Volkswagen Air-Cooled 1970-1981 Repair Guide

Pistons and Cylinders

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Pistons and cylinders are matched according to their size. When replacing pistons and cylinders, make sure that they are properly sized.

See the``Engine Rebuilding''portion of this section for cylinder refinishing.

REMOVAL & INSTALLATION



Cylinder

See Figures 1 and 2



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Fig. Fig. 1: Slide the cylinder off of the mounting studs and the piston



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Fig. Fig. 2: Prior to installing the cylinders and cylinder heads, make certain that the cylinder sealing surfaces (arrows) are perfectly clean and true

  1. Remove the engine. Remove the cylinder head, pushrod tubes, and the deflector plate.
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  3. Slide the cylinder out of its groove in the crankcase and off of the piston. Try not to damage the cooling fins, as they chip easily. Matchmark the cylinders for reassembly. The cylinders must be returned to their original bore in the crankcase. If a cylinder is to be replaced, it must be replaced with a matching piston.
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To install:
  1. Cylinders should be checked for wear and, if necessary, replaced with another matched cylinder and piston assembly of the same size.
  2.  
  3. Check the cylinder seating surface on the crankcase, cylinder shoulder and gasket for cleanliness and deep scores. When installing the cylinders, a new gasket, if required, should be fitted over the base of the cylinder and worked up to the crankcase-cylinder mating surface. These gaskets are usually made of paper, so be careful. Oil the gasket with regular engine oil after it is installed.
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  5. The piston, as well as the piston rings and pin must be oiled before reassembly.
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  7. Be sure that the ring gaps are of the correct dimension. Stagger the ring gaps around the piston, but make sure that the oil ring gap is positioned up when the pistons are in position on the connecting rods.
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  9. Turn the crankshaft until the intended piston is out as far as possible, then fit the ring compressor, oil the cylinder walls and slide the cylinder onto the piston. Make certain that the other exposed piston skirts do not strike the crankcase when the crankshaft is turned. The bottoms of the cylinder barrels have a slight camfer to aid ring fitting. Make sure that the cylinder base gasket is in place on the cylinder barrel.
  10.  

Use a ring compressor that pulls apart or you won't be able to get it off the piston once the cylinder barrel is over the rings. These are available at most automotive stores.

  1. Install the deflector plates.
  2.  
  3. Install the pushrod tubes using new gaskets. Install the pushrods. Make sure that the seam in the pushrod tube is facing upward.
  4.  
  5. Install the cylinder head.
  6.  

Piston

See Figures 3 through 11



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Fig. Fig. 3: To remove the pistons, first remove the circlip from both ends of the piston pin bore . . .



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Fig. Fig. 4: . . . then slide the piston pin out of the piston and connecting rod



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Fig. Fig. 5: Remove the piston from the connecting rod-the arrow (next to the G) should point toward the flywheel end of the engine during assembly



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Fig. Fig. 6: Use a ring expander tool to remove the piston rings



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Fig. Fig. 7: Clean the piston grooves using a ring groove cleaner



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Fig. Fig. 8: 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. 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 to ensure proper positioning of the piston pin-dimension (a) should be 0.059 in. (1.5mm)

See the''Engine Rebuilding''section for piston ring procedures.

  1. Remove the engine. Remove the cylinder head and, after matchmarking the cylinders, remove the cylinders.
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You must remove both cylinder barrels from the bank to be worked on even if you are only removing one piston.

  1. Matchmark the pistons to indicate the cylinder number and which side points toward the flywheel.
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  3. Remove the circlips which retain the piston pin.
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  5. Heating the piston will aid in piston pin removal. To heat the piston, boil a clean rag in water and wrap it around the piston. You can fashion a pin remover by shaving an old piston pin down so that it will slide through the piston. Use it with a mallet to knock out the pin. Be sure to hold the piston when removing the pin so that the connecting rod is not bent.
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  7. Remove the piston from the connecting rod.
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To install:
  1. Before installing the pistons, they should first be cleaned and checked for wear. Remove the old rings. Clean the ring groove with a ring groove cleaner or a broken piece of ring. Clean the piston with solvent but do not use a wire brush or sand paper. Check for any cracks or scuff marks. Check the piston diameter with a micrometer and compare the readings to the specifications. If the running clearance between the piston and cylinder wall is 0.008 in. (0.2mm) or greater, the cylinder and piston should be replaced by a set of the same size grading. If the cylinder shows no sign of excessive wear or damage, it is permissible to install a new piston and rings of the appropriate size.
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  3. Place each ring in turn in its cylinder bore and check the piston ring end-gap. If the gap is too large, replace the ring. If the gap is too narrow, file the end of the ring until the proper gap is obtained.
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  5. Insert the rings on the piston and check the ring side clearance. If the clearance is too large, replace the piston. Install the rings with the marking ``Oben'' or ``Top'' pointing upward.
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  7. If new rings are installed in a used piston, the ring ridge at the top of the cylinder bore must be removed with a ridge reamer.
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  9. Install a circlip on each piston on the side toward the flywheel, indicated by the arrow on the top of the piston. Install each piston so the arrow points toward the flywheel. If necessary, heat the piston to 167F (75C), then install the piston pin and fit the other circlip. Make sure the circlips are seated in their grooves properly.
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  11. Install the cylinders and the cylinder heads.
  12.  

 
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