Volkswagen Air Cooled 1949-1969 Repair Guide

Pistons

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REMOVAL & INSTALLATION





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Fig. Fig. 1 To remove the pistons, first remove the circlip from both ends of the piston pin bore ...



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Fig. Fig. 2 ... then slide the wrist pin out of the piston and connecting rod



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Fig. Fig. 3 Remove the piston from the connecting rod



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Fig. Fig. 4 Use a ring expander tool to remove the piston rings



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Fig. Fig. 5 Clean the piston grooves using a ring groove cleaner



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Fig. Fig. 6 You can use a piece of an old ring to clean the piston grooves, BUT be careful, the ring is sharp



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Fig. Fig. 7 Measure the piston's outer diameter using a micrometer



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Fig. Fig. 8 Checking the ring-to-ring groove clearance



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Fig. Fig. 9 Identification of the various markings on the top of a typical VW piston-make sure that arrow (b) is oriented toward the front (flywheel end) of the engine



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Fig. Fig. 10 The rings must be installed as shown, otherwise they will not produce a proper seal with the cylinder wall-the word TOP must be positioned toward the piston crown



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Fig. Fig. 11 Since the piston pins are slightly offset from the piston centerline, make certain that the arrow on the piston crown points toward the flywheel end of the engine-this will ensure the proper positioning of the piston pin



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Fig. Fig. 12 The offset piston wrist pins were designed to reduce piston slap as the angle of thrust (white and thick black arrows) in the piston bores changes with the rotation of the crankshaft (thin black arrows)

Following the removal of the cylinder head and the cylinder, the pistons should be marked with a number (cylinder number) and an arrow (pointing to the clutch side of engine) if they are to be reinstalled in the engine. The pistons are removed as follows:

Using piston circlip pliers, remove the circlips used to retain the piston wrist pin. Heat the piston to 80°C. (176°F.), remove the piston pin and take the piston off the end of the connecting rod. If it is necessary to remove the piston rings, use piston ring pliers in order to avoid damage.

Install the piston as follows: First, clean the piston and the ring grooves, taking care to see that the ring grooves are not scratched or otherwise damaged. The piston should then be checked for wear and, if necessary, replaced by one of corresponding size and weight. Weight between pistons must not be greater than 10 grams. If the running clearance between the piston and cylinder is 0.2mm (0.008 in.) or more, the piston and cylinder should be replaced by a set of the same size grading. If, however, the cylinder of a worn or damaged piston shows no signs of wear, it is permissible to install a new piston of appropriate size. See accompanying diagram for piston markings.

After making a decision concerning the piston to be used, select piston rings of the correct size. After the ring has been inserted in the cylinder and pushed down about 0.2 in. by the piston, check the gap with a feeler gauge. After using a piston ring tool to install the rings, check the side-clearance of the rings in their grooves with a feeler gauge. Ring side-clearance and end-gap should be as specified in the Engine Rebuilding Specifications Chart for Pistons, Cylinders, and Rings in this section.

Because the compression rings are slightly tapered, they should be installed with the marking "Top" or "Oben" toward the top of the piston. Insert the piston pin circlip which faces toward the flywheel. Because piston pin holes are offset, make sure that the arrow (or word "vorn") points toward the flywheel. This offset is to help accommodate thrust loads which amplify and lead to objectionable piston slap.

Check and fit the piston pin. The pin may be found to be a light finger-push fit in the piston, even when the piston is cold. However, this condition is normal, even to the extent of the pin sliding out of the piston under its own weight. Clearance between the piston pin and the connecting rod bushing should be as specified in the Engine Rebuilding Specifications Chart. If the clearance is near the wear limit, renew the piston pin and the rod bushing. It is not advisable to install an oversize pin in this case. In all cases where the pin is not a light finger push fit in the cold piston, heat the piston in oil to about 176°F. Insert the second circlip and make sure that the circlips fit perfectly in their grooves. A good barometer in deciding whether or not a new cylinder and piston should be installed is oil consumption. If the engine uses more than one quart of oil each 600 miles, it is quite likely that the engine is in need of reconditioning.

 
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