How to inspect engine cylinders with a borescope

Introduction: Peeking Inside the Heart of an Engine

Ever wondered what’s going on inside your engine’s cylinders without tearing the whole thing apart? Let me tell you—it’s not just possible, it’s surprisingly easy (and kind of fun) once you know how to inspect engine cylinders with a borescope.

I remember the first time I used a borescope. I wasn’t sure what to expect. It felt a bit like sending a tiny submarine into an unexplored cavern—only the cavern was filled with carbon deposits, valve seats, and glistening piston crowns. [emotion-driven description] It gave me a weird thrill. Like, “Whoa—I’m actually inside my engine right now.”

Here’s the thing: engines can hide a lot. Scoring, carbon buildup, valve damage, gasket leaks… all the sneaky little problems that don’t always show up in a compression test or a quick look under the hood. But with a borescope? You see it all. And you don’t have to be a pro mechanic to pull it off.

That’s why this guide exists. I’m going to walk you through the whole process—step by step—from choosing the right borescope to interpreting what you see. No confusing jargon, no over-complicated tech talk. Just real, honest help from someone who’s been there, scratched their head, and figured it out (with a little trial and error).

And the best part? You’ll learn how to catch issues before they turn into expensive repairs. That alone is worth it, right?

So, grab your curiosity (and maybe a coffee), and let’s dive in. By the time you’re done reading, you’ll know exactly how to use a borescope to check your engine’s health—like a seasoned DIYer or even a low-key pro.

 

Why Inspect Engine Cylinders with a Borescope?

Alright, let’s be real—tearing down an engine just to “take a look” inside? That’s time-consuming, messy, and can cost you a fortune if something goes sideways. But knowing how to inspect engine cylinders with a borescope? That’s a total game changer. It’s like having X-ray vision for your engine—without even removing the head.

Catch Problems Before They Become Nightmares

Ever heard a faint knock or noticed your engine burning a bit of oil and thought, Eh, it’s probably nothing? Yeah… been there. But guess what? That “nothing” could be early signs of cylinder wall scoring, carbon buildup on the piston, or a valve starting to stick. Tiny issues that—if left unchecked—can snowball into catastrophic engine failure.

With a borescope, you can spot:

• Cracks or damage on the piston crown
• Burnt or leaking valves
• Scored cylinder walls
• Carbon deposits or oil pooling
• Head gasket issues (yep, even that!)

Pretty handy, right?

Save Time, Money, and Wrenching Effort

Think about it: instead of taking apart the top end of your engine (which can take hours, not to mention the cost of gaskets and lost coolant/oil), you can simply remove a spark plug, slide in the borescope, and boom—you’re seeing what the piston sees. It’s efficient. And if you’re working on multiple vehicles? It pays for itself fast.

Whether you’re a DIY enthusiast or a pro tech in a busy shop, this tool helps you make smarter calls:

• Is that engine worth rebuilding?
• Can I get away with a carbon clean?
• Do I need to replace a cylinder head or valve?

It takes the guesswork out of engine diagnostics.

Trusted by Pilots and Aviation Techs

Here’s a fun fact: aircraft mechanics use borescopes all the time. Before every major flight, borescope inspections are used to check combustion chambers, valves, and piston conditions. Lives literally depend on it. If it’s good enough for aviation? It’s definitely good enough for your daily driver, race car, or weekend project.

Peace of Mind (Because Anxiety Sucks)

Look, I get it. The sound of a misfire or the sight of smoke can mess with your head. But using a borescope lets you face your fears with facts. When you see the problem—or confirm there isn’t one—you can relax a little. There’s something empowering about knowing what’s really going on in your engine.

Can you imagine how it feels to finally know that odd rattle isn’t the end of the world? Or to spot an issue early enough that fixing it takes an hour instead of a whole weekend? That’s the real win here.

 

Preparing for a Cylinder Borescope Inspection

Alright, before we dive inside the engine like a mini explorer, let’s get one thing straight: preparation is everything. Trust me, nothing kills the vibe faster than realizing mid-inspection that your borescope cable is too thick—or your flashlight is dead.

So, here’s how to get set up properly for a smooth, stress-free inspection.

Choose the Right Type of Borescope

First up: not all borescopes are created equal. Picking the right one can make your job 10 times easier—or way more frustrating than it needs to be.

Rigid vs. Flexible Borescopes

• Rigid Borescopes: These are straight and sturdy. Great for shallow inspections or areas with a direct line of sight (like spark plug holes). Super durable, but kind of limited in where they can go.
• Flexible Borescopes: These bad boys bend and twist. Perfect for getting around tight engine corners or through intake runners. They’re a little more delicate, but incredibly versatile.

Tip: For most automotive and aviation cylinder inspections, a flexible video borescope is the sweet spot.

Digital Video Borescope? Highly Recommended

Sure, older fiber-optic models are cheaper, but modern digital video borescopes let you:

• View everything on a crisp screen (no squinting through an eyepiece)
• Record HD images and videos
• Zoom in for detail shots
• Adjust LED brightness for dark areas

If you’re a visual learner or just love geeking out over engine internals, this is a no-brainer.

Know Your Specs: Probe Diameter, Length & Articulation

Can we talk about probe size for a sec?

• Diameter: Most spark plug holes range from 10mm–14mm, so go with a probe under 8mm to be safe.
• Length: At least 24 inches gives you enough reach to fully explore the chamber and piston crown.
• Articulation: Some high-end scopes allow you to control the tip like a joystick. Super handy for inspecting valves and combustion chamber walls from different angles.

It made me feel like a surgeon when I first used an articulating scope. So precise. So satisfying.

What You’ll Need Before You Start

Let’s build your inspection checklist. Make sure you’ve got:

• Your chosen borescope
• A charged battery or USB power supply
• Spark plug socket and ratchet
• Compressed air (for blowing out debris)
• Nitrile gloves (trust me, engines are grimy)
• A clean worklight for your setup area
• Notepad or laptop to jot down what you see

Friendly reminder: the engine should be completely cool before you even think about poking anything inside it. Hot internals can mess up your scope—and your fingers.

Set the Scene: Workspace Prep

A clean space = a focused mind. Wipe down the valve cover area, keep your tools organized, and make sure the vehicle is parked securely. For aircraft? Chock the wheels and follow standard maintenance protocols.

Also, have a small towel or parts tray handy. You’ll be removing spark plugs, maybe valve covers, and you don’t want to be chasing bolts across the floor.

 

Step-by-Step Cylinder Inspection Process

So, you’ve got your borescope, your tools are laid out, and your engine’s cool to the touch. Feels like a mini pit crew moment, right? Let’s walk through the inspection together—step by step—like we’re in your garage, sleeves rolled up, figuring it out as we go.

This part is where the magic happens.

Safety First—Always

Let’s not skip this part, okay? It’s easy to get caught up in the excitement and forget the basics.

• Make sure the engine is completely cool.
• Disconnect the battery if you’re working near sensitive electronics.
• Use eye protection—you never know what’s hanging around the spark plug holes (dust, oil mist, or that one stubborn spider).

Pro Tip: Put the car in neutral or the aircraft in maintenance mode. You don’t want anything to move unexpectedly while you’re inside the engine. That’d be… uh… bad.

Remove Spark Plugs

Grab your spark plug socket and carefully remove the plugs—one at a time—from each cylinder you plan to inspect.

• Blow out the area around the plug with compressed air first. You do not want any junk falling into the cylinder.
• Keep track of which plug came from which hole. If you find anything weird during inspection, you’ll want to reference it later.

You ever pull out a plug and find it wet or crusty? That right there is a clue—and a perfect reason for a borescope inspection.

Set the Piston to Bottom Dead Center (BDC)

Why BDC? Because it gives your borescope enough room to fully explore the cylinder without the piston crown blocking your view.

• You can do this by turning the crankshaft manually using a ratchet on the harmonic balancer bolt.
• For aircraft engines, use your propeller carefully (if allowed by your maintenance procedures).

Don’t overthink it—just make sure the piston is sitting low in the bore. You’ll know because the borescope will be able to look side-to-side instead of hitting a wall of metal.

Insert the Borescope Carefully

Now’s the moment of truth.

• Feed the probe gently through the spark plug hole.
• Move slowly. Don’t force it—if it feels stuck, pull back and adjust the angle.
• Once it’s inside, stabilize the handle. A shaky hand makes for blurry images.

Connector tip: It feels a bit awkward at first. Like threading a noodle through a keyhole. But you’ll get the hang of it, I promise.

Rotate and Adjust for the Best View

This is where the fun starts. Once the scope is inside:

• Rotate the probe to inspect the piston crown
• Angle it to view cylinder walls for scoring or glazing
• Move upward to peek at valves and seats
• Check the combustion chamber area

Use the LED brightness control to avoid overexposure. A good image is clear, balanced, and doesn’t wash out.

If you’ve got articulation: Play with the joystick or tip control to angle your view perfectly. You’ll feel like a high-tech surgeon or one of those underwater drone operators. Seriously.

Take Photos and Notes

When you see something interesting—or questionable—snap a photo or record a quick video.

• Label your files by cylinder number (trust me, this saves time later).
• Jot down what you’re seeing: “#3 has mild scoring, light carbon on piston, exhaust valve looks clean.”
• Use your phone or laptop to organize notes. Future-you will thank you.

I remember the first time I saw cracked valve seats on cylinder #5. My heart sank a bit. But I was also relieved—because now I knew. No more guessing.

Repeat for Each Cylinder

Repeat the whole process for each cylinder, one at a time. Yes, it takes a bit of time. But each one tells its own story.

Some will look spotless, others might show signs of wear, and a few could scream “HELP ME!”—but at least now, you’re in control.

Wrap Up and Clean Your Gear

Once you’re done:

• Carefully remove the borescope
• Wipe the probe with a microfiber cloth and a bit of isopropyl alcohol
• Store everything in its case

Don’t forget to reinstall the spark plugs (use a torque wrench!) and reconnect the battery if you unplugged it earlier.

That’s it! Inspection complete.

How Does It Feel?

You just looked inside your engine. That’s a huge deal! For real—how awesome is that? You’ve got knowledge that most people pay hundreds (or thousands) to get from a shop. That’s something to be proud of.

Now you’re probably wondering…

“What exactly am I supposed to be seeing in there?”

Don’t worry—I’ve got you. Next, we’re going to break down what healthy vs. unhealthy cylinders look like.

 

What to Inspect Inside the Cylinder

So, you’ve slid the borescope into the spark plug hole, adjusted the lighting, and now you’re staring at the inner world of your engine. It’s kind of surreal, right? Like opening a little window into a hidden, high-stakes world. But here’s the big question:

What are you actually supposed to look for in there?

Let’s break it down into manageable parts. Each cylinder has a few key areas you’ll want to examine. Don’t worry if it feels like a lot—I’ll walk you through it like we’re doing this together, side by side in the garage or hangar.

Cylinder Walls – Your First Clue

Let’s start with the walls. These guys take a serious beating every time your piston fires.

Here’s what to check for:

What’s Normal:

• A visible cross-hatch pattern—those diagonal lines left from honing. This helps retain oil on the walls and reduce wear.
• A clean, shiny surface with no grooves or gouges.

Red Flags:

• Vertical scoring or scratches — these might mean the rings are worn or a piece of debris got stuck.
• Glazing — if the wall looks like polished glass, oil isn’t sticking like it should. That leads to blow-by and oil burning.
• Rust spots or pitting — water intrusion or long periods of inactivity.

It made me feel nervous the first time I saw light scratches. But I later learned—some faint lines are okay. Deep gouges? That’s a different story.

Piston Crown – Where the Magic Happens

The piston top is where combustion happens. It’s like the battlefield of your engine.

What’s Normal:

• Even carbon deposits—a soft, black or dark brown film is okay.
• Maybe a little ash or soot.

Red Flags:

• Heavy carbon buildup — could mean poor combustion or oil entering the chamber.
• Washed areas — super clean spots may show where raw fuel is washing the piston (bad injector, bad timing).
• Cracks or damage — any visible damage is a no-go. That’s a teardown-level issue.
• Melted edges or pitting — could indicate detonation or pre-ignition. Super dangerous if left unchecked.

I once found a piston so clean in one spot, it looked polished. Turns out, the injector above it was leaking badly—raw fuel was scrubbing the carbon right off. Wild, right?

Intake and Exhaust Valves – Silent Storytellers

Next, tilt your borescope upward toward the cylinder head to see the intake and exhaust valves. They’re critical to the breathing of your engine.

What’s Normal:

• Slight carbon coating
• Smooth edges
• Symmetrical seating

Red Flags:

• White or flaky deposits — could mean coolant or oil leakage.
• Burnt edges — a sign of heat damage or incorrect valve timing.
• Uneven wear or a missing chunk = big trouble.

Seeing a valve seat that’s not uniform? That might be a reason your compression numbers were low. Sometimes it’s all connected.

Combustion Chamber – Check for Cleanliness & Leaks

This is the space above the piston, between the head and cylinder. It should be tight and clean-ish.

What’s Normal:

• Some carbon on the ceiling
• No visible residue around the edges

Red Flags:

• Oil residue or pooling — valve seal or ring issue
• Coolant traces — green or white goo means a leaking head gasket
• Blow-by marks — look for streaks near the gasket line

Seeing discoloration on one side of the chamber might indicate uneven combustion. That stuff messes with performance and fuel economy.

Spark Plug Hole & Threads

Don’t forget to inspect the inside of the plug hole:

• Make sure there’s no damage to the threads
• Look for signs of oil or carbon blow-back

If the plug hole is oily or looks burnt? That could mean trouble with cylinder sealing or even pre-ignition.

What Does “Healthy” Look Like?

Here’s a mental picture of a good cylinder:

• Wall shows a clear cross-hatch with minimal lines
• Piston has a light, even layer of carbon
• Valves look symmetrical, no crusty white deposits
• Chamber is dry and clean
• No debris or discoloration

It filled me with relief the first time I scoped a cylinder and everything looked normal. Like, “Yes! I didn’t mess this engine up!”

Not Sure What You’re Seeing?

If you’re unsure whether something’s a problem or just “normal wear,” you’re not alone. Even pros double-check sometimes.

You can:

• Compare cylinders against each other (in the same engine)
• Share images on a trusted forum (like r/mechanics or an aircraft maintenance group)
• Consult manufacturer service manuals for known wear indicators

 

Capturing and Managing Images & Video

You’re peering into the engine and spot something interesting—maybe scoring on the wall or a weird carbon pattern on a piston. You’re like, Whoa, what is that? But if you don’t snap a photo or jot a note, it might be gone from your memory in five minutes.

Let’s make sure that doesn’t happen.

How to Take Clear, Useful Images

Most borescopes come with image and video recording features these days. Here’s how to make the most of them.

Focus is Everything

• Hold the borescope steady—even the slightest movement can blur your image.
• Adjust the distance between the lens and the surface. Too close? It’s a pixel mess. Too far? Everything’s tiny.
• Use the LED brightness control—too much light can wash out detail; too little, and you’ll be guessing.

Friendly tip: Take multiple shots from slightly different angles. It made me feel like an engine paparazzi—click, click, click from every corner.

Don’t Skip Video

Video is even better than photos in some cases.

• You can slowly pan across cylinder walls
• Catch valves opening or closing if you’re turning the crank
• Narrate what you’re seeing so you don’t forget later

Ever watched a video you shot weeks ago and thought, Ohhh, that’s what I missed? Yeah. Videos help you connect the dots.

 

File Organization for the Win

Your phone or scope might dump everything into one folder. Don’t let that become a chaotic mess.

Here’s a super simple naming system that works:

plaintext

CopyEdit

Car_Engine_Cyl1_PistonCrown_2025-07-28.jpg

Aircraft_Lycoming_IO540_Cyl3_ValveSeat.mp4

Create a folder for each inspection session:

• Project name (Car, Plane, etc.)
• Date
• Cylinder number
• View type (valve, piston, wall, etc.)

Bonus tip: Sync your borescope with your phone or laptop and back up the files. If you’re working in a shop or aviation hangar, cloud backups (like Google Drive or Dropbox) help you stay organized.

Quick Note-Taking

Use a notebook, phone app, or digital maintenance log to:

• Note what you saw
• Mark which cylinders had issues
• Track any patterns (e.g., “only Cyl 4 and 6 showing wash”)

Even something simple like:

“Cyl 2 – light glazing, even carbon, valve edges good. Cyl 5 – vertical scoring visible.”

…can save hours down the road.

I can’t tell you how many times I’ve pulled out those notes and thought, Thank goodness I wrote that down.

Sharing With Others (Optional, but Helpful)

If you’re stumped or just want a second opinion, post your images (anonymously if needed) on:

• Mechanics forums
• Reddit communities like r/cars or r/aviationmaintenance
• Facebook groups for aircraft engine maintenance or DIY builds

Sometimes, a seasoned tech can spot a problem you didn’t even know to look for. And it’s cool being part of a community, right?

Interpreting Findings — What It All Means

Alright—so now you’ve scoped out the engine, captured a bunch of photos, maybe even a few videos. You’ve seen carbon, maybe some scratches, maybe some gooey stuff (ew). But how do you tell if what you saw is normal wear, a warning sign, or something that screams major repair incoming?

Normal vs. Abnormal: A Quick Overview

Let’s start with a super-basic mental checklist:

Part Inspected	Normal Signs	Warning Signs	Red Flags
Cylinder Walls	Cross-hatching	Light scoring	Deep gouges, rust
Piston Crown	Light carbon	Uneven soot	Melted spots, holes
Valves	Even edges	White buildup	Burnt seats, cracks
Combustion Chamber	Dry, some carbon	Wet soot	Oil pooling, coolant
Spark Plug Hole	Dry, clean threads	Slight carbon	Oil-soaked or stripped

Now let’s break these down in more detail so you really know what’s up.

Cylinder Walls

Good:

• Cross-hatch pattern still visible = great ring sealing.
• No discoloration, no scoring? Perfect.

Caution:

• Light scoring? Keep an eye on it. It could be wear from high mileage or a tiny contaminant that got through.
• Glazing (walls look polished) may mean poor ring seating or excessive oil.

Bad:

• Deep vertical gouges = probably metal-on-metal. Could be a broken ring or debris.
• Rust or pitting = likely from moisture or coolant intrusion. Bad news for compression.

Quick test: Try dragging your probe slowly down the wall. If your image “catches” on lines? It might be deeper than it looks.

Piston Crown

Good:

• A soft, dark coating of carbon is normal—think of it like an old cast iron skillet.

Caution:

• Ashy or flaky buildup? Maybe oil burning or low-grade fuel.
• A “clean” area in the middle with carbon around it? That’s often a hot spot—watch for detonation.

Bad:

• Melted piston edges or pockmarks (like craters) = detonation or pre-ignition damage. That can blow your engine if ignored.
• Cracks = you’re looking at a piston replacement, possibly a full rebuild.

Can you imagine how it feels to see a piston half-burnt through? It’s terrifying. But catching it before it fails completely? That’s a win.

Valves & Seats

Good:

• Uniform shape, smooth edges.
• Black carbon coating but nothing thick or flaky.

Caution:

• Light-colored buildup = burning coolant or oil.
• Valves that look uneven or slightly recessed may not be sealing well.

Bad:

• Cracks in the valve face.
• A chunk missing (burnt valve).
• Deposits thick enough to look like stalactites.

If the exhaust valve looks bleached white? That’s heat stress. Been there, seen that. You’ll want to check valve clearance and timing.

Combustion Chamber

Good:

• Dry, some dark deposits, normal wear.

Caution:

• Clean areas surrounded by carbon could mean poor combustion pattern.
• Slight discoloration on chamber walls = lean running or excess heat.

Bad:

• Liquid oil sitting in the chamber? Rings or valve seals are done.
• Coolant residue (green, white foam)? Classic blown head gasket.

Helpful trick: If you smell coolant while inspecting, that’s another tell-tale sign. Trust your nose!

Spark Plug Hole Threads

This part’s quick but crucial.

Good:

• Threads are clean, dry, and undamaged.

Bad:

• Stripped threads (you’ll feel it when reinstalling the plug).
• Oil or gunk inside? Time to figure out where that leak is coming from.

Bonus: Look for Patterns

Sometimes one bad cylinder isn’t as telling as a pattern across multiple cylinders.

• Are all even-numbered cylinders dirty and the odd ones clean? Might be an intake issue.
• Only the rear cylinders showing detonation? Could be a cooling imbalance.
• Front cylinder on an aircraft engine showing oil deposits? Maybe oil is pooling during shutdown.

See how much you can learn with just a borescope and a few clues?

 

What to Do With the Results

Once you’ve finished your inspection and noted the findings, it’s decision time.

If Everything Looks Good:

• Congrats! You just did a full engine health check like a boss.
• Keep the images and notes for your records or for resale value.

If You Found Minor Issues:

• Plan preventive maintenance.
• Use fuel additives to remove carbon buildup.
• Consider replacing valve seals or rechecking timing.

If You Found Major Issues:

• Don’t panic—but don’t ignore it either.
• Share your findings with a trusted mechanic or inspector.
• Use your documentation to estimate repair needs.

 

Remember: This Isn’t Just for Diagnosis

Borescope inspections are also great for:

• Verifying work after a rebuild
• Pre-purchase inspections
• Routine checks during annual aircraft maintenance
• Monitoring engine wear over time

It gave me so much peace of mind knowing exactly what was going on inside my engine—no guessing, no surprises.

 

Final Thoughts — Taking Control of Engine Health

So, here we are. You’ve just learned how to inspect engine cylinders with a borescope—step-by-step, from setup to interpretation. And if you followed along, you now know something most people don’t: what’s really going on inside your engine.

That’s not just cool—it’s empowering.

Because now:

• You’re not relying on guesswork or vague engine sounds.
• You’re spotting issues before they become breakdowns.
• You’ve taken ownership of your engine’s health like a true gearhead (or pilot… or weekend warrior).

And hey, even if you didn’t find any major problems? That’s worth celebrating. Knowing your engine is in great shape fills you with confidence—whether you’re taking it on a road trip or cruising 8,000 feet above ground in your Cessna.

Can you imagine how it feels to save hundreds in mechanic labor just because you learned to borescope a cylinder? It’s not just satisfying—it’s addictive. You’ll want to inspect everything now!

The truth is: this little tool—the borescope—opens a big door. Behind that door? Better maintenance. Smarter decisions. And engines that live a longer, happier life.

So go ahead… crack open those spark plug holes and take a peek. Your engine’s been waiting for you to say hi.

Please read more about the best borescope.

 

FAQs – How to Inspect Engine Cylinders with a Borescope

Do I need to remove the cylinder head to use a borescope?

Nope! That’s the beauty of it. Just remove the spark plug and insert the borescope through the hole. It gives you a clear view of the piston, valves, cylinder walls, and combustion chamber—no disassembly required.

What’s the ideal borescope diameter for engine cylinder inspections?

Generally, a probe under 8mm works best. Most spark plug holes are around 10–14mm wide, so you want a little room to maneuver. The slimmer the scope, the easier it is to explore tight spaces.

How often should I perform a cylinder inspection?

For cars, once a year or every 15,000–30,000 miles is a good baseline. For aircraft engines, follow manufacturer guidelines—typically during every annual inspection or every 100 flight hours.

What are the signs of a failing valve when viewed with a borescope?

Look for:

• White, flaky buildup (burning coolant)
• Uneven seating or bent appearance
• Burnt or missing chunks from the valve edge
• Cracks in the valve face or seat

Can I use a borescope to diagnose a misfire or low compression?

Absolutely. If a cylinder is misfiring or has low compression, scoping it can show you what’s causing it—burnt valve, worn rings, piston damage, carbon buildup, etc. It’s an incredibly useful diagnostic step before doing major repairs.