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Rebuilding The GM Quad 4
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There have been both SOHC and DOHC heads used on the Quad 4 with several variations of each due to changes in valves, ports and structural design.
1987-’89 VIN D The ’87 Quad 4 came with a 16-valve aluminum head that was a 22530955 casting. It had a "modified pent roof" design and siamesed ports for each chamber. The intake valves were 35.5mm and the exhaust valves were 30.0mm.
1989-’92 VIN A (H.O.) and 1990-’92 VIN D When the H.O. motor was introduced in late ’89, it had a new head with bigger valves, along with subtle revisions to the chamber and ports to "reduce restriction and improve flow.". The intake valves were increased from 35.5mm to 36.5mm and the exhausts went from 30.0mm to 31.5mm. This head, c/n 25539086, was also used on the VIN D engines from ’90 through ’92.
1992 VIN 3 SOHC When the SOHC version of the Quad 4 family came out in ’92, it had an all new head with only one cam. The original 24573087 casting had a tendency to crack externally down across the second outer head bolt and down into the second exhaust port, so it was replaced by an improved design in ’93.
1993 VIN A (H.O.) and 1993 VIN D The ’93 DOHC engines came with a new head that had smaller exhaust ports and two larger 10.0mm studs for the exhaust manifold. This revised head, c/n 24570753, was used on both the VIN A and VIN D applications in ’93. The service replacement is a 24573303 casting.
1993 VIN 3 SOHC The new head for the SOHC motor had more metal around the threaded holes adjacent to two of the spark plug wells and reinforcements around the three middle head bolt bosses. These improvements kept the 24574468 casting from cracking externally.
1994 VIN 3 SOHC The SOHC head was changed one more time in ’94. It still looked the same on the outside, but it had smaller exhaust ports and a revised hole for the water outlet. The thermostat was moved to a remote location, so the notch for the coolant bypass was eliminated along with the machined step for the thermostat itself. It’s a 24573302 casting.
1994-’95 VIN D The head for the ’94 DOHC engine had the smaller exhaust ports and the modified hole for the water outlet, just like the one on the ’94 SOHC head. It’s a 24575456 casting, and it was used in ’95, too.
1996-’98 VIN T The new 2.4L engine came with a different head that had several changes. The chamber was shaped more like an oval with straight sides, both the intake and exhaust valves were smaller, both the intake and exhaust ports were different, and there was an EGR crossover passage cast into the head just below the water outlet. It’s a 24574683-18 casting.
There was only one cam used for all of the SOHC motors, but there were four pairs of cams for the 2.3L DOHC engines, depending on the year and application, plus another pair for the 2.4L. Most of them can’t be identified by the casting number alone, so rebuilders should check both the casting number and the lobe height before reusing any of these cams. The right pair of cams must be used together in the right application in order to avoid performance and emission problems.
1987-’89 VIN D DOHC The original intake cam had a 225/309 casting number with a lobe height of .3400". The exhaust cam was a 225/312 casting that had a lobe height of .3500".
1989-’94 VIN A (H.O.) DOHC The H.O. engines all came with a better cam that had more lift and duration. Both the intake and exhaust cams have a 225/455 casting number and a valve lift of .4100" at the lobe.
1992-’94 VIN 3 SOHC The single overhead cam motors all used the same cam. It has eight lobes, each in a different place, instead of the two pairs of four lobes found on the DOHC cams. Look for either 245, 704 or 78 somewhere between the first and third lobes.
1990-’94 VIN D DOHC These cams have the same 225/455 casting number as the H.O. cams described earlier, but the lift and duration are different. The lift for both the intake and exhaust lobes measures .3750". GM says the specs were changed "to improve idle stability."
1995 VIN D DOHC Both the intake and exhaust cams share a new 245/742 casting in ’95, so they both have a raised area about half way around the cam between the third and fourth lobe, even though it’s only needed on the intake cam for certain applications. It provides an input for the cam position sensor that bolts into the cover for the intake cam.
The signal from this sensor is used to index the sequential fuel injection found on the ’95 J cars with the 4T40-E automatic transmission. Although both cams share the same casting, it’s easy to tell them apart because the back of the intake cam is machined for the hex shaft that drives the power steering pump that’s mounted to the back of the engine. The valve lift measures .3600" at the lobe.
1996 VIN T DOHC Both of the cams for the 2.4L use the same castings (245/742) that were used for the ’95 VIN D cams, but the lift at the lobe is slightly less. The intake checks at .3540" and the exhaust measures .3450". GM says the cam was changed "to improve low end torque."
The SOHC engines came with one cam housing and the DOHC engines each had two one for the intake and one for the exhaust. They are split in the middle and sealed by four separate molded seals that are each designed to fit into a specific groove. But, there’s a catch; the depth and location of the seal grooves was changed in ’94 so you can make a simple mistake and end up with big problems.
1987-’89 VIN D These engines originally came with a 22535436 intake cam housing cover and a 22535435 exhaust cam housing cover. The lower halves of both housings each have a different casting number. Both the upper and lower housings were sand castings. The seal grooves for both the intake and exhaust are in the lower half of the housing and measure .070" deep.
1989-’93 VIN A (H.O.) and 1990-’93 VIN D The original cam housings were replaced by another pair that were die castings. The intake cover was a 22542961 and the exhaust cover was a 22542963. Both still had the shallow, .070" seal groove in the lower half of the housing.
1992-’93 VIN 3 SOHC The SOHC engine had its own special cam housing. The cover has a 24572808 casting number on it. The shallow seal groove was in the lower half of the housing.
1994 VIN A (H.O.) and VIN D There were two important changes made to the cam housings in ’94: 1) The seal grooves were moved from the bottom of the cam housings to the covers that bolted on the top; and 2) they were considerably deeper (.150"), so they required thicker seals. The top edges of the lower housings were left "as cast" in ’94. We don’t have casting numbers, but they can be identified by the deep grooves in the cover along with the unmachined mating surfaces on the lower halves.
1994 VIN 3 SOHC The seal groove was apparently moved to the top cover of the cam housing assembly for the SOHC in ’94, too, because the part number for the housing assembly changed along with the part number for the seals. It would be best to check it so you don’t mix and match the wrong pieces.
1995 VIN D and ’96 VIN T There were three changes made to the cam housings in ’95: 1) The power steering was driven directly off the intake cam so there were two new bosses on the end of the housing; 2) The bores for the lifters were smaller (33.0mm); and 3) There was a boss cast on the intake cover that could be drilled for the cam position sensor and a holddown.
These holes may or may not be drilled, depending on whether or not the car had sequential fuel injection. All of the ’96s had SEFI, but only the "J" cars with the 4T40-E automatic transmission had it in ’95. The intake cover was a 24574057 casting and the exhaust was a 24572810 casting.
There have been several housings and front covers used on the Quad 4 engine. The location of the dowels for the front cover have changed along with the hole for the vent tube. No one claims to know exactly what GM did, however, these combinations seem to be right most of the time. Start here and be sure to double check it before you sell the engine.
1987-’89 VIN D The front housing has a small nipple on the driver’s side for a vent tube and there is no tube on the front cover. The dowels for the front cover are located on the inside of the housing. There were at least two different castings that came with and without the vent hole drilled, so be sure to find a 22547879, a 22534007 or a similar casting with the hole and nipple.
1989-’91 VIN A (H.O.), 1990-’91 VIN D The front housing came without a nipple so there was a large vent tube on the front cover. The dowels are still toward the inside of the housing. Look for either a 22547879, a 22534007, or a similar casting without the nipple. Use it with the front cover that has the big vent tube on the front.
1992-’94 VIN A (H.O.) and VIN D The front housing was changed along with the chain and tensioner in ’92. It’s a 24570408 casting. The dowels for the front cover are on the outside edge of the housing. There is no vent tube in the housing, but there is one on the front cover.
1992-’94 VIN 3 SOHC The single overhead cam engines had their own special front housing and cover. The housing is a 24570263 casting with wide dowels on the outside of the housing and no vent tube. The front cover had the big vent tube.
1995 VIN D The ’95 balancer motor came with another new cover. It’s a 24574164 casting. It has the wide dowels and a bigger, angled hole for the vent tube. The front cover doesn’t have a vent tube.
1996 VIN T The 2.4L has another all new cover. It still has the bigger, angled hole for the vent tube, but there are several other differences including a large threaded hole for the oil filler cap. It’s a casting number 24574741. The front cover comes without a vent tube.
CHAINS AND TENSIONERS
There have been two different timing chains and tensioners used for the DOHC, along with another version for the SOHC.
1987-’91 DOHC These engines came with a double-roller timing chain and a tensioner that had a separate, replaceable shoe.
1992-’96 DOHC Olds used a link-style timing chain with powdered metal gears on these engines along with a modular tensioner that had the shoe attached to it. Handle the tensioner with care when you remove it from the engine so you don’t dislodge or damage the internal relief valve that’s located in the tensioner itself. It can be reused if the shoe isn’t too badly worn.
1992-’94 SOHC All of these engines came with the link chain and the modular tensioner. The chain was shorter because the engine only had one cam gear.
That’s the story on the bits and pieces. The chart shows how the block, crank and heads all fit together, but there are still some things every rebuilder should know about the Quad 4 in order to save time and money:
The H.O. engines make more power because they have more compression (10.0:1 versus 9.5:1), better cams with more lift and duration, and the best head available at the time.
All of the Quad 4 heads tend to crack in the chambers. The early SOHC head cracks on the outside, too, so check all of them over carefully and expect to do a lot of welding.
It’s almost impossible to get the spark plugs out without using an impact wrench and stripping the threads in the process, so plan on installing some thread inserts.
The valve springs were all conical-shaped through ’95. They were changed to a tapered, bee hive design in ’96.
The heads can’t be machined very much. The minimum thickness at the front of the head measured from the deck surface to the face of the bolt boss is 2.260".
These head gaskets are very prone to leakage. GM has released several different head gaskets for the Quad 4 and changed the torque sequence more than once. We recommend using only graphite head gaskets along with new bolts and holes which have been thoroughly cleaned. Follow these steps:
Clean the threads for head bolt holes thoroughly, but don’t retap them;
Make sure there isn’t any oil, antifreeze or debris left in the bolt holes;
Oil the threads and flange on the bolts sparingly;
Follow the torque sequence shown on the chart.
The housings for the balancer are the same in ’95 and ’96, but the balance shafts used for the 2.4L engine are heavier. The short one weighs 30 grams more and the long one weighs 45 grams more. Rebuilders will have to mark the balancer at teardown or take it apart and weigh the shafts to make sure that they have the right ones for the engine.
The balancer is timed by 1) bringing the #1 cylinder up to 900 BTDC; and 2) positioning the shafts so that both weights are topside with the flats parallel to the pan rail and held in place with a J41088 tool before installing it on the block.
Note that the sprocket on the balancer is held on with a left hand bolt. GM recommends replacing it whenever it’s removed. It should be torqued to 30 ft. lbs. plus 45°.
The cam housings can be interchanged as assemblies from ’87 through ’94 as long as the correct seals are used in the housings. The intake and exhaust housings are not interchangeable with each other.
There are four different seals used for the DOHC cam housings. They are color-coded with blue for the intakes and red for the exhausts to make sure the installer notices the difference and installs each of them in the correct groove.
The seals for the ’87-’93 cam housings are "thin" (.070") and fit in the lower half of the housing. The seals used in the ’94 and later housings are "thick" (.150") and fit in the cam housing cover. If the early, thin seals are used in a late cover with the deep grooves, they will leak. Likewise, if the thick seals are used in an early cover with the shallow grooves, the cam clearance may be affected in the short term and the seal will probably end up leaking in the long term.
The cam housings must be torqued from the center out in two steps to avoid splitting the gasket between the cam housing and the head. Be careful, because it’s very easy to strip the threads.
The power steering pump bolts onto the back of the intake cam housing beginning in ’95, so it is a completely different casting that can’t be interchanged with any of the earlier versions.
Be sure to identify the cams and match them up correctly in pairs before installing them. Mixing them up in pairs or using the wrong ones in an engine will cause all kinds of really hard-to-find problems.
There is a check valve in a passage located in the right front corner of the block that keeps oil topside when the engine is shut off. The original design caused a lot of problems because the check ball came out of the holder, allowed oil to drain back from the head, and caused top end failures.
The check valve can also stick open or closed if it gets sludged up. Be sure to remove it, clean the passage thoroughly and replace it with the improved version that’s available under p/n 22548701.
The water pump bolts to the front cover with the seal facing toward the engine, so if it leaks, you can get water in the oil. The gear that drives the water pump must have a hole in the middle to get oil to the splines that drive the pump itself. The original drive gear didn’t have this hole, so the splines ran dry and eventually wore out. Then, the water pump quit and the engine failed.
That’s the story on the Quad 4. There are lots of them out there in cars that are worth fixing, so there’s a real opportunity for the rebuilder who can do them right. Now that you know how they go together, you’ll have a head start on the competition.
Doug Anderson is the former vice president of Grooms Engines, Parts, Machining, Inc., located in Nashville, TN. He has authored numerous technical articles on engine rebuilding over the years.
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