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BALANCE SHAFT & CRANKSHAFT COMBINATIONS |
Balancer Assembly and Crankshaft Combinations On
GM 2.5L (VIN U) Engines
General Motors has provided the remanufacturing industry with another challenge when it comes to assembling GM 2.5L engines with balancer assemblies.
The balancer assembly first appeared in 1987 GM N body vehicles equipped with manual transmissions, such as the Pontiac Grand Am and Buick Somerset. This engine uses a crankshaft with the casting number 10044390. This crankshaft gear features 82 teeth while the driven balancer gears have 41 teeth.
Some OE parts books may list 625 as the casting number for the 1987 model year crankshaft. To-date AERA members have been unable to find crankshafts with this casting number.
Vehicles with VIN Code U engines may also use a crankshaft with the casting number 10044406. Unfortunately, there are two versions of this crankshaft. One version has a 78-tooth gear, which mates with 39 tooth balancer gears. The other version still uses 82 teeth and requires a 41-tooth balancer assembly.
Vehicles with VIN Code U engines manufactured for 1988 model year vehicles should only use casting number 1000406 crankshafts with 78 teeth.
Using the wrong combination of crankshaft and balancer assembly has caused complaints ranging from significant noise in the lower end of the engine, to premature engine failure. AERA members have reported 2.5L truck engines equipped with crankshafts that have a balancer drive gear although a balancer assembly is not used in this application.
For additional information see AERA Technical Bulletins: TB 778. 720, 690R & 511.
The AERA Technical Committee |
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LOW OIL PRESSURE ON 1987-90 'N' BODY ENGINES |
Low Oil Pressure On
1987-90 GM 2.5L (151 CID) N Body Engines
AERA members have reported low oil pressure conditions on 1988-90 GM 2.5L (151 CID) engines used in N body vehicles such as the Pontiac Grand Am and the Buick Somerset.
These engines are equipped with a combination balancer/oil pump assembly located in the crankcase to reduce high rpm engine imbalances. Furthermore, the oil filter cartridge is housed behind the filter access plug in the oil pan.
If the oil pan has been distorted by overtightening the filter access plug or drain plug it is possible for oil to leak back into the pan at the discharge side of the filter. This can results in extremely low or even no oil pressure.
This situation can be avoided through careful inspection of the oil pan area that houses the filter cartridge. Warped or otherwise damaged oil pans should be replaced.
For additional information see AERA Bulletin SB 157.
The AERA Technical Committee |
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CYLINDER HEAD IDENTIFICATION FOR 1985-87 2.5L ENG |
Cylinder Head Identification For
1985-87 General Motors 2.5L (151 CID) Engines
AERA members have reported confusion over replacing cylinder heads for 1985-87 2.5L (151 CID) engines even when using cylinder heads with the same casting number. The source for this confusion lies with General Motors using two differently machined configurations of a head carrying the same casting number for both the standard engine as well as the shortened version used in N body vehicles, such as the Pontiac Grand AM, Buick Somerset, etc. In 1985-86 this head carried the casting number 10027767. In 1987 it was replaced by casting number 10038808.
GM uses a shorter version of the 2.5L engine for the N body FWD cars, VIN code U, than for the cars that have VIN code R or 2. Although some components will interchange, the key pieces such as the block, head, crankshaft and camshaft will not. By measuring the center-to-center dimension of the rear holes of the cylinder head parallel to the flywheel, you can easily distinguish between the two applications. If the measurement is 3.670 it is the shortened version for the N body cars (VIN code U). If it is 3.980, it is the longer head for all other
vehicles (VIN codes R and 2). GM cast these bolt hole pads in an elliptical shape to allow for both versions.
The AERA Technical Committee |
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CONNECTING ROD OIL SQUIRT HOLE ELIMINATED |
Connecting Rod Oil Squirt Holes Eliminated On
Most 1973 GM Pontiac Engines
The connecting rod oil squirt holes were eliminated in all GM Pontiac V-8 engines on September 18, 1972, starting with engine number 106178. Some engines prior to this date and engine number had connecting rods both with and without squirt holes. Replacement rods may be of either type and may be used interchangeably.
The AERA Technical Committee |
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TIMING GEAR NOISE |
Timing Gear Noise Or Knock On
General Motors (Pontiac) 2.5L 1-4 Engines
The following information lists characteristics of timing gear
noise to assist diagnosis of problem cases involving the subject
engines.
Loose or improperly seated camshaft timing gears are usually
loudest when warm. They are sensitive to speed only, not load
sensitive. Cam gear noise will be noticed at a warm idle and
sounds much like a loose timing chain noise. It is recommended
to remove the drive belts and use a sounding device on the timing
pointer. This will provide a definite indication of timing gear
noise.
Timing gear noise is most noticeable at about 800 rpm. It can be
heard the loudest at the timing gear cover and at the oil pan
between #3 and #4 cylinders.
If the noise has been diagnosed as timing gear related, Pontiac
Motor Division recommends AERA members use the following
procedure for checking timing gear backlash:
1. Remove the rocker arm cover and loosen all rocker arm
retaining nuts on pre-1981 vehicles and shouldered bolts on
1981 and later models.
2. Remove the timing gear cover.
3. Check the camshaft end clearance to determine if the
gear is fully seated. End clearance should be .0015 to
.005.
4. Using a magnetic dial indicator positioned on the front
face of the engine block, place it on one tooth of the
camshaft gear. Be certain that the crank gear hub is
torqued.
5. Rotate the camshaft gear back and forth. Camshaft gear
backlash should not be less than or exceed .0005 to .0095.
6. If the camshaft end clearance is over .005 or gear
backlash exceeds .010 over the above limits, the timing
gear and/or thrust plate should be replaced.
The AERA Technical Committee
September 1983 - SB 105
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ENGINE MISS & EXHAUST SMOKE AT HIGHWAY SPEEDS |
Engine Miss & Exhaust Smoke At Highway Speeds On
1982-83 General Motors (Pontiac) V-6 Diesel Engine (Vin Code T)
If you have a customer complaining about an engine miss followed
by a puff of blue smoke out the exhaust pipe, the problem may be
caused by engine oil leaking into the intake area of the cylinder
head.
In such a case, AERA members may wish to advise their mechanic
customers to inspect the pipe-thread plugs that cover the upper
Torx(R) head bolts. These may be a source of an oil leak if not
fully seated.
The AERA Technical Committee
June 1983 - SB 102
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ROCKER ARM INSTALLATION |
Rocker Arm Installation Caution On
Pontiac V-8 Engines
As indicated in the drawing, the nut which is used to secure the rocker arm to the rocker arm stud, has an internal taper which intersects an external taper on the rocker arm stud. Overtorquing of this nut will cause spreading and result in cracking the nut. A cracked nut will climb the external taper on the stud and
position the rocker arm too low for proper valve lifter function.
The AERA Technical Committee |
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EXCESSIVE SMOKE ON V6 DIESELS |
Caution On Cylinder Head Bolts On
1982-83 GM (Pontiac) V6 Diesel Engines
The Torx(R) drive cylinder head bolt (part no. 22515533) is used
in 3 locations on each cylinder head in the subject engines and
is installed under the pipe plug as shown. Some of these bolts
may have a washer face thickness of approximately 2.0mm (.080).
If work is done on this engine that requires the removal of these
bolts, do NOT reuse them unless the washer face thickness is a
minimum of 2.8mm (.112).
Bolts that do not meet the minimum thickness should be discarded.
Bolts with the thicker washer face are available under part no.
22515533.
(insert illustration)
The AERA Technical Committee
February 1983 - TB 270
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SCUFFING AND SCORING |
Scuffing And Scoring
Distortion can result in scuffing and scoring. Through the years emphasis has been placed on the importance of proper torquing of various bolts to avoid cylinder distortion which can reduce the piston operating clearance. This includes the torquing of main bearing caps in place prior to boring cylinders so they remain round when the engine is assembled. cylinders which are bored
without the main caps being installed and properly torqued are inclined to pull out of round (distort) when proper tension is put o the main bearing bolts in the final assembly.
Distortion of block bores is still of much concern with many late engines. an example is the 1978 Pontiac 4.9L (301 CID) VIN code Y and W. Final bore operations were reportedly done in production using a deck plate. The deck plate simulates the cylinder head in its installed position. Thus, the boring and
finish operations are truer with less chance of the cylinders being distorted when assembled. The use of deck plates had generally been a procedure used mainly by high performance.
Engine manuals list many torque specifications which are intended to reduce the distortion of various areas that could initiate a problem. We strongly suggest that you follow the engine manufacturer's torque specifications and procedures. This information shows the importance of the torque wrench.
The AERA Technical Committee |
