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Posted on Jan 02, 2017
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.
Exhaust flange nuts and bolts
Head Gasket (preferably OEM)
Ten head bolts
Two valve cover end seals
Tube of RTV silicone
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 .
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 .
Here is what other FAQ Farmers have contributed:
Posted on Jul 01, 2008
Buy a Subaru tech and repair manual $34.95 for 72hrs use I believe it can be downloaded i think around 250MB.. Dave www.techinfo.subaru.com/html/index.jsp
Posted on Aug 08, 2008
Head Bolt Torque For your 1994 Oldsmobile Cutlass Supreme (3.4L SFI DOHC): Foot pounds (Final torque) Note: Torque sequence --------- | 6 2 3 7 | | 5 1 4 8 | --------- Step 1: torque in sequence to 33 Ft/Lbs Step 2: turn an additional 90 degrees Recheck final torque in sequence *** CAUTION ***engine uses Torque To Yield head bolts (TTY) thatpermanently stretch during the initial installation.New head bolts must be used when cylinder head isreplaced or re-installed to obtain proper torque. Foot pounds (Final torque) Note: Torque sequence --------- | 8 4 1 5 | | 7 3 2 6 | front --------- of engine | 6 2 3 7 | | 5 1 4 8 | Step 1: torque to 40 Ft/Lbs --------- Step 2: turn an additional 90 degrees Recheck final torque in sequence *** CAUTION ***engine uses Torque To Yield head bolts (TTY) thatpermanently stretch during the initial installation.New head bolts must be used when cylinder head isreplaced or re-installed to obtain proper torque.
Posted on Feb 07, 2009
frajogag: First off, be aware that these bolts are "torque to yield" bolts (streach bolts). What this means is that instead of torqueing the head bolts to a specific torque specification, they are torqued down to a set spec and then tightened by rotating the bolts a certain angle, like 90 degrees. and all of them are turned the same amount.
This means that the shanks of the bolts must be checked to make sure they are not too thin (or the bolt has already stretched beyond limits and is prone to snap if used)
Here is how you check the bolts. Measure the bolt using a micrometer, at the base, or within the first 13mm from the end where it threads in. Then go to about 10mm before the threads end heading toward the top of the bolt. There should not be more than a 0.23mm (.0091 inch) or less difference or the bolt should be discarded.
Torque the bolts down to 98.1Nm ( 72.ft lb)
Looking at the head from the side, so you are looking at the full length from side to side, I will number the head bolts in this fashion.
#1 & 2 are directly in front of you and in the center of the cylinder head crossing it width wise.
#3&4 are to the left of #1&2, / #5&6 are to the right of #1&2
#7&8 are to the left of #3&4 / #9$10 are to the right of #5&6
Now, you have the sequence.
After the initial pull, back off all the bolts in the same sequence and then retorque them to 36 Nm ( 28 ft lb)
Using a torque angle wrench or having the ability to accurately judge turning angles. Rotate (clockwise) to a 75 degree angle. do this to all the bolts using the sequence I had provided.
Rotate the bolts (clockwise) 75 degrees again on all bolts in the same sequence. The proceedure is complete!
Posted on Apr 23, 2009
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.
Posted on Jul 15, 2009
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