Chevrolet 3.4L intake manifold gasket

 

 

 

 

The Chevy 3.1L and 3.4L lower intake gaskets are fairly high failure items and potentially very good revenue producers for an automotive repair shop. They are, however, deceptively difficult jobs. This article will cover the 3.4L engine, but the 3.1L and 3.4L engines are nearly identical with only a few small differences.

 

The first thing to do is to determine the source of the leak by looking behind the power steering pump and underneath the throttle body. Look for signs of either oil or coolant leaking from the gasket surface, especially where the intake manifold meets the cylinder head. The intake gaskets often leak from both the front and the rear of the intake and are easy to verify. The picture below shows a leak on the front side behind the power steering pump.

 

 

This is what you want to see; definitive proof that the gasket has truly failed, enough even for a skeptical customer to observe.

 

 

 

 

Initial disassembly

Once the repair has been approved, begin by draining the coolant and disconnecting the battery. The serpentine belt will have to be partially removed to access the alternator and power steering pump. After this, use your judgment and start removing the rest of the miscellaneous hoses, sensors, bolts etc. around the upper intake area. Most of the upper portion of this engine will be on your work bench by the time it is completely disassembled. There is no "secret trick" to doing this job that will save time or hassle. The best way to approach this repair for the first time is to take as much time as needed to properly remove all components and place them in some sort of order so that at the end of the job you won't have to waste time guessing which order to re-install them.

 

 

 

Here you can see one of the three 13mm bolts retaining the power steering pump. The pulley must be rotated around to access the other two. There is very little clearance to remove the pump, unscrewing the fuel pressure test port cap gives just enough room to slide it up and out (don't forget to put the cap back on when re-assembling). Then, place the pump up on the shock tower or any other area that is out of the way. There is no need to remove the hoses from the pump. Next, remove the alternator and coil packs and pull aside all related wiring.

 

 

 

On the other end of the engine, remove this coolant tube while being careful to not damage the small hoses at the throttle body. Once again, this is a fairly tricky item to remove from this engine. Try using a pair of needle nose pliers and push the hoses off of the tube like a Chinese finger puzzle.

 

 

The picture above shows what the engine needs to look like before removing the upper plenum. All of the various vacuum hoses are removed, and the wiring harness, EGR tube, and coolant tubes are removed or pushed out of the way. Now, remove the six bolts retaining the upper plenum and set it aside.

 

 

After removal of the upper plenum, loosen the two 13mm nuts on the driver's side of the block and head retaining the lower coolant tube and fuel lines. Next, relieve fuel pressure at the test port and remove the fuel pressure regulator, then the fuel inlet line. Be very careful when pulling both of these components from the fuel rail, as the o-rings can pop off and are very difficult to find proper replacements for if they cannot be located

 

Now remove the valve covers. Be certain that your socket (8mm or 5/16) fits very tightly on the bolt because they can round off easily. One of the valve cover bolts on the rear head is obstructed by the stud that the coil bracket mounts to. If you do not have a swivel socket or can't access this bolt well enough, the stud must be removed (it is much easier to take the stud out than it is to try to extract this bolt if it rounds).

 

 

This photo shows five of the eight bolts for the lower intake. It is not necessary to remove the fuel rail and injectors; although you may want to if you are not familiar with this repair. Note that the plenum gaskets have four plastic studs that center them. These studs have #1 Phillips heads and can be gently turned out and removed.

 

 

 

Inspection

 

 

The pictures above show why we are doing this job. Not only did this car have an external oil leak, but coolant was leaking into the crankcase from this coolant passage as well! Usually, the external leak is the only indication that there may be more serious problems not visible without disassembly.

 

 

As you can see, the gasket routes behind many of the push rods. BE EXTREMLY CAREFUL WHEN REMOVING THEM. The intake and exhaust rods are slightly different lengths. Many a tech has had to buy a valve job for the customer because he got in a hurry, didn t see this, and upon cranking of the engine bent one or more intake valves. When the push rods are removed, set them aside in the order they were taken out so that you will be able to put them back in the proper order. Also, as they are removed, note that the exhaust rods are the longest.

 

 

 

 

Here, you can see the after affects of corrosion that has formed around one of the coolant passages. In cases as bad as this, be sure to apply a small amount of silicone to the affected are to aid in sealing. Do not grind the surface down until it is smooth, the new gasket will never seal. In extreme cases, it may be necessary to send the head out to a machine shop or replace it entirely.

 

 

 

Surface preparation

 

It would be better to spend an extra hour cleaning and prepping the mating surface than to do the job again next week for free when it comes back leaking. Spend as much time here as you need to do the job right. I prefer to scrape the large pieces off with a razor blade, then go back with a very fine grit bristle disc suitable for aluminum to finish prep the surface. Do not ever use a sanding disc. Follow this up with a thorough cleaning in the parts washer and a good wipe with a quick drying cleaner. The bolt threads must also be clean and free of oil and debris. Use a wire brush wheel on a bench grinder or a thread chaser (not a die) to remove any old sealer, and then clean them with the same solvent. BE CAREFUL, do not allow trash and gasket material to enter the valley of the engine. Place some shop towels across the engine valley to captures as much debris as possible.

On the upper plenum gasket surface and the corresponding surface on the lower intake, never use any sort of power tools to remove any gasket that is stuck on. The trueness of these surfaces is critical to sealing, and any variances will cause a vacuum leak. Use only a razor blade or flat scraper to clean these areas.

 

 

 

To the left is the oil pump drive shaft at the rear of the block. When the engine is assembled, it is nearly impossible to access, and if it's sealing o-ring leaks it looks identical to an intake gasket leak. To prevent a perceived comeback in the future, it would be a good idea to re-seal it now. It is sometimes necessary to twist the oil pump drive shaft back and forth several times with a pair of pliers while pulling up to free it from the block.

 

This is the oil pump drive shaft cleaned and ready to be reinstalled. Note not only the new o-ring, but also the bead of silicone around the top flange as insurance against any possible leaks. Before installation, be sure to apply a small amount of oil or grease to the gears to prevent unnecessary wear upon startup.

 

 

Re-installation

 

At this point, the lower intake is nearly ready to go back on. But first, make sure to wash out the lifter valley with ATF (automatic transmission fluid). A large amount of particulate matter and solvent has entered this area during the cleaning and prep procedure. The ATF will wash all contaminants down the oil pan and will help lubricate the lifters and cam bearings. Next, place the intake gaskets on the heads and place the pushrods back in their corresponding lifters. When this has been done, torque the rocker arm bolts to 124 in. lbs., ensuring that the pushrods are properly seated in their cups. Listen for the sound of oil being compressed from the lifters. You may need to make several passes to ensure that the proper torque has not been compromised by the lifters bleeding down. After this initial step, torque the bolts an additional 30 degrees.

 

 

 

 

The above picture shows what the bead of silicone at either end of the block should look like. Be certain that the surface is clean and free of oil or it will leak. Note how the silicone extends up onto the surface of the gasket, it also must extend under the gasket as well. The lower intake is now ready to be set down on the new gaskets. Be extremely careful to set it down so that it is perfectly aligned with the heads. If it is not, do not slide it to align it. Instead, pick it back up and reposition it. Also apply a small amount of thread-locker to all eight lower intake bolts to ensure that they stay in place.

 

 

Torque is Critical!

 

The torque step is very critical in all repair procedures, but plays an even bigger part in this one. If the lower intake is over tightened by only a few foot pounds, it will crack the plastic gasket and ruin the repair. Under torquing, of course will cause leaks as well. Apply a small amount of thread locker to all of the bolts before installing them. This will keep them from backing out due to the extremely low torque required by these gaskets.

 

After starting all of the eight bolts, torque the four vertical bolts first to 115 in. lbs. Do this in several stages, increasing the torque with each pass. Then, torque the four diagonal bolts to 115 in. lbs. as well. Two of these bolts are obstructed by a portion of the intake, so a crows foot on an extension will be needed to properly tighten them. If the vertical bolts are not tightened first, the gasket will leak.

GM has recently released a bulletin (# 03-06-01-010) with revised torque procedures for many vehicles. These new procedures are used in conjunction with a newly designed lower intake gasket (# 89017279). The updated gaskets are identified by metal inserts to prevent crushing the sealing surface. The affected vehicles are:

1996 Chevrolet APV
1997-2003 Chevrolet Venture
1999-2000 Chevrolet Lumina
1999-2003 Chevrolet Malibu
2000-2003 Chevrolet Impala & Monte Carlo
1996-1999 Pontiac Trans Sport
2000-2003 Pontiac Montana, Grand Prix
1999-2003 Pontiac Grand Am
2001-2003 Pontiac Aztec
1996-2003 Oldsmobile Silhouette
1999-2003 Oldsmobile Alero
2000-2003 Buick Century
2002-2003 Buick Rendezvous

The revised torque procedure (which only applies to the new-style gaskets) is as follows: Torque all eight bolts to 62 in. lbs. Then, torque only the vertical bolts to 115 in. lbs. Finally, torque only the diagonal bolts to 18 Ft. lbs.

Aside from the tightening sequence, the rest of the repair procedure is the same for all vehicles.

Now install the valve covers and new gaskets. Ensure that a small amount of silicone is placed in the groove where the cylinder head meets the lower intake. Then torque the valve cover bolts to 89 in. lbs.

Next, after re-installing the fuel lines and other components that were removed after the upper plenum, place the plenum gaskets on the lower intake followed by the plenum. Then torque these bolts to 18 ft. lbs.

 

 

At this point the repair is nearly complete; however, this is also where many techs get in a hurry and start throwing parts back on. In most cases, this will cost you time rather than save it. This engine is a puzzle and will only go back together one way. Do yourself a favor and take your time here as with the rest of the repair. Once the engine and all of its accessories are back together, fill it up with coolant (make sure to use the bleeder screw on the black coolant tube) and then drain the oil and change the filter. This ensures that most of the harmful particles and solvents are out of the crank case and the new filter will remove any debris that didn't come out with the oil.

 

After adding oil and checking the coolant level again, the engine is ready to be started. Carefully watch the oil pressure light or gauge and make sure the engine gets oil pressure in a reasonable amount of time. Next, monitor the engine, and make sure that there are no catastrophic leaks, and that all external moving pieces are not contacting any part of the wiring harness or any other potentially mis-routed components. Continue to monitor the instrument cluster and engine for any signs of overheating or any other problems. Listen for any noises that may have not been present before the repair.

If, upon initial startup, the engine spins over quickly and seems to have little compression, don't panic. This most likely means that the lifters have pumped up while the pushrods were out and are holding the valves partially open. Continued cranking or waiting several hours will almost certainly yield better results. In either situation, however, don't be surprised if the engine runs roughly for the first minute or two. The lifters may tick as well. This is not to be confused with the sounds of valves contacting the pistons; lifter tick is a softer noise that fades as the engine warms up and the oil thins. A valve contacting a piston is a much sharper noise that most likely can be felt by touching a valve cover. It will not go away as the engine warms up and will most likely be accompanied by a rough idle. If the engine reaches and maintains operating temperature, test drive the vehicle, listening again for any noises that may not have been present before. After the test drive, bring the vehicle back into the shop and look over the repair. Check all gasket surfaces for leaks, and double check the oil and coolant level. If everything looks fine, the repair is complete.

 

 

Conclusion

 

In conclusion, this repair is not as easy as it may initially seem. However, as with all other repairs, it will get easier each time you do it. Don't be discouraged if it takes all day the first time. The quality of a repair is only as good as the tech doing it, and the quality of the parts used. Don't allow the use of inferior gaskets or low grade silicone, as these will be more likely to fail and cause a leak, ultimately reflecting on the tech that performed the repair.

So, take your time, use good parts, and do it right the first time.

 

 

Adam Riggs

ASE Certified Master Technician