Animated service guide
How to Replace a Dirt Bike Chain and Sprockets
Chain and sprockets wear as a set. A new chain on hooked teeth wears out fast, and a stretched chain chews up new sprockets, so KTM, Yamaha and D.I.D all say to replace them together. The job is mostly bolts. The parts that matter are sprocket torque, the master link clip and the slack at the end.
The animated guide loads here. Every step is also written out below.
Before You Start
Tools
- Lift stand
- Sockets for the axle, sprocket nuts and front sprocket
- Torque wrench
- Chain breaker (and press or riveting tool for press-fit or rivet links)
- Pliers for the clip
- Flat chisel or punch for a lock washer (some models)
Parts And Supplies
- Chain, front and rear sprocket as a set
- Master link of the right type for the chain
- Thread locker where the manual calls for it
- New lock washer for the front sprocket nut (Yamaha)
- Chain lube
Safety
- Engine off and in gear only while you break fasteners loose. Never run the engine to turn the wheel.
- Sprocket and axle nuts are safety fasteners. Torque them to the manual value, every time.
Step By Step
Break the nuts loose first
With the bike on a stand and the old chain still on, put it in gear and crack the front sprocket nut or bolt loose. Step on the rear brake to crack the rear sprocket nuts. It is much easier while the chain holds everything still.
- Lift stand
- Sockets
Shop tip. If you are reusing nothing, check the new kit’s tooth counts against the old ones before you start. Changing either sprocket changes the chain length you need.
Split the old chain
Turn the wheel until the master link sits on the rear sprocket. Pry the spring clip off with pliers, pull the side plate, and push the link out. A riveted chain has no clip; grind the pin heads or push a pin out with a chain breaker.
- Pliers
- Chain breaker
Swap the front sprocket
Take off the sprocket cover and remove the nut or bolt. Slide the old sprocket off the shaft and the new one on, same way round. Torque the fastener with thread locker if your manual says so. On a Yamaha, fit a new lock washer and bend its tab onto a flat of the nut.
- Socket
- Torque wrench
- Thread locker
Front (engine) sprocket fastener Bike Spec Source KTM / Husqvarna / GASGAS 2-stroke 60 Nm (44.3 lbf ft) M10 screw with Loctite 2701. KTM 250/300 SX/XC 2024 OM PDF p. 134 KTM / Husqvarna / GASGAS 4-stroke 60 Nm (44.3 lbf ft) M10 screw with Loctite 243. KTM 250 SX-F 2024 OM PDF p. 151 Yamaha YZ250F 75 Nm (55 lb ft) M18 nut, new lock washer, bend the tabs onto a flat. Yamaha YZ250F 2026 OSM PDF p. 65, 205 Yamaha YZ450F 90 Nm (66 lb ft) M20 nut with lock washer. Yamaha YZ450F 2026 OSM PDF p. 64 Use the engine sprocket torque from your manual. Honda’s CRF-R owner’s manual refers this job to the service manual.
Swap the rear sprocket
Pull the rear wheel. Remove the sprocket nuts, clean the hub face where the sprocket sits, and bolt the new sprocket on. Torque the nuts in a crisscross so the sprocket pulls down flat.
- Socket
- Torque wrench
Rear sprocket nuts Bike Spec Source KTM / Husqvarna / GASGAS 35 Nm (25.8 lbf ft) M8 nuts. KTM 250/300 SX/XC 2024 OM PDF p. 139; KTM 250 SX-F 2024 OM PDF p. 159 Yamaha YZ250F / YZ450F 42 Nm (31 lb ft) M8 self-locking nuts. Yamaha YZ250F 2026 OSM PDF p. 68, 144; YZ450F PDF p. 66 Use the rear sprocket torque from your manual. Honda says to check sprocket bolts and nuts are tight between motos.
Careful. Check the bolts behind the nuts are tight in the hub. A spinning bolt won’t torque.
Size the new chain
New chains usually come long. Lay the old chain next to the new one and count pins, because the old one is worn longer and a ruler will fool you. With the same sprockets as stock, match the stock link count. Break the extra links off with a chain breaker.
- Chain breaker
Chain length Bike Spec Source Yamaha YZ250F / YZ450F 114 links, 520 Yamaha YZ250F 2026 OSM PDF p. 60; YZ450F PDF p. 59 KTM / Husqvarna / GASGAS 520 (5/8 x 1/4 in) Chain size only; count your old chain. KTM 250/300 SX/XC 2024 OM PDF p. 135 Match the old chain’s link count if the gearing is the same. Your manual or parts list gives the stock count.
Fit the master link
Wrap the chain around both sprockets and join the ends on the rear sprocket. Push the link through, fit the side plate, then the clip with its closed end facing the direction of travel. Press-fit and rivet links need the right press or riveting tool.
- Pliers
- Press or rivet tool if needed
Careful. A clip on backwards can catch and pop off. Closed end leads, every time. KTM and Yamaha both call this out.
Set slack, torque the axle
Refit the wheel, set the chain slack with the adjusters the same amount on each side, and torque the axle nut. Measure the slack again after torquing, because tightening the axle can pull it out of spec.
- Torque wrench
- Ruler
Chain slack Bike Spec Source KTM / Husqvarna / GASGAS MX 58 to 61 mm On a lift stand, at the end of the chain slider. KTM 250 SX-F 2024 OM PDF p. 87 Yamaha YZ250F / YZ450F 50 to 60 mm On a maintenance stand. Yamaha YZ250F 2026 OSM PDF p. 60, 206 Measure where and how your manual says. Each brand measures at a different spot.
Lube it and recheck soon
Torque the axle nut, lube the new chain and spin the wheel to check it runs straight on both sprockets. A new chain beds in fast, so check the slack after the first ride. KTM schedules a chain tension check after the first hour.
- Torque wrench
- Chain lube
Rear axle nut Bike Spec Source KTM / Husqvarna / GASGAS MX 80 Nm (59 lbf ft) M22x1.5. KTM 250/300 SX/XC 2024 OM PDF p. 139; KTM 250 SX-F 2024 OM PDF p. 88 Yamaha YZ250F / YZ450F 135 Nm (100 lb ft) M22. Yamaha YZ250F 2026 OSM PDF p. 68; YZ450F PDF p. 66 Use the axle nut torque from your manual. It is a safety fastener.
Sources
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