| 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 |
| MAIN BEARING BOLT HOLE CHANGE |
Main Bearing Bolt Hole Change On
1983 Pontiac V-6 Diesel
The main bearing bolt hole thread pitch for #2 and #3 main
bearings has been changed from 1.75mm to 1.76mm on V-6 Pontiac
diesel engines (VIN CODE T). The main bearing bolt has not
changed. The result is an interference fit with the last few
threads when the bolt is screwed into the hole. This
interference spreads the load throughout the bulkhead rather than
concentrating it at the surface.
Engine blocks that have a main bearing bolt hole pitch of 1.76mm
for #2 and #3 main bearings are identified by a stamped letter
G behind the cast part number. the cast part number is located
on the top rear of the block next to the oil pump assembly.
AERA members are cautioned when installing these bolts, it is
essential that engine oil be applied to the threads to prevent
galling. It is normal for the bolt to tighten up slightly during
the last few turns of installation. Do not attempt to clean up
#2 and #3 main bearings block threads by retapping with standard
tap size M12-1.75. The M12-1.76 tap used is not a standard tap
size.
The AERA Technical Committee
June 1983 - TB 278
##END## |
| 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
##END## |
| 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 |
