How to Set Yanmar Diesel Valves

by Kyle McBride
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Yanmar diesel engines are popular for recreational use, especially in the sailboat sector. Their light weight and ease of maintenance makes them ideal for vessels between 28 and 40 feet long. Proper maintenance is essential to keep the engine in top working order. The valve train consists of the valve cam, pushrods, rocker arms and valves. The valve head gap is adjusted with the screw and locknut assembly on the valve arm. The valve head gap is measured between the valve stem tip and the valve arm contact surface with the engine cold.

Step 1

Remove the two valve arm chamber cover bolts with a wrench. Lift the cover off of the engine. Remove and discard the cover gasket.

Step 2

Rotate the engine by hand until the front cylinder is at top-dead-center (TDC) on the compression stroke with both the intake and exhaust valves fully closed and no pressure on the valve springs from the valve arm. Both valves are adjusted before moving to the next cylinder.

Step 3

Loosen the adjuster locknut with a wrench. Back off the adjuster with a flat screwdriver.

Step 4

Insert the 0.2mm feeler gauge between the valve arm and the valve stem. Tighten the adjuster until a slight drag is felt with the feeler gauge.

Step 5

Remove the feeler gauge and tighten the adjuster locknut with the wrench while holding the adjuster in position with a screwdriver. Recheck the adjustment with the feeler gauge after the locknut is tightened.

Step 6

Roll the engine by hand until the next cylinder comes up to TDC on the compression stroke. Repeat the process for each of the cylinders.

Step 7

Install the new valve arm chamber cover gasket. Place the chamber cover in position on the head. Install the chamber cover bolts and tighten them with a wrench.

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