KTM 125 Duke (All years) Simplified Maintenance Schedule

This is the simplified maintenance schedule for the KTM 125 Duke, the smallest Duke in KTM’s line of attractive and peppy street sport bikes.

The KTM 125 Duke is powered by a 125 cc (surprise!) single-cylinder liquid-cooled engine. It has dual overhead cams and four valves. With a high compression ratio of 12.8:1, KTM squeezes an impressive 11 kW / 15 hp out of the motor, with peak power arriving at 10500 rpm (similar to previous generations).

KTM has made the 125 Duke for over a decade. But like other Dukes, KTM has restyled the duke significantly in recent years, keeping it in line with the rest of the Duke model range. The engine has stayed fundamentally the same though, so the maintenance schedule is the same.

The KTM Duke is a little sibling to other modestly sized KTM bikes, like the immensely popular KTM 200 Duke, for example.

See some photos of earlier generation 125 Dukes in the slideshow below.

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KTM 125 Duke Service Intervals

The KTM 125 Duke is a compact sport motorcycle that, despite its sharp good looks and peppy engine, is oriented towards a lot of low-speed start/stop-work. Thus, the KTM 125 Duke has relatively short service intervals of 4650 miles or 7500 km, at which point you should change the oil and filter, change the air filter, and do a whole host of checks.

Every two services (every 9300 miles or 15000 km), change the spark plug and check the valve clearances. The KTM 125 Duke is a naked bike and there’s just one cylinder, so the valve clearance check is not actually too bad. But there are four valves, in contrast with many other “simple” motorcycles like the Kawasaki Z125 Pro, which have two-valve engines.

Finally, the 125 Duke is a liquid-cooled bike, so change the coolant periodically, and keep the brake fluid up to date.

KTM 125 Duke Maintenance Schedule

Like other KTM motorcycles, the 125 Duke’s maintenance schedule in the manual is broken up into “required” and “recommended” work. But many of the items in the “recommended” section are either easy to do or frequently required work in other motorcycle schedules (e.g. to replace the coolant every 4 years). So we’ve included them together.

To simplify this we’ve split it into the standard service and the scheduled maintenance table, so you can easily see what to do every service, and what is only done occasionally.

KTM recommends most of the work be done by mechanics, and users only do the following:

  • Check brakes (maybe replace if necessary)
  • Check/adjust tyre pressures
  • Check/adjust chain tension
  • Check coolant and brake fluid levels

And very little else. So KTM doesn’t want you to, for example, change brake pads or brake fluid.

Of course, servicing the 125 Duke isn’t hard as a single-cylinder naked bike, so it’s up to you.

KTM 125 Duke — Standard Inspection Checklist

Below is the inspection checklist for the KTM 125 Duke. Do this according to the schedule below (every service).

KTM 125 Duke Standard inspection checklist
[Dealer] Check the fault memory using the KTM diagnostics tool.
Check that the electrical system is functioning properly.
Check the brake discs (thickness, evenness of wear)
Check the front brake linings.
Check the rear brake linings.
Check the brake lines for damage and leaks.
Check the front brake fluid level. (Note: Brake fluid changes with pad wear)
Check the rear brake fluid level
Check the tire condition, replace as necessary
Check tire pressure, adjust as necessary
Check the shock absorber and fork for leaks
Check the chain tension; adjust as necessary.
Check the coolant level
Check the antifreeze / antiboil if you have the right equipment
Check that the radiator fan is functioning properly (with engine warm)
Chek that the throttle cables are undamaged, routed without sharp bends, and set correctly.
Check the cables for damage and routing without sharp bends
Check the steering head bearing play.
Empty the drainage hoses
Check all hoses (fuel, coolant, bleeder, drainage etc.) and sleeves for cracking, leaks, and incorrect routing
Grease all moving parts (e.g. side stand, hand lever, chain) and check for smooth operation
Check the tightness of the safety-relevant screws and nuts which are easily accessible.
Final check: Check the vehicle for safe operation and take a test ride.
[Dealer] Read out the error memory after the test ride using the KTM diagnostics tool.
[Dealer] Set the service interval display.
[Dealer] Make a service entry in KTMDealer.net
KTM 125 Duke — Standard inspection checklist

KTM 125 Duke — Maintenance Schedule

Below is the scheduled maintenance table for the 125 Duke.

Notes

  • Keep following the schedule in the pattern shown.
  • Some items have a time-based schedule only (e.g. fluids), some a distance-based schedule only (e.g. valve clearance), but many items have both.
  • We’ve rounded some of the interval distances (nobody is going to do a service at exactly 4650 miles, so we put it at 4700 for example)
mi x 10000.64.79.31418.6
km x 100017.51522.530Every
Conduct a standard inspection service (see list above)Year
Change the engine oil (Motorex 15W-50)Year
Change the oil filterYear
Clean the oil screenYear
Clean the dust boots of the fork legs
Change the air filter, clean the air filter box.
Check the chain, rear sprocket, and engine sprocket
See below for notes on chain maintenance
Year
Check the valve clearances
Intake: 0.10-0.15 mm (0.0039-0.0059 in)
Exhaust: 0.15-0.20 mm / 0.0059 – 0.0079 in
Change the spark plug (Bosch VR 5 NEU)
Earlier manuals specified VR 5 NE
Check the frame (rust, cracks)
Check the link fork
Check the fork bearing for play
Check the wheel bearing for play
Change the front brake fluid. (Castrol DOT 4)2 years
Change the rear brake fluid. (Castrol DOT 4)2 years
Change the coolant (Motorex M3.0 Coolant)4 years
Check the headlight setting
KTM 125 Duke Maintenance Schedule

Maintaining the Chain on the KTM 125 Duke

As a commuter bike, or even as a delivery bike (a common use for the smaller Dukes), the 125 Duke needs regular attention to the chain.

Generally speaking, clean your chain at least every 1000 km or 600 miles, or more often if you’ve been riding in the wet or in dirty conditions. Use a good quality chain lube. KTM recommends Motorex Chain Lubricant and Motorex Chain Cleaner, but most other similar products should suffice. Motul chain paste is well-liked and portable.

At every service, check the chain tension. Put your Duke up on a stand or the kickstand, find the spot on the chain right behind the chain sliding guard, and push it up. The distance should be 5-7mm (0.2-0.28 in) from the swing arm. If it’s not, then adjust the chain tension.

If you’re on a kickstand, you may need to roll the bike around a bit to find the tightest spot. Otherwise, just spin the back wheel.

KTM 125 Duke chain tension diagram

Adjust the chain tension on a rear stand. Follow this process

  1. Loosen the rear nuts
  2. Use the chain adjuster bolts on either side to change the chain tension.
  3. Tighten the rear axle nut to 98 Nm / 72.3 lb-ft (which is quite a lot)

Make sure your rear wheel is aligned at the end, too — it should move back the same amount on either side.

Wheels, Tires and Tire Pressures for the KTM 125 Duke

The 125 Duke ships with Metzeler Sportec M5 Interact tires tires, but any street/sport tires in the below sizes should suit.

WheelTire sizeTire pressure (cold)
Front110/70 ZR 17 M/C 54W TL2 bar / 29 psi
Rear150/60 R 17 M/C 66W TL2-2.2 bar / 29-32 psi
(Depending on load / passenger)
KTM 125 Duke tire sizes and pressures

Adjust the tire pressures depending on your load, passenger, and also your riding style.

About the KTM 125 Duke

2021 KTM 125 Duke RHS Static night
2021 model KTM 125 Duke, night-time static image

The KTM 125 Duke is another KTM compact motorcycle that really punches above its weight.

KTM makes a bunch of small, lightweight motorcycles, including the 200 Duke and the 390 Duke. So they’re no strangers to small displacement.

But what makes the 125 Duke different from other bikes you might be tempted to put in its class is that it’s both surprisingly high powered and also high spec.

The engine, for starters, makes over 50% more claimed power than many motorcycles of similar displacement, like the uber-popular Honda Grom for example, which has a much more rudimentary air-cooled 2-valve engine.

It’s really modern, with liquid cooling, four valves, and two camshafts in that tiny block.

The 125 Duke shares a lot of specs with its slightly bigger sibling, the 200 Duke. For example, both bikes have WP inverted forks, and both have four-piston calipers on 300 mm rotors.

The 125 Duke also has a high-quality build, and looks fantastic. It borrows a lot of styling elements from the KTM 1290 Super Duke, which has over ten times the engine capacity and power output.

But of course, the two bikes have different engines with markedly different power output. The 200 Duke puts out quite a lot more power, and is geared slightly lower.

KTM has made some small changes to the 125 Duke over the years. They’ve moved between waved and non-waved rotors, upgraded the console and display, and changed the general design slightly.

But the engine has always remained roughly the same, putting out around 15 hp at around 10000 rpm, with most of the torque coming around up top. You have to keep the engine singing between 6 and 10K to really get the most out of the KTM 125 Duke. Of course, the fun is that you can do so without going to jail (or the hospital).

The KTM 125 Duke has capable brakes, too, especially given its light weight. There’s a four-piston caliper up front made by ByBre (the company that kind of shares branding with Brembo… kind of) gripping on a generous 300 mm disc.

And the 125 Duke has inverted forks, something you don’t often see on “budget” motorcycles.

Other touches you’ll see on the KTM 125 Duke that you may not see on other cheap motorcycles include the colour TFT display (from 2017 onward) and a six-speed transmission, to help you get to freeway speeds… barely (and only the slower 60 mph / 100 km/h freeways). Anyway, that’s not a place you’ll stay for long!

Reference — Maintenance schedule screenshots from the KTM 125 Duke Manual

The above information came from the 2021 manual for the KTM 125 Duke, looking at various years for comparison.

The earlier years did not break up the maintenance schedule into “recommended” and “required” work, and also had fewer items on the list. But they’re functionally the same motorcycle and same maintenance schedules.

Some screenshots for the manual for reference are below.

You can download manuals for KTM motorcycles from ktmshop.se.

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