This enabled GM to shorten the development process dramatically because it was able to adapt a proven design. But it also allowed it to share a lot of the existing tooling from the V8 production lines so the engines could be on the road sooner.
The original 200 V6 that came out in 1978 was based on the 262 V8, and the 229 V6 that came out in ’80 that was based on the 305. By 1985, both were replaced by the 262 V6 that was based on the 350. It was originally installed in both cars and trucks; since ’87 it has been used primarily as a truck engine. It also has been updated several times to make it one of the best in the industry. The engine combines performance and economy in a reliable package for most of GM’s pickups, vans and sport utility vehicles.
Although the basic architecture has remained the same, GM has made a lot of changes to the 262 as it has continually upgraded and improved the original design. In the process, it has changed the block to accommodate a one-piece rear seal, added a roller cam and a balance shaft, modified the crank and rods, upgraded the pistons and revised the heads for better performance and emissions.
There are some subtle differences between the engines built in the two different plants, too. For example, the cranks and rods used in a Tonawanda engine are not the same as the ones used in a Romulus engine. There can be problems if they are intermixed. So, let’s take a look at how it all began in 1985 and see how the 262 has evolved over the past 13 years, remembering that most of these changes were made to improve power; reduce emissions; increase mileage; and reduce noise, vibration and harshness (NVH).
1985: The original block in ’85 was a 14071177 casting. It had a two-piece rear seal, a flat tappet cam and a fuel pump hole because all of the trucks still had carburetors. Just for the record, there were some ’86 blocks shipped with pans for ’85 service replacements, so it is possible for a customer to have an ’85 car or truck with a one-piece rear seal.
1986: In 1986, the block (c/n 14088553) was modified to accommodate the new one-piece rear main seal. The fuel pump hole was still open, even though it wasn’t always needed, because all of the cars and some of the trucks came with throttle body injection.
1987- ’94 WITHOUT BALANCE SHAFT: In 1987, a roller lifter cam was installed, so the block was changed again. Two bolt bosses were added in the middle of the valley for the lifter retainer that kept the rollers properly located on the cam and perpendicular to it. This same basic block was used through ’91 for everything, and in ’92 through ’94 for all of the engines without balance shafts except for one small difference some of the blocks came with four bolt holes for the tunnel style retainer beginning in ’92. There were several different castings used, including the 10105867, 10172756, 14099073, 14093683 and 10066011 with the two-bolt retainer, and the 10172756, 14099073 and 10066061 blocks with the four-bolt retainer.
1992 WITH BALANCE SHAFT: The L35 balance shaft engine was introduced in ’92, so the block was modified to make room for it above the camshaft. The lifter retainer was changed to the tunnel design because of the balance shaft; it had two bolts on each side instead of the two in the middle.
There were two versions of the balance shaft blocks in ’92. The "first design" block had a needle bearing on the back of the balance shaft that was lubricated by the oil mist from the valley. The "second design" had a sleeve bearing that was pressure fed through an additional drilled passage in the back of the block.
All of the 1992 "first design" (c/n 10105903) and "second design" (c/n 10224834) blocks were missing the two bolt bosses, one on each side, that were used with the reinforcing struts for the automatic transmission on some of the ’93 and later applications, so they can only be used in ’92. Be sure to double-check the 10224834 "second design" blocks, though, because some of them came with the strut bosses in the later years so they can be used for the ’93s and ’94s.
1993-’94 WITH BALANCE SHAFT: Things got more confusing with the balance shaft blocks in ’93-’94. All of these engines have to have the two extra bolt holes for the strut bosses and 10 bolt holes for the tin front cover. See photo. There are five castings that may or may not be right:
All of the 10224534 and 10224535 blocks have the two strut bosses and 10 holes for the front cover, so they will fit everything in ’93 and ’94;
The 10227196 castings have the strut bosses, but they came with either six or 10 holes;
The 10224834 blocks have 10 bolt holes, but they came with or without the strut bosses;
The 10235359 blocks were the most confusing because they came with or without the two strut bosses and with either six or 10 holes for the front cover!
Consequently, all of these castings must be checked and sorted by both casting number and features in order to be sure that they will work in everything in ’93 and ’94.
1995 WITH BALANCE SHAFT: 1995 isn’t a whole lot better. All of the ’95 engines had a balance shaft and the strut bosses, but the flange around the timing gear was changed to accommodate the new plastic front cover. The overall shape stayed the same, but the flange was noticeably wider with big bulges around six of the bolt holes. See photo.
There was a mid-year change that can cause problems, too. The early engines used a "first design" tin front cover with 10 bolt holes. The later ones had the "second design" plastic cover that had only six bolts, so the flange can have either six or 10 holes drilled in it. See photo. That means that the tin cover won’t work on a block that was drilled for a plastic cover, so the blocks aren’t always interchangeable.
Things can get confusing in ’95, because the 10227196 and 10235359 castings that were used in ’95 came with the narrow flange in ’94 and were converted to the wide flange in ’95. All of the 10227196 castings had the strut bosses, but some of the earlier 10235359 castings didn’t.
You can use either one of these blocks in ’95 as long as it has the strut bosses and the wide flange with either six or 10 holes drilled for the front cover. But, you must be sure that the corresponding first or second design front cover is installed on the block.
Given the possible confusion over which cover the customer has and which block he really needs, it’s probably better to make sure all the blocks have 10 bolt holes so they will work with either front cover. Do not use an earlier block with the narrow flange with a plastic front cover under any circumstances because it will leak oil.
1996-’98: The block was changed again in 1996. Structural reinforcing ribs were added on both sides of the timing cover and both sides of the block were contoured to follow the shape of the cylinders more closely. See photo. This one is a 14099090 casting. This same block is used up through 1998.
MORE ABOUT BLOCKS There is one other subtle difference in the blocks. The cam bearing sets are different, depending on whether the block was made in Romulus or Tonawanda. The Tonawanda blocks use two larger diameter cam bearings, one in front and one in back, instead of only one large one in the front. Both bearing sets are available in the aftermarket.
There are three characteristics of each block which will tell you where it was manufactured:
If it’s a Tonwanda engine, it will have a "T" stamped on the machined surface on the block just in front of the right cylinder head. The engine ID will be number stamped on the pad, and the chamfer on the cylinders will be quite shallow;
If it’s a Romulus engine, it will have an "R" stamped on the machined surface on the block. The ID number will be made up of a series of dots, and the cylinders will have a deep chamfer on them.
Some of the blocks are drilled for a knock sensor and some aren’t. It’s almost impossible to know which applications came with and without the sensor hole, so most rebuilders drill and tap every block so the hole is there when it’s needed.
LIFTER RETAINERS The roller cam motors have used three different lifter retainers. All of the ’87 through ’91 non-balancer blocks and some of the ’92s used a flat retainer (p/n 10046165) with two bolt holes in the middle. As of ’92, all of the balancer motors and some of the non-balancer motors came with the tunnel-shaped retainer (p/n 10105916) with four bolt holes, two on the outer edge on each side.
Starting in ’94, Chevy used two plastic retainers (p/n 12551431) that are bolt-in replacements for the tunnel-shaped version. There are some later intakes that will hit on the reinforcing ribs on the tunnel-shaped retainer, so it’s best to use the plastic retainers in all of the blocks that have the four bolt holes.
FRONT COVERS There have been three front covers used on the 262. The first one came on the ’85 to ’94 non-balancer engines. It’s the same one that was used on the small block Chevy. The second one was a tall, metal cover with 10 bolt holes that was used from ’92 through the ’95 "first design" balancer motors. See photo.
The latest version is a unitized plastic cover that is held on with only six bolts. It came out mid-year in ’95 and was installed on the "second design" engines that had the wide flange with only six bolt holes drilled in it. The plastic cover fits on the earlier balance shaft blocks, but it shouldn’t be used on them because it leaks around the bolt holes. It comes with or without a large hole drilled in the bottom corner for the crank position sensor that was installed on the engines that came with OBD II.
CRANKS Chevy has used several different cranks in the 262. They came with one- or two-piece rear seals and in both light and heavy versions that were specific to each engine plant. Here’s an overview:
1985: The 1174N casting came with a two-piece rear seal and a flange in the back. See photo.
1986-’87: The 14088640 and 10105865 Tonawanda castings with a one-piece seal were both used only for heavy applications during these years. See photo.
1988-’98: The Tonawanda cranks were all 10105865 castings that came in both light and heavy versions.
1988-’98: The Romulus cranks were all 10055480 castings that came in light or heavy versions.
All of the engines with the one-piece seal were externally balanced with specific flywheels and dampers, but the cranks were also balanced according to the weight of the pistons and rods that were installed in the engine; it’s important to use the right combination of parts. Unfortunately, there’s no sure way to tell a light crank from a heavy one short of knowing where it came from and marking it at teardown or spinning it on a balancer. There are a couple of clues that can help, though:
All of the 14088640 castings are heavy cranks that can be used in either the ’87 to ’94 non-balancer engines or in the ’93 to ’95 VIN "Z" balance shaft motors with the heavy pistons.
If a 10105865 Tonawanda casting came without a hole in the first rod pin, it’s definitely a heavy crank. If there’s a hole in the first rod pin, it’s probably a lightweight crank. However, there were a few early 10109865 cranks that had the hole drilled in the rod pin to correct the production process, so having the hole drilled doesn’t always guarantee a lightweight crank.
The 10055480 Romulus crank came both ways, too. If it has a hole in the first rod pin, it’s the lightweight version, and if it doesn’t, it’s always a heavy crank.
The heavy cranks were used in all of the engines without a balance shaft and in all the VIN "Z" balance shaft motors with the heavy pistons, including the ’95 "second design" versions. The lightweight cranks were used with the lightweight pistons in the ’92-’98 VIN "W," the ’95 VIN "Z," "first design" engines, and in the ’96-’98 VIN "X" engines. Using the right crank in the right engine will help prevent balance problems out in the field.
However, you should also be aware that all of these engines are externally balanced with various combinations of flywheels/flexplates and dampers for balance, and that they are "trimmed" at the factory after the hot-run test by pounding balance weights into the holes that are already drilled in the damper. So, if you build them right and still have a shaker, the customer will have to add or subtract weight from the damper and/or flywheel/flexplate in order to get it right.
There is one other subtle difference in the cranks, too. Any of the engines that were installed in ’96 or later and all of the ’95 "S" and "T" trucks with OBD II, including all of the Olds Bravadas, any Blazer with California emissions, and about 10% of the Blazers with federal emissions, had a reluctor wheel installed in front of the crank gear for a crank position sensor that was a part of OBD II. The raised, machined area on the snout is about .100" longer on these cranks than it was on the earlier ones so the reluctor wheel has a slight press fit. Be sure to sort out the 10105865 and 10055480 cranks with this longer, machined step and save them for the engines that have the crank position sensor.
RODS There are four different rods in two different weights that come from two different engine plants, so there’s plenty of room for confusion, but it all works out if you follow these two rules:
Rule 1: Keep similar rods in sets by both appearance and weight;
Rule 2: Use only Romulus rods with Romulus cranks.
Then, the question is, how do you tell them apart so you can follow the rules? Start by sorting them by engine plant based on the shape of the balance pad on the big end. If the rod has a cast pad that’s only machined on the face, it’s a Tonawanda rod. These rods don’t have a forging number and may or may not have a dot on the shank. See photo.
If the weight pad on the big end is long and narrow and has been machined on all five surfaces including the sides, the ends and the face, it’s a Romulus rod. All of these rods will have an 818 or 045 forging number on the shank so they’re easy to identify.
After you have separated the rods by source, sort them by weight and put them in sets. The lighter ones will weigh around 662 grams, and the heavier ones should weigh about 675 grams.
The light and heavy rods can be interchanged in engines in sets, but it’s best to use the Romulus rods only on Romulus cranks because you may end up with a ticking noise if they are used with a Tonawanda crank. The Romulus rods have a wider face adjacent to the parting line that can hit on the side of the split pin rod journal, so the Romulus cranks are machined to provide additional clearance for the rods.
The Tonawanda cranks aren’t relieved in this area, so there can be light interference and a noise problem. The Tonawanda rods have the narrower face at the parting line so they can be used with either crank.
PISTONS There have been five different pistons used in the 262 along with two versions of the lightweight piston.
1) The original, heavy piston used in the 262 was the same as the one that was used in the 350 V8 except that the pin boss was opened up slightly for the offset rod. It weighed about 745 grams with the pin and had a 9.1:1 compression ratio. It was used in all of the light duty engines without the balance shaft from ’85 through ’94 and in the VIN "Z" balance shaft motors from ’93 through part of ’95.
The parts catalog identifies the ’95 VIN "Z" engines with this heavy piston as the "second design" version even though they were built during the first part of the year. They will have one of the following engine codes: ALH, ALA, ALB, ALC, ALD, ALF, ALH, ALJ, ALL, ALP, ALS, AJS, AJT, AJW and AJU.
2) The lightweight piston weighs about 675 grams with a pin. It was used in all the high output, balance shaft engines (VIN "W") from ’92 through ’98 and in all the VIN "X" engines from ’96 through ’98. It was also used in the "first design" VIN "Z" engines that were built during the latter part of model year ’95, including those with the following engine codes: AAB, AAC, AAF, AAJ, AAK, AAL, AAP, AAS, AAW, AFC, AFD, AHC and AHD.
The lightweight piston was originally a Mahle, full-round design (p/n 2753), but GM switched to its own "RPM" (Revised Permanent Mold) design with a short slipper skirt and a narrower pin boss in ’95. Both of these pistons have very short skirts, so the clearance must be right or they tend to make noise at startup.
3) There was a heavy duty engine offered for trucks and vans with over 8500 GVW from ’89 through ’95. It used a heavy duty, Zollner piston that had an 8.3:1 compression ratio and weighed the same as the regular heavy piston.
4) There was also a high output, VIN "B" (LU2) engine offered in the Astro van in ’90 and ’91. It used a special, hypereutectic, strutless piston that is available from GM under p/n 10181389 in standard, or from Zollner as a H-8269-D. It weighs about 745 grams, just like the rest of the heavy pistons.
5) There was one more piston used in the 262. It’s a low compression (8.6:1), strutless, hypereutectic piston with a deeper dish that was used in the turbocharged Syclones and Typhoons from ’91 through ’93. The OEM standard piston is p/n 12508702 and the Zollner number is a H-8269-E.
All of these pistons are specific to the application, so they should not be interchanged. Building an engine with pistons that have the wrong weight or compression ratio will guarantee a comeback, so it’s better to play by the book.
BALANCE SHAFTS Any 90° V6 creates some strong, primary imbalance forces, especially in the vertical mode. The 262 is no exception. Chevy originally underbalanced these engines by putting about 46% on the bobweights instead of the usual 50%. This reduced the vertical imbalance that was trying to lift the engine up off the mounts, but created a strong horizontal imbalance that shook the engine from side-to-side instead. So, in order to eliminate a lot of the "noise, vibration and harshness" in the engine and make it into a world-class motor, Chevy added a balance shaft to the premium engines in ’92 and included it in all of them by ’95.
There are two balance shafts, a light one and a heavy one, and two versions of the light one. See photo. The light one is either a 10224542 or a 10172748 casting that comes with or without a metal wear sleeve installed on the back journal, depending on the application. The wear sleeve was used on the lightweight balance shaft when it was installed in a ’92 "first design" engine with the needle bearings in the back, but it wasn’t used when the lightweight shaft was installed in the "second design" engine that had a bushing in the back of the block.
This "first design" shaft should not be used in a "second design" engine because the wear sleeve shortens the surface area needed for the bushing. These lightweight shafts were installed in all of the engines that had the light pistons including the ’92-’98 VIN "W," the ’96-’98 VIN "X" engines and the "first design" VIN "Z" engines in ’95 that were built with the lightweight pistons.
The heavy balance shaft is either a 10224541, a 10105902 or a 12550286 casting. It can be visually identified by the raised identification band around the middle of the shaft. It was used in all the ’93-’94 VIN "Z" balancer engines and in the ’95 "second design" VIN "Z" balancer engines with the heavy pistons. The heavy balance shaft weighs about 125 grams more than the light one, so it shouldn’t be interchanged with the lighter one.
The balance shafts rotate at engine speed and are gear driven off the front of the cam. There are two different gear sets, one with "wide" teeth and one with "narrow" teeth. The ones with the "wide" teeth were used in the "first design" engines along with the needle bearing balance shaft. Some of these early balance shaft engines had a whine to them, so the gears were modified at the same time the block was changed over to the "second design" version with the sleeve bearing in the back. We recommend using only the "second design" gears to help avoid any possible noise problems.
CAMS, LIFTERS, TIMING GEARS Several cams have been used in the 262. There are important differences in both the specifications and the base circle diameter.
1985-’86: The same flat tappet cam was used in ’85 and ’86.
1987- ’91 VIN "Z": The original roller cam used for the throttle body motor was a 10088148 or a 14093686. It had a 1.380" intake base circle, a 1.335? exhaust base circle, and a pretty mild grind.
1990-’91 VIN "B": The H.O. motor had a much hotter cam that should not be interchanged with any other application. It’s a p/n 10055487.
1992-’94 VIN "Z" WITHOUT BALANCE SHAFT: The specs for this cam were comparable to the earlier VIN "Z" cams, but the base circle on both the intake and exhaust was reduced to 1.260?. The OEM part numbers are 10144176, 10214713 and 10172776.
1993-’95 VIN "Z" WITH BALANCE SHAFT: The specs on this cam were similar to the ones used in the VIN "Z" without a balance shaft, but a snout was added for the balancer drive gear. It’s a p/n 10144065.
1992-’95 VIN "W" WITH BALANCE SHAFT: The premium high output engine came with central fuel injection, a balance shaft and a better cam starting in ’92. The original cam, p/n 10144047, was used from ’92 to ’94. It was replaced by p/n 10241693 in ’95. They are comparable grinds so most rebuilders are interchanging them.
1996-’98 VIN "X" WITH BALANCE SHAFT: The VIN "X" engine replaced the VIN "Z" in ’96. It is identical to the ’96 VIN "W" engine except for a milder cam and 10 less horsepower. The cam is a p/n 10241692.
1996-’98 VIN "W" WITH BALANCE SHAFT: The VIN "W" engine has a 10541691 camshaft and makes 10 more horsepower than the VIN "X" engine. There is also a special roller cam for the VIN "Z" turbocharged engines (p/n 10214714) along with a couple more with a fuel pump lobe for marine and industrial applications, but these are the common ones that were used in most of the cars and trucks. All of these cams can be identified by the last three digits of the part number that is stamped on the barrel of the cam, just behind the last lobe and in front of the distributor gear.
Matching the right cam with the right lifter and adjusting the valves correctly is important in order to avoid noisy lifters at startup, a problem that’s commonly known as "morning sickness." Prior to ’92, the 262 had the traditional adjustable rockers that had been used on all of the small block Chevys for years. The cam had a 1.380"/1.335" base circle and used a short-travel lifter. Turning the rocker nut one turn gave the lifter a .040" preload and put the plunger in the middle of its travel.
In 1992, when Tonawanda switched to a "net lash," non-adjustable valvetrain; the base circle was reduced to 1.260" on all of the cams, and a lifter with more travel was used across the board, apparently to provide more latitude for manufacturing tolerances with the "net lash" rockers. (Note: The Romulus plant did not switch to "net lash" until ’95). Unfortunately, this combination can cause noise problems in the field because it takes longer for the lifter to refill at startup when it has bled down overnight, unless the preload is set at .080".
This problem can be cured by turning the rocker nut two turns with the adjustable rockers, but that can’t be done with the "net lash" setup, and it’s contrary to everything everybody knows about setting the valves on a Chevy, too. The best approach requires the replacement of the "net lash" studs with a set of special conversion studs that have metric threads on the bottom, along with 3/8" threads on the top, and using them along with the short lifters that are preloaded one turn.
If you prefer to rebuild the engines as they came and use the longer lifters with the adjustable rockers, increasing the preload to two turns will help avoid "morning sickness." Carefully controlling the stem heights and clearances with the "net lash" rockers will help ensure that you have enough preload to avoid noisy lifters most of the time.
Just for the record, there’s one extra benefit to switching to the short lifters and the adjustable valvetrain on everything; you can disregard the base circle issues and consolidate more of the cams.
There are two cam thrust plates used for the roller cam engines. The one for the non-balancer engines that are smooth on both sides are available under either p/n 14093636 or p/n 10088128. The thrust plate for the balancer engines is smooth on one side and has four radial grooves on the other side. It’s a p/n 10144059.
Chevy has used three different timing gears for the 262 since ’85. The flat tappet engines used a p/n 340235, the non-balancer, roller cam engines had a p/n 12552128 and the balancer engines used a p/n 10144121. They are not interchangable.
CYLINDER HEADS There have been several cylinder heads used on the 262 since it began in ’85. Some of the changes appear to be minor, but most of them will create problems if the wrong head is used in the wrong place. Here’s an overview year by year:
1985-’86: The 1985 and ’86 engines used a 14079248 casting. It had two holes on one end and three on the other end.
1987-’91 TRUCK, EXCEPT HEAVY DUTY AND ’87-’93 CARS: These heads were the same as the earlier ones except that they had three bolt holes on both ends. The intake surface above the ports was quite narrow; it’s only about 0.250" wide. The unmachined, cast ledge on the top edge of the head was 0.600" wide. Look for c/n 14094768, 10144103, 14099067 or 12553050. All of these heads had adjustable rockers.
1992 TRUCK WITH TBI AND NO BALANCE SHAFT: These heads had a wider surface for the intake gasket even though they didn’t need it because all of the tooling was changed to accommodate the new heads for the VIN "W" CFI engines that were introduced in ’92. The 10144103 casting was carried over from ’91, but it had the wide intake with straight ports on the top. It can be used along with any of the earlier 14094768, 10144103, 14099067 or 12553050 castings from ’87 through ’91.
1992-’93 TRUCK WITH CFI, BALANCE SHAFT: When the high output VIN "W" engine with central fuel injection was introduced in ’92, the heads were redesigned for the application. They had "eyebrows" added to the top of the intake ports to make room for the injector nozzles, so the intake surface above the ports was increased by 0.250? for improved sealing, and the cast ledge above it was narrowed down to 0.350? to provide more room for the intake manifold.
The 10077626, 14099064, 10240209 or 10238181 castings were used, but be sure to check them over carefully because there are two versions of the 10238181 and 10240209 castings with an important difference. In