PURPOSE: To set a cap of a marine engine clamped by a cap bolt and vice versa from an access opening by installing this access opening in a lower part at the side of a cylinder block, and dividing a connecting rod into the rod and the cap horizontally in a clamp pin part.

CONSTITUTION: A cap bolt 13 clamping a cap 12 of a connecting rod 10 tight enough is increased to four pieces in total. A crankshaft 3 is rotated, making the cap 12 approximate to an access opening 2 of a cylinder block 1, and a barrier wrench 20 is inserted thereinto from this access opening 2, whereby a socket 21 is set to the cap bolt 13. In succession, a ratchet wrench 23 is set to a driving hole 22 of the barrier wrench 20, thereby performing both clamping and loosening operations on the cap bolt 13, and setting of the cap 12 and vice versa is carried out from the access opening 2. Since the cap bolt 13 is four pieces in total, the extent of clamping torque is small in force so that its setting operation can lee done so easily. Accordingly, a thorough overhaul in a piston 4 is made achievable without lifting an engine down.