How to Find the Right Size Roller Chain When Transmission Chain has Stretched
If your roller chain is worn or stretched, figuring out the correct replacement can feel daunting. But with a straightforward approach and the right tools, you’ll be back on track in no time.
To break it down clearly: most roller chains in use today fall into one of two standard types – British Standard (BS) or American Standard (ANSI). Knowing which standard you’re working with makes the process easier. Each uses its own sizing system, but the measurements you need to identify them are universal.
What you Will Need to Measure:
You’ll need a couple of basic tools:
- Vernier calliper
- Wear gauge
Three Key Dimensions
Like many things within the engineering and power transmission world, there are three main dimensions that can get you close to identification. For example, with bearings, you measure the Inner diameter, outer diameter and width whereas v and wedge belts are measured by the top width, depth and length. And Chain is no different, the there are three dimensions to look at:
Pitch
This is the distance between the centres of two adjacent pins.
- Tip: The pitch determines the chain’s size class, so get this one as accurate as possible.
Roller Diameter
Measure the diameter of the roller that engages with the sprocket itself.
- Tip: Measuring the roller helps confirm the pitch and avoids confusion with worn or non-standard chains.
Inner Width
Measure the internal width between the inner plates across the roller. This helps determine how the chain fits with your sprockets.
- Tip: If your chain doesn’t have rollers (roller-less chain), the inner width becomes the defining measurement alongside pitch.
Step-by-step Guide to Measuring Your Chain
Step 1: Check for Markings First
Most chains are stamped with their size on the outer plate, usually at regular intervals. For ANSI chains you might see 40, 50, or 60, and for BS chains, look for 08B, 10B, etc.
- 08B-1 – Simplex (single strand)
- 08B-2 – Duplex (double strand)
- 08B-3 – Triplex (triple strand)
- … and so on, up to 08B-10 – Decaplex
Step 2: Measure the Roller Diameter
Using your vernier calliper, measure the diameter of one of the rollers. It’s a quick and accurate first step and helps cross-reference with the pitch.
Step 3: Measure the Chain’s Pitch
Measuring the pitch directly across pins can be awkward, especially if the chains still installed. Here’s a reliable workaround:
- Measure the total distance from the outside of one roller to the outside of the next (i.e., across two rollers).
- Subtract one roller diameter from this total.
- What you’re left with is your pitch, the centre-to-centre distance between pins.
- Example: If the total distance across two rollers is 21.21 mm, and the roller diameter is 8.51 mm, the pitch is 21.21mm – 8.51mm = 12.7mm (which corresponds to an 08B chain).
Step 4: Measure the Chain Inner Width
Now measure the space between the two inner link plates, this is your inner width. Take this measurement at the roller, across the inside faces of the plates. It helps match the chain to the right sprocket and ensures proper fit.
Why Accurate Chain ID Matters
Getting the chain size right the first time means no wasted time ordering and returning the wrong part, reducing the risk of downtime and ensuring proper sprocket engagement, leading to a longer lifespan for your drive systems. And if the chain has stretched beyond acceptable limits, even a perfect re-lube won’t save it. Replacing it quickly with the correct size ensures continued performance and safety.
Talk to the ACORN Experts
Even with measurements sorted, chain dentification can sometimes be tricky, especially if you’re dealing with an unusual setup, heavy wear, or a modified system.
Send us a photo of your chain alongside your measurements or bring a sample into your local ACORN branch. Our team of power transmission experts are on hand to help you identify your chain quickly and accurately and get the replacement to you fast.
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