The Husqvarna 55 is one of those chainsaws that earned its reputation the old-fashioned way — by showing up and doing the work, year after year, without complaint. First introduced in 1990, it quickly became a go-to for homeowners, farmers, and weekend warriors who needed a reliable saw for firewood cutting, storm cleanup, and general property maintenance. With a 53.2 cc two-stroke engine pushing out 2.4 kW (about 3.3 horsepower), it packed enough punch to handle most jobs that didn’t require a professional-grade machine.
What made the Husqvarna 55 stick around for well over a decade was its smart blend of materials and engineering. The motor housing combined die-cast magnesium with injection-molded plastic, keeping weight down to about 5.2 kg while maintaining the toughness you need in a chainsaw. Its three-piece crankshaft, anti-vibration dampeners, and inertia-activated chain brake all spoke to a saw built with the user’s comfort and safety in mind.
Even though Husqvarna discontinued the model years ago, the 55 still has a loyal following. Plenty of these saws are still running strong in workshops and sheds around the globe. And whether you’re rebuilding one, fixing a problem, or just trying to understand what makes it tick, a good parts diagram is your best friend. That’s exactly what we’re breaking down here — every key component, what it does, and why it matters.
Husqvarna 55 Parts Diagram & Details
The diagram shown here is an exploded view of the Husqvarna 55 crankcase assembly — the core structural section of the chainsaw’s engine. An exploded view pulls every part apart and spreads them out spatially, so you can see exactly how each piece fits together with the rest. Think of it as a “deconstructed” look at the engine’s main housing and all the components that bolt, snap, or seal into it.
In this particular diagram, you can see the two halves of the crankcase at the center, with gaskets, sealing rings, fasteners, and auxiliary parts radiating outward. Each component carries a specific Husqvarna part number (like 501 76 22-02 for the crankcase or 505 27 57-19 for the sealing rings), making it straightforward to identify and order replacements. The layout flows from the top cover down through the main housing, with the clutch-side and flywheel-side components clearly separated.
Understanding these parts is critical whether you’re doing a full engine rebuild or simply replacing a worn gasket. Below, you’ll find each major component identified, explained, and put into practical context so you know what you’re looking at and why it matters.
1. Crankcase Assembly (Part #501 76 22-02)
The crankcase is the backbone of the entire Husqvarna 55. Sitting at the heart of the diagram — labeled compl 501 76 22-02 — it’s the main structural housing that everything else attaches to. Made from die-cast magnesium, it’s both lightweight and remarkably tough, which is exactly the combination you want in a chainsaw that might get dropped, bumped, or used in rough conditions.
Inside the crankcase, the crankshaft spins, the piston drives power, and combustion gases flow through their designated channels. It also houses the oil passages that keep the bar and chain lubricated during operation. Every seal, gasket, bolt, and component in this diagram either attaches directly to the crankcase or functions in partnership with it.
If the crankcase develops a crack or a warped sealing surface, you’re looking at a serious repair — potentially even a full replacement. That’s why experienced Husqvarna owners treat this part with care, checking it during every rebuild for hairline fractures, stripped threads, or any signs of damage that could compromise the engine’s ability to hold compression.
2. Crankcase Lid (Part #501 76 44-03)
Positioned at the upper-left area of the diagram, the crankcase lid (part #501 76 44-03) serves as a protective cover for the top section of the engine housing. It’s a relatively simple part, but its role is anything but minor. This lid seals off the crankcase from dust, debris, and moisture — three things that can wreak havoc on internal engine components over time.
The lid fits snugly against the crankcase body using a combination of screws and alignment pins. A proper seal here is essential because even a small air leak can throw off the fuel-to-air ratio in a two-stroke engine, leading to poor performance, hard starting, or overheating. If your Husqvarna 55 is running lean and you’ve already checked the carburetor, a loose or damaged crankcase lid is worth investigating.
3. Air Conductor (Part #501 76 30-03 & #503 73 04-01)
Two air conductor components appear in this diagram — one on the right side (part #501 76 30-03) and another closer to the center (part #503 73 04-01). Together, they form the cooling air pathway that directs airflow from the flywheel fan across the engine cylinder and exhaust areas. Without them, your saw’s engine would overheat in minutes.
Two-stroke engines like the one in the Husqvarna 55 run hot by nature. They fire on every crankshaft revolution, and there’s no water jacket or radiator to dissipate that heat. Instead, they rely on air cooling — and the air conductors are the parts that make sure that moving air actually reaches the hottest spots on the engine. They channel and focus airflow so that cooling happens efficiently, even when you’re cutting in hot weather or pushing the saw hard through thick wood.
Over time, these plastic air conductor pieces can crack, warp, or accumulate grime that restricts airflow. If your saw starts running hotter than usual, or you notice performance dropping off during extended cuts, a damaged air conductor might be the culprit.
4. Air Nozzle (Part #503 72 98-01)
Located at the upper-right corner of the diagram, the air nozzle (part #503 72 98-01) is the curved, deflector-style component that helps direct cooling air to specific areas around the cylinder. While the air conductors handle the broader airflow channels, the air nozzle fine-tunes where that air goes once it reaches the engine.
You can think of it as the last mile of the cooling system. It takes the pressurized air generated by the flywheel fan and aims it precisely where temperatures are highest. This targeted approach means the engine doesn’t just get blanketed with air — it gets cooled strategically, which keeps thermal stress more even across the cylinder surface.
Because of its exposed position and thin profile, the air nozzle is one of those parts that’s easy to overlook during routine maintenance. But a cracked or missing nozzle can cause localized hot spots on the cylinder, which over time may lead to scoring, seized rings, or worse.
5. Crankcase Gasket (Part #503 78 24-01)
Centered in the diagram between the two crankcase halves, the gasket (part #503 78 24-01) creates an airtight seal where the two sides of the crankcase meet. In a two-stroke engine, crankcase pressure is everything. The alternating pressure and vacuum inside the crankcase is what drives the fuel-air charge from the carburetor into the combustion chamber, so any leak here means lost power, rough running, or even engine damage.
This gasket is typically made from a heat-resistant, oil-resistant material that can withstand the constant temperature swings and vibration a chainsaw produces. Despite being paper-thin in many cases, it carries enormous responsibility. A compromised gasket often shows up as an air leak that makes the engine run lean — you’ll notice the saw revving too high at idle, or it may be difficult to tune the carburetor properly.
Replacing this gasket is a standard part of any Husqvarna 55 engine rebuild. Even if the old one looks fine, reusing it is a gamble. Fresh gaskets are cheap insurance against the headache of a crankcase leak.
6. Sealing Rings (Part #505 27 57-19)
Two sealing rings appear in the diagram — one on each side of the crankcase — both carrying part number 505 27 57-19. These are the crankshaft oil seals, and their job is to keep the crankcase sealed at the points where the crankshaft exits the housing on either end (the flywheel side and the clutch side).
These seals prevent air from leaking in and keep the crankcase pressure stable. If a seal wears out, air gets sucked into the crankcase, leaning out the fuel mixture on that side of the engine. The result is often a saw that idles fine but bogs down under load, or one that runs erratically and is nearly impossible to tune. Experienced chainsaw mechanics will tell you that bad crank seals are one of the most common — and most overlooked — causes of poor performance in older two-stroke saws.
Replacing the sealing rings requires splitting the crankcase, which means a full teardown. It’s not a quick job, but if your Husqvarna 55 has high hours on it, fresh seals can make the saw feel like new again.
7. O-Ring (Part #740 44 05-00)
A small but mighty component, the O-ring (part #740 44 05-00) sits near the center-bottom of the diagram. It provides a secondary seal at a critical junction point within the crankcase assembly, typically where the oil delivery system or fuel system interfaces with the main housing.
O-rings work by compressing slightly when two surfaces are brought together, filling any microscopic gaps and preventing fluid or air from passing through. They’re made from synthetic rubber compounds that resist fuel, oil, and heat — all of which are present in abundance inside a running chainsaw engine.
The tricky thing about O-rings is that they deteriorate slowly and invisibly. You won’t notice a failing O-ring until it starts leaking, and by then, the leak may have already affected engine performance or caused oil starvation to the bar and chain. During any teardown, inspect every O-ring carefully. If there’s any sign of hardening, cracking, or deformation, replace it. They cost almost nothing and take seconds to install.
8. Bar Bolt (Part #503 68 42-42)
The bar bolt (part #503 68 42-42) is the fastener responsible for securing the chainsaw’s guide bar and chain tensioning mechanism to the crankcase body. You’ll find it toward the bottom-center of the diagram, protruding from the crankcase at the point where the bar-side cover attaches.
This bolt takes a beating during normal operation. Every time the chain catches, kicks, or loads up in a cut, that force transfers through the bar and into this bolt. A loose or damaged bar bolt can cause the guide bar to shift during cutting — which is both a performance issue and a safety hazard. The chain can jump off the bar, or the bar can twist under load, putting you at risk.
Checking the bar bolt’s tightness should be part of your pre-use checklist every single time you fire up the saw. It only takes a few seconds with a wrench, and it could save you from a dangerous situation.
9. Bumper Spike (Part #501 79 50-01)
Positioned at the lower-left area of the diagram, the bumper spike (part #501 79 50-01) — sometimes called a felling spike or dog — is the toothed metal piece that mounts to the front of the crankcase, just behind the guide bar. Its purpose is to give you a pivot point when making cuts. You dig the spike into the wood, then lever the bar downward through the log.
This technique dramatically reduces the physical effort of cutting, especially with larger logs. Instead of pushing the running chain straight into the wood with brute force, you use the spike as a fulcrum and let leverage do most of the heavy lifting. It’s one of those features that separates a well-designed chainsaw from a cheap one.
Over time, the spike’s teeth can dull or chip, especially if they contact metal (nails in firewood, for example). A dull spike slips on the wood surface instead of gripping, which makes the saw harder to control. Replacement spikes are widely available and easy to swap.
10. Tank Vent Assembly (Part #503 66 84-01)
The tank vent assembly (part #503 66 84-01) appears on the left side of the diagram, tucked into the crankcase body near the fuel tank area. It’s a small valve that allows air to enter the fuel tank as fuel is consumed, preventing a vacuum from forming inside.
Here’s why that matters. As the engine burns fuel, the level in the tank drops. Without a vent, the empty space above the fuel would create a vacuum that eventually stops fuel from flowing to the carburetor. The saw would sputter, lose power, and stall — typically after running fine for a few minutes. A clogged or malfunctioning tank vent is actually one of the most common causes of intermittent stalling in older Husqvarna chainsaws.
Testing a tank vent is straightforward. If your 55 runs well for a few minutes then dies, try loosening the fuel cap slightly. If the saw stays running, the vent is likely blocked. Replacing this tiny component can solve what feels like a much bigger problem.
11. Tank Cap Holder (Part #503 57 89-01)
Sitting near the bottom-center of the diagram, the tank cap holder (part #503 57 89-01) is the retention mechanism that keeps the fuel cap tethered to the saw body. It might seem like a minor convenience feature, but there’s a practical reason behind it.
Chainsaws are often used in dirty, cluttered environments — sawdust piling up, wood chips flying, tools spread across a stump. Losing a fuel cap in that mess is easier than you’d think. And running a chainsaw with an open fuel tank is a fire hazard, not to mention the debris that would contaminate the fuel. The holder keeps the cap attached so it’s always right there when you’re done refueling.
12. Fasteners — Screws, Nuts, and Pins
Throughout the diagram, you’ll see a variety of fasteners identified by their individual part numbers: screws (503 20 02-16, 503 20 02-25, 503 20 02-50, 724 33 25-56), nuts (503 22 62-01, used three at a time), a grooved pin (721 12 10-40), and parallel pins (720 13 07-10). These aren’t glamorous parts, but they hold every single component in place.
Husqvarna uses specific fastener types and sizes for different joints throughout the crankcase assembly. The socket head cap screws (IHSCFM type) at various lengths handle the main crankcase-to-cover joints, while the cross-recessed pan-head screws secure lighter components. The parallel and grooved pins provide alignment and retention for parts like the starter pawl mechanism, making sure everything stays precisely positioned during operation.
One common mistake during reassembly is using the wrong screw in the wrong hole. It might thread in fine, but if it’s too long, it can bottom out and crack the magnesium crankcase. If it’s too short, it won’t clamp properly. Always reference the parts diagram to match each fastener to its correct location — it saves a lot of grief down the road.
