Are there adjustments that can be made instead of replacing it?
It depends on what you mean by 'loose'... Chains stretch naturally over many hundreds of miles, and the stretching of the links is actually a good indicator of wear.
If, instead, it seems like there is a lot of slack or 'extra' chain, this is an indicator of one of two issues:
- The chain is simply too long. All new chains (not already on bicycles) come longer than they need to be. If you recently replaced your chain, and didn't remove the extra links, this would cause the chain to be loose.
- The dérailleur is not creating chain tension. If you find that the chain seems to sag at both the top and the bottom, this may mean that your dérailleur has lost some of it's 'springiness' and is not effectively creating chain tension. It's hard to determine without further details, but if this is the case, the dérailleur may need to be replaced.
I believe you can just remove a link if it's that loose. But beware that more stress could cause it to break.
If the bike has hub gears, then you can undo the wheel nets and firmly push the wheel back into the axle slots while doing up the nets. There is a neck to this, as you don’t want chain too tight and you need the wheel to be aligned when turning.
If it's a single-speed or fixed-gear bike: Loosen the back wheel pull the tire back into the dropouts,tighten wheel - whaala.. tightened your chain.
This is a temporary fix, you will eventually need to replace your loose chain or your entire drivechain due to wear.
You can loosen the back wheel's axle then pull it back so the chain is tight. After you do this you can tighten it in place. If the back axle nut is rusted and stuck, you must buy a new one.
There’s a screw behind the derailed spring (not the hi and low adjustment screws) that will tighten or loosen tension a bit. Of thi