Renold - Troubleshooting Guide: Fracturing

A motorbike chain fracturing is not very common, as most experienced riders will take preventative action before it occurs. That being said, it's essential to know what preventive measures you should take to ensure this unlikely but severe mode of chain failure never happens to you.

What is 'Fracturing'

First, we must understand what fracturing is. To do this, let's look at the most common use of the term we've all come across before; a broken bone. In the context of a medical setting, the terms' broken' or 'fractured' are interchangeable, with the latter just sounding more professional.

Fundamentally, however, there is a loss of continuity in the bone, whether it be a small hairline crack or a complete shattering of the bone.

Now, how does this relate to your motorbike chain? Similar in some ways but different in others. A fractured motorbike chain usually describes the early hairline cracks that occur before a complete break. So, for the purposes of this article, we'll treat a fracture as these early warning signs before a critical break occurs.

What Causes a Motorbike Chain to Fracture?

The simple answer would be an excessive force placed on a chain. This could be a sudden, hard impact or a lesser, more gradual force applied over a more extended period.

While possible in theory, a one-off impact of such significant force to fracture a motorbike chain is extremely unlikely. Such a force would likely cause critical damage to the entire motorbike. Our focus will therefore be on the more gradual causes of fracturing that build up over time.

These include;

  • Excessive loads placed on the chain
  • Incorrect chain tension
  • Stretching due to wear

Spotting and Preventing a Fracture

Fractures will usually start small on a single link in the chain. That means getting up close to your chain and inspecting it. However, fractures are most likely to occur in weak areas of the chain, so focus on those first.

All chains will have one link that was broken to get the chain on your bike, but if you've had to repair your chain before, that may have created other points of weakness.

While this might sound like an uphill task, the good news is the regular maintenance you undertake will not only help prevent most causes of a fracture, but also give you the perfect opportunity to check for signs.

Even the most basic chain maintenance that sees you cleaning away grime and applying lubricant will get you close enough to check for issues.

Another critical preventative action you can take is to ensure you do not exceed the load limit of your chain. More can be read about the importance of load limits in our 'Fatigue' guide, but as a quick summary, increasing the load on your chain can stretch it beyond repair. When this repeatedly happens, fatigue sets in, and fracturing soon follows.

What to do if I Spot Signs of Fracturing

Unfortunately, it's probably too late to save the chain, as a fracture in one location is usually the precursor to fracturing in others. The best and safest course of action would be to replace the chain as soon as possible and limit any further riding on it.

While motorbike chains are robust, and complete breaks are very unusual, the risks are not worth taking, as any accident on a bike can have dire consequences.

If a temporary fix is required, you will need to remove the areas of failure using a chain tool. If the fracture has occurred due to stretching, you might simply be able to shorten the chain. You must remember that motorbike chains are designed to be a specific length for the function of the drive chain. 

A shortened chain might also mean you can't shift 'up' a gear where the rear sprocket is smaller. As such, you'll need to stay in a lower gear. However, be wary of placing more stress on the chain at this point by riding too fast in a lower gear. This will increase the load on the chain and increase the risk of further fractures.

If shortening is not an option, you will need to install a temporary link until you can get to a garage for a more permanent fix.

The Bigger Picture

A fractured or broken chain is highly unusual on a motorbike. Typically, it's either a sign of severe neglect or another problem somewhere else on the bike. However, the fact you've spotted a fracture almost certainly means you've not neglected your bike, so it's likely not to be an isolated issue. 

For this reason, we'd always recommend speaking to a professional when you spot a fracture. If there are other underlying issues, they might create additional problems. At the very least, however, if they're not resolved, they will cause another fracture in the future, even if you replace the chain.