| 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 |
| 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 |
| 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 |
| ELIMINATION OF END BOLTS ON EXHAUST MANIFOLDS |
Elimination Of End Bolts &
Locks From Exhaust Manifolds On
GM (Pontiac) Engines Except Super Duty
All GM (Pontiac) engines after serial number 191552, except the super duty engine, will have the front and rear end bolts and locks omitted from both right and left side exhaust manifolds.
The drilled holes in the exhaust manifolds have not been removed, and the cylinder heads will still have drilled and tapped holes. These end bolts and locks have been removed to improve the durability of the exhaust manifolds.
Caution: Do not install bolts or locks in these end holes.
The AERA Technical Committee |
| 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 |
| PISTON SCUFFING AND PIN WEAR ON LIGHT WEIGHT CAST. |
Piston Scuffing And Pin Wear On
GM 2.5L (151 CID) Engines
Scuffing of piston skirts and excessive piston pin wear are common complaints with General Motors' 2.5L (151 CID) four cylinder engines. Piston pin wear seems to be restricted to OE pistons while the piston scuffing occurred with both OE and aftermarket pistons.
General Motors uses a torque plate during production of these engines and General Motors (Pontiac) engineers recommend using a torque plate to bore and hone these engines. AERA field reports indicate cylinder distortion exceeding .002 when torque plates have been removed from blocks after boring and honing. The two center cylinders are affected the most.
GM has changed the design of this piston a number of times, as well as the type of material used, in efforts to solve a variety of problems. Some aftermarket piston suppliers have followed OE designs while others have not.
Because of the variety of piston designs and differences in materials it becomes extremely important for AERA members to carefully check their piston suppliers's recommendations for fitting these pistons. You must mic the pistons at the point specified by the manufacturer and fit to that manufacturer's
recommended clearances. Using one manufacturer's clearances with
another manufacturer's piston could create problems on this engine.
Piston noise appears to be a bigger complaint than scuffing of piston skirts. This could be due to excessive clearances from not following the piston manufacturer's recommendations. AERA members report decreased customer piston noise complaints when using a torque plate to bore and hone these engines and following the minimum recommended clearances.
Some piston suppliers feel that the pin wear problem is a design problem in how the pin gets its oil supply. Most of the OE pistons oil the pin with oil scrapped from the cylinder walls. If the engine is not properly maintained, contaminants such as carbon deposits and aluminum from top ring poundout can find their way to the pin where they will accelerate wear. Laboratory
analysis has upheld this view in some cases.
The AERA Technical Committee |
| 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
##END## |
| 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
##END## |
| 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 |
| CRACKED CYLINDER HEAD |
Cracked Cylinder Head On
GM (Pontiac) 1.8L & 2.0L (112 & 121 CID) Engines
A coolant loss may develop due to a cracked cylinder head on 1.8L (112 CID) engines coded L46 and LJ9, and 2.0L (121 CID) engines coded LQ5, LQ2 and LR9. The suspect engines are available in GM Pontiac 2000 vehicles manufactured between 1982 and 1984.
The crack develops across the #6 intake valve spring seat area and continues across and behind the #4 and #5 exhaust valve spring seat. Because the crack may be invisible to the unaided eye, some form of dye check or magnetic particle inspection is required to locate the fault.
Illustration of crack has been enlarged and made bold to help show approximate location. The actual crack may not be noticeable to the unaided eye.
The AERA Technical Committee |
