| CRANKSHAFT REPLACEMENT CAUTION FOR 1998-2003 GM ENGINES |
Crankshaft Replacement Caution For
1998-2005 GM 4.3, 4.8, 5.3, 5.7 & 6.0L Engines
The AERA Technical Committee offers the following information on crankshaft replacement caution for 1998-2003 GM 4.3, 4.8, 5.3, 5.7 and 6.0L engines. Design changes in the flywheel flange thickness have been made to some crankshafts used in the above-mentioned engines. This bulletin is being re-published with additional information.
The later crankshafts are shorter on the flywheel flange as seen in the listing below. These changes are due to the many different vehicle / transmission combinations being built by GM.
A flywheel spacer ring GM Part #12563532 and a longer bolt set GM Part #12563533 is required when using a thin flange crankshaft to replace a thick flange crankshaft. Also, if the crankshaft is being used in a vehicle, which is a standard shift application, you also need pilot bushing GM Part #12557583 or 12479894.
Note: GM part numbers correct as of 12-18-04.
Years Liters Casting # Trans Flange Thickness
1998 early 4.3L 236, 255 V-6 1.62 thick flange
1998+up 4.3L 236, 255 V-6 1.500 thick flange
1999-2000 4.8L 312 V-8 M/T 1.250 thick flange
1999-2000 6.0L 215 V-8 1.250 thick flange
1999-2005 4.8L 482 V-8 A/T .857 thick flange
2001-2005 4.8L 482 V-8 M/T .857 thick flange
1999-2005 5.3L 216 V-8 A/T .857 thick flange
1997-2005 5.7L 216 V-8 .857 thick flange
2001-2005 6.0L 216 V-8 .857 thick flange
All GEN III crankshafts used in Camaro, Corvette and Firebird have a .857 thick flange and also have a freeze plug installed at the bottom of the pilot shaft hole. The 4.8, 5.3 + 6.0L don?t have the freeze plug. The drilled hole thru the centerline of the 5.7L LS1 & LS6 crankshafts allows a path to balance crankcase pressure within the lower crankcase. Doing so has eliminated possible oil consumption when the engine is operated over 4800 RPM.
Caution: Early crankshafts use a flat reluctor wheel and late have a recess. Recess will work on all years. Do not use a flat reluctor on late applications as it will cause an engine misfire.
The AERA Technical Committee |
| TIMING CHAIN TENSIONER CAUTION 5.7L VIN J |
Timing Chain Tensioner Caution On
1990-95 GM 5.7L VIN J Engines
The AERA Technical Committee advises the following caution when examining timing chain tensioners on 1990-95 GM 5.7L VIN J engines. This engine is also referred to as the LT5 or Corvette engine.
The left and right side timing chain tensioners on the LT5 engine should not be installed in their fully extended position. If a tensioner is installed in its extended position, it will create an extreme loading condition on the timing chain. This extreme loading has been the cause of timing chain breakage, which results in piston to valve contact and extreme engine damage. Attempting to compress a
fully extended tensioner may damage the internal seals and result in component failure after installation.
General Motors recommends replacement of both tensioners anytime they are removed from the engine. It is also recommended to check a new tensioner for overall length as shown in the illustration below. Any tensioner that is longer than 2.165 (55 mm) should be returned to GM as a defective unit. The right side tensioner is available under Part #10174324 and the left side is Part #1017425.
The AERA Technical Committee |
| REVISED CYL. HEAD TORQUES ON 1997-99 5.7L VIN G |
Revised Cylinder Head Torque Procedure On
1997-99 GM 5.7L VIN G Engines
The AERA Technical Committee offers the following information on a revised cylinder head torque procedure on 1997-99 GM 5.7L VIN G engines. This procedure should be used anytime the cylinder head is being installed and supersedes information found in 1997-99 service manuals. This engine has an aluminum cylinder head and block and is referenced as the LS1 or Corvette engine.
The reason this procedure has been revised is the bolt material has been modified, which allows additional clamping force. The 11 mm head bolts should be replaced at the time of cylinder head installation and the new bolts come with a pre-applied sealer and lubricant.
1. Tighten new 11 mm bolts (1-10) in sequence to 22 ft/lbs (30 N.m).
2. Rotate those bolts (1-10) in sequence an additional 90° turn using a torque angle meter.
3. Rotate only bolts 1-8 in sequence an additional 90° turn using a torque angle meter.
4. Rotate remaining 11 mm bolts 9 & 10 in sequence an additional 50° turn using a torque angle meter.
5. Apply a .200 (5 mm) bead of locking compound (GM P/N 12345382 or equivalent) to 8 mm bolt threads, and tighten bolts (11-15) in sequence to 22 ft/lbs (30 N.m).
Note: Do not re-use 11mm bolts.
The AERA Technical Committee |
| 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*
--------------------------------------------------------
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 |
| NEW LIGHTWEIGHT PISTON DESIGN ON 1990 ENGINES |
New Lightweight Piston Design on
1990 GM 5.7L (350 CID) Engines
General Motors Corporation has introduced a new lightweight
piston design for 1990 5.7L (350 CID) engines used in the
Caprice, Camaro and Corvette.
The new piston is a low friction, flat top design and is not
interchangeable with previous designs. At a weight of only 540
grams, the piston should improve engine fuel economy. Depending
on cylinder head combustion chamber design, the new piston
results in a compression ratio of 10.25:1 on the Corvette and
9.75:1 in the Camaro.
The ring set for this piston is also new and does not interchange
with the former design. The top compression ring is 2mm thick
while the second ring is 1.5mm thick. Both rings have a narrower
radial width and shallower groove depth than previous. The oil
control ring assembly now measures 4mm in thickness and is also
new for this piston.
While the piston to cylinderwall clearance remains unchanged,
.0007-.0017 (.017-.043mm), it is now measured at .450 (11.5mm)
above the bottom of the skirt (see illustration). The
barrel-shaped piston skirt cannot be measured for taper.
The AERA Technical Committee
September 1990 - TB 691
##END## |
| CYL HEAD INSTALLATION ON 89-95 GM 5.7L VIN J ENG |
Cylinder Head Installation On
1989-95 GM 5.7L VIN J, DOHC Engines
The AERA Technical Committee offers the following information on cylinder head installation for 1989-95 GM 5.7L VIN J, DOHC engines. This engine is used exclusively in the Corvette ZR1 model. Previously, there has been limited information published on this engine.
GM has determined the cylinder head mounting bolts may be reused if they show no signs of stretching or thread damage. Follow the steps listed below and refer to the illustrations to follow the torque sequence while installing the head.
1. Make sure alignment dowels are correctly located in block deck.
2. Install head gasket over dowels onto block deck. Caution: Head gaskets are
specific to their proper bank.
3. Lubricate clean head bolt threads and washers with light engine oil. Install
bolts in proper locations and finger tighten.
4. Torque all bolts in proper sequence to 45 ft/lbs.
5. Torque all bolts in proper sequence to 75 ft/lbs.
6. Torque all bolts in proper sequence to 118 ft/lbs.
The AERA Technical Committee |
| IDENTIFYING ONE PIECE REAR MAIN SEAL CRANKSHAFTS |
Identifying One Piece Rear Main Seal
GM 5.0 & 5.7L (305 & 350 CID) Crankshafts
Identifying the Chevrolet 5.0 & 5.7L (305 & 350 CID) crankshaft used in various GM cars and trucks has not been made any easier since the introduction of the one piece rear main seal crankshaft.
Currently AERA is aware that casting numbers 14088526 and 14088535 are cast iron crankshafts used in either 5.0L (305 CID) or 5.7L (350 CID) engines. Again, GM is using the same crankshaft castings in two differently balanced engines. A steel crankshaft with the forging number 14088532 is used in the 5.7L (350 CID) Corvette engines.
Both engines are externally balanced and use the same counterweighted flexplate or flywheel and a non-counterweighted damper. Equally shared are the connecting rods which weigh 603-604 grams. The rotating (big) end of the connecting rod weighs 424 +/- 2 grams while the reciprocating (pin) end weighs
179 +/- 2 grams.
The weight for a 5.0L (305 CID) piston and pin is 646 +/- 3 grams, whereas a 5.7L (350 CID) piston and pin come in at 743 +/- 3 grams. The total bob weight for the 5.0L (305 CID) engine is 1815 grams in comparison to the 5.7L (350 CID) engine at 1916 grams.
AERA mrmbers have visually differentiated the crankshafts by the balance holes drilled into the front and rear counterweights. Machinists using these specifications should be aware that all of the measurements are approximate and may vary slightly from crankshaft to crankshaft.
The holes drilled in the 5.0L (305 CID) crankshaft front counterweight vary somewhat. There are either two 1 holes drilled to a combined depth of 2.563, or two similarly drilled 1 holes along with a third .750 hole drilled to a depth of
.125-.313. The rear counterweight is much the same with either two 1 holes drilled to a combined depth of 2.250, or two similarly drilled 1 holes along with a third .750 hole drilled to a depth of .188-.313
The 5.7L (350 CID) crankshaft's front counterweight has two 1 holes drilled to a combined depth of 1.188. The rear counterweight also has two 1 holes drilled to a combined depth of 1.563.
To-date visually separating the crankshafts using the specifications outlined above has been validated by later balancing.
The AERA Technical Committee |
| VALVE CROSSHEAD CLEARANCE |
Valve Crosshead To Rocker Lever Clearance On
NH, NT & V-1710 Series Cummins Engines
Valve crosshead nose to rocker lever clearance on the subject engines must be checked during engine rebuild and at any time valve crossheads are replaced on engines using crossheads No. 123416 & 3000326. A minimum of .020 (.51 mm) clearance must be present as illustrated in Fig. 1, on the cylinder being checked with valves completely closed and crosshead in the upmost position. After installing rocker lever assemblies, check crosshead to rocker lever clearance as follows:
1. Turn crankshaft slowly in direction of rotation until the valves are closed on the cylinder being checked. With rocker lever held firmly against the stellite pad of the crosshead, a .020 (.51 mm) wire type feeler gauge must pass between the crosshead nose and the lower beam section of the rocker lever.
2. If the feeler gauge does not pass through:
a. Remove the rocker lever and/or crosshead and grind the nose of the crosshead or rocker lever beam in the area circled in Fig. 1 until enough clearance is obtained.
b. If the rocker is ground, grinding should cover the complete area illustrated in Fig. 2 in a continuous arc. Do NOT grind just the contact area.
Caution: A sharp depression in this area will cause a stress riser and eventual failure of the lever. Grind only enough material to achieve the required clearance. If grinding enters the oil passage, the rocker lever must be junked.
c. Grind sharp edges smooth.
The AERA Technical Committee |
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