[Justin Stiltner]

The problem you were likely encountering is fatigue failure. You are not loading the chain to its tensile limit(although you may be) but you are coming close, and when you come close enough times the damage begins to accumulate and eventually it fails.

You should calculate the load you are putting on the chain(it will surprise you) and provide yourself a factor of safety on that so you do not exceed the abilities of the chain.

In your particular case I wager that if you were to increase the size of both of your sprockets (to maintain the same gear ratio) you would see far less chain failure. You are increasing the length of the moment arm by using a bigger sprocket, and this will reduce the tension in the chain, but provide the same speed and torque at the wheel. For example if you were previously using a 10 tooth sprocket and a 20 tooth one, change them out for a 20 and a 40.

Also, I have found and been told that half links are weaker than master links. Make sure to get a good brand chain, Diamond is a brand I trust when it matters. All #25 chain is not created equally, and I have never seen a use for #35 chain in a drive system, unless you cannot align your sprockets well enough to use #25.

Good luck