How to determine the remaining life of starter-generator brushes through visual inspection.

Outline (quick skeleton)

• Hook: starter-generator brushes wear down with use, and their condition tells you a lot about remaining life.

• Why brushes matter: the role of brushes, friction, and the commutator.

• The key takeaway: visual wear is the most direct clue to life remaining.

• What not to chase: why electrical resistance, temperature, or cycle counts aren’t enough on their own.

• The visual inspection routine:

• tools and safety

• what to look for (length, wear patterns, damage)

• interpreting what you see (when to replace)

• Practical tips and common mistakes

• Real-world context: how this fits into overall powerplant maintenance

• Final thought: keep a simple habit of checking brushes to stay ahead

How long do starter-generator brushes really last? In a word: wear. If you’re looking at topics that show up time and again in Jeppesen Powerplant discussions, brush wear is one of those little-but-crucial details that separates the steady operators from the hands-on folks who catch issues before they bite. Brushes ride on the commutator, rubbing away a little bit each time the generator runs. That friction is exactly what lets the machine work—but it also wears the brushes down. So, the question isn’t whether they wear out; it’s how to tell when they’re worn enough to replace.

Why brushes wear and what that means for service life

Breathing life into a starter-generator means you’ve got a clean, solid contact between brush and commutator. Over time, that contact wears the brush’s tip, and the surface can become flat, glazed, or chipped. If the brush becomes too short or develops irregular wear, it can slip, create poor electrical contact, or cause arcing. The result? Degraded starting performance, uneven voltage, or misbehaving generator output. In other words, don’t wait for a dramatic failure to notice something’s off.

But here’s the thing: you can’t always judge the health of brushes by one clue alone. Electrical resistance, temperature readings, or counting how many times the system has started can provide useful data about overall performance, sure—but they don’t reliably reveal the actual physical wear. That’s why the most dependable assessment is a direct, visual check of the brushes themselves. If you skim over that step, you’re guessing about parts that physically wear down with use.

Visual inspection: the most reliable method

Think of visual inspection as your cockpit eyewitness. It shows you the actual condition of the brushes—their length, their surface, and any visible damage. If you see that a brush is long and even, with a clean, flat tip, you’re probably in the safe zone for a while. If you notice that a brush is shortened, rounded, cracked, pitted, or has an uneven surface, that’s a signal to take a closer look or plan a replacement.

Here’s how to approach it in a calm, methodical way—think of it as a quick routine you can perform during standard maintenance checks.

What you’ll need and safety basics

• Clean hands or gloves to avoid contaminating the brushes or the commutator.

• A good light source (a flashlight or a portable lamp helps).

• A small ruler or caliper for measuring brush length.

• A clean, lint-free cloth to wipe away dust or debris.

• The generator’s maintenance manual for manufacturer-specific brush length and wear limits.

• Safety first: disconnect power, tag out, and follow your organization’s lockout/tagout procedures. It’s mechanical wear we’re looking at, but you’re still around live circuits if you’re not careful.

What to look for when you peer at the brushes

• Length: brushes have a minimum functional length. If the brush is significantly shorter than its original length or near the wear limit specified by the manufacturer, that’s a sign to replace soon.

• Even wear: brushes should wear evenly across their face. Uneven edges, glazing (a shiny, glassy surface), or a narrow shoulder can indicate inconsistent contact with the commutator.

• Cracks, chips, and pits: any cracking or pitting weakens the brush and can lead to uneven contact or debris on the commutator.

• Surface condition: a smooth, consistent surface is ideal. A rough or severely grooved surface suggests wear that could compromise contact quality.

• Debris and dust: a lot of carbon dust nearby can be normal, but an unusual buildup or signs of excessive wear may point to brush friction issues or misalignment.

Translating what you see into a plan

• If brushes are wearing toward a minimum length or show any of the damaging signs above, plan for replacement. It’s not about chasing a number; it’s about ensuring consistent contact and avoiding sudden performance dips.

• If wear looks uneven, check alignment and mounting hardware. Misalignment can accelerate wear and create hot spots on the commutator.

• If you notice glazing or a rough surface, you may need a closer inspection of the commutator as well; worn brushes can leave irregular impressions, and a damaged commutator can accelerate brush wear in return.

How long should you wait before replacing?

• Follow the manufacturer’s specs for minimum brush length and wear limits. Those limits aren’t random; they’re tied to the geometry of the brush and how it contacts the commutator during operation.

• If you’re unsure, err on the side of a proactive replacement. It’s cheaper and safer to replace a set of brushes before a flight than to chase a scheduled failure later.

Common mistakes to avoid

• Relying only on resistance or temperature readings. They’re useful, but they don’t tell you about the metal-to-metal wear happening at the contact point.

• Ignoring signs of damage beyond the tip. Even a small crack or chip can propagate, causing erratic behavior or debris in the system.

• Skipping a proper cleaning step. Without wiping away dust and debris, you might misinterpret wear or miss signs that something else is amiss.

• Measuring from the wrong point. Use the brush’s base or the tip, as specified in the manual, and measure the actual remaining length with the brush seated in its holder.

Putting the routine into a bigger maintenance picture

Brush wear is one piece of the powerplant health puzzle. The starter and generator must work in harmony: you want clean electrical contact, predictable voltage, and reliable starts. Visual inspection of brushes fits neatly into a broader maintenance habit—periodic checks, clean components, and a simple record-keeping approach. A quick photo log can help you compare wear over time, and keeping a running note of when replacements were made helps crews plan ahead.

A few practical tips to keep things smooth

• Keep a simple visual reference: mark the original brush length with a non-permanent marker when you first inspect. It’s a quick way to see how much has worn away in subsequent checks.

• Create a quick checklist you can use during each inspection: brush length, wear pattern, surface condition, any cracks, and the condition of the mounting hardware.

• Pair the brush check with a look at the commutator. A smooth, clean commutator surface supports good contact, and roughness or heavy deposits can compound wear.

• Document clearly. Photos plus notes can be a powerful combo when you revisit the task next time.

• Tie it to flight-critical indicators. If performance starts to feel unusual during engine starts or electrical load changes, a brush inspection becomes even more relevant.

Real-world context: how this topic shows up in powerplant expertise

In the broader world of aviation maintenance, there are a few topics that recur across the Jeppesen Powerplant landscape: electrical system health, alternating current behavior, commutator condition, and proper lubrication and torque of mounting hardware. Brush wear lives at the intersection of mechanical wear and electrical performance. It’s one of those practical checks that keeps the whole system honest—no hidden surprises, no sudden wear spirals.

Let me tie this back with a simple thought: the phrase “visual inspection” sounds almost too easy, but it’s incredibly powerful here. You’re not guessing about metal losing conductivity or insulation failing in a vacuum. You’re seeing the tangible sign of wear—the brush’s length and surface. And you’re using that sign to decide when to replace. That clarity matters when you’re on a ramp or in a hangar, where decisions need to be reliable and fast.

A final nudge toward everyday mastery

If you’re curious how this fits into the larger skill set, think of brush inspection as the gateway habit: a small, repeatable action that guards a larger function. It’s like checking tire tread before a road trip or testing a battery before a long flight. The mental model is the same: a quick visual check, a quick decision, and a quick action that prevents bigger problems.

In the end, the brush’s life isn’t just about a number or a headline spec. It’s about the lived reality of keeping a starter-generator dependable. Visual wear is the most direct, trustworthy clue you’ve got. It’s the best way to gauge remaining service life, preserve performance, and keep the powerplant humming smoothly.

If you’re exploring Jeppesen powerplant topics, you’ll notice how much emphasis is placed on practical, hands-on understanding—on seeing and interpreting real-world signs rather than plowing through theoretical pages alone. Brush wear is a perfect example: simple to observe, critical to monitor, and essential for safe, reliable operation. So next time you’re inside the nacelle or panel, take a moment to look closely at those brushes. You might just prevent a bigger headache down the line.