Renewing the chain

The camshaft chains will have to be replaced when their elongation reaches 1% or after 15 years. The reason for placing a limit on it’s elongation is that as the chain gets longer the pitch increases and is not matched to the wheel teeth, and continued use would result in excessive wear.

The chains are replaced one at a time. This is so that the connected chain can be used to turn the engine whilst the new chain is pulled round.

To change a chain on a large 2 stroke engine, the chain is slackened off at the tensioner. The top chain case cover is removed, and one of the chains is split at the point indicated. see here on how to split the chain.

The new chain is attached to the old chain with a temporary link, and as the engine is turned, the old chain is pulled out of the engine, the new chain is fed in. Once the new chain has been joined, the process is repeated for the second chain and the chain retensioned. The camshaft may now have to be retimed as described here, as it may have been adjusted to compensate for elongation in the old chain.