Condensed answer: Re-using a chain pin on a multi-speed chain is considered bad practice because the pin loses its upper layer during the removal process and becomes ever so slightly slimmer. The chain plates are slightly damaged too.
This outcome compromises the chain’s integrity.
For that reason, re-using a pin is acceptable only in an emergency. Otherwise, it’s recommended to insert a new pin or use a master/power link at the connection point
Note: Chains with bushings are an exception and allow the re-usage of connection pins.
Pin Damage During Chain Adjustment
There is a great number of chain tools out there, but they all share the same basic mechanism – a threaded rod with a thin end pushes the pin out.
When that happens the pin grinds against the exits of both the inner and outer plates and loses some material.
Then, when you push the pin back in, the same happens again. Thus, the pin ends up losing two layers and thins out.
The aftermath is a weak, compromised spot in the chain. This greatly increases the likelihood of having a chain break on you, especially when exerting lots of effort uphill.
That said, failure is not guaranteed by any means.
Chain Plate Damage
When the pin is pushed out, it damages the entry points on the plates too.
And if it’s a “mushroomed pin” with a wide end and a narrow body, the entry points on the chain plates will become too wide to securely hold the pin once it’s re-installed.
Shimano Chain Pins
Shimano’s chain pins address this issue. They are extra thick to make up for the widening of the plates and the pin material lost during the installation.
The inserting end of the replacement pin is pointy whereas the end pressed into the chain is wide and flat. This makes the pin installation easier. The first part guides the pin whereas the wide end facilitates the pressing in process.
Just like regular pins, Shimano’s single pins are not supposed to be re-used due to the loss of material.
The two safe and accepted methods of shortening a multi-speed chain are as follows:
Chain Pin. The user removes the necessary amount of chain links and then connects the chain via a new unused chain pin.
Power links. The user shortens the chain one extra link so that both ends of the chain end up having only inner plates. Then, the user installs a master link and uses it to re-connect the chain.
Note: Not all power links are re-usable. (read more)
Bushed and Bushingless Chains
The inner plates on a bushed chain connect via a bushing acting as a hollow rivet. This makes the chain much stronger at the expense of lateral flexibility.
For that reason, bushed chains are commonly found on single-speed and fixed-gear bikes but are absent on multi-speed bikes.
Single-speed bikes need extra chain strength because the rider is always operating at a fairly high gear. During a climb, the stress on a single-speed chain augments greatly due to the high gear ratio and extra torque.
The stiffer architecture of bushed chains makes the re-usage of a pin a lot safer.
Also, single-speed chains are just thicker overall and thus less susceptible to damage.
That said, even those models can benefit from a quick link for easier maintenance.
As the name suggests, bushingless chains do not have standard bushings.
However, this is not entirely true. Bushingless chains have bushings, but they’re shorter and part of the inner links themselves.
The protruding shoulders of the inner plates on bushingless chains act as a bushing but do not connect to one another. As a result, the chain is more flexible laterally. This property makes the chain great for shifting but reduces its strength.
FAQ: How can I know if I have a bushed or a bushingless chain?
If the chain is made for fewer than 8-speeds, there’s a chance that it’s bushed. If it’s designed for more than 8 speeds, chances are that it’s a bushingless model.
That said, the surest way to know if the chain is bushed or not is to break it with a chain tool and examine it.
Another option is to look up the chain model online to find its characteristics.
FAQ: What will happen if I re-use a pin?
I had an 8-speed bushingless chain that I would open for cleaning by pushing the pin just enough to break the chain but not enough for it to fall out.
Then, I would simply flip the tool and use it to press the pin back in. At the time, I didn’t know any better and even thought that this was common practice.
The process was somewhat inconvenient but worked. And I never experienced chain failure. In fact, I rode the same chain until the cassette itself was completely worn.
My guess is that I never had trouble because 8-speed chains are fairly thick.
Today, however, I have a quick link on the chain for convenience.
What’s the worse that can happen after re-using a link?
A broken chain can lead to a serious accident because the failure is always sudden and unexpected.
Imagine the following situation. A cyclist is pedaling up a steep hill out of the saddle. The fatigue and extra effort required to push forward reduce his awareness.
The chain breaks. The cyclist loses balance because the leg on the drive side sinks down unexpectedly. The cyclist hits the handlebars with his torso and loses control of the bike.
If there’s traffic behind or in front of the cyclist, the loss of balance could lead to a lethal end.
That said, the reality of the situation is that cycling isn’t the safest activity in the world even if your bike is maintained by the best mechanics in the universe. A component can always fail even if it’s in pristine condition.
For example, there are expensive cranks and frames costing hundreds of dollars that crack unexpectedly.
In the end, however, one is obliged to focus on the controllable variables and make a conscious effort to increase cycling safety.
Summary: What You Need To Know
- Re-using a chain pin on a bushingless chain is considered bad practice because the pin and the plates experience damage in the process.
- If you have a multi-speed chain, the acceptable protocol is to use a new pin (e.g., Shimano’s pin) or a master/power link.
- A re-usable master/power link is the most practical and economical choice.
- Quality single-speed chains are thicker and have bushings strengthening the chain plate connection. Re-using a pin on such a chain is a lot less risky.
- If the chain fails, the rider can lose balance unexpectedly and hurt themselves badly.