Most overhaul procedures for gasoline and diesel engines are fairly standard. In addition to specific parts replacement procedures and complete specifications for each individual engine, this section is also a guide to acceptable rebuilding procedures. Examples of standard rebuilding practice are shown and should be used along with specific details concerning your particular engine.
Competent and accurate machine shop services will insure maximum performance, reliability and engine life. In most instances, it is more profitable for the do-it-yourself mechanic to remove, clean and inspect the component, buy the necessary parts and deliver these to a shop for actual machine work.
On the other hand, much of the assembly work (crankshaft, block, bearings, piston rods, and other components) is well within the scope of the do-it-yourself mechanic.
The tools required for an engine overhaul or parts replacement will depend on the depth of your involvement. With few exceptions, they will be the tools found in any mechanic's tool kit (see General Information & Maintenance ). More in-depth work will require some or all of the following:
The use of most of these tools is illustrated in this section. Many can be rented for a one-time use from a local parts jobber or tool supply house specializing in automotive tools. Occasionally, the use of special tools is called for. See the information on Special Tools and Safety Notice in the front of this guide before substituting another tool.
Procedures and specifications are given in this section for inspecting, cleaning and assessing the wear limits of most major components. Other procedures such as Magnaflux® and Zyglo® can be used to locate material flaws and stress cracks. Magnaflux® is a magnetic process applicable only to ferrous (iron containing) materials. The Zyglo® process coats the material with a fluorescent dye penetrate and can be used on any material Check for suspected surface cracks can be more readily made using spot check dye. The dye is sprayed onto the suspected area, wiped off and the area sprayed with a developer. Cracks will show up brightly.
Aluminum has become extremely popular for use in engines, due to its low weight. Observe the following precautions when handling aluminum parts:
When assembling the engine, any parts that will be in frictional contact must be pre-lubed to provide lubrication at initial start-up. Any product specifically formulated for this purpose can be used, but engine oil is not recommended as a prelube.
When semi-permanent (locked, but removable) installation of bolts or nuts is desired, threads should be cleaned and coated with Loctite® or other similar, commercial non-hardening sealant.
REPAIRING DAMAGED THREADS
See Figures 1, 2, 3, 4 and 5
Several methods of repairing damaged threads are available. Heli-Coil® (shown here), Keenserts® and Microdot® are among the most widely used. All involve basically the same principle (drilling out stripped threads, tapping the hole and installing a pre-wound insert), making welding, plugging and oversize fasteners unnecessary.
Two types of thread repair inserts are usually supplied: a standard type for most Inch Coarse, Inch Fine, Metric Course and Metric Fine thread sizes and a spark lug type to fit most spark plug port sizes. Consult the individual manufacturer's catalog to determine exact applications. Typical thread repair kits will contain a selection of pre-wound threaded inserts, a tap (corresponding to the outside diameter threads of the insert) and an installation tool. Spark plug inserts usually differ because they require a tap equipped with pilot threads and a combined reamer/tap section. Most manufacturers also supply blister packed thread repair inserts separately in addition to a master kit containing a variety of taps and inserts plus installation tools.
Before effecting a repair to a threaded hole, remove any snapped, broken or damaged bolts or studs. Penetrating oil can be used to free frozen threads. The offending item can be removed with locking pliers or with a screw or stud extractor. After the hole is clear, the thread can be repaired.
CHECKING ENGINE COMPRESSION
See Figure 6
A noticeable lack of engine power, excessive oil consumption and/or poor fuel mileage measured over an extended period are all indicators of internal engine wear. Worn piston rings, scored or worn cylinder bores, blown head gaskets, sticking or burnt valves and worn valve seats are all possible culprits here. A check of each cylinder's compression will help you locate the problems.
As mentioned in the Tools and Equipment portion of General Information & Maintenance , a screw-in type compression gauge is more accurate than the type that is simply held against the spark plug hole, although it takes slightly longer to use. It's worth it to obtain a more accurate reading. Follow the procedures below.
- Warm up the engine to normal operating temperature.
- Remove all spark plugs.
- Disconnect the primary lead from the ignition coil/module.
- Disconnect all fuel injector electrical leads, if applicable.
- Screw the compression gauge into the No. 1 spark plug hole until the fitting is snug.
Be careful not to crossthread the plug hole. On aluminum cylinder heads use extra care, as the threads in these heads are easily ruined.
- Have an assistant depress the accelerator pedal fully. Then, while you read the compression gauge, ask the assistant to crank the engine two or three times in short bursts using the ignition switch.
- Read the compression gauge at the end of each series of cranks, and record the highest of these readings. Repeat this procedure for each of the engine's cylinders. Compare the highest reading of each cylinder to the compression pressure specification in the Tune-Up Specifications chart in Engine Electrical . The specs in this chart are maximum values.
A cylinder's compression pressure is usually acceptable if it is not less than 80% of maximum. The difference between any two cylinders should be no more than 12-14 pounds.
- If a cylinder is unusually low, pour a tablespoon of clean engine oil into the cylinder through the spark plug hole and repeat the compression test. If the compression comes up after adding the oil, it appears that the cylinder's piston rings or bore are damaged or worn. If the pressure remains low, the valves may not be seating properly (a valve job is needed), or the head gasket may be blown near that cylinder. If compression in any two adjacent cylinders is low, and if the addition of oil doesn't help the compression, there is leakage past the head gasket. Oil and coolant water in the combustion chamber can result from this problem. There may be evidence of water droplets on the engine dipstick when a head gasket has blown.
See Figures 7, 8 and 9
Special Volvo adapter (tool 5191) and a compression gauge which reads to at least 600 psi (4137 kPa) must be used to test the compression on the Volvo diesel.
Checking cylinder compression on diesel engines is basically the same procedure as on gasoline engines except that a special compression gauge adaptor suitable for diesel engines (because these engines have much greater compression pressures) must be used.
Don't forget to remove the washer underneath each injector. Otherwise, it may get lost when the engine is cranked.
- Disconnect the wire at the stop valve on the fuel pump so that the pump will not spray fuel while the compression is being tested.
- Unbolt and remove the vacuum pump and its plunger from the engine.
- Clean all of the fuel delivery pipes and connections, then unbolt and remove the fuel delivery pipes from the fuel injection pump and the injectors. Plug all connections to prevent dirt from entering the fuel system.
- Using a 17mm socket, remove the injectors. Remove the disc-like heat shields under the injectors otherwise they will blow out and be lost during the compression test.
- Beginning with cylinder No. 1, fit the heat shield in place, screw in the adapter (Volvo tool 5191) and seal and tighten to 50 ft. lbs. (68 Nm).
- Connect the compression tester to the adapter.
- Crank the engine with the starter motor and read the compression pressure:
- After reading the compression pressure for all six cylinders, install new washers under each of the injectors with their heat shields and torque them to 50 ft. lbs. (68 Nm). Install the heat shields as shown in the illustration.
- Install the fuel delivery lines and torque their attachments to 18 ft. lbs. (24 Nm).
- Re-connect the wire to the stop valve on the fuel injection pump and install the vacuum pump and its plunger. Ensure that the O-ring on the pump is in good condition.