If valve clearances in the Volkswagen engine are too small, the valves can be seriously damaged by warping or burning, and compression will eventually suffer from lack of proper valve sealing. Valves are cooled by resting against the valve seat-if the valves are opened for too long, they have insufficient time to rest against their seats, and hence to transfer their heat to the cylinder head. On the other hand, if the valve clearance is too great, the result will be rough running, loss of power, and excessive wear of the valve train components. However, if error is necessary, it is best to err in the direction of too large a clearance. A few thousandths of an inch of excess clearance will be much less harmful than the same error in the opposite direction. As long as you can hear the valves clicking, you are at least assured that they are not burning.
Before the valves can be adjusted in any Volkswagen, the engine must be cold, preferably after sitting overnight. Volkswagen valve clearances vary somewhat between models of different years. To determine the correct setting, refer to both the Tune-Up Specifications Chart and the engine sticker.
Preference is to be given to the valve clearance specified on the engine fan housing sticker, if one is present. On models built after late 1964, such a sticker will be on the fan housing. Such stickers will also be present on all factory rebuilt engines, regardless of horsepower output, and the clearances specified should be followed closely.
- Remove the distributor cap and turn the engine until the rotor points to the notch in the distributor rim and the crankshaft pulley timing mark is aligned with the crankcase split or pointer. No. 1 cylinder is now at top dead center of its compression stroke. In type 3 engines, the belt housing cover must be removed so that the engine can be turned by hand.
- Remove the rocker arm cover of cylinders No. 1 and No. 2.
- With the proper feeler gauge, check the clearance between the adjusting screw and the valve stem of both valves for the No. 1 cylinder. If the feeler gauge slides in snugly without being forced, the clearance is correct. It would be well to use the "go, no go" gauge system in which the proper leaf slides in but one which is 0.002 in. thicker will not.
- If the clearance is incorrect, the locknut must be loosened and the adjusting screw turned until the proper clearance is obtained. After tightening down the locknut, it is then advisable to recheck the clearance, because it is possible that the adjustment was altered when tightening the locknut.
- Turn the engine one-half revolution counterclockwise. This will turn the distributor rotor 90 degrees counterclockwise so that it will now point to the spark plug wire for cylinder No. 2. No. 2 cylinder is now at top dead center.
- Repeat adjustment process for cylinder No. 2.
- Replace valve rocker arm cover on cylinders Nos. 1 and 2, using a new gasket and cleaning off the seating surfaces to guard against leakage.
- Remove the valve rocker arm cover on cylinders Nos. 3 and 4.
- Turn the engine another one-half turn counterclockwise so that the distributor rotor now points to the spark plug wire of cylinder No. 3. No. 3 cylinder is now at top dead center.
- Adjust the clearances on cylinder No. 3.
On type 1 and 2 engines, No. 3 cylinder runs hotter than the other three cylinders because its cooling air flow is partially blocked by the oil cooler. To counter a tendency for this cylinder to burn exhaust valves, some mechanics set the No. 3 exhaust valve clearance 0.001-0.002 in. bigger than specified.
- Turn the engine a further one-half turn counterclockwise and adjust the clearances of the valves in cylinder No. 4.
- Replace the rocker arm cover of cylinders Nos. 3 and 4, cleaning the sealing surfaces and using a new gasket.
- Replace the distributor cap. Replace the belt housing cover in type 3 models.
While correct valve clearance is important to all Volkswagen engines, it is especially important in those having a specified clearance of 0.008 and 0.012 in. (intake and exhaust respectively). In these engines the valve clearance actually decreases as the engine warms up, so too little initial clearance, or a clearance obtained with a warm engine, can lead to trouble within a short time. On engines with 0.004 in. clearance, the clearance increases as the engine temperature increases.
It is also possible to adjust valves in normal firing order sequence, 1-4-3-2, rotating the engine clockwise. It is helpful to mark the crankshaft pulley directly opposite the 0° mark in order to determine precisely when the engine is turned one-half revolution.