Replacing head gasket

SOURCE: Head Gasket

Replacing a head gasket is not a DIY job, unless the person has plenty of experience, knowledge, and the proper tools. The fact that a person would even ask, "How to replace a head gasket", would indicate to some that they should not trying to do that repair.
To replace a head gasket you must remove the intake manifold, exhaust manifold, valve train, and then the head. This is very involved and requires disconnecting lots of sensors and the ignition system. The head must then be checked to see if it is warped, or cracked, and repaired if necessary. You must then know how to put all this back together and torque all the bolts in the proper sequence. This takes training and skill which the average shade tree mechanic does not have.
There is a difference between say a over head cam (OHC) engine and a internal cam engine. And then if it is a V6 or V8 then both head gaskets must be replaced even if only one blew. And last but not least, you have to find out if there is other engine damage and what caused it to blow the gasket in the first place. Definitely not for an amateur.
The best answer to this question: Take it to a professional.
The second-best answer: Get a repair manual and follow directions. A repair manual does not provide the training necessary to do this repair correctly, and not near enough information, but it can provide more info than can be written out in an answer like this.
Below is the best answer we can provide in this format.
Parts
Exhaust flange nuts and bolts
Head Gasket (preferably OEM)
Ten head bolts
Two valve cover end seals
Tube of RTV silicone

Disassembly
1. Disconnect the battery negative terminal
2. Drain the cooling system
3. Raise the front of the vehicle and support it with jack stands .
4. Remove the two 13mm exhaust bolts holding the exhaust pipe to the exhaust manifold, lower the vehicle
5. Remove the air cleaner assembly
6. Remove the upper radiator hose
7. Loosen the 13mm nut holding the dipstick tube bracket to the thermostat housing and remove the coil (if it is attached to the thermostat housing) and unplug the coolant temperature sensor
8. Remove the spark plug wires from the plugs, remove the distributor water shield and the distributor cap (this step is so you don't damage the distributor cap).
9. Remove the two uppermost 15mm-head bolts from the top of the a/c , alternator bracket where it attaches to the head and unplug the single wire temperature sending unit
10. Remove the upper half of the timing belt cover
11. Remove the valve cover
12. Disconnect the wiring harness connector that is just to the right of the throttle body
13. Disconnect the throttle cables from the throttle body and remove the two 10mm head bolts holding the bracket
14. Disconnect the vacuum lines from the throttle body
15. Disconnect the fuel lines - NOTE : The fuel lines may be under pressure , use extreme care when removing them
16. Disconnect the throttle position sensor connector and the EGR valve connector (if equipped)
17. Carefully lift up the throttle body wiring harness , the fuel lines , and the vacuum lines together and use a bungee cord to hold them out of the way
18. Remove the ground strap that is attached to the intake manifold from the fire wall
19. Remove the 15mm-head bolt holding the battery ground cable to the engine
20. Disconnect the vacuum hose from the power brake booster and the heater hose from the intake manifold left side
21. Use two plastic tie straps to secure the timing belt to the camshaft pulley and remove the pulley . Hold upward tension on the pulley and secure it with a bungee cord to the right hood hinge - NOTE: be sure to hold the upward tension with the bungee cord so the timing belt doesn't jump a tooth on the lower pulleys
22. Remove the head bolts and lift the head off the engine block . (I suggest having an assistant help to lift off the head) With the head removed , carefully check the head casting for signs of cracks. Also use a straight edge to check the head casting for warpage (maximum allowable warpage is .00
23. Clean all the head gasket mating surfaces and wipe clean with a little brake cleaner on a rag. Use a round plastic bristled brush to clean out the head bolt holes in the engine block and blow them out with compressed air .

Reassembly
1. After the gasket surfaces are prepared, set the new head gasket in place and CAREFULLY place the head into position, take extreme care not to place the head on the head gasket until it is in the proper position.
2. With the head in place, install the head bolts. You will need to tighten the head bolts in a circular pattern starting from the center and working your way out. I recommend hand tightening all the bolts before beginning the torque sequence. Head bolt torque: For older style 10mm head bolts : 35 - 45 - 45 - and a 1/4 turn; For newer style 11mm head bolts : 45 - 65 - 65 - and a 1/4 turn
3. Use the two rubber valve cover end seals and a bead of RTV silicone to reseal the valve cover.
4. Do Not let the silicone skin-over before setting the valve cover into place and tightening the bolts, also be sure that both mating surfaces of the valve cover are clean and oil free .
5. After the head is reassembled you will need to reset the base timing to specs. You will also want to double check the timing belt position . Use a variable timing light and set the timing mark on zero degrees . Save the setting on the timing light and shine it through the inspection hole in the top of the upper timing belt cover . If the belt timing is correct , you will see the oblong hole in the camshaft sprocket centered in the inspection hole .
Other Answers
Here is what other FAQ Farmers have contributed:

• Water is a by product of combustion, therefore water dripping from the exhaust should be an indication that your engine is operating efficiently, especially if there is no sign of water in your oil. There are other signals that would indicate a blown head gasket, such as loss of compression/loss of power, unexplained coolant loss, and clouds of white smoke from your exhaust, especially noticeable upon acceleration. Overpressurizing of the cooling system can also result in overheating.

• A lot more information is needed. For example, what kind of car is it, etc. This is a major service and should be done by an experienced technician.

• The short answer: Remove the head, check the head for warp-age and cracks, and install a new gasket.

• This depends on the type of engine that you have. You will need a well stocked tool box which must include a torque wrench. Import car engines will require a good selection of metric tools. You will need to drain and recycle the engine oil and coolant. It is best to rotate the engine so that the piston in number one cylinder is at top dead center of the compression stroke. At this point, take careful note of the position of the distributor rotor and make match marks as necessary so that it can be realingned when it is reassembled into the engine. Older American made V8 engines will usually require the removal of the intake manifold, exhaust manifolds,ignition distributor and associated wiring harnesses. If you are replacing the head gasket on an engine with dual overhead cams, the situiation is complicated by having to remove timing chain covers, cams and timing chains. These parts must be replaced exactly as they were removed. Manifold and cylinder head bolts should be removed in the reverse of the installation and torque sequence to avoid warping and possible cracking. This is especially important when dealing with aluminum parts. The cylinder head bolts must be tightened and torqued in a specified sequence and Foot/pound specification as per the engine manufaturer. The best advice would be to obtain a maintenance manual for the vehicle you intend to service. Most aftermarket parts dealers either stock or can order this for you. In the manual you will usually find step by step instructions that are for the specific engine/vehicle that you are servicing.

• Before attempting a gasket replacement you should consider what else might be done. Since it requires removing the exhaust header, intake and cylinder head from your car, you might want to see what other work needs to be done at the same time. The first thing is do a check up on your car: 1. Check spark plugs to see what they tell you about the condition of the engine. 2. Do a compression check. Then determine why it failed and what you need to rebuild. If you take the cylinder head off then you might want to replace it with a rebuilt one. Or at least get a valve job done. If you decide to do this yourself ensure you either rent all the tools or purchase them. For the first timers I would recommend a rebuilt head they will run between $150-$300 with a core exchange. Or you can bring it to a local shop and expect to pay around $150-$250 for labor and parts to have your rebuilt.

SOURCE: 1992 Toyota Previa van,Oil dripping onto exhaust manifold, replace head gasket? need a free manual!

The toyota previa uses a formed silicone gasket for the valve cover and the cover is held in place by metric shoulder bolts ( 10mm). The valve gasket leaks because you can't get enough preload on the bolts to re-seat the old gasket when it gets old and shrinks. The shoulder bolts only allow you to tighten the gasket enough to seat the shoulder on the bolt. If you continue to torque down the suspected bolts, you will snap the bolt off ( don't ask me how I know this ). You can either 1.)replace the old gasket with a new one or 2.) remove the existing bolts around the leak area and put in new metric bolts that do not have a shoulder. You may want to put in a small sleeve into the existing bolt hole but shorter than the thickness of the valve cover to account for the smaller diameter bolt. You can now torque down the bolt and get enough preload to seal the valve cover without removing the old gasket. Make sure you use a torque wrench ( in-lbs) or be very careful not to snap these small valve cover bolts.

SOURCE: need to replace blown head gasket on the above vehicle

are you sure head is not cracked

SOURCE: Torque Specs for Head Bolts on 1997 GMC Sierra V8 5.0 Vortec?

.0L Torque Specs Belhousing to engine bolts 28-38 ft/lbs Camshaft sprocket bolt 40-45 ft/lbs Camshaft thrust plate to engine block bolts 108-144 in/lbs Crankshaft pulley to vibration damper bolts 35-50 ft/lbs Cylinder head bolts -1979-1992 --Step 1 55-65 ft/lbs --Step 2 65-72 ft/lbs -1993-up --Step 1 25-35 ft/lbs --Step 2 45-55 ft/lbs --Step 3 75-85 ft/lbs Differential shaft lock bolt 15-30 ft/lbs Driveshaft U-joint to pinion flange bolts 70-95 ft/lbs Exhaust manifold bolts 26-32 ft/lbs Flywheel mounting bolts 75-85 ft/lbs Front engine mount nuts 72-98 ft/lbs Intake manifold to head bolts --Step 1 96 in/lbs --Step 2 16ft/lbs --Step 3 23-25 ft/lbs Intake manifold (upper intake to lower) 12-18 ft/lbs Oil filter insert to engine block adapter bolt 20-30 ft/lbs Oil pan mounting bolts -1979 --Step 1 (Large bolts) 11-13 ft/lbs --Step 1 (Short bolts) 7-9 ft/lbs --Step 2 (Large Bolts) 15-17 ft/lbs --Step 2 (Short Bolts) 10-12 ft/lbs -1980 to 1987 9-11 ft/lbs -1988 to 1993 6-9 ft/lbs -1994-up 110-144 in/lbs Oil pickup tube to main bearing cap nut 22-32 ft/lbs Oil pickup tube to oil pump bolts -1979 to 1987 10-15 ft/lbs -1988-up 12-18 ft/lbs Oil pump mounting bolts 22-32 ft/lbs Pinion bearing preload 8-14 in/lbs Pressure plate to flywheel bolts 12-24 ft/lbs Rocker arm fulcrm bolts 18-25 ft/lbs Spark plugs 7-14 ft/lbs Timing chain cover bolts 12-18 ft/lbs Vibration damper to crackshaft bolt 110-130 ft/lbs Wheel lug nuts 85-105 ft/lbs

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