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Rebuilding The GM Quad 4

The Olds Quad 4 was the first production, four-valve, DOHC four cylinder engine built by General Motors. When it was introduced in 1987, it was heralded as a revolutionary new design that was expected to be as historically significant as the original Olds Rocket V8 was in 1949.

By Doug Anderson

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The Quad 4 had four valves per cylinder, tuned intake and exhaust manifolds, no distributor, no plug wires, lightweight rods and pistons to reduce shaking forces, and a crank with eight counterweights that was designed to reduce noise, vibration and harshness (NVH) and bearing wear. It didn’t have an A.I.R. pump or an EGR system, but it still managed to pass all the emissions tests.

Even though it was a big four cylinder, it didn’t come with balance shafts because the engineers who designed the Quad 4 were convinced that it really didn’t need them, probably by the bean counters who didn’t want them to spend the extra money.

Ten years later, hindsight says the Quad 4 was historically significant, but not for all of the right reasons. The Quad 4 never lived up to its promise because it didn’t have enough low end torque to satisfy the average American car buyer, and it was too rough and noisy once it started making some serious horsepower.

It has had its share of problems, too, so it has been constantly "revised" and "improved" ever since it was introduced in an ongoing effort to get it right and make it more successful in the market. The current 2.4L Quad 4 has evolved into an engine that is actually quite pleasant to drive, but it’s almost too late, because it’s due to be phased out when GM’s all new DOHC engines are introduced in a couple of years.

Over the past 12 years, Olds has had to deal with leaking head gaskets and cracked heads, along with a variety of oiling problems and several other glitches ranging from timing chain noise to stripped splines on the water pump drive. There have been a number of changes that were meant to improve performance and durability, too, including the addition of balance shafts to reduce NVH.

Our extensive research shows there are actually a total of six different blocks, three cranks, three rods, seven heads, four cam housings, four front covers and three oil pumps used on these engines from 1987 through 1995, and that doesn’t include the changes that were made for the 2.4L engine! It’s no wonder that everyone seems confused about what goes where, when and why.

So, here’s our best take on the Quad 4 with our thanks to the people at Consolidated Manufacturing, Hutchinson, KS, along with several other friends in the industry. There have been lots of changes that have created several different combinations, so take good notes if you want to know how to build these engines the right way the first time.

BLOCKS
1987-’88 VIN D – The original block for the Quad 4 was either a 22535788 or a 22534033 casting. It was used for the VIN D engines in ’87 and ’88. There is a recessed area between the inside of the pan rail and the outer edge of the #3 main cap that is unique to these blocks.

1989 VIN D – A slightly different block was used for the VIN D engines in ’89. It had a 22538061 or 22538062 casting number and came with one small internal change – the main web next to the #3 main cap was now flush with the pan rail instead of being recessed as it had been on the earlier blocks.

This web has a threaded hole in it that intersects with one of the main oil galleries, but we have never seen anything bolted to it, so it appears that the earlier 788/033 blocks with the recessed main web could be used instead of the later block. However, the GM reman program for the Quad 4 specifies two different applications for these blocks, so it’s probably a good idea to keep them separate.

1989-’90 VIN A (H.O.) and 1990 VIN D – The next block showed up in late ’89 for the new H.O. engine. It was either a 22539326 or a 22545442 casting and it came with two important changes: 1) There was another hole drilled in the pad on the back corner of the block on the driver’s side, right above the flange for the bell housing and 2); There were coolant passages added between the siamesed cylinders, just below the deck surface. You can tell the difference between these later blocks and the earlier ones because there are two teardrops between each cylinder instead of the plain, round holes that were found on the earlier blocks.

1991 VIN A (H.O.) and 1991 VIN D – In 1991, there were two more bolt holes drilled and tapped on the side of the starter housing perpendicular to the pan rail for a brace or a mount of some kind. This new block is a 24570377 casting. It appears that the earlier 326/442 blocks could be converted by drilling and tapping these two holes if you were short of the later blocks, but be sure to check it out carefully before you try it.

1992-’94 VIN A (H.O.), VIN D and VIN 3 SOHC – GM began using a "torque axis mount" in ’92 to help quiet things down in the engine compartment, so there was another new casting that came with a heavy duty, reinforced, triangular mount on the front of the block. It had thicker webs and larger (12mm) bolt holes. Look for a block with either a 24570661 or a 24572927 casting number.

1995 VIN D – The 2.3L Quad 4 block was revised once more in ’95. This time there were additional holes drilled in the main webs for the balance shaft assembly that was added to reduce noise, vibration and harshness. And, the two holes in the "ears" on the back of the block were no longer drilled; it’s a 24574400 casting.

1996 VIN T – The 2.3L Quad 4 became a 2.4L with a smaller bore and a longer stroke in ’96, so the block was modified again. There were additional bolt bosses added on the side of the block so both the alternator and the air conditioning compressor could be mounted directly to the block. The vent system was changed, the crank sensor was moved, the holes on the side of the starter mount were moved up higher, and the ear on the right rear corner of the block was no longer there. Consequently, it’s an all new block with a 24574250 casting number.

CRANKS
There have been four different cranks used in the 2.3L Quad 4 besides the stroked version that came in the 2.4L in ’96. They can all be identified by the casting number except for the original casting that came in two flavors.

1987-’88 VIN D – The original crank was a 25532120 casting. The notches on the reluctor wheel were located at 0° when the engine was introduced in ’87, but by late ’88 or model year ’89, depending on who you talk to, the notches on the reluctor wheel were advanced by 15° even though the casting number on the crank stayed the same.

This can create a real problem for the rebuilder, because an engine that’s supposed to have a 0° crank will have a floating idle and surge at road speed if a 15° crank is used in it. An engine that is supposed to have a 15° crank will have no power if a 0° crank is used instead.

So, all of the 25532120 cranks must be visually identified by checking the location of the notch relative to the casting seam on the top. With the snout toward you and the keyway at 12 o’clock, note the location of the upper notch. If it’s slightly off to the left of the seam and located at about 11 o’clock, it’s a 0° crank. If the notch is at 12 o’clock and right on the edge of the casting seam, it’s a 15° crank.

1989 VIN D – These engines came with the 25532120 casting that had the 15° advance. The later 22545690 crank that originally came in the ’89 H.O. (see description on the following page) can be used for this application, too.

1989 VIN A (H.O.) – The H.O. engine came with the 22545690 crank. It looks like the later 25532120 casting with the 15° advance except that the notches are square-cut instead of radiused on the bottom. Some rebuilders are using the 25532120 casting with the 15° advance instead of the 22545690 in the later engines, but we prefer to use the later crank in the later engines just to be on the safe side.

1990-’94 VIN A (H.O.), VIN D and VIN 3 SOHC – All of the SOHC and DOHC motors used the 22545690 crank from ’90 through ’94.

1995 VIN D – When the balancer assembly was added in ’95, the crank was changed again. The helical gear that drove the oil pump was replaced by a chain sprocket pressed onto a hub behind the last counterweight. This crank has a 24574115 casting number on it.

1996 VIN T – The crank for the 2.4L engine has a longer stroke, narrower rod journals, a smaller, but wider reluctor wheel that has all the notches in different locations, and a chain sprocket for the balancer. It’s a 4620 casting.

RODS
There have been three different rods used in the 2.3L Quad 4, plus the short one that was used for the 2.4L with the longer stroke. All three of the rods that were installed in the 2.3L are slightly different, but it doesn’t really matter because they can all be interchanged in sets from ’87 through ’95.

That’s good news because it’s hard to know exactly when each version was used since the parts book doesn’t agree with what we have seen in cores. Here’s how it looks today according to the GM microfiche:

1987-’89 ALL – The original rod that was used from ’87 through ’90 measured 1.086" wide at the big end and had a pin bushing in the small end. It has "B63" cast on the shank.

1990-’95 ALL – There were two more rods used in the Quad 4 engines during these years. Both have been superseded to one part number according to the microfiche. The second version of the rod looked just like the first one, but the pin was floated in the pin bore without a bushing. It had "A94" cast on it.

The third version of the rod came without a pin bushing, too, but it had more of a rounded weight pad on the bottom. We have seen some of them in sets with "B67" on the shank, and others with four different casting numbers – A233, B233, A240 and B240 – all in one motor.

1996 VIN T – The rods for the 2.4L are about .060" shorter than the ones for the 2.3L to help compensate for the longer stroke with the same deck height. The rod journals on the new crank are narrower, so the rods are only .915" wide. We have seen them with A76 and B77 cast on the beam.

OIL PUMPS
There have been three oil pumps used on the 2.3L Quad 4. The oil pump was bolted to the block and driven by a helical gear on the crank until ’95 when it became part of the balancer assembly and was driven by the secondary balance shaft.

The original pump that was used in ’87 and part of ’88 (it’s called "first design ’88" according to GM) is no longer serviced by GM or the aftermarket. So, the revised pump that was introduced as "second design ’88" is the only one that’s available for the earlier engines. This creates a problem, because the early oil pan and fill tube will not work with the "second design" oil pump, so they both have to be replaced with the later pan and tube (for about $150) when the "second design" pump is installed.

The oil pumps are easy to tell apart because the "first design" pump has an aluminum gear cover with the pickup tube bolted to the pump while the "second design" pump has a one-piece, crimped metal cover combined with the pickup tube.

Starting in 1995, the gerorotor oil pump was housed in a two-piece, split aluminum housing that was bolted on the back corner of the balancer assembly. The oil is picked up through a screen (p/n 24573826) that covers the oil passage that’s located in the middle of the balancer assembly.

The ’96 oil pump appears to be similar to the ’95 version, but it has a new part number. GM had problems with excessive oil pressure caused by the relief valve sticking in the bore, so the original pump was superseded with a new version that had improved clearance for the relief valve.

OIL PANS
The Quad 4 has had a total of five oil pans, four for the 2.3L and one for the 2.4L.

1987-’88 ALL – The original pan (c/n 22531766) that was used with the "first design" oil pump had an indented area adjacent to the sump for the pickup tube and screen. This pan was designed specifically for the "first design" oil pump that’s no longer available anywhere; it must be replaced whenever the "first design" oil pump is replaced with a "second design" pump.

Rebuilders should be aware that there are differing opinions on the years the original pump and pan were used. The GM microfiche lists them both as ’87 and "first design ’88", but some rebuilders say they were used all the way through ’88 while others believe that they were installed on some early ’89s. There’s no way to know for sure, but the point is, this early pan can’t be used with the "second design" oil pump; it has to be replaced whenever the "second design" pump is installed on an early engine that came with the original pump.

1989-’91 ALL – The "second design" oil pan has a flat bottom for the revised, "second design" oil pump. It carries a 22538921 casting number and is available from GM under the same part number for about $150.

1992-’94 ALL – The oil pan was changed again in ’92. The two threaded bosses that had been on the side of the pan since ’87 were eliminated and another large hole was added by the drain hole for the low oil sensor. Both the casting number and the part number are the same; it’s a 24571250.

1995 ALL – The oil pump and screen were a part of the balancer that was added to the Quad 4 in ’95, so there’s another new oil pan that has more room for the balancer. Although we haven’t seen one, we suspect that the casting number will be the same as the part number which is a 24574440.

1996 – The 2.4L engine was virtually "all new" with a different block and a new front cover, so it’s no surprise that it also has a new oil pan. It’s a p/n 24574397, and it probably has the same number cast on the pan.