Mercury F7CZ-6507-CB Valve - Inlet

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For DIV purposes, the checking of the valve clearances is easy but the replacement of the shims requires a special tool from the manufacturer and owners may want to have their vehicle checked by the dealer. To measure the clearances, firstly, unbolt the valve cover and position the Number 1 cylinder at the TDC of the compression stroke so that the intake and exhaust cam lobes are lifted upwards. Check the clearance between the cam lobe base and the shim employing the feeler gauges: Record the shim thickness required to give a tight fit on all the four valves of the Number 1 cylinder. After that, turn the crankshaft in the clockwise direction to the angle of 180 degrees and take the clearance measurements for cylinder Number 3; likewise, for the cylinder Number 4 and Number 2, repeat the 180 degrees crankshaft turning. When any clearances are outside this range, corrections are required. For adjustments, it is suggested that the manufacturer special tool should be used as is due to the special design of the camshafts and cylinder head. If necessary, shim thicknesses can be changed-for this, it is necessary to press the cam follower and then extract the old shim before installing a new one. Chock the wheels, start the engine and do not allow the piston to reach TDC again as this will bend the valve, rather, lower the piston from TDC by rotating the crankshaft about 90 degrees clockwise. The service tool 303-563A used by dealer technicians is bolted or screwed into the cylinder head above each camshaft and one has to be very careful not to damage the cam follower while using this tool. When measuring the thickness, if the clearance turns out to be small put on a thinner shim, if it is large use a thicker shim. Subtract the measured shim thickness from the required shim thickness if the clearance obtained is lesser than the required clearance or add the required shim thickness from the measured shim thickness, if the clearance is lesser than the required clearance. Bolt he correct shim into place and then turn the crankshaft two full turns before again returning to TDC and rechecking the clearances and again adjusting the shims as required. This should be done on all cylinders, with records kept of the shim thicknesses for future adjustments, while shims can be swapped for others, attempt not to turn the camshaft with shims off for risk of damage. After ensuring that all the clearances are proper, get rid of the tool and replace the valve cover as it was earlier.

The required thickness can be calculated using the formul Thickness required (D) equals Tappet thickness found (C) + Measured clearance (B) - Desired clearance (A).

Thorough cleaning of the cylinder head and valve components, followed by a detailed inspection, will enable you to decide how much valve service work must be carried out during the engine overhaul.