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ABNORMAL COMBUSTION |
Abnormal Combustion On
Saab 2.0L B201 & B202 Engines
AERA members have reported engine damage from abnormal combustion in Saab automobiles equipped with the 2.0L B201 and B202 engines. The resulting damage has ranged from premature head gasket failure to piston damage shortly after remanufacture of the engine.
After machining the deck surface of the cylinder head, it is important to chamfer the combustion chamber edges. If left unchamfered, the sharp edges may act as a heat sink during the normal combustion process and start to glow. This glowing or hot spot may increase the possibility of abnormal combustion, in
particular premature ignition of the air/fuel mixture, leading to a component failure.
Removing burrs, nicks and sharp edges from the combustion chamber
will result in longer engine service.
The AERA Technical Committee |
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DISK BRAKE REFINISHING |
Disc Brake Refinishing
Brake discs can be refinished if precision equipment is a available and a few simple rules are followed. The first thing to do is to determine which of the following will need to be done. Resurface-Recondition or Replace.
Resurface with a flat sanding disc (with disc rotating) if scoring is light or if the disc surface has severe rust scale.
Recondition if scoring is deep or if runout, thickness variation flatness and parallelism are out of specification. Scoring of the brake disc surfaces not exceeding .015 in depth, which may result from normal use, is not detrimental to brake operation.
Note: Both sides of the disc must be treated in the same manner. If one side
needs resurfacing or reconditioning the opposite side should be
treated in the same manner.
Replace if the disc cannot be reconditioned to bring it within specifications and meet the minimum thickness specification after reconditioning.
Remember: The number cast into the brake hub is a discard dimension not a refinish dimension. Note the following chart for each vehicle line:
Minimum Thickness Discard
Model After Reconditioning Thickness*
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Chevrolet 1.230 1.215
Monte Carlo & .980 .965
Chevelle
Camaro .980 .965
Nova .980 .965
Corvette 1.230 1.215
Vega .470 .440
Truck C-K-P 1.230 1.215
10-30 Series
* This dimension is past into the hub surface. Following is a picture story of the specifications as printed in the 1971 Chevrolet Shop Manuals.
All specifications are important and should be held even though must customer complaints will result from specifications as shown in Figures 6 & 7 not being within limits.
The AERA Technical Committee |
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EXCESSIVE OIL CONSUMPTION |
Excessive Oil Consumption On
1986-94 Saab 2.0L DOHC Engines
AERA members have reported excessive oil consumption on 1986-94 Saab
2.0L DOHC engines. The source of this oil consumption has been traced to the engine's positive crankcase ventilation system (PCV). Apparently the original camshaft cover allows excessive amounts of oil to enter into the induction system.
A modification was made to the camshaft cover Part #8788135 during the 1994 production year to reduce the amount of oil mist reaching the PCV system. The part number for the cover, however, did not change. The identification of the revised cover, requires removing it from the head and inspecting it for the additional tube shown in the illustration below.
The AERA Technical Committee |
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IMPORT ENGINE THRUST BEARING PROBLEMS |
Import Engine Bearing Problems
The addition of many aftermarket main bearing sets for import automotive engine applications has caused a frequent complaint that the thrust bearings cannot be installed.
The reason is that in most import engine applications, the flanged bearing length is increased with the undersize of the bearing. This means those grinding the crankshaft must grind the thrust face of the crank to accommodate the increased bearing length and secure proper clearance of the crankshaft end thrust.
A typical example may be found with the 1.5L and 1.7L Saab engine utilizing a common aftermarket main bearing set:
The .010 undersize is .004 oversize length.
The .020 and .030 undersize has a .010 oversize length and
the .040 undersize has a .020 oversize length.
The AERA Technical Committee |
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REVISED CYLINDER HEAD ASSEMBLY |
Revised Cylinder Head On
Saab 2.0L DOHC Engines
The AERA Technical Committee advises members of a design change on
Saab 2.0L DOHC engines. Previously this engine used an external oil system feed to the cylinder head. This design changed to an internal function beginning with engine #J0825B6 in mid 1988. The affects of this change have reduced the number of locations for possible external oil leaks as well as shortening repair times.
This new head design can be retrofit on all previous engines and is available under Part #7586142, without valves. All cylinder head specifications and mounting parts are still shared, excluding the external oiling tubes and fittings. There are three external pipe plugs (Part #8123143) that also need to be installed on the new head.
Saab recommends pressurizing the oiling system before the first engine start-up when this new head is used.
The AERA Technical Committee |
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NEW CYLINDER LINER O-RINGS |
New Cylinder Liner O-Ring Seals On
Cummins NH/NT 6 Cylinder Engines
Cummins Engine Company has released new O-ring seals for the cylinder liners in NH/NT 6 cylinder engines. The new seals are made of an EP material and have a smaller diameter cross-section.
The new seal replaces both the old center seal #3008998 and the old lower seal #183049. The new seal carries Cummins part #3032874 and is black in color with one blue dot.
The new O-ring seals are not to be intermixed with the former seals on the same liner. Cylinder liner deformation will result. You can use the former seals and new seals in the same engine as long as they are used in the correct combinations on each liner. The illustration below shows the correct combinations.
The AERA Technical Committee |
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OIL IN COOLANT |
Oil in Cooling System on
VW 1.5L & 1.6L Diesel Engines
AERA members have reported instances of engine oil in the cooling system on VW 1.5L diesel engines. According to AERA sources, the problem is related to a crack in the cylinder head bolt hole located near the oil gallery feeding the cylinder head.
The oil feed gallery in the block is located on one side of the center head bolt hole and a coolant jacket is on the opposite side of the bolt hole. Pressurized engine oil is diverted through a slot in the head gasket and is feed up the side of the head bolt to the cylinder head. The oil also follows the bolt back down to the bottom of the bolt hole. Should the crack in the head bolt hole extend to the coolant jacket, oil can mix with engine coolant.
This problem is generally found on engines equipped with 11mm head bolt holes. Later design engines utilize 12mm head bolts and do not exhibit this defect. At the time of this writing no successful repair procedure is available.
The AERA Technical Committee |
