What’s a Timing Belt? 6 Checks to Run Before You Rush-Order a Replacement

If your line just stopped and you’re about to search for a replacement part, start here. I work on the application-support side at Tsubaki of America (the folks behind the tsubaki-chain catalog), and part of my job is taking emergency calls from plants that need a drive component identified, sourced, and shipped before the shift ends. Last quarter alone we handled 47 rush orders, and I’d estimate a good third of them almost shipped with the wrong part name on the box.

This is a six-check checklist I walk through when I can’t see the machine myself. It assumes you have a broken component in front of you (or at least a decent photo) and you want to order the correct replacement quickly. If that’s your situation, take ten minutes and run these checks before you call anyone. It’s cheaper than express-shipping the wrong part.

The Six Checks at a Glance

1. Is the failed motion linear or rotary?
2. Rubber or steel? Identify the broken material.
3. If it’s toothed rubber, confirm it’s a timing belt.
4. If it’s metal links, confirm the roller chain pitch and width.
5. Could it be a gear drive instead?
6. Inspect the sprockets, pulleys, and tensioners before ordering.

Check #1: Is the Failed Motion Linear or Rotary? (Think Hydraulic Linear Actuator)

This is the step most people skip, because they’ve already decided they have a chain or belt problem before looking at what’s actually moving. What I mean is: a machine can stop because a cylinder stopped moving, not because the motor or the belt feeding it broke.

If the failed motion is a straight push, pull, lift, clamp, or press, your likely suspect is a hydraulic linear actuator. Look for oil film on the rod, leakage around the seals, or a cylinder that drifts when the pump is off. If you see any of those, ordering a timing belt won’t fix a thing.

If it is an actuator, record what’s on the nameplate before disassembly: bore, rod diameter, stroke, mounting style, and port sizes. If the nameplate is gone, measure carefully and expect a longer lead time. And before you ask—no, converting the machine to a chain-driven linear mover during an emergency is not a shortcut. That changes the machine’s force and speed behavior completely. It’s a redesign, not a replacement part.

Check #2: Look at What Actually Broke — Rubber or Steel?

Take a photo before you clean anything or pull parts off. It’s surprising how much you can identify from a five-second photo once oil and grime are out of the way. I’ve had calls where the customer was sure they needed a belt, and the photo showed steel link chain sitting right next to the rubber dust. The eye sees what it expects.

• Rubber, polyurethane, or flexible material with teeth = belt.
• Steel links with pins and rollers = chain.
• Two or more steel gears meshed directly, with no flexible element = gear drive.

Also look for part numbers. A timing belt often has a number printed on the back, but the printing can wear off long before the belt fails. That’s why you photograph it before cleaning it. A chain may have a brand mark and chain number stamped on the side plates. US Tsubaki chain products are usually marked this way, though chains that have been painted over are a different story.

Check #3: So, What’s a Timing Belt? Here’s How to Confirm It

In short, a timing belt is a toothed belt that keeps two or more shafts rotating in time with each other. In a car engine, it keeps the crankshaft and camshaft synchronized. In an industrial machine, it does the same job for two rolls, spindles, or indexing shafts—no slip and no skipped rotation. The teeth lock into matching sprockets, which is why a timing belt isn’t anything like a V-belt.

If the belt is smooth or has small ribs running along the length, it’s not a timing belt. Those are V-belts or serpentine accessory belts, and they’re ordered by length and cross-section, not tooth profile. Don’t let anyone upsell you into a synchronous belt for a V-belt drive, or vice versa. Put another way: a timing belt is a synchronous drive; a V-belt is a friction drive.

If it is a timing belt, you need three numbers:

• Pitch — the distance from tooth center to tooth center.
• Width — measured across the belt itself, not between flanges.
• Length, or better, tooth count around the full loop.

Here’s the mistake I see most: measuring only the width and overall length. Two belts can be the same width and length but have different tooth profiles—HTD/GT curved tooth, trapezoidal, T5/T10 metric, 8mm pitch, 14mm pitch. If the profile doesn’t match the pulley, the belt will ride wrong and fail quickly. If you can’t identify the profile from a photo, measure the tooth pitch and the tooth shape, and send that info to a supplier who knows drives.

I remember a March 2024 rush order where a customer sent a photo of a “broken timing belt” and asked us to match it by width. The width was right; the pitch was off by a few millimeters. The replacement arrived next morning and didn’t fit the sprocket. We covered the freight to make it right, but the line sat down an extra day (ugh). That’s the kind of downtime this checklist is meant to prevent.

Check #4: If It’s Steel Links, Confirm Roller Chain Pitch and Width

If the broken material is steel links with small rollers between the inner plates, it’s usually a roller chain. Roller chain is the workhorse of industrial power transmission—conveyors, mixers, packaging equipment, and dozens of other applications. When someone searches for “US Tsubaki chain” or “tsubaki roller chain,” this is normally the product they’re after.

Ordering roller chain isn’t hard if you have the old chain or its markings. Check the side plates for a stamp. For ANSI chain, the number tells you the pitch in eighths of an inch. A #60 chain has 6/8” pitch, which is 3/4”. A #80 chain has 8/8” pitch, which is 1”. A #40 is 4/8”, or 1/2”.

If there’s no stamp, measure from the center of one pin to the center of the next pin across three consecutive pitches, then divide by three. That gives you pitch. Then measure the width between the inner plates and count the total number of links. A chain can have the right pitch and the wrong width—both must match the sprockets.

One more thing: if you’re replacing only one strand of a multi-strand drive, look at the other strands first. If they’re stretched or heavily worn, you’ll be doing this again soon. And a new chain running on old, hooked sprockets wears out fast. I recommend replacing the chain and sprockets as a set when the sprocket teeth show a hook-shaped wear pattern. Spending a bit more on the full set is often the faster route overall, not the slower one.

(Not every steel-link component is roller chain. Leaf chain has no rollers, and engineering steel conveyor chain is a different product. If the links don’t have rollers, slow down and get a second opinion before ordering.)

Check #5: Could It Be a Gear Drive? (And What Happened to Pete Jackson Gear Drives)

If you see two or three steel gears meshed directly, with no belt and no chain in between, that’s a gear drive. Some older machines use them, and classic V8 engines sometimes run them on the camshaft. That’s where a question I get a lot comes from: “What happened to Pete Jackson gear drives?”

Pete Jackson was one of the better-known names in aftermarket gear drives for older American V8s. I don’t have the company’s full corporate history memorized, so don’t quote me on owners or dates. The technology part I can explain: a gear drive replaces the timing chain with metal gears. Gears don’t stretch, so valve timing stays locked at high RPM, which made them popular with drag racers and engine builders. They also make a distinctive whine that some people love and others hate.

What happened to them as a product category? Engines moved toward overhead-cam designs with timing belts or chains, and later toward variable valve timing systems that need a flexible belt or chain. A rigid gear drive can’t adjust cam timing the way a computer-controlled phaser requires. Gear drives are still sold for classic-car restoration and niche racing, but they’re not in new vehicles. As of January 2025, I still see the classic gear-drive kits in specialty catalogs. The market is just much smaller than it was.

If you do have a gear drive with a chipped or broken tooth, don’t order a chain conversion kit as a rush fix. The cam gear, crank gear, and any idler gear must match each other, and the idler has to stay in mesh with both main gears. This is a case where measurements and tooth counts matter more than the brand name on the cover.

Check #6: Inspect Sprockets, Pulleys, and Tensioners Before You Call

A new belt or chain is only one component. The reason the old one failed may still be sitting on the machine. Check the sprocket or pulley teeth for wear patterns—hooks on chain sprockets, polished or rounded teeth on timing pulleys. If one sprocket is damaged, ordering a single belt or chain isn’t an emergency solution; it’s a second failure waiting to happen.

Also check tensioners and idlers. If a bearing is dry, rough, or wobbly, replace it while you’re in there. On engine timing belt jobs, the normal practice is to install a new tensioner along with the belt. On industrial drives, the same logic applies: labor and downtime cost more than the tensioner does. If it feels suspect, don’t reuse it just to save one part number.

Common Mistakes That Turn a Rush Order Into a Return

Ordering by “it looks like the same size.” Belts and chains that look identical can have different pitches, tooth profiles, widths, or roller styles. If you don’t have a part number, measure and photograph before calling.

Trusting a partially worn part number. Belt numbers rub off, and chain stamps get covered by paint or rust. An incomplete number can send you to the wrong page of the catalog. Confirm the number with at least one physical measurement.

Assuming a new flexible component fixes a worn sprocket. It won’t. The worn sprocket will wear the new part quickly, and you’ll be back to square one in weeks instead of years.

What I’d Tell a First-Time Buyer

If the machine came with a timing belt, stay with a timing belt during an emergency breakdown. Converting to a chain or gear drive is possible in some cases, but it’s a design change that involves different sprockets, tensioners, housings, and sometimes lubrication. It is not a same-day decision. I recommend matching what’s already installed unless an engineer has already approved a conversion.

This checklist also has limits. It assumes the machine is basically standard and the failed part is visible. If the drive was modified somewhere along the way—a gearbox swapped, a gear drive added, a belt drive converted to chain—you’re outside the normal replacement path. Then the right move is to stop and get help from someone who can look at the actual machine or detailed photos. Context matters more than brand preference. I can only speak to the industrial drives I handle in North America; if you’re working with equipment built to different standards overseas, verify before you spend money on expedited shipping.

Rush orders are stressful, but the goal isn’t to order fast. It’s to order correctly, fast. These six checks take ten minutes. In my experience, those ten minutes are the difference between a same-day fix and a next-day apology.