A multi-cylinder engine comprising: a cylinder block including a plurality of cylinder bores; an upper crankcase and a lower crankcase that form, in combination, a plurality of crank chambers respectively corresponding to the cylinder bores; a bulkhead (23, 25) that partitions between the cylinder bores and the crank chambers adjacent to each other; and a honing release portion having a cylindrical honing release surface formed continuously with the cylinder bore in the upper crankcase and the bulkhead, characterized in that the cylinder block and the upper crankcase are formed integrally, the honing release surface is formed with a diameter larger than the cylinder bore, and an arcuate recessed portion is formed in the bulkhead (23, 25), the bulkhead (23, 25) is formed with a communication hole that communicates with the crank chambers adjacent to each other, the bulkhead (23, 25) including a first opening edge on a side of the cylinder bore extending in a direction substantially perpendicular to a cylinder axis, a second opening edge on a side of the crank chamber having an opening width decreasing with a distance from the cylinder bore, and a third opening edge that extends substantially in parallel with the cylinder axis and connects between the first opening edge and the second opening edge, the communication hole has a maximum opening width in a direction substantially perpendicular to the cylinder axis, which is larger than a width (d) of the recessed portion, the honing release surface is extend below the communication hole, and the second opening edge is formed from the cylinder bore to the recessed portion to prevent the honing release surface from being divided. a cylinder block including a plurality of cylinder bores; an upper crankcase and a lower crankcase that form, in combination, a plurality of crank chambers respectively corresponding to the cylinder bores; a bulkhead (23, 25) that partitions between the cylinder bores and the crank chambers adjacent to each other; and a honing release portion having a cylindrical honing release surface formed continuously with the cylinder bore in the upper crankcase and the bulkhead, characterized in that the cylinder block and the upper crankcase are formed integrally, the honing release surface is formed with a diameter larger than the cylinder bore, and an arcuate recessed portion is formed in the bulkhead (23, 25), the bulkhead (23, 25) is formed with a communication hole that communicates with the crank chambers adjacent to each other, the bulkhead (23, 25) including a first opening edge on a side of the cylinder bore extending in a direction substantially perpendicular to a cylinder axis, a second opening edge on a side of the crank chamber having an opening width decreasing with a distance from the cylinder bore, and a third opening edge that extends substantially in parallel with the cylinder axis and connects between the first opening edge and the second opening edge, the communication hole has a maximum opening width in a direction substantially perpendicular to the cylinder axis, which is larger than a width (d) of the recessed portion, the honing release surface is extend below the communication hole, and the second opening edge is formed from the cylinder bore to the recessed portion to prevent the honing release surface from being divided.