Please note, the information in this tip sheet is not intended to take the place of a factory service manual or manufacturer’s instructions. Please verify all procedures and specifications outlined in the service and owner’s manuals for the year, make, and model you are working on. Be sure to follow all instructions for the equipment and tools you will be using provided by the manufacturer of that equipment. Read the Material Safety Data Sheets provided by the manufacturers of chemicals, chemical compounds, and mixtures, understand the risks, take appropriate safety measures, and wear personal protective equipment. Wear safety glasses, always adequately and redundantly support a vehicle, be careful around moving parts (fans, belts), and have a plan in case of fire.
The following are additional notes not found in the factory service manual to answer some questions that might come up, make the process go more smoothly, and increase preparation. Always verify thread sizes before using a tap or die by comparing to both an SAE and Metric thread gauge, and look up and verify part numbers as well. The factory service manual is still necessary and should be considered a must-have. It contains critical information on torque sequences, torque procedures, bolt coatings, and precautions.
It is significantly more difficult to do this job on a 3.8L six cylinder fourth generation F-body than most vehicles. Access to the engine is made more difficult because much of the engine is located underneath the cowl, and access to the rear of both cylinder heads to remove bracketry is very tight. There are many other sequencing problems and challenges as well. You should not consider doing this if you have limited experience, the car is needed for transportation this week, you do not have alternative transportation that is available for many weeks, you are working outdoors, your tool set can fit in a box that has a handle, or if you do not truly love your fourth gen F-body. Preferably you should have some sort of sentimental attachment to it, otherwise you will probably give up before it is done.
Your tool set should include 3/8 and ½ inch torque wrenches, a set of O-ring picks, fuel line spring lock connector tools, harmonic balancer removal tool if doing the front seal or pulling the front cover, reversible ratcheting wrenches (the kind with the flipper to reverse direction and a slight offset up on the box end, not the flat kind that you turn the wrench over to reverse direction). Some of the recurring sizes that you need a large selection of wrenches and sockets is 8mm, 13mm, and 15mm. Make sure you have a high quality 8mm or 5/16 socket in six-point, 3/8 drive for torquing bolts. The intake manifold bolts are very sensitive to rounding off if you are using lower quality tools.
This job is a combination of both Metric and SAE standard sizes. Threads can be either Metric or SAE. Generally speaking, stuff on the inside of the engine is standard, like the head bolts, rocker arm bolts, probably because this engine was designed in the early 1960’s. Stuff on the outside of the engine is more commonly metric (read the specific exceptions on the exhaust manifolds), including the accessory bolts and studs that are mounted on the front and rear of the cylinder heads such as the engine lift brackets and the left front EGR; which are 10mm x1.50 or 8mmx1.25. In addition to standard and deep well sockets in both standard and metric, you will need 3/8 drive swivel sockets. 13mm was used often and it especially helps to have a several different styles of wrenches to choose from. It helps to have ¼ and 3/8 drive extensions in 1” or 2” length as well, because there were several situations where a 3” long extension with short socket was too long, and a deep well socket was too short or awkward. 13mm deep 3/8 drive sockets in differing lengths (such as a mid-length) also help. Wobble extensions were used. I had a Creftsman 5/16 polished (long) combination wrench, and it rounded out and damaged an intake manifold bolt and wrench. I picked up a Mac 5/16 combination wrench, and there were no further problems.
Taps you will need include 7/16-14 (cylinder head bolt holes), 5/16-18 (rocker arm bolt holes, exhaust manifold stud holes, lower intake manifold bolt holes), 10mm x 1.50, a set of thread pitch gauges in both SAE and metric to make sure you are using the correct size before putting a tap in any hole.
At 172,000 miles on an engine with above average maintenance, the condition was as follows:
Coolant was leaking from the front of the engine. A pressure test made the problem worse, and finished off whatever was left of a weak gasket. It was done.
Ring ridge in cylinders: zero to none
Valve sealing: With the heads off the vehicle, I flipped them upside down, leveled them out, and poured solvent in the combustion chambers. The solvent held for over 5 minutes in all the combustion chambers, indicating decent sealing. I elected not to do a valve job. It is best to do a compression test prior to starting a complicated procedure, so you have some idea if it is not savable.
Valve stem seals: Somewhat hardened and in need of replacement. They were intact and not crumbling.
Head gaskets: Were actually ok on mine and could have gone longer. Having iron cylinder heads in this application certainly helped. Head bolts are torque to yield (stretch) and must be replaced if they are loosened. Fel-pro does sell them as a set. They do not come with the head gasket set and must be ordered separately. They come coated with a hardened red substance on the threads. They are installed just like they come out of the box; do not coat them with additional materials. The rocker arm bolts are also torque to yield (stretch). I could not find an aftermarket source for them and had to go to the former Pontiac dealer to order them. The part number was 24503515, there were 12 qty, and the cost was 2.30 each. The rocker arm bolts also come with the same hardened red substance on them, but the service manual says they should also be installed with the GM 12345493 or equivalent thread lock compound (High Temperature High Strength red Loctite). The freeze plugs were stainless steel and did not need touched. Aftermarket ones are zinc plated steel (inferior), or brass if you do some extra sourcing. Please read the notes below about accessing the valve cover gaskets if you are thinking of doing the head gaskets. Don’t forget to unhook the ground strap leading to the back of driver’s side cylinder head, at the firewall before pulling it.
Exhaust manifold studs are hybrid SAE/Metric with 5/16-18 going into the head itself, and 8mmx1.25 on the nut end. Restated, just to be clear, the studs have two different thread patterns; on one end is Standard SAE (American) threads and the other end is Metric for attaching any additional heat shielding. There are 6 studs per side for a total of 12 studs. 8 of the studs are the same (4 per side). Once you have the heat shield off, as you loosen the “nut” on the 8 similar studs, the whole stud unscrews. It turns out the structural nut is permanently affixed to the stud in that case. If you think that later on you will need to loosen the “nut” from the stud before reassembling, you will only ruin them. They do not come free. I tried heating the nut with a torch, and all I succeeding was in deforming the stud. I went to the dealer to order new ones and we realized that it is all one-piece; a fake stud. It is not easy to make out that kind of detail when they are rusty and crusty. Should any of the 8 not be serviceable the part number was 24502332 stud, and the cost was 3.48 each.
The other 4 exhaust manifold studs are real studs, and the 8mm x 1.25 nut on the end does come free; but again going into the cylinder head itself is 5/16-18. The purpose is to have the two real studs installed on the cylinder heads before beginning the assembly process. Then you put the exhaust manifold over these two studs, and just barely start the nuts to keep it from falling off. The exhaust manifold gasket can then be slid down from the top, because at the location of the two real studs the gasket is slotted. It makes the job slightly easier. When reassembling the engine note that the passenger side exhaust manifold should be loosely in place in the engine bay before putting the valve cover on, because it will be impossible to get past the air conditioning lines with the valve cover in place (do you really want to pull the a/c compressor bracket loose from the front of the engine, or try to remove the engine lift bracket again to remove the valve cover?!) The exhaust manifold flange to the y-pipe at the bottom utilizes long 8mm x 1.25 bolts. The two on the driver’s side manifold snapped off in the manifold when loosening, and I ended up drilling them out on the bench and installing Heli coils. The passenger side ones came free (I was using heat in both cases), and I used a tap and die to clean up the threads. The exhaust doughnut was serviceable in my application by Fel-Pro as 61018. When reinstalling, be careful not to overtorque the studs, they will break, and extraction can cause a person to have to start the whole job over, or use creative techniques to extract in the chassis, such as a left hand drill bit and specialized tools from the yardstore.com.
Lower intake manifold gasket to cylinder head: In need of replacement, nearly breached or breached around coolant ports. This is a common problem on the 3800. These were plastic gaskets with embedded O-rings that deteriorate over time, especially in the presence of acidic cooling systems that have not had much maintenance.
The lower intake bolts use the GM 12345493 or equivalent thread lock compound. There appeared to be a mistake in the torque sequence on my 1998 GMP/98-F-3 Manual, in that #6 and #7 were pointing to the same bolt, and one of other bolts was not labeled. I made an obvious assumption.
Upper intake manifold to lower intake manifold gasket: Completely blown out at the front where the coolant passes through, a few inches under the thermostat. This was the primary culprit. It was a plastic gasket that had deteriorated and had become brittle. It was broken in many areas. Coolant was starting to get into the number 1 cylinder, because that runner was much cleaner than the rest.
1997 Pontiac Firebird 3.8L V6 Heater hose pipe (90 degree elbow): in poor condition, failing. It is a common coolant leakage problem on the 3.8L. This plugs into the front of the lower intake manifold and connects it to the tensioner assembly. The original is composite; aftermarket ones are aluminum (probably better). This is an O-ringed part. Note that you only need one on this particular 3.8l V6 variant. Some of the aftermarket kits, such as Help! Have two in the package. One is symmetrical, the other one is not. I just needed the symmetrical one. There are some sources that contain just the one that you need, though that do not get stocked locally in my case. It was a choice of paying 6 bucks for the one and waiting on it, or 11 bucks for the two and them having it in stock.
1997 Firebird 3.8l V6 timing chain notes: looked to be in good condition on my engine, but when I began removing it for replacement the plastic tensioner block broke in half at the pivot point from embrittlement. This can be purchased separately from the timing chain if you want to just replace the plastic piece.
If the front cover is off to access the timing chain, it is very easy to knock out the front oil seal from behind with a flat blade screwdriver and a hammer. If you have to pull it out from the front (not removing the front cover), it would be more difficult, but not impossible. Accessing the front cover area is time consuming and certainly added to the job. The gasket kits for the timing set do not include an abbreviated version of the oil pan gasket at the front. In the old days, you would cut the remnant of the oil pan gasket off flush with the block and replace just the portion at the front that is common to the timing cover. It is not included in the kit because the oil pan gasket is a metal core with an embedded O-ring. It would not be very possible to cut it off, so you just reuse it. I put a little RTV on the old oil pan gasket to feel better. The service manual said you should also loosen more of the oil pan bolts at the front of the engine, to let the oil pan drop down just a little to facilitate getting the front cover back in place.
Getting the front cover wiggled on is challenging, because you must also align the cogs from the oil pump at the crankshaft snout with the cogs in the lower timing gear that drive it. Then you have to clear the power steering pump pulley while aligning the front cover on the two dowel pins as well. Make sure you have a good mirror handy, to align the oil pump cogs. The oil pump can be rotated slightly to align it with the lower timing gear, by using an O-ring pick or a small screwdriver. It was difficult, when everything finally came together it was sudden and surprised me.
Per the manual, front cover bolts are installed with the equivalent of GM 12346004 sealant, which is Loctite PST 592 Thread Sealant, High Termperature, per the Loctite Automotive Aftermarket OEM Connection Brochure .pdf.
Front cover crankshaft seal: leaking
1997 Firebird 3.8L V6 valve cover gaskets: they are O-rings and were leaking. It is somewhat difficult to even do valve cover gaskets on this car. On the passenger side, the engine lift bracket at the firewall has to be removed to remove the valve cover, because the bottom rear valve cover bolt is completely obscured by it. Removing the engine lift bracket is very difficult. Before starting any of this job or ordering any parts, go out to your car and attempt to get to the bolts that hold it on. The bracket is held on by two short bolts in the rear of the cylinder head. The outboard bolt is the easier of the two. You might be able to hook onto it using a 13mm ratcheting reversible wrench with fine teeth. A flat ratcheting wrench that is not reversible will not work (the kind where you have to flip the wrench over to make it go in the opposite direction). The offset of the reversible kind is beneficial. The inboard bracket bolt has a stud projecting out from the end of the bolt. First the nut must be removed; it holds on the transmission dipstick tube tab. Then the bolt/stud is removed. It takes a 13mm open end wrench (the bolts are 10mm x1.50). It is most easily done with the intake manifold off. When reassembling, it is best to have the valve cover on and the engine lift bracket on before installing the upper intake, because it will be nearly impossible to get to later. You might note that all of this would be just a little easier if the wire harness could be moved slightly. There are two sheet metal loop clamps the bundle routes through on top of the bellhousing area at the back of the block that can be delatched. It is a standard S-hook, like a bra, with the clasp just being in the center of the width of the loop. The problem is that you really can’t get to them until the upper intake is off. It is easiest to work with them with both the upper and lower intake off. Once the lower intake is on, you will no longer be able to see what you are doing, but might be able to get them relatched. Once the upper intake is on, there is no chance in latching them back up. The driver’s side valve cover is a bit easier. Instead of having the engine lift bracket on the aft end of the engine, it is under the forward end of the engine. It also must be removed, but it is easy to get to. Two EGR related plumbing pipes must also be removed, the EGR, the ignition coil all must be removed. The coil bracket that is mounted to the rear of the cylinder head can actually stay on, including through upper and lower intake manifold replacement.
The upper manifold bolts are reusable if in good condition. The service manual did not talk about coating the upper intake manifold bolts with anything, so I installed mine dry. Many of the upper intake manifold bolts are wrenched with a 5/16 or 8mm. I would recommend having a 3/8 drive socket in that size in 6-point, as they are highly sensitive to stripping out around the corners. It should be a quality socket as well. When working on the upper intake manifold, look at the torque sequence diagram at the bolt in sequence number 7. It is at the rear of the upper intake manifold, and the upper intake plenum covers it up. There is just enough room to get a ratcheting 8mm or 5/16” wrench on it, again, the kind that is reversible and has a slight offset to it. The flat kind of ratcheting wrenches will not work well, you need that offset, and the teeth in the flat kind of ratcheting wrenches are too coarse. I ended up delivering the bolt to the hole with a very long pair of stork needle nose pliers. Then I took a pair of needle nose vise grips and clamped onto the open end of the ratcheting wrench. I was then able to deliver the ratcheting wrench clear back to the head of the bolt. Once the wrench had been delivered to the bolt head, there is just enough room to tighten it down.
1997 Firebird 3.8L V6, removing the fuel rail to remove the upper intake manifold: Removing the electrical connectors going to each injector: I used an O-ring pick to detach the turned down end of the wire clip from its cove, then the wire clip can be pulled from the base end. It is hard to get to the rear cylinder on the passenger side of the car. When I finally got it, the wire clip went flying and has yet to be found. The parts guy at the dealership could not find a separate listing for just the wire clip. I had to order a new replacement electrical connector, and that had the wire clip on it. The cost for just one of these connectors was $29.57, so be really careful in policing the clips up (the part number was 12085491). Incidentally, he said that GM will sell most any electrical connector on the harness separately, but that it takes calling a special phone number to find out what the part number is, because he did not have the breakdown available on his end. The cost is usually more than the one I ordered- think double or triple). To undo the fuel lines you will need the special tool for releasing the spring lock, I had that but they were still stuck on somewhat from age. I had to apply more force after the tool was engaged than I would have thought necessary. I thought maybe the tool was not suitable for this application, but no, they were just stuck on there real good. There are 4 nuts that hold the fuel rail assembly to the upper intake manifold. After loosening the four nuts, the fuel rail can then be wiggled out with the injectors still attached, as each injector only has a fat O-ring sealing it into the lower intake; they are not screwed into the manifold. The head gasket set came with 12 fuel injector O-rings, there is also one O-ring each at the top of each injector. It is easy to replace the top O-rings with the fuel rail assembly out of the car. There is another clip; a fatter sheet metal clip that holds them in that is easy to work with. These clips are available from RockAuto as ACDelco 17111800, but they are not the ones that go on the electrical connector. They are not needed unless lost.