A motorcycle oil filter must match your engine, maintain steady oil flow, and hold up to heat, pressure, and vibration. The K&N Motorcycle Oil Filter KN-138 adds a practical service feature: a welded 17 mm Wrench-Off nut that can make removal easier during an oil change. It also uses synthetic-blend filter media inside a heavy-duty spin-on canister. This review explains its verified specifications, fitment limits, installation points, and who gets the most value from it.
Quick Verdict
Rating: Recommended with caveats
Best For: Riders whose exact motorcycle application is listed for KN-138 and who want wrench-assisted filter removal.
Bottom Line: The KN-138 combines high-flow synthetic-blend media, a durable canister, and a useful 17 mm removal nut. Its main limitation is strict vehicle-specific fitment, so you must confirm the model, year, engine, and filter cross-reference before ordering.
Key Specifications
| Specification | Detail |
|---|---|
| Brand | K&N |
| Model | KN-138 |
| ASIN | B000E2CVDI |
| Product type | Vehicle-specific powersports oil filter |
| Design | Spin-on filter with heavy-duty canister |
| Filter media | High-flow synthetic-blend filtration media |
| Height | 3.031 inches (77 mm) |
| Outside diameter | 2.813 inches (71 mm) |
| Thread specification | M20 × 1 |
| Gasket material | Nitrile rubber |
| Valves | Anti-drain-back valve, bypass valve, and pressure-relief function listed |
| Removal feature | Welded 17 mm hex nut, pre-drilled for safety wire |
| Weight | 0.6 lb (0.3 kg) |
| Oil compatibility | Synthetic, conventional, and blended motor oils |
| Package quantity | One oil filter |
| Warranty | K&N one-year limited warranty |
| Compatibility | Select Suzuki and other listed powersports applications. Confirm exact fitment before purchase. |
What Is the K&N Motorcycle Oil Filter KN-138?
The K&N KN-138 is a replacement spin-on oil filter for specific motorcycles and powersports vehicles. K&N designed it to provide consistent oil flow while its pleated synthetic-blend media removes harmful contaminants from circulating engine oil.
The model is commonly associated with many Suzuki applications, and K&N also lists cross-references and fitments beyond Suzuki. The KN-138 is not universal. Its M20 × 1 thread, 71 mm outside diameter, gasket, valve setup, and clearance must match the vehicle.
Who Should Buy It?
Best For
- Riders whose owner’s manual, current filter, or official fitment lookup identifies KN-138.
- DIY owners who want a welded 17 mm nut for easier filter removal.
- Street, touring, sport, or powersports users who need compatibility with synthetic, conventional, or blended oil.
Skip If
- Your motorcycle does not list KN-138 or a verified cross-reference.
- You need a cartridge-style filter rather than a spin-on canister.
- You plan to choose a filter only by diameter or appearance without checking threads, gasket, valves, and clearance.
Before You Buy: KN-138 fitment varies by exact make, model, year, and engine. Confirm it through K&N’s vehicle lookup, your owner’s manual, or the part number printed on the filter you are replacing.
Filtration, Oil Flow, and Easy Removal
Synthetic-Blend Filter Media
K&N uses pleated synthetic-blend media in the KN-138. The media is designed to capture harmful engine contaminants while allowing a consistent flow of oil. That balance matters because the filter must clean the oil without creating unnecessary restriction in a correctly matched lubrication system.
The filter supports synthetic, petroleum-based conventional, and blended motor oils. This does not change your motorcycle’s oil requirement. You still need the viscosity, service classification, and change interval listed by the vehicle manufacturer.
Heavy-Duty Spin-On Canister
The metal canister is built for the heat, vibration, pressure, and road exposure found in powersports use. K&N states that the filter is laboratory tested for capacity, efficiency, and mechanical strength. The design also includes an anti-drain-back valve, a bypass valve, and pressure-relief functionality.
Those internal features must match the engine application. A filter that screws on is not automatically correct if its bypass setting, sealing surface, or internal valve arrangement differs from the required part.
17 mm Wrench-Off Nut
The welded 17 mm hex nut is the KN-138’s clearest convenience feature. It gives you a solid point for filter removal when hand grip is limited or the old filter is tight. The nut is also pre-drilled for safety wire attachment where a vehicle, event, or racing rule requires it.
Use the nut mainly for removal unless K&N or your motorcycle manual states otherwise. Over-tightening a spin-on filter can damage the gasket, make the next service difficult, or contribute to leaks.
How It Performs in Real Use
For Routine Street Maintenance
For normal street riding, the KN-138 works as a direct service replacement when the fitment is correct. Its broad oil compatibility makes it easy to pair with the manufacturer-approved oil you already use. Replace it at the interval specified by the motorcycle maker rather than assuming the filter alone extends the service schedule.
For Touring and High-Mileage Riding
Touring riders may value the durable canister and the manufacturer’s stated high-flow design. Long rides still demand regular oil-level checks and scheduled maintenance. The filter cannot compensate for incorrect oil, low oil level, overheating, or an interval that exceeds the motorcycle manufacturer’s recommendation.
For DIY Oil Changes
The 17 mm removal nut is most useful during home maintenance. It can reduce the need for a strap wrench or filter pliers when access is tight. You still need enough clearance to place a socket or wrench squarely on the nut.
For Safety-Wired Applications
The pre-drilled nut gives you an attachment point for safety wire. This is useful only when safety wiring is required and installed correctly. Follow the event rules, service manual, and accepted safety-wiring practice rather than improvising the wire path.
Fit, Construction, and Compatibility
The verified KN-138 dimensions are 77 mm high and 71 mm in outside diameter, with an M20 × 1 thread and nitrile-rubber gasket. These measurements help identify the product, but they are not enough to prove fitment by themselves.
K&N lists several Suzuki original-equipment cross-references, including 16510-03G00, 16510-03G00-X07, 16510-06B00, 16510-06B01, and 16510-34E00. It also lists cross-references for selected Aprilia, Arctic Cat, Kymco, and Fram applications. Always verify the exact vehicle, because cross-reference lists can include model-year limits and application exceptions.
Pro Tip: Compare the KN-138 number with the old filter before draining the oil. Also confirm that you have enough room for the canister and the 17 mm nut once the filter is installed.
Installation Tips for the KN-138
Install the KN-138 only after confirming vehicle compatibility and reviewing the motorcycle’s oil-change procedure. Work on a stable motorcycle, protect yourself from hot oil and exhaust parts, and use a drain pan suitable for used engine oil.
- Remove the old filter and make sure its gasket did not remain stuck to the engine sealing surface.
- Clean the filter mounting surface without scratching it or pushing dirt into the oil passage.
- Apply a light film of clean engine oil to the new filter’s nitrile-rubber gasket.
- Start the filter by hand to avoid cross-threading the M20 × 1 threads.
- Tighten it according to the motorcycle manual or K&N instructions. Do not guess at a torque value.
- Refill with the correct oil quantity and specification, start the engine, and inspect the gasket area for leaks.
- Shut the engine off, wait as directed by the manual, and recheck the oil level.
After the first short ride, inspect the filter area again. Stop the engine immediately if you see active leakage or receive an oil-pressure warning. Used oil and filters should go to an approved recycling or disposal facility.
Pros and Cons
Pros
- Synthetic-blend media is designed for high flow and contaminant capture.
- Works with synthetic, conventional, and blended motor oils.
- Welded 17 mm nut can simplify removal in confined spaces.
- Pre-drilled nut supports properly installed safety wire where required.
- Heavy-duty canister and one-year limited warranty add practical value.
Cons
- Vehicle-specific fitment creates a real risk of ordering the wrong filter.
- The removal nut does not eliminate the need for correct hand-starting and tightening.
- It may offer less value if your correct OEM-style filter is easier to source or costs less.
Is It Worth the Price?
The KN-138 sits in the premium replacement-filter category rather than the most basic budget tier. Its value comes from the welded removal nut, high-flow synthetic-blend media, heavy-duty canister, tested construction, and one-year limited warranty.
It is worth considering if you do your own oil changes and the 17 mm nut will make service easier. It may be less compelling if an approved OEM filter is cheaper, readily available, and easy to remove on your motorcycle. Fitment should decide the purchase before convenience or brand preference.
How It Compares to Alternatives
An OEM Suzuki oil filter is the simplest comparison because it is designed around the original application and service requirements. Hiflofiltro HF138 is another commonly cross-referenced motorcycle filter, while Fram PH6018 appears in K&N’s cross-reference data for KN-138.
Compare verified fitment, filter construction, removal method, warranty, and availability. The K&N makes the most sense when you specifically want its 17 mm Wrench-Off nut and your vehicle is confirmed on the application list.
Frequently Asked Questions
Does the KN-138 fit every Suzuki motorcycle?
No. It fits selected Suzuki models and years, not the entire brand. Check the official K&N application lookup, your owner’s manual, or a verified filter cross-reference for your exact motorcycle.
Can I use the KN-138 with full synthetic oil?
Yes. K&N states that it works with synthetic, conventional, and blended motor oils. Your oil still needs to meet the viscosity and service specification required by the motorcycle manufacturer.
What size wrench fits the removal nut?
The welded removal nut takes a 17 mm wrench or socket. Use it carefully and keep the tool square on the nut to avoid slipping.
Should I tighten the KN-138 with the 17 mm nut?
Start and tighten the filter according to K&N’s instructions and your motorcycle service manual. The nut is primarily promoted for Wrench-Off removal, so do not use it to over-tighten the filter.
How often should I replace the KN-138?
Follow the filter-replacement interval in the motorcycle owner’s manual. Riding conditions, oil choice, engine design, and manufacturer instructions determine the correct schedule.
Does the package include more than one filter?
The verified Amazon listing identifies one KN-138 oil filter per package. Check the seller’s current quantity details before ordering, especially when comparing multipacks or marketplace offers.
What warranty covers the KN-138?
K&N lists a one-year limited warranty for this filter. Review the current warranty terms and required proof of purchase before relying on coverage.
Can the KN-138 replace an HF138 or Fram PH6018?
K&N lists Fram PH6018 in its KN-138 cross-reference data, and HF138 is a common competing application number. A cross-reference is not a substitute for checking the exact vehicle, year, engine, clearance, and manufacturer requirements.
The Bottom Line
The K&N KN-138 is a practical premium filter for riders who have confirmed fitment and value easier wrench-assisted removal. Its main strengths are the synthetic-blend media, durable spin-on construction, broad oil compatibility, and 17 mm nut. Skip it when your application is uncertain or when an approved OEM option better fits your maintenance needs and budget.
Ready to Buy?
Confirm your motorcycle’s fitment, then check the latest product details before you decide.
