[Evert Timberg]

Our team loves to use simple aluminum spaces as a temporary tensioning method. We use a lathe to make a hole down the axis of a cylindrical piece of aluminum and bolt it in place. The chain runs over the aluminum spacer and the size and diameter of the spacer can be easily changed. This works fairly well as a temporary measure and is lightweight.

That being said, the spacers are damaged by the chain and eventually break. I'd use them only if you really need to, otherwise the idler gear would be a better bet as there is no risk of damaging the chain.

Another solution we found was half links. Until this year we'd never heard of them but when used with a chain puller, its easier to make chains that are of the proper length.