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Discussion Starter #1
First, i'm not one who toys with engines much, change my own oil, replace spark plugs, simple things like that. When I finally accepted the fact that my headgasket needed replacing I just couldn't pay someone $800-$1100 to replace a $20 headgasket. After discussing it with a mechanically-inclined friend I decided to attempt it. He told me to get a Haynes or Chilton's manual. I decided on a Haynes manual and downloaded the FSM for the 1.8L engine. I thought i'd post some details to maybe help out someone else who's gonna replace their own headgasket. As stated earlier, i'm not a mechanic so those of you with experience please take it easy on me if I don't describe something correctly. This is for inexperienced folks like me. This is random thoughts guys so please bear with me, it's important that I get as much info out as I can remember!

Q. How did I decide the headgasket was the problem?
A. For the past couple of months I had to keep adding fluid to the radiator reservoir, I wasn't sure where it was going but it always needeed more. I had no antifreeze in my oil, my oil was clean.
My car was getting hard to start (compression). Sometimes it would take four or five times before it finally started.
Couldn't keep air out of my heater core. One heater hose hot, one cold, kept bleeding the system but it would come back in three days.
P0303 cylinder #3 misfire, replaced spark plug, swapped ignition coil but it stayed in cylinder number three.
After reading the forums all these problems led to one answer, the headgasket!

Things I should've done before disassembling the engine,
1. I should've gotten the headgasket before I began, after I got it taken apart I couldn't find a headgasket anywhere! I figured every parts store would have some on hand. I was delayed two days waiting on the UPS truck.
2. I should've verified exactly which torque wrenches I would need, I ended up buying one.
3. I should've studied the manuals better, it's hard to read them once you and the manual are covered in oil.

Issues,

1. Haynes manual, this manual has good information but it covers four engines at the same time, QG18DE, QR25DE, SR20DE and GA16DE. The problem arises when your on -for eaxmple- page 2A-13 under "Head Removal" instructions, the pictures on the page are for the other engines while the instructions are for the QG18DE. Not a problem if your familiar with this stuff but a real pain when you've never done it before and your looking at the pictures while reading the instructions.

2. FSM, good stuff but it assumes you've done this a time or two. Between both manuals lies the answer, cross reference them and you'll be good to go.

3. Rocker cover, I had problems getting this off. I was smart enough not to pry hard on it so I wouldn't damage it. The diagram doesn't show the two bolts on the top-left of the cover.

I ended up ordering a Felpro cylinder head gasket kit plus Felpro head bolts, total cost including shipping $166. Everything I read said to also replace the head bolts.

Tough stuff,

1. Top bolt on the exhaust pipe. It was pretty tough to get to but with a coupld of extensions I got it out.

2. Timing chain installation. I had a difficult time getting the timing chain over both camshaft sprockets. As one helpful person on here suspected, I had to push the chain tensioner farther to the left, got it moved and the chain went on with no more problems.

Things I did,

1. I put fingernail polish on both the chain and camshaft sprockets to get it lined up correctly when reassembling.

2. I went ahead and replaced the starter. Since it had gotten so hard to start I had really worked the starter so after seeing how easy it was to access with everything removed I decided to go ahead and swap it out while it was a simple job.

3. I also replaced the belts for obvious reasons.

4. Removed the radiator reservoir and power steering reservoir to give me easier access to the belts.


It took me about five hours to disassemble everything and about six hours to reassemble. I got it back together at about 2:00A.M. Saturday morning. I've driven it over three hundred miles since then and she's running great. I was surprised how easy it was to get all the air out of the cooling system once I replaced the headgasket.

Anyway, I posted this to try and help someone else who's about to do what I just did. If I can replace a headgasket anyone can! Thanks for reading my random thoughts :)
 

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That's really great 04Sentra!! Not an easy job for the first time.... glad everything worked out. Well DONE!!:fluffy:
 

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Good job man. I went through this hellish procedure last August in my garage that was 120 degrees on my wife's 04 1.8S Sentra. Do you live close to a Nissan dealership? They had all the parts I needed. I went with the $60 Nissan head gasket and Nissan head bolts. Did you inspect the head for warping? How hard was the intake camshaft sprocket bolt to remove? That was a mother...... for me. That and the damn catalytic converter bolts.
 

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I'm in the same situation, removing the intake. The book says put comp air to the oil feed, rotate the cam & lock the sprocket in the advanced position w/Allen wrench. The cam didn't advance. Anyone got any insight
 

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Discussion Starter #6
Good job man. I went through this hellish procedure last August in my garage that was 120 degrees on my wife's 04 1.8S Sentra. Do you live close to a Nissan dealership? They had all the parts I needed. I went with the $60 Nissan head gasket and Nissan head bolts. Did you inspect the head for warping? How hard was the intake camshaft sprocket bolt to remove? That was a mother...... for me. That and the damn catalytic converter bolts.
joerr77, I live about 35 miles from a Nissan Dealership. I ordered Felpro gaskets and head bolts, I heard good things about that brand. The intake camshaft sprocket bold was a B!t<h to remove! The toughest bolts for me were the catalytic convertor bolts! It was a huge sense of accomplishment to do this myself, i'm a middle-aged guy but I don't have much experience with this type of work. Congratulations to you too!
 

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Discussion Starter #7
I'm in the same situation, removing the intake. The book says put comp air to the oil feed, rotate the cam & lock the sprocket in the advanced position w/Allen wrench. The cam didn't advance. Anyone got any insight
patxburx, i'm embarrassed to say this but I missed this step completely! It was confusing going between the Haynes manual and the factory service manual so I didn't catch this till I was already past that step. Guess what, it didn't make any difference! I was worried when I realized I had missed this step but I put everything back together and she's been running like a top ever since. I know this is a weak answer but I wanted you to know that missing this step had no effect on my car, still running smooth and getting 35mpg!
 

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I'm in the same situation, removing the intake. The book says put comp air to the oil feed, rotate the cam & lock the sprocket in the advanced position w/Allen wrench. The cam didn't advance. Anyone got any insight
just did mine today, while pumping the air in the last oil port, (closes to the bulkhead) tap the variable timing sprocket housing w/ a small hammer (lightly) and/or rock the cam back and forth slightly w/ a 21 mm open end wrench on the hex part of intake cam shaft. you will see the Variable timing face rotate forward where a small hole on the face of the variable timing housing (9:00) will open up- put a small allen wrench in (small end) and tape it to face of housing. it really does work, I've had to do it 2x in 2 days-I messed up replaceing a head qasket.
 

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just did mine today, while pumping the air in the last oil port, (closes to the bulkhead) tap the variable timing sprocket housing w/ a small hammer (lightly) and/or rock the cam back and forth slightly w/ a 21 mm open end wrench on the hex part of intake cam shaft. you will see the Variable timing face rotate forward where a small hole on the face of the variable timing housing (9:00) will open up- put a small allen wrench in (small end) and tape it to face of housing. it really does work, I've had to do it 2x in 2 days-I messed up replaceing a head qasket.
I'm stuck at this part. For the life of me I can't get the face to rotate to completely cover the hole, only partially. I can still stick a small allen wrench in there but only at an angle and not very far. I think I'm going to press forward. The OP here didn't have any problems, and I found a pretty thorough procedure online for the QR25DE engine that doesn't mention this step, but otherwise is pretty much identical to the FSM for the QG18. I hope I'm not making a huge mistake. Here is the QR25DE procedure I was talking about:
Change the headgasket on the QR25DE. (Altima Sentra) - B15U.com - Nissan Sentra Forum
 

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advancing variable intake cam

I put air to advance the cam but never found the hole to put the allen wrench in.
Long as you bottom the cam chain tensioner & lock it, you have plenty of slack
Do a thorough job of painting the chain & sprockets alignment marks.
I didn't...
 

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I replaced the head gasket on my 2003 Sentra, with 93,000 miles, last November without doing the intake timing chain sprocket advance procedure. I marked the timing chain and sprockets before removal. The engine ran perfectly after reassembly, even though the engine light came on and stayed on. As long as it ran fine, I wasn't concerned about the light. About two months ago it began running rough almost like it had no power to accelerate. The problem is intermittent. Some times it comes and goes while driving at various speeds and you feel it in the acceleration, and other times it never shows up. I took it to Auto Zone and they checked the codes, which showed everything from clogged fuel injectors to cam sensor faulty. I added fuel injector cleaner and changed the plugs hoping that would fix the problem. Next, I took off the valve cover to redo the timing chain sprocket procedure in hopes that would fix the problem. More recently, I took the car to a mechanic friend who said he believes it is electrical not mechanical, being that it was intermittent, but did not think the cam sensor was the culprit. Does anyone have any suggestions?
 

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Cam Sensor

Cam sensor is $28. I would just change it if the ODB says it's bad. If you lined up the cam sprockets with the chain properly you should be fine.
 

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I know this thread is a little old but I am also replacing the head gasket on a 2004 Sentra, my dad and I bought this car because it needed a little body work but after sitting for a few days we went to start it and it wouldn't fire up. After a compression test revealed low compression in 2 cylinders we figured the head gasket needed to be replaced. We made sure to make very good marks on the sprockets and chain while taking everything apart, however, when putting it back together we noticed that the face of the intake sprocket was not horizontal as shown in the FSM. So we were wondering if the timing could have been off in the first place (there were a few things that make me wonder if someone had been inside this engine before). Then I started wondering if it could be off because we did not advance the variable timing with air pressure? Looking at the cam if we make it look the way it does in the FSM all of the valves are in a neutral position but if we line up the marks that we made the intake valves on the #3 cylinder are engaged. I am just wondering if anyone can help me out, the difference between the two positions is one tooth on the timing chain. I know that some of you did the head gasket without advancing the timing first so was the slot on the face of the sprocket fully horizontal? Thanks for the help.
 

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mkb

I've had plenty of experience tearing apart the head on my 03 Sentra, 13 times to be exact. After replacing the head gasket the car ran fine until about a week or so later, when it started running real rough. I could not get anyone to give me a proper diagnosis, even the guys at Just Answers were not helpful. I thought it had to do with the alignment marks on the cams or that "sprocket advance procedure" using air. I had aligned my marks and tried the air scenario to no avail. Then I went through the tedious routine of advancing the cams one or two teeth at a time, putting it all back together; then I tried retarding them one or two teeth at a time, putting it all back together each time. None of it worked, it still ran like crap. I put it all back to my original positions, which were exactly as shown in the diagram, took it once more to Auto Zone. This time they said #2 :givebeer:misfired, for some reason. After some conversation he sold me a coil for #2. I replaced it immediately in the parking lot and it ran like a champ. It is still running smoothly. The moral of this story is, put it back together like the diagram and forget about all the air sprocket advance crap. It should run fine. And if it should begin running rough, check the coils!!
 

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Thanks this is exactly what I was looking for. So you put it back with the sprocket at 90 degrees/horizontal like the FSM shows or did you put it back with it slightly down at 11 degrees like the image I posted? The only reason I am wondering is that we marked the sprocket very well and with the marks lined up it isn't horizontal it looks like the picture I posted. But if we move it a tooth to bring the sprocket horizontal than the cam sits nicely with all valves ins a neutral position. We are just worried that it jumped a tooth or someone worked on it in the past and had it one tooth off.

Also it seems like you are saying that if I am 1 tooth off I most likely wont bend a valve or mess up the head?
 

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mkb

Your earlier thread, the one with the diagram, talks about "it also causes the valves one #3 intake side to be engaged". That indicates to me that you may not be at TDC. When your cams are in the positions as shown in the diagram none of your valves should be engaged and you should be at TDC, otherwise you are 180 degrees off. The firing order, I believe, is 1-4-3-2. Slowly turn the cam shafts using two open-end wrenches simultaneously on the shafts. As you turn in a clockwise direction the #1 intake should engage. If #3 intake is engaging, then I believe you are 180 degrees off TDC. If that is the case, then take both wrenches and turn the cams clockwise until the sprockets line up again as shown in the diagram. Once you've done that, then check again to see if #1 intake engages. I don't believe the actual cam alignment on my engine was exactly as shown in the diagram. So if your cams are off a fraction or so it should be just fine. You need to rotate your engine several times. Each time make sure when you reach TDC the #1 piston should be at the top and no valves are open on any of the cylinders. Then check your cam alignment marks, they should be as shown in the diagram.
 

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The engine is definitely at TDC when the head was off #1 and 2 were at the top and #2 and 3 were all the way down. If we line up our marks, which is the way the engine was before we touched it, then the lobes on cyl #3 intake are contacting the valve but none of the other lobes are in contact. If we make the grooved portion in the sprocket horizontal our marks are off one tooth but the valve is not engaged. I did just notice though that the picture in the FSM that I had been looking at was for the dowels on the cam itself not the cut out on the actual sprocket.
 

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When I did my head gasket on my '02 GXE, I never had to mess with the cat. I just removed the manifold heat shields, unbolted the exhaust manifold from the head and left the entire exhaust system in tact and in place. Just took a little extra maneuvering of the unbolted head to slip the studs (or rather just over half of them) out of the manifold with them in the head, and back in on reassembly with the gaskets hanging on the studs.

Having already read that the intake cam advance business was unnecessary, I didn't bother scrounging use of a compressor for that. Then the index mark I had painted onto the timing chain for the intake cam didn't stay, and the crankshaft got slightly turned while the engine was apart waiting for the machine shop to mill and pressure-test my head.

So I first put the crank back to TDC before putting the head back on (pretty obvious where the pistons are in that state of assembly, and the mark on the pulley still got it centered perfectly at TDC.) Then so long as the index marks I painted for the exhaust cam lined up perfectly with the chain taut from the crank to it and the cam's knock pin at the 12:00 as per the FSM, I put the intake cam's knock pin at 9:00 by the same illustration, put the sprocket and chain on with the chain taut across the top from exhaust to intake and everything turned to the proper position.

Runs like a top. Looking forward to next year taking that vacation road trip I couldn't take this year because the head gasket was leaking.
 
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