Most 1986-89 models are equipped with hydraulic valve lifters. No adjustment is necessary on models equipped with hydraulic lifters. A label usually found on the valve cover will help you identify the type of lifter (mechanical or hydraulic) with which the engine is equipped. The underhood emissions label will also state whether the valve lash is or is not adjustable.
Valve adjustment is one factor which determines how far the intake and exhaust valves open into the cylinder. If the valve clearance is too large, part of the lift of the camshaft will be wasted in removing the excessive clearance, therefore the valves will not open far enough. This has two ill effects; one, the valve gear will become noisy as the excess clearance is taken up and, two, the engine will perform poorly. This is because intake valves which don't open the full distance will admit less air/fuel mixture into the cylinders. Exhaust valves which aren't opening the full amount create a greater back pressure in the cylinder which also prevents the proper air/fuel mixture from entering the cylinder.
If the valve clearance is too small, the intake and exhaust valves will not fully seat on the cylinder head when they close. When a valve seats on the cylinder head it does two things; it seals the combustion chamber so that none of the gases in the cylinder can escape and it cools itself by transferring some of the heat absorbed from the combustion process through the cylinder head and into the cooling system. Therefore, if the valve clearance is too small, the engine will run poorly (due to gases escaping from the combustion chamber), and the valves will overheat and eventually warp (since they cannot properly transfer heat unless they fully seat on the cylinder head). While all valve adjustments must be as accurate as possible, it is better to have the valve adjustment slightly loose than tight.
See Figures 1 and 2
The overhead cam acts directly on the valves through cam followers which fit over the springs and valves. Adjustment is made with an adjusting disc which fits into the cam follower. Different thickness discs result in changes in valve clearance.
VW recommends that two special tools be used to remove and install the adjustment discs. One is a pry bar to compress the valve springs and the other a pair of special pliers to grasp the disc. Ask your local VW dealer for current tool part numbers. If the purchase of these tools is not possible, a flat metal plate can be used to compress the valve springs if you are careful not to gouge the camshaft lobes. The cam follower (lifter) has two slots which permit the disc to be lifted out. Again, you may improvise by using a thin bladed tool. An assistant to pry the spring down while you remove the disc would be the ideal way to perform the operation if you must improvise your own tools.
Valve clearance is checked with the engine moderately warm (coolant temperature should be about 95°F (35°C).
- Disconnect the accelerator linkage (if equipped with automatic transmission). Remove the upper drive belt cover (if necessary), the air cleaner and any hoses or lines which may be in the way. When disconnecting the accelerator cable, do not allow the cable to become kinked or twisted. Route the cable neatly off to side and out of the way.
- Remove the camshaft cover and gasket. Valve clearance is checked in the firing order 1-3-4-2 for 4 cylinder engines and 1-2-4-5-3 for 5 cylinder engines, with the piston of the cylinder being checked at TDC of the compression stroke. Both valves will be closed at this position and the cam lobes will be pointing upward.
When adjusting the clearances on the diesel engines, the pistons must NOT be at TDC. Turn the crankshaft1/4turn past TDC so that the valves do not contact the pistons when the tappets are depressed.
- Turn the crankshaft pulley bolt with a socket wrench to position the camshaft for checking. There is a hole behind the front license plate, on Dasher models, through which a wrench can be used.
- With the No. 1 piston at TDC ( 1 / 4 turn past for the diesel) of the compression stroke, determine the clearance with a feeler gauge. Compare this reading with the correct clearance from the tune-up charts in this section or from the underhood label.
- Continue to check the other cylinders in the firing order, turning the crankshaft to bring each particular piston to the top of the compression stroke ( 1 / 4 turn past for the diesel). Record the individual clearances as you go along.
- If measured clearance is within tolerance levels, it is not necessary to replace the adjusting discs.
- If adjustment is necessary, the discs will have to be removed and replaced with thicker or thinner ones which will yield the correct clearance. Discs are available in 0.002 in. (0.05mm) increments.
The thickness of the adjusting discs are etched on one side. When installing, the marks must face the cam followers. Discs can be can be reused if they are not worn or damaged.
- To remove the discs; turn the cam followers so that the grooves are accessible when the pry bar is depressed.
- Press the cam follower down with the pry bar and remove the adjusting discs with the special pliers or a similar tool.
- Replace the adjustment discs as necessary to bring the clearance within the tolerance level. If the measured clearance is larger than the given tolerance, remove the existing disc and insert a thicker one to bring the clearance up to specification. If it is smaller, insert a thinner one.
- Recheck all valve clearances after adjustment.
- Install the cylinder head cover with a new gasket.
- Install the accelerator linkage, the upper drive belt cover and any wires or lines which were removed.