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Rebuilding Saturn Engines
By Doug Anderson
In Jan. 7, 1985, Saturn was born when Roger Smith, the President of General Motors, announced the decision to create a whole new car company from the ground up. There were 99 people chosen to create a vision of what GM needed to do in order to prosper in the small car business into the 21st century.
GM designed a whole new car with an all new drivetrain that was surrounded by a space frame structure and covered with a combination of plastic and metal body panels. It negotiated an innovative labor contract that revolved around teamwork and involved the UAW in the decision making process from day one. And, it created a whole new dealer body that treated the customer with respect. It was truly "A Different Kind of Car" and "A Different Kind of Company," just like the ads said. Roger Smith’s dream became a reality in 1990, and, since then, the great Saturn experiment has affected all of GM in one way or another.
These new cars came with all new engines that incorporated some interesting new technology, too. Both the blocks and heads were made of aluminum that was cast using the lost foam technology that Saturn pioneered for production use. With this process, polystyrene granules are expanded by steam and blown into molds to make foam patterns. Several patterns are glued together to create a mold that is the exact replica of the finished casting, both inside and out.
The mold is then dipped in a ceramic coating and dried before it is placed in a bucket that is filled with casting sand. When molten aluminum is poured into the exposed risers that are part of the mold, it vaporizes the foam and solidifies into a casting that is the exact shape of the original mold. This process allows greater design flexibility and fewer parts that require less machining. It also offers better dimensional control than traditional casting methods.
Unfortunately, this process also created a brand new problem for the rebuilder because it allowed Saturn to cast the oil passages in the block and SOHC heads instead of drilling them; consequently, there are no plugs and there is no access to the oil galleys. The SOHC heads can be drilled and tapped where the oil passages intersect so they can be properly cleaned before being rebuilt, but the block presents a unique challenge because it can’t be drilled at every junction.
The block should probably be immersed in cleaning solution that is also circulated through all the oil passages in order to make sure they are absolutely clean. Checking them with a borescope prior to assembly would be wise, too. Rebuilders need to give this problem some serious thought before deciding to tackle these engines. With this caveat in mind, here’s the rest of the Saturn story.
There are two 1.6L engines available from Saturn. They share a common block, crank, rods and oil pump, along with several other components. They both have an 82mm x 90mm (3.23" x 3.54") bore and stroke. The cast crank is supported by five mains. Forged rods are used with full-floating pins and cast pistons that have short skirts. The oil pump is driven by two flats on the crank sprocket.
The SOHC motor uses a dished piston without valve reliefs, along with a small chamber in the head to get a 9.3:1 compression ratio (the minimum compression is 180 psi). An eight-valve head is used with the cam located in a tunnel, just like the one on the Ford Escort.
The cam is chain driven and hydraulically tensioned. Roller hydraulic lifters are used along with shaft-mounted rockers that pivot on needle bearings. Conical valve springs are used. The engine is not free-wheeling, but that shouldn’t create a problem since it is chain driven.
The DOHC motor has pistons with a large shallow dish and two valve reliefs. The compression ratio is 9.5:1. It uses multiport injection instead of the throttle body setup that was used on the SOHC motor through ‘94. It’s a 16-valve engine with two chain-driven cams that are held in place with 10 bearing caps. Hydraulic bucket lifters act directly on the cam and the valves. Conical valve springs are used on the DOHC head, too. This engine is not free-wheeling either.
So, there are two distinctly different engines that share a number of common components. Now, let’s look at the pieces that will affect the rebuilder.
There are two block castings. The original block (c/n 21000950) that was used in ‘91 and ‘92 (with a few carried over into early ‘93) had two threaded bosses on the outer edge of the water pump housing. They were only used for an extra transmission support in ‘91 when the manual transmission was used with the DOHC engine, but all of the early blocks had them. They were eliminated on the ‘93 and later blocks (c/n 21007255) because they were no longer used. See photo.
There is only one crank casting (c/n 21000883), but it comes in two flavors, so it can be difficult to identify. Both versions have a notched reluctor wheel for direct ignition, but the notches in the 1993-’94 version were advanced 10 degrees more than they were on the early crank.
Here’s a quick way to tell the difference: With the snout facing you and the keyway at six o’clock, check the location of the double notches to the right of 12 o’clock; if the one on the far right is about even with the end of the cast window in the reluctor wheel, it’s a late crank with advanced timing. If both of the double notches are closer to 12 o’clock and both are well beyond the left edge of the window, it’s the early version with retarded timing. These two cranks cannot be interchanged. See photo.
All the connecting rods are the same. They are bushed in the small end. There is no casting number.
REAR SEAL HOLDER
Both engines share a common rear seal holder. It has a 21006826 casting number on it.
The original SOHC head (c/n 21006649) that came out in ‘91 was used through 1994. When Saturn switched to sequential port injection in ‘95, it added "eyebrows" at the top of the intake ports to make room for the individual injectors that were angled down in from the intake manifold. The ‘95 head is a 21007136 casting. See photo.
The original DOHC head (c/n 21006469) had four center bolts that held the rocker cover on. It was used in 1991,’92 and into the early part of ‘93 when it was replaced by a revised version with the same casting number that only had three center bolts for the rocker cover.
The four-bolt head can be used to replace a three-bolt version, so Saturn still supplies it as a fits-all service head for all the DOHC applications through ‘94. The third DOHC head was introduced in ‘95 because the angle of the EGR mounting pad was changed. It’s a 21006937 casting, and it was used up through 1997.
These engines use different front covers. The SOHC cover is a 21006370 and the DOHC is a 21006371. The same gerotor oil pump is used for both of them. It is driven by two flats on the crank sprocket.
The SOHC engines use a short-skirted piston with a small, deep dish in the center and no valve reliefs. The same piston was used from 1991 through ‘94. In 1995, the top ring was moved closer to the crown to reduce the crevice volume and hydrocarbon emissions. It’s now only 3mm from the top of the piston. This required a special piston that used a nickel alloy bonded into the top land in order to prevent ring groove pound out.
The DOHC piston is similar to the SOHC piston except that it has a shallow dish that’s larger in diameter with two small valve reliefs that are side-by-side. See photo. The top ring was moved up closer to the crown in 1995, too.
The same rings were used for both engines from 1991 through ‘94. They are 1.5mm/1.5mm/3mm in width. We suspect that both ring sets were changed in 1995 due to the revised placement of the top ring.
That’s about all a rebuilder needs to know about the main pieces of both Saturn engines. Chart 1 at bottom shows the casting numbers by year and application, along with some of the more important identifying features. Based on all these variations, there are two block castings with six short blocks, four heads and nine completes used from 1991 through ‘97.
Now let’s see what it takes to rebuild these engines. The biggest challenge for the rebuilder is devising a process that will get the oil galleries in every block and head clean every time. Cleaning the oil passages that are cast in place could create some real problems, especially for the blocks and the SOHC heads as was noted earlier.
Cleaning the DOHC heads will be easier because most of the oil galleries are accessible, except for the two crossovers at the front end of the head. Otherwise, the rebuilding process is pretty straightforward.
The cast iron sleeves are press fit in the block with a .001" to .003" interference. Saturn says they can be removed by heating the block to about 350° F, but we have actually had some fall out in the jet spray at 190° F. New sleeves should be installed with liquid nitrogen, according to the book.
The sleeves can be safely bored up 0.4mm according to Saturn, so it offers pistons in both 0.125mm and 0.4mm oversizes. The aftermarket currently has 0.50mm and 1mm oversizes. The liners are only 5mm thick, so let your conscience be your guide on the appropriate oversize.
The cranks have a rolled radius on both the rods and mains. Saturn recommends grinding them no more than 0.25mm undersize, but they can probably be ground down to 0.50mm undersize as long as you don’t grind out the rolled radius.
Watch out for porosity that could cause leaks on both the front and rear seal surfaces. Cover the rear seal surface with a sleeve if there is any porosity.
Saturn uses cast iron main caps on an aluminum block, so align honing requires special stones and a different approach. If too much material is removed from the block, the mains will be improperly sized and out-of-round.
The rods should be reconditioned, and the pin bushings should be replaced at the same time. You may encounter some bushings with abnormal wear caused by improper machining from the factory, so it’s important to replace all of them.
Inspect the front of the block very carefully for damage caused by a loose timing chain. If the oil isn’t changed often enough, the relief hole in the tensioner gets plugged up, causing the tensioner to put too much pressure on the chain. Once the tensioner is fully extended and the chain gets sloppy, it chews away on the adjacent surfaces of the block. So, plan on replacing all the tensioners and repairing some damaged blocks.
The early SOHC cylinder heads aren’t cracked very often, but a high percentage seem to have bad cams and cam bores. This is because of either oil starvation during startup, or due to the debris from the timing chain problem that was noted previously in this article. The later SOHC heads should be checked very carefully because they sometimes crack in the front cam bore and topside into the lifter bores.
The cam bore is too tight for a sleeve and the lobes are too big to allow grinding the journals undersize, so the only solution appears to be an oversize cam. Unfortunately, there isn’t one on the market yet, so the only alternative is to use a new head with a new cam until someone comes up with a better mousetrap.
There have been some reports of scuffed valve stems on a few of these engines, too. Using a shorter guide seems to help if there’s a problem with a particular application.
The DOHC engines don’t seem to be as prone to loose cams and heads, but they do occasionally crack in between either the third and fourth or fourth and fifth cam journals. It’s best to check them over carefully. If you get oil in the water on a DOHC motor, it’s probably coming from a crack in the head.
The oil was restricted to the topside with an "integral cylinder head oil feed orifice" in all of the 1991 and ‘92 engines. Beginning in 1993, the oil flow topside is limited by a 4mm restriction in the head gasket itself instead of this orifice, so it should be removed from the blocks on the
older engines when they are rebuilt. It’s located in the front oil passage on the right side of the deck surface, just behind the alternator bracket. If it’s not removed, you may encounter scuffing of the cam and lifter bores during startup.
These engines are very rebuildable as long as you get them clean inside and out. Some of the parts are a little expensive right now because they are still "dealer only" items, but more and more pieces are showing up in the aftermarket. Buying new heads and cams for nearly $400 is an expensive answer to a short term problem on the SOHC engines, but someone will solve that with an oversize cam before too long.
There is one other factor to consider, too. Saturn has chosen to price their new engines very competitively at this time, so the customer has an affordable alternative, especially for the SOHC motor. You will need to keep that in mind when rebuilding and pricing these engines for the aftermarket.
There are more than a million Saturn cars on the road, so these engines are starting to come of age. Many are going well over 100,000 miles, so there isn’t a lot of demand yet, but there should be a growing market before long. Saturn owners like their cars well enough to keep them on the road for a long time. The resale values are strong enough to support the cost of a remanufactured engine even in a six-year-old car, so there will be a good opportunity for the rebuilder who is ready for the business when it comes.