Use vernier calipers to measure the
timing sprocket outside diameter.
The sprocket wears out between its teeth.
Sprocket wear causes the chain to rest too deeply on the sprocket, reducing the
outside diameter of the chain when it is mounted over the sprocket. Therefore,
mount the chain over the sprocket and then measure the outside diameter of the
chain to judge whether the sprocket is normal.
Allowing the sprocket wear to progress may cause tooth missing or tooth skipping
due to the loose chain, which may result in damage to the valve mechanism.
