

• Surface finish: 32-63 microinch Ra

• No scratches, gouges, or irregularities allowed

VW / PORSCHE average builder equivalent: Wire wheel, ScotchBrite pad, maybe a file on the high spots

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5. Test Cell Validation - Proving Airworthiness

After assembly, every aircraft engine undergoes 3-5 hours of test cell operation:

Test protocol:

• Break-in at varying RPM (30 minutes)

• Full-power run at 100% rated output

• Oil pressure verification at all RPM ranges

• Compression testing on all cylinders

• Ignition timing and magneto drop testing

• Leak testing (oil, fuel, intake, exhaust)

• Temperature stabilization verification

Test cell equipment: $50,000-$150,000 investment Fuel consumed: 15-25 gallons at $6-8/gallon Technician time: 8-12 hours (setup, run, teardown, analysis)

Data recorded:

• Oil pressure vs. RPM curves

• Cylinder head temperatures (all cylinders)

• Exhaust gas temperatures

• Vibration analysis

• Power output verification

VW / PORSCHE average builder equivalent: "Broken-in on the test stand and started it in the driveway, sounds good!"

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PART 3: THE COATING STANDARD

Aircraft Industry Practice: ALWAYS Coat Magnesium

After $30,000-$60,000 of precision overhaul, aircraft shops don't leave expensive magnesium cases bare and unprotected.

Standard aircraft engine coating system:

1. Chemical cleaning: Solvent degreasing, alkaline wash

2. Conversion coating: Alodine/Iridite treatment (chromate or non-chromate) 

o Creates molecular bond with magnesium

o Gold/iridescent protective layer

o Corrosion resistance even if topcoat chips

3. Epoxy primer: 2-3 mils thick 

o Excellent adhesion to conversion coating

o Fuel, oil, and chemical resistant

4. High-temperature topcoat: 2-3 mils thick 

o Lycoming grey, Continental gold, or custom colors

o Heat-resistant to 500°F+

o UV and weathering resistant

Total coating thickness: 4-6 mils (0.004-0.006 inches)

Why coat?

• Corrosion protection (magnesium corrodes aggressively)

• Fuel/oil resistance (prevents surface degradation)

• Professional appearance (customer confidence)

• Case longevity (protection = longer service life)

What about heat retention? Aircraft engineers aren't concerned because physics prove it's a non-issue.

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PART 4: THE PHYSICS OF HEAT TRANSFER

Why Thin Coatings Don't Trap Heat

Air-cooled engine heat dissipation occurs through three mechanisms:

1. Convection (90% of cooling):

• Moving air over finned surfaces

• Heat transfer rate = h × A × ΔT

• Where: h = convection coefficient, A = surface area, ΔT = temperature difference

• Paint thickness effect on convection: ZERO (airflow pattern unchanged)

2. Radiation (10% of cooling):

• Infrared radiation from hot surfaces

• Heat transfer = ε × σ × A × T⁴

• Where: ε = emissivity, σ = Stefan-Boltzmann constant

• Paint emissivity (0.85-0.95) actually IMPROVES radiation vs. bare magnesium (0.55-0.75)

3. Conduction through coating (negligible):

• Thermal resistance = thickness / conductivity

• Magnesium conductivity: 156 W/(m·K)

• Paint conductivity: 0.2-0.5 W/(m·K)

• At 5 mils (0.127mm) thickness: thermal resistance = 0.00025-0.00064 K/W

• Temperature drop across coating: 0.5-1.0°F maximum

This is within normal engine temperature variation from ambient conditions.

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The Numbers Don't Lie

Scenario: VW Type 1 case at operating temperature

• Bare magnesium case temperature: 320°F

• Same case with 5 mils coating: 320.7°F

• Temperature difference: 0.7°F

Measurement reality:

• IR temperature gun accuracy: ±2-3°F

• Normal temp variation from airflow: ±5-10°F

• Temp variation from load changes: ±15-25°F

The coating effect is UNMEASURABLE in real-world conditions.

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Aircraft Engine Validation

Lycoming and Continental engines prove this in the field:

• Operating temperature: 350-450°F case temps (70-100°F HOTTER than VW)

• Duty cycle: Continuous high-power operation

• Coating: 100% of factory-overhauled engines are coated

• Failure rate from coating: ZERO documented cases in 80+ years

If coating caused overheating:

• FAA would prohibit it (they regulate everything aggressively)

• Insurance companies would refuse coverage (liability-driven)

• Engine manufacturers would eliminate it (cost reduction opportunity)

None of these have happened because the physics prove coating is benign.

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PART 5: WHAT ACTUALLY CAUSES VW OVERHEATING

The "don't paint magnesium" myth persists because people correlate coincidental events:

Common scenario:

1. Builder paints case with thick, wrong paint (20+ mils of rattle-can enamel)

2. Builder also has missing cooling tin, wrong fan, or lean carburetion

3. Engine overheats during operation

4. Builder blames the paint (visible change, easy scapegoat)

5. Myth spreads: "Never paint magnesium!"

Actual causes of VW overheating (ranked by frequency):

1. Airflow Problems (75% of cases)

• Missing or damaged fan shroud (CRITICAL component)

• Bellows or cooling tin missing/disconnected

• Wrong fan (upright vs. Porsche 914 vs. doghouse)

• Oil cooler blocked or undersized

• Debris/wasp nests in cooling fins

• Thermostat (cooling flaps) stuck closed

2. Combustion/Tuning Issues (15%)

• Lean fuel mixture (runs 50-100°F hot)

• Over-advanced ignition timing

• Insufficient octane for compression ratio

• Detonation/pre-ignition events

3. Mechanical Problems (8%)

• Inadequate oil flow (worn pump, restricted passages)

• Wrong oil viscosity for conditions

• Bearing clearances too tight (friction = heat)

• Excessive blow-by from worn rings

4. Paint Thickness (2%)

• Only if absurdly thick (20+ mils)

• Only if blocking cooling fin gaps

• Only if restricting airflow passages

Thin, proper coating (4-6 mils): 0% contribution to overheating

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The Cooling System Reality

VW Type 1 cooling is MARGINAL by design:

Why VW engines run hot:

• Cost-optimized design (cheaper = less robust)

• Minimal fin area compared to aircraft engines

• Fan-driven cooling (belt-driven losses)

• Tin work often poorly fitted from factory

• Operating conditions (stop-and-go traffic = low airflow)

Why aircraft engines don't overheat:

• Generous fin area (more surface for heat transfer)

• Direct-drive or geared cooling fans (no belt losses)

• Constant high airflow (airplane always moving)

• Precision cooling baffle systems

• Temperature monitoring (CHT/EGT gauges standard)

The difference isn't coating - it's engineering budget and safety margins.

PART 6: THE CORRECT COATING SYSTEM FOR VW

Aircraft-Inspired Process for Vintage Flat-4

Apply aviation best practices to your VW/Porsche magnesium case:

Step 1: Surface Preparation (CRITICAL)

• Degrease thoroughly with acetone or MEK

• Remove any corrosion with ScotchBrite (not wire wheel)

• Clean again with final solvent wipe

• Allow to dry completely

Step 2: Adhesion Promotion

• Product: U-POL Adhesion Promoter (Clear, Multi-Surface)

• Application: One light, even coat

• Thickness: <1 mil

• Flash time: 5-10 minutes

• Purpose: Creates chemical bond between magnesium and topcoat

Step 3: Heat-Resistant Topcoat

• Product: VHT Engine Enamel (Satin Black or Metallic)

• Chemistry: Urethane + ceramic resins

• Temperature rating: 550°F continuous

• Application: Two thin coats (3-5 mils total)

• Flash time between coats: 10-15 minutes

• Cure: Air dry 24 hours, then heat cure at operating temp

Total system thickness: 4-6 mils

This mirrors aircraft practice at 1/10th the cost.

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Why This System Works

U-POL Adhesion Promoter:

• Multi-surface formula (aluminum, galvanized steel, magnesium)

• Creates bonding interface (prevents delamination)

• Clear formulation (won't affect topcoat color)

• Fast-drying (efficient workflow)

VHT Engine Enamel:

• High-temperature ceramic formulation

• Chemical resistant (fuel, oil, cleaners)

• Thin film build (2-3 mils per coat)

• Excellent adhesion to prepared surfaces

• Available in multiple colors

Combined result:

• Excellent corrosion protection

• Zero impact on heat dissipation

• Professional appearance

• Long service life

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Application Best Practices

Temperature and humidity:

• Apply at 65-85°F ambient

• Relative humidity <70%

• Avoid direct sunlight during application

Spray technique:

• Light, overlapping passes

• 8-12 inches from surface

• Multiple thin coats > one thick coat

• Avoid runs and sags

Curing protocol:

• Air dry 24 hours minimum

• Install engine and run through heat cycles

• Operating temperature fully cures coating

• Coating reaches maximum hardness after 3-5 heat cycles

Areas to avoid coating:

• Machined mating surfaces (case faces)

• Cylinder sealing surfaces

• Threaded holes (can be carefully masked)

• Dowel pin holes

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PART 7: SYSTEMS ENGINEERING & PDCA

Continuous Improvement Methodology

Apply aircraft-industry quality management to your builds:

PLAN:

• Define success metrics (corrosion resistance, adhesion, temperature)

• Establish baseline (document current practices)

• Research improvements (aviation standards, new materials)

• Design test protocol

DO:

• Implement coating system on test piece or next build

• Document process with photos and notes

• Measure coating thickness with mil gauge

• Record application conditions

CHECK:

• Monitor engine temperatures (IR gun measurements)

• Inspect coating after break-in period (adhesion, color retention)

• Evaluate after 500, 1000, 2000 miles

• Compare to previous builds or uncoated reference

ACT:

• Refine process based on results

• Standardize successful procedures

• Share findings with community

• Continue iteration

Measurement tools:

• Coating thickness gauge: $50-$200 (non-destructive measurement)

• IR temperature gun: $20-$100 (real-time temp monitoring)

• Digital calipers: $20-$50 (dimensional verification)

• Photo documentation: Free (record condition over time)

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Data Collection Protocol

Baseline measurements (uncoated reference):

• Case temperature at idle (5 min warmup)

• Case temperature at cruise (15 min steady state)

• Case temperature at load (climbing grade)

• Ambient temperature during testing

Coated engine measurements:

• Same test protocol as baseline

• Multiple location measurements (front, rear, oil sump)

• Record coating thickness at test locations

• Document environmental conditions

Expected results:

• Temperature difference: <2°F (within measurement error)

• Coating adhesion: No flaking or delamination

• Corrosion protection: No oxidation or pitting

• Appearance: Color retention, professional finish

If problems occur:

• Flaking = inadequate surface prep or too thick

• Discoloration = wrong paint type or temperature rating

• Corrosion = coating defect, incomplete coverage

Solution: Refine process, not abandon coating practice

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PART 8: DEBUNKING THE MYTHS

Myth #1: "Paint traps heat"

Claim: Coating magnesium prevents heat from escaping, causing overheating.

Reality:

• Heat transfer through 5 mils of coating: negligible (<1°F)

• Convection (airflow) dominates cooling (90% of heat dissipation)

• Paint thickness has ZERO effect on airflow patterns

• Aircraft engines prove this under far more severe conditions

Physics: Thermal resistance = thickness / conductivity

• At 5 mils: R = 0.00025 K/W (insignificant)

Verdict: FALSE - coating effect is unmeasurable in practice

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Myth #2: "Magnesium needs to breathe"

Claim: Raw magnesium must be exposed to air for proper engine function.

Reality:

• Magnesium is not alive - it doesn't "breathe"

• Proper coating PREVENTS moisture intrusion (opposite of "breathing")

• Corrosion occurs when magnesium DOES contact air + moisture

• Protection = sealing OUT corrosive elements, not "breathing"

What people mean: They fear moisture trapped UNDER coating Solution: Proper adhesion prevents delamination and moisture intrusion

Verdict: FALSE - nonsensical concept based on misunderstanding

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Myth #3: "Factory didn't paint, so we shouldn't"

Claim: VW left cases bare, therefore bare is correct.

Reality:

• Factory decisions are cost-driven, not performance-driven

• VW also left bare metal on bodies (they rust - was that optimal?)

• Porsche 356/911 engines came with various protective finishes

• Aircraft manufacturers ALWAYS protect magnesium (safety > cost)

Why factories skip coating:

• Manufacturing cost reduction

• Time savings in production

• Cosmetics not prioritized (hidden under tin work)

Why YOU should coat:

• Long-term ownership (not building to minimum spec)

• Corrosion protection extends case life

• Professional appearance

• Zero performance penalty

Verdict: FALSE - factory cost-cutting ≠ optimal practice

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Myth #4: "Thick cooling fins = needs bare metal"

Claim: Fins need maximum heat transfer, coating interferes.

Reality:

• Fin effectiveness = surface area × airflow × temperature difference

• Coating adds negligible thickness (0.005" on 0.125" fin)

• Airflow is UNCHANGED (cooling isn't disrupted)

• Bare aluminum fins on cylinders are often ANODIZED (coated!)

What matters for fin cooling:

• FIN AREA (surface for convection)

• AIRFLOW (fan performance, ducting)

• FIN CLEANLINESS (debris blocks airflow)

What doesn't matter:

• 5 mils of coating (0.4% of fin thickness)

Verdict: FALSE - fin geometry and airflow dominate, not coating

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Myth #5: "I knew a guy whose painted engine overheated"

Claim: Anecdotal evidence that coating causes problems.

Reality - What actually happened:

• Guy used WRONG paint (house paint, wrong chemistry)

• Guy applied THICK coating (20+ mils of buildup)

• Guy ALSO had cooling system problems (tin missing, lean tune)

• Engine overheated from ACTUAL problems

• Guy blamed VISIBLE change (paint) not INVISIBLE problems

Correlation ≠ Causation

Proper diagnosis:

• Thick, wrong paint can restrict fin gaps (airflow problem, not thermal)

• Missing cooling tin (airflow problem)

• Lean carburetion (combustion problem)

• Combination of problems = overheating

Verdict: FALSE - correlation error, wrong paint type/thickness

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PART 9: THE AIRCRAFT SHOP CERTIFICATION

What Professional Standards Look Like

Aircraft engine overhaul shops operate under FAA oversight:

Facility requirements:

• FAA Repair Station Certificate (14 CFR Part 145)

• Quality Control Manual (documented procedures)

• Calibrated measuring equipment (annual certification)

• NDT equipment and certified operators

• Environmental controls (temperature, humidity, cleanliness)

Personnel requirements:

• A&P (Airframe & Powerplant) Mechanic certification

• IA (Inspection Authorization) for final signoff

• Manufacturer-specific training (Lycoming, Continental courses)

• Continuing education requirements

Process requirements:

• Written procedures for every operation

• Inspection criteria with accept/reject limits

• Traceability for all replacement parts

• Documentation of all measurements and findings

• Test cell validation before release

Why this matters: These standards ensure ZERO shortcuts and maximum reliability.

VW / PORSCHE average builder equivalent: None of this exists (which is fine for personal builds, but understand the difference)

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Liability and Insurance

Aircraft shops carry massive liability insurance:

Coverage required:

• $1,000,000+ per occurrence

• $5,000,000+ aggregate

• Product liability coverage

• Professional liability (errors & omissions)

Annual premium: $10,000-$50,000+ depending on volume

Why so expensive?

• Engine failure can cause fatalities

• Lawsuits routinely reach $5-10 million

• Shops must prove they followed ALL procedures exactly

This drives adherence to proven processes - including coating magnesium for corrosion protection.

If coating caused reliability problems, insurance companies would prohibit it (they're entirely risk-driven).

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PART 10: CONCLUSION & RECOMMENDATIONS

The Engineering Case for Coating

Proven by aircraft industry:

• 80+ years of magnesium case coating

• Zero documented overheating from proper coating

• FAA certification and oversight

• Mandatory practice for $30K-$60K overhauls

Supported by physics:

• Thermal resistance of thin coating: negligible

• Convection dominates heat transfer (airflow unchanged)

• Radiation improved by coating (higher emissivity)

• Temperature difference: <1°F (unmeasurable)

Validated by field experience:

• Aircraft engines run hotter, coated, no problems

• Proper VW coatings show no temperature increase

• Corrosion protection extends case life

• Professional appearance inspires confidence

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Recommended System for Vintage Flat-4

For VW Type 1 or Porsche 356/912 magnesium cases:

Products for COST EFFECTIVE – BUDGET BUILDS

(VF4 Basic HP Engine Edition or Custom Budget Builds)

1. U-POL Adhesion Promoter (Clear) - $15

2. VHT Engine Enamel (color choice) - $12-15/can

Process:

1. Thorough degreasing and cleaning

2. Light ScotchBrite scuffing (create tooth)

3. Final solvent wipe and dry

4. One light coat U-POL (let flash 5-10 min)

5. Two thin coats VHT (10-15 min between coats)

6. Air dry 24 hours minimum

7. Install and heat-cure through operation

Total thickness: 4-6 mils (same as aircraft standard)

Cost: ~$30 in materials

Benefit: Professional corrosion protection with zero thermal penalty

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Products for HIGH END ENGINE BUILDS 

(VF4 Premium / Platinum / Heritage Standard)

1. Extensive mechanical cleaning
   • Media selection safe for magnesium
   • No surface erosion or detail loss

1. Magnesium-specific chemical pretreatment
   • Removes oxides without attacking base metal

1. Aircraft-grade conversion coating application
   • Chemically bonds to the magnesium
   • Primary corrosion protection layer

1. Optional ultra-thin air-cooled topcoat
   (Only where required for environment or appearance)
   • No thermal insulation
   • No dimensional change
   • Fully compatible with conversion layer

1. Controlled curing and inspection

Results & Benefits

• Maximum corrosion resistance
• Zero thermal penalty
• No loss of heat dissipation
• Preserves original casting detail
• Allows future rebuilding and machining
• Matches aircraft engine longevity expectations

This is not cosmetic paintwork—
It is engineered surface preservation.

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PDCA Implementation

For continuous improvement:

PLAN: Document current process, research improvements DO: Apply system to next build, measure and record CHECK: Monitor temps, inspect after break-in, evaluate over time ACT: Refine process, standardize success, share results

Measurement tools to invest in:

• Coating thickness gauge ($50-200)

• IR temperature gun ($20-100)

• Digital calipers ($20-50)

Testing protocol:

• Baseline temps (before coating)

• Post-coating temps (same conditions)

• Long-term inspection (adhesion, corrosion)

• Photo documentation (condition over time)

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Share Your Results

The vintage VW/Porsche community needs DATA, not folklore.

When you coat your engine:

• Document the process with photos

• Measure and record temperatures

• Report results honestly (good and bad)

• Share findings on forums and social media

• Challenge the "don't paint" myth with facts

Help advance the community's understanding by applying systems engineering principles and aircraft industry standards.

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FINAL STATEMENT

The "don't paint magnesium" myth persists because:

1. Home builders saw bad paint jobs (thick, wrong type)

2. Correlation was confused with causation

3. Myth spread faster than facts

4. Echo chamber reinforcement in forums

The engineering reality:

• Aircraft industry coats magnesium (proven over 80 years)

• Physics supports thin coating (thermal effect negligible)

• Field testing confirms zero temperature increase

• Corrosion protection extends case life

Your VW Type 1 magnesium case SHOULD be coated using proper materials and methods.

The aircraft engine overhaul process proves this is not only safe, but STANDARD PRACTICE in the most demanding air-cooled engine applications.

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REFERENCES & FURTHER READING

Aircraft engine overhaul standards:

• FAA Advisory Circular 43.13-1B (Acceptable Methods, Techniques, and Practices)

• Lycoming Service Instruction 1009 (Overhaul Manual)

• Continental M-0 (Overhaul Manual)

Heat transfer fundamentals:

• Incropera & DeWitt, "Fundamentals of Heat and Mass Transfer"

• ASME Heat Transfer Division publications

VW/Porsche technical:

• "How to Rebuild Your Volkswagen Air-Cooled Engine" - Tom Wilson

• "101 Projects for Your Porsche Boxster" (air-cooled section)

• Gene Berg Enterprises technical bulletins

NDT standards:

• ASTM E1444 (Magnetic Particle Testing)

• ASTM E1417 (Liquid Penetrant Testing)

• MIL-STD-1907 (Military NDT standards)

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ABOUT THIS DOCUMENT

Purpose: Technical rebuttal to automotive folklore using aerospace engineering standards

Audience: Vintage VW and Porsche flat-4 builders, restorers, and enthusiasts

Author perspective: Systems engineering approach with PDCA methodology

Revision: 1.0 (December 2025)

Distribution: Free for non-commercial use, share widely

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"In God we trust. All others must bring data." - W. Edwards Deming, Quality Management Pioneer

"The factory left it bare because paint costs money, not because bare works better." - Every aircraft engine overhauls shop in existence

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COAT YOUR MAGNESIUM CASES. THE AIRCRAFT INDUSTRY HAS PROVEN IT FOR 80 YEARS.

YOU'RE NOT SMARTER THAN LYCOMING, CONTINENTAL, THE FAA, AND BASIC PHYSICS.

Dale Hansen

Owner / Sr. Engine Builder

  Rebuilding Magnesium Engine Cases

(Lycoming / Continental / FAA Repair Station Practice)

· IMPORTANT CONTEXT (NON-NEGOTIABLE)

Aircraft magnesium case processing is NOT a DIY procedure.

These processes are performed by:

• FAA Part 145 repair stations

• Aerospace chemical processors

• Defense / aviation-approved coating facilities

Why: Magnesium reacts violently to incorrect chemistry. Improper handling can:

· Destroy castings

· Create hydrogen ignition risk

· Cause intergranular corrosion

· Permanently weaken the case

STANDARD AIRCRAFT PROCESS FLOW

(Magnesium Engine Cases)

1. MECHANICAL STRIP & DECONTAMINATION

Purpose

Remove oils, carbon, sealants, corrosion products without embedding media.

Methods Used

• Plastic media blasting (PMB)

• Fine glass bead (controlled, low pressure)

• Walnut shell (legacy systems)

⚠ NO aluminum oxide, steel shot, or aggressive grit

2. ALKALINE DEGREASING (MAGNESIUM-SAFE)

Chemical Class

Low-alkaline, magnesium-compatible aqueous cleaners

Typical Aircraft Products

• Turco® 4215-NCLT

• Ardrox® 6344

• Brulin® 815GD (magnesium approved variants)

Purpose:

• Remove hydrocarbons

• Avoid caustic attack

• Prepare surface for acid activation

3. ACID ACTIVATION / DEOXIDATION

Purpose

Remove native magnesium oxides without etching base metal.

Chemical Class

Fluoride-containing acidic deoxidizers

Aircraft-Standard Products

• Turco® Magnesium Deoxidizer 4004

• Ardrox® 4017 / 4027

• Henkel Alodine® MG Deoxidizers

⚠ This step is critical and tightly controlled.

4. MAGNESIUM CONVERSION COATING

(PRIMARY CORROSION PROTECTION)

This is the core aircraft process.

OPTION A — CHROMATE CONVERSION (LEGACY / STILL USED)

Process Spec

• MIL-DTL-5541 (Class 1A)

• AMS-M-3171

Chemistry

• Hexavalent chromate-based conversion coating

Known Aircraft Products

• Dow 7® (historical reference)

• Alodine® 1200 for Magnesium

Benefits:

• Best corrosion protection ever developed

• Self-healing properties

Limitations:

• Environmental restrictions

• Controlled use only

OPTION B — MODERN CHROMATE-FREE SYSTEMS

(Current aerospace standard)

Chemistry Families

• Zirconium-based conversion coatings

• Rare-earth metal conversion systems

• Phosphate-fluoride systems

Aircraft-Approved Products

• SurTec® 650 / 650V

• Henkel Alodine® 5700 / 5200

• Chemetall® Oxsilan® Mg systems

These form:

• Micron-thick ceramic/chemical layers

• Zero dimensional change

• Excellent corrosion resistance

5. POST-CONVERSION SEAL / STABILIZATION

Purpose

Lock conversion layer and stabilize chemistry.

Method

• Deionized water rinses

• Controlled dry cycle

• No aggressive heat

No mechanical abrasion permitted after this point.

6. OPTIONAL AIRCRAFT-STYLE THIN FILM TOPCOAT

(Used selectively)

Aircraft engines do not rely on paint, but when required:

Coating Types

• Phenolic wash primers

• Epoxy wash primers (ultra-thin)

• Silicone-modified engine coatings

Known Aircraft Products

• PPG CA7700 / CA7500 wash primers

• Akzo Nobel aerospace epoxy wash systems

⚠ Applied at micron-level thickness only

7. FINAL BAKE / STABILIZATION

Purpose:

• Drive off moisture

• Stabilize coating chemistry

• No cosmetic curing goals

WHY THIS WORKS (AIRCRAFT LOGIC)

• Corrosion protection comes from chemistry, not thickness

• Heat transfer remains unimpeded

• Castings retain full rebuild potential

• No trapped moisture

• No stress risers

This is why:

Aircraft magnesium cases last 50–70 years and multiple overhauls.