Rebuilding the New Chevy 262

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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 ’92 and ’93, they came with an 8° top angle on the intake seat and a 75° throat, but that was changed to a 30° top angle with an 80° throat in ’94. Separate the 8° heads from the 30° heads and use them only on the ’92 and ’93 engines.

Tonawanda switched to "net lash" rockers in ’92, so some of these are adjustable and some aren’t.

1993 TRUCK WITH TBI, EXCEPT HEAVY DUTY: The intake manifold on the TBI motor was modified in ’93 to take advantage of the wider intake surface that was machined on the ’92 and up heads, so these engines must have the heads with the wide intake and should use the castings with the 8° top angle on the intake seat.

1994-’95 TRUCK WITH TBI OR CFI, EXCEPT HEAVY DUTY: The top angle for the intake seat was changed from 8° to 30° and the throat was opened up from 75° to 80° to give a 10% increase in intake airflow for better performance in ’94. The same heads were used on both the TBI and CFI engines through ’95.

Both the 10238181 and 10240209 castings were used, but they have to be visually sorted because the early ones with the 8° seat probably shouldn’t be used on the ’94s and ’95s. If you do decide to stretch the rules and use the ’93 heads on a ’94-’95 engine, be sure to use them in pairs. Some of the ’94s still had adjustable rockers because Romulus didn’t switch over to "net lash" until ’95.

1996-’98 ALL TRUCKS EXCEPT HEAVY DUTY: There was another all new head introduced in ’96. It had bigger intake and exhaust ports, no exhaust crossover and four angled bolts for the intake. It’s the 10235772 casting that was used up through ’98.

1989-’95 HEAVY DUTY TRUCK WITH TBI: There have been three different heads used on the heavy duty 262 since ’89.

1) 1989-’92: The original head, c/n 14099066 was used up through ’91. The 10144115 casting with the wider intake surface showed up in ’92 even though the narrow one still worked. Both of these castings are interchangeable.

2) 1993: The 14099070 casting came with an 8° top angle on the intake seat in ’93, but it was also available with the 30° top angle in ’94 and ’95. Sort them accordingly and use them in pairs.

3) 1994-’95: The 14099070 casting with the 30° top angle for better airflow should be used on the ’94 and ’95 engines. Be sure to use them in pairs. See photo.

All of these heavy duty heads had hard donut seats, replaceable guides and heavy duty exhaust valves with 3/8" stems.

1991-’93 SYCLONE AND TYPHOON WITH TURBOCHARGER: The turbo motors used the same heads that were installed on the VIN "Z" throttle body motors. It appears that they came with the narrow intake surface all the way through ’93. Look for the 14094768, 10144103 and 1409967 castings.

KNOCK SENSORS
Beginning in ’86, some of the 262s had fuel injection, and by ’87 all of them were fuel injected and computer controlled, so they had either one or two knock sensors. It’s almost impossible to know whether the engine came with one or two and where they were located, because it varied by year, model, engine and application.

The sensor has been installed in the top or bottom hole in the left head, in the bottom hole in the right head, in the back of the block or in the back of the right head. The wiring harness will not reach if the sensor is in the wrong location and that the sensors can’t always be interchanged because some of them have tapered pipe threads and others have metric threads.

So, it comes down to practicing damage control by building all of these engines with a fail-safe combination like this:

•Drill and tap every block for a metric knock sensor.

•1987-’92: The left head must have two holes with at least one wet hole on the bottom. The right head must have at least one wet hole in the bottom location.

•1993-’95: The left head must have two wet holes. The right head must have at lest one wet hole in the bottom location.

You may have to drill some that came with a dry hole on the top and convert others by drilling and tapping a second hole in order to have enough heads. Check to see if the casting is thick enough before drilling it. Some of them like the 10077626 don’t have the pad so they can’t be converted, but others like the 14099064 can be drilled even if the second hole isn’t there. It may take some extra time, but using one of these combinations will avoid all kinds of problems in the field.

REBUILDING TIPS
Rebuilding these engines is pretty straightforward. The blocks seldom crack, except some of the 10227196 castings, and the heads are usually good. The cranks are another story, though, with about 30 percent down on at least one rod journal, usually toward the front of the crank. Cam mortality can be a problem, too, with up to 20 percent of the roller cams needing replacement. There are some other areas that can cause problems, too:

OIL PUMPS
From ’85 through early ’93, the 262s used the regular small block oil pump with the 0.620" (5/8") hole for the pickup tube. In mid-’93, the pump was changed because the pickup tube was enlarged to 0.742" on the "S" and "T" trucks. After ’93, all of the engines used the pump with the big hole.

PICKUP TUBES
There are several different pickup tubes used, depending on the application, and there are two different diameters, depending on the year and application. Be sure to check it out carefully and match them up at the sales counter if at all possible.

WATER HOLES
The intake gaskets may have the rear water holes open or restricted, depending on the application. The holes are always open on the carbureted truck engines, but they may or may not be open on the injected engines. When the blocked gaskets are installed correctly, there will be two small tabs sticking out from the front of the intake. If they are installed backwards, the tabs will not be showing and the engine will overheat because there is no circulation.

CONCLUSION
That’s the story on the 262 and the changes that have been made over the years. It all makes sense when you see it in the perspective of time, but these engines can still be a handful to catalog and build. Just treat it like it’s a part of the small block family, and you’ll know what goes where and how it all fits together.

Thanks to all of those who have contributed information for this article, including the people at GM Powertrain - Lansing Engine.