Mazda 323/626/929/GLC/MX-6/RX-7 1978-1989

Diesel Engine

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See Figures 1 and 2

Adjusting the valves on the Mazda diesel engine involves replacing discs that rest in a recess in the top of each tappet. To do this, a special tool (MAZDA tappet holder 49 S120 220 or equivalent) is required, along with a selection of discs of different dimensions. The tool depresses the valve tappet, opening the valve slightly, for access to the replaceable disc.

  1. Remove the valve cover, as described in Engine & Engine Overhaul of this repair guide. Rotate the engine by the crankshaft pulley bolt until the valve cams of the No. 1 cylinder are both pointing upward (not contacting the shims), and the timing marks indicate that No. 1 cylinder is at Top Dead Center (TDC) on the firing stroke.
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  3. Measure the clearance between the top surface of the tappet and the cam's lower surface, as shown in the illustration. Check the intake valves of cylinders No. 1 and No. 2, and the exhaust valves of cylinders No. 1 and No. 3. The proper clearances are-Intake: 0.008-0.012 in. (0.2-0.3mm); Exhaust: 0.012-0.016 in. (0.3-0.4mm).
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  5. If the clearance is outside the specified range, determine the thickness of the required new disc. Discs are marked to indicate their thickness in millimeters. Thicknesses range from 3.70mm to 4.30mm in intervals of 0.050mm. For example, 3825 means 3.825mm. Calculate the required thickness of the new disc using the following, simple formula:
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Fig. Fig. 1: Measuring diesel engine valve clearance



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Fig. Fig. 2: During valve adjustment on the diesel engine, tappet holder 49 S120 220, or equivalent, must be used to depress the valve tappets

The new shim which is required in order to achieve the specified clearance is equal to the thickness of the original disc PLUS the measured clearance, then MINUS the required clearance specification. Think of this another way, if you added the measured clearance and the thickness of the original shim, then selected a shim based on that number, you would have zero clearance. But zero clearance is not what you what. Since a certain clearance is necessary, subtracting the specification from the total thickness just calculated (current shim plus current clearance) tells you what size shim will leave the specified clearance between the new shim and the cam lobe.


WARNING
The engine must be positioned so that the intake cam lobe for the cylinder you are working on is facing directly upward before installing the special tool. Attempting to depress the valve without properly positioning the engine may cause damage to the valve train.

  1. If the valves you have checked require adjustment, turn each of the tappets around so one of the notches is facing toward the left side of the car for access to the discs. Before working on each valve, rotate the engine by the crankshaft pulley bolt so that the intake cam lobe for that cylinder is pointing straight upward. Then, install the tool in the position shown (right between the cams). Tighten the bolt to force the tool halves together and depress the tappets. Then, pry the disc out with a small prytool and replace it with one of the proper thickness (as determined by your calculation).
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  3. Rotate the crankshaft one full revolution (360 degrees). Repeat the inspection procedure for the intake valves of cylinders No. 3 and No. 4, and the exhaust valves of cylinders No. 2 and No. 4. Then, adjust those valves, as necessary. When you are finished, install the valve cover as described in Engine & Engine Overhaul of this repair guide.
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