This section describes, in detail, the procedures involved in rebuilding a horizontally opposed, air-cooled Volkswagen/Porsche four cylinder engine. It is divided into two sections. The first section, Cylinder Head Reconditioning, assumes that the cylinder head is removed from the engine, all manifolds and sheet metal shrouding is removed, and the cylinder head is on a workbench. The second section, Crankcase Reconditioning, covers the crankcase halves, the connecting rods, crankshaft, camshaft and lifters. It is assumed that the engine is mounted on a work stand (which can be rented), with the cylinder heads, cylinders, pistons, and all accessories removed.
In some cases, a choice of methods is provided. The choice of a method for a procedure is at the discretion of the user. It may be limited by the tools available to a user, or the proximity of a local engine rebuilding or machine shop.
The tools required for the basic rebuilding procedures should, with minor exceptions, be those included in a mechanic's tool kit: An accurate torque wrench (preferably a preset, click type), inside and outside micrometers, electric drill with grinding attachment, valve spring compressor, a set of taps and reamers, a valve lapping tool, and a dial indicator (reading in thousandths of an inch). Special tools, where required, are available from the major tool suppliers (i.e. Zelenda®, Craftsman®, K-D®, Snap-On®). The services of a competent automotive or aviation machine shop must also be readily available.
When assembling the engine, bolts and nuts with no torque specification should be tightened according to size and marking (see chart).
Any parts that will be in frictional contact must be pre-lubricated before assembly to provide protection on initial start-up. Many different pre-lubes are available and each mechanic has his own favorite. However, any product specifically formulated for this purpose, such as Vortex Pre-Lube®, STP®, Wynn's Friction Proofing®, or even a good grade of white grease may be used.
Do not use engine oil only, as its viscosity is not sufficient.
Where semi-permanent (locked but removable) installation of nuts or bolts is required, the threads should be cleaned and coated with locking compound. Studs may be permanently installed using a special compound such as Loctite® Stud and Bearing Mount.
Aluminum is used liberally in VW and Porsche engines due to its low weight and excellent heat transfer characteristics. Both the cylinder heads and the crankcase are aluminum alloy castings. However, a few precautions must be observed when handling aluminum engine parts:
To install a Heli-Coil® insert, tap drill the hole with the stripped threads to the specified size (see chart). If you are performing this operation on a spark plug hole with the head installed, coat the tap with wheel bearing grease to prevent aluminum shavings from falling into the combustion chamber (it will also help if the engine is rotated so that the exhaust valve of the subject cylinder is open, so that when the engine is initially started, if any chips did fall into the engine, they will be blown out the exhaust instead of scoring the cylinder walls, and, if compressed air is available, it may be applied through the spark plug hole and the chips blown out the exhaust port).
Heli-Coil® tap sizes refer to the size thread being replaced, rather than the actual tap size.
Using the specified tap, tap the hole for the Heli-Coil®. Place the insert on the proper installation tool (see chart). Apply pressure on the insert while winding it clockwise into the hole, until the top of the insert is one turn below the surface. Remove the installation tool and break the installation tang from the bottom of the insert by moving it up and down. If, for some reason, the Heli-Coil® must be removed, tap the removal tool firmly into the hole, so that it engages the top thread, and turn the tool counterclockwise to extract the insert.
K-D® makes an insert specifically designed for the 14mm spark plugs used in all VW's. The steel insert is 3 / 8 in. deep and has a lip which will seat the insert automatically to the correct depth. To install the K-D® insert, screw the combination reamer and tap into the damaged hole to ream the hole to the proper size and cut new threads for the insert. Then, screw the insert onto a spark plug, and torque the plug to 15-18 ft. lbs. to seat the insert.
Apply locking compound to the threads of the insert (cylinder head side) to make the installation permanent.
Another spark plug insert that has come into favor is the Keenserts® insert. The special features of this type of insert are the locking keys and gas tight sealing ring. The Keenserts® kit consists of a ream and countersink tool, a tap with pilot point, an installation tool (drift), and the inserts. To install a Keenserts® insert, the following procedure is used:
- Ream and countersink the damaged spark plug hole.
- Check the countersink depth. It should be 13 / 16 tool in until the stop comes into full contact with the head.
- Tap the hole.
- Select an insert. Mount the insert on the installation tool.
- Rotate the tool and insert clockwise until the insert bottoms in the hole.
- Drive the special anti-rotation keys into the head using the installation tool, sleeve, and a hammer.
- g. Remove the installation tool. Check that the insert is flush with the cylinder head surface and that all keys have seated at the undercut portion of the insert.
- To install the sealing ring, place it squarely around the top of the insert. Then, install a flat seated spark plug, with the plug gasket removed, and tighten it to 35 ft. lbs. Remove the plug and check the seating of the ring. This should provide a gas tight seal, flush with the insert top.
- Finally, install the spark plug with its gasket into the insert, and tighten it to its normal 18 ft. lbs.
To remove a Keenserts® insert, use a 21 / 32 drill through the center of the insert to a depth of 1 / 4 in. Remove the locking keys with a punch and remove the insert with an E-Z out® tool.
Snapped bolts or studs may be removed using Vise-Grip® pliers. Penetrating oil (e.g. Liquid Wrench®, CRC®) will often aid in breaking the torque of frozen threads. In cases where the stud or bolt is broken off flush with, or below the surface, the following procedure may be used: Drill a hole (using a hardened bit) in the broken stud or bolt, about 1 / 2 of its diameter. Select a screw extractor (e.g. E-Z Out®) of the proper diameter, and tap it into the stud or bolt. Slowly turn the extractor counterclockwise to remove the stud or bolt.
One of the problems of small displacement, high-revving engines is that they are prone to developing fatigue cracks and other material flaws because they are highly stressed. One of the more popular procedures for checking metal fatigue and stress is Magnafluxing®. Magnafluxing® coats the part with fine magnetic particles, and subjects the part to a magnetic field. Cracks cause breaks in the magnetic field (even cracks below the surface not visible to the eye), which are outlined by the particles. However, since Magnafluxing® is a magnetic process, it applies only to ferrous metals (crankshafts, flywheels, connecting rods, etc.) It will not work with the aluminum heads and crankcases of these engines which are most prone to cracking.
Another process of checking for cracks is the Zyglo® process. This process does work with aluminum alloy. First the part is coated with a flourescent dye penetrant. Then the part is subjected to a blacklight inspection, under which cracks glow brightly, both at or below the surface.
A third method of checking for suspected cracks is the use of spot check dye. This method is quicker, and cheaper to perform, although hidden cracks beneath the surface may escape detection. First, the dye is sprayed onto the suspected area and wiped off. Then, the area is sprayed with a developer. The cracks will show up brightly.
If any of the threaded studs for the rocker arms or manifolds become damaged, and they are not broken off below the surface, they may be removed easily using the following procedure. Lock two nuts on the stud and unscrew the stud using the lower nut. It's as easy as that. Then, to make sure that the new stud remains in place, use locking compound on the threads.