Track Rollers Guide: Choosing, Confirming and Replacing Bottom Rollers

A track roller - bottom roller, lower roller, or just roller - is the part that carries the machine's weight on the lower run of the chain. It is the first undercarriage component to wear and the one whose failure spreads fastest: a roller that seizes skids along the chain and grinds a flat onto the link it drags against, and a roller whose running surface has grooved drops the chain lower on the frame and transfers load onto its neighbours. Choosing the right one is a fitment question first and a price question a distant second.

Last updated: October 6, 2026

This page is the doorway to everything we publish about track rollers: what they do, how to confirm fitment, what separates a roller that lasts from one that does not, how to read the roller you are taking off, and how to buy in Canada. If you already know the part number, the track roller range is the fastest route.

What the roller does, and where it sits

Every bottom roller does three jobs. It carries a share of the machine's weight, it keeps the chain travelling in a straight line between the front idler and the drive sprocket, and it absorbs the shock of the ground the chain rolls over. On a compact excavator that share is significant: the frame is short, the machine pivots constantly, and the rollers nearest the idler take the lateral load of every turn.

Construction is simple and everything important is sealed inside. A roller is a hardened shell on a shaft, with bearings behind seals at each end. Because it cannot be re-greased in service, the seal decides how long it lasts - once grit and water get past it, the oil leaves, the bearing fails and the roller stops turning. That is the failure that damages the chain, and it is the reason a weeping seal is a replace-now finding rather than something to note for next season.

Confirming the right roller

Five measurements, all taken from the roller you are removing rather than from a catalogue drawing. The part number against your machine's model and serial number, which is the fitment answer and should come back in writing. Running-surface diameter, which sets how high the chain sits. Running-surface width, which has to suit the chain the machine runs. Flange type - single or double - with the flange height, because the flange is what holds the chain in line. And the mounting: bore diameter, bolt pattern and overall height, measured with the hardware off, because those dimensions cannot be checked once the roller is bolted up.

Two further items belong in the same conversation and sit outside the size figures: the bearing type and load rating, and the seal design. On a machine working in mud, water and abrasive dust - most of what a compact excavator does in Canada - those two decide service life more than the price does. The same discipline applies across the range; where a machine runs a different bottom roller for a heavier class of work, the fitment example in whether a Komatsu undercarriage bottom roller fits PC200 models shows how series-specific the answer can be.

What decides how long a roller lasts

Three things, in order. The seal, because contamination rather than load ends these parts. The running surface, which has to be hard enough to resist the groove the links cut without being so hard that it cracks under side impact when the machine pivots on rock - so the question to ask is "what material and what treatment", not "how hard". And the tension the machine is run at, since a belt run tight loads every roller and the idler continuously, while one run slack lets the chain slap and climb.

A fourth factor is the state of the rest of the assembly. Rollers wear into the pattern of the chain and sprocket they run with, so a new roller under a stretched chain or behind a hooked sprocket wears out early. That is the argument for judging the assembly rather than the part, and it is the same reasoning behind how sprockets and rollers relate.

Reading the roller you are removing

With the machine raised and the track slack, four observations cover most of it. A roller that will not turn freely by hand has lost its bearing, and it will drag a flat onto the chain. Play felt with a bar under the roller means the shaft or bearing is worn - worth measuring rather than judging by feel, because the roller's whole job is holding a precise line. Oil or grease weeping at the seal is the end of the roller, since there is nothing left to top up. A groove or flat worn into the running surface is normal end of life, but note where it sits, because a replacement that wears into the same pattern means the chain is not running true.

Inspection is covered in more detail in how to inspect track rollers for wear and damage, and the parts of the job that come up on specific machines are gathered below.

Buying track rollers in Canada

Four items belong in writing: the part-number cross-reference for your model and serial number; the specification as supplied, including flange type, bore and running-surface diameter; the warranty terms as a period plus an operating-hours cap, whichever comes first, with freight responsibility named; and the stock position with a delivery date. On a machine that is earning, the delivery date is usually the line that decides the purchase.

Where rollers are being replaced as a set - which is the sensible approach when they share the same hours and ground - the same four items apply to each number in the order. It is also worth asking whether the supplier can quote the whole assembly, because the belt, idler and sprocket usually come due together, and the access work is the expensive part of any undercarriage job.

Rollers as a set, and what to keep

Track rollers are almost never replaced one at a time on a machine that has done real hours. They share the same ground and the same chain, so they wear at similar rates, and when one has failed the rest are usually close behind. Replacing the set in one job also avoids the trap that catches single replacements: a new roller running beside worn ones sits at a slightly different height, so it carries more than its share of the load and wears into the pattern the old set already had.

The exception is damage rather than wear - one roller cracked by impact, or one that has seized because its seal failed early. There, a single replacement is reasonable, provided the rest of the set is measured and found within its limits. What matters either way is that the decision comes from the inspection rather than from the invoice history.

For anyone keeping a machine running rather than rebuilding it, two numbers are worth holding: the total number of rollers per side, and the mix of flange types along the frame. Both are easy to record the first time the track is off, and both are the questions a supplier will ask when a set is being ordered. The same record is what makes a repeat order a one-line email instead of a second measurement session.

The rest of this cluster

What a roller does on a machine: the role of track rollers in heavy machinery. How they are built: Bobcat E35 bottom rollers and their bushings. How they behave over time: roller performance in forestry applications and Hitachi EX200 bottom roller longevity.

Fitment on specific machines: whether a Kobelco roller fits SK210 models and what to expect on a Case CX210 roller. Buying: the buyer's checklist, what to compare online and why aftermarket rollers are worth considering. For how rollers fit with the rest of the system, see how track rollers and carrier rollers differ, and the top-level guide at excavator undercarriage parts.

FAQs

What is the difference between a track roller and a carrier roller?

The track roller - bottom roller - carries the machine's weight on the lower run of the chain. The carrier or top roller runs on the upper run and holds it up. They use different part numbers and sit at different positions on the frame.

How do I know which track roller fits my machine?

By the part number cross-referenced against your model and serial number, then confirmed against the running-surface diameter and width, the flange type, the bore and the mounting pattern of the roller you are removing.

How long should a track roller last?

Life depends on the seal, the running surface and how the machine is run rather than on a single hours figure. The reliable measures are a groove worn into the running surface, play on the shaft and the state of the seal at each inspection.

Can a roller be re-greased instead of replaced?

No. These rollers are sealed, so once the seal has failed there is nothing to top up. Replacing it promptly matters because a seized roller also wears the chain it drags against.

Should track rollers be replaced as a set?

Where they share the same hours and the same ground, yes. The rest are close behind, the track is already off, and a new roller running beside worn ones wears into the same pattern the old set had.