Engine - Tick Or Rattle/Detonation Or Rattle Noise
FILE IN SECTION: 6 - EngineBULLETIN NO.: 23-61-11
DATE: June, 1995
SUBJECT:
CPI Engine Noise (Install New Gears/New MEM-CALs)
MODELS:
1992 Chevrolet and GMC Truck S/T, M/L Models
1992 Oldsmobile Bravada
with 4.3L CPI Engine (VIN W - RPO L35)
This bulletin is being revised to update engine scrapping information. Previous divisional publication numbers were:
Chevrolet 92-244B-6
GM of Canada 93-6A-121
GMC Truck 92-6A-153A
Oldsmobile 92-T-168
CONDITION
Some 1992 model year 4.3L CPI engines may exhibit one or both of the following noises:
I. A tick or rattle noise at idle or low engine speeds up to 1300 RPM. The noise may occur hot or cold in Park/Neutral or in gear.
II. A detonation or rattling type noise under acceleration at engine speeds between 2000 - 2500 RPM. It is usually most noticeable at the shift points under moderate acceleration with the transmission torque converter unlocked. Premium grade fuel does not affect the noise.
III. If an engine has both noises (conditions "I" and "II"), follow condition "II" for cause and correction instructions and information.
CAUSE
I. The most probable cause for the idle tick or rattle (condition I) is due to zero or near zero lash between the balance shaft drive gears. Some gears may feel as if the lash is acceptable but there is most likely an area on one of the teeth which is not meshing properly with the other gear.
II. The source of the detonation or rattling type noise under acceleration between 2000 - 2500 RPM (condition II) is the rear balance shaft needle bearing. With some engines, the rear needle bearing is excited by a combination of factors (i.e., engine case, combustion events, balance shaft gear lash, valve train torque reversals, cam chain play, needle bearing clearance, etc.).
Important:
If there is any question about the proper diagnosis of the noise, call Technical Assistance. The unnecessary customer inconvenience and/or replacement of parts must be avoided. It is important to note that neither noise is a reliability or dependability concern. The noises are a customer pleasability issue only. The life of the engine will not be shortened due to the above causes.
CORRECTION
I. The following steps should be followed to correct an idle tick noise (condition I).
1. Remove the accessory drive belt.
2. Start the engine and note the noise. If it is still present proceed to step "3"; if not, proceed with diagnosis of accessory drive per the service manual procedures.
Important:
Do not allow the engine to operate for an extended period of time with the accessory drive belt off. Remember the water pump and fan are not functioning. Overheat will eventually occur.
3. Order GMSPO B/S Gear Kit # 12513234 and W/P; front cover gaskets.
Use the following steps to replace the balance shaft gears.
1. Disconnect battery.
2. Drain coolant.
3. Remove fan shroud.
4. Remove accessory drive belt.
5. Remove fan.
6. Remove the water pump.
7. Remove crankshaft pulley and harmonic balancer.
8. Remove transmission torque converter cover. Let it lie on top of exhaust crossover pipe.
9. Drop the oil pan by leaving the rear two nuts on the crankshaft seal studs about 1/4 inch from tight. The two studs will stabilize the oil pan and the oil will not have to be drained.
10. Remove the front cover.
11. It is recommended that the engine be turned over by hand so the crankshaft and camshaft sprocket timing marks are dot to dot.
12. Loosen the small diameter balance shaft gear bolt. This is the driven gear and has a TORX drive bolt.
13. Remove the camshaft sprocket by taking off the lock nut first, then the two bolts.
14. Remove the large diameter balance shaft (drive) gear.
15. Remove the small diameter balance shaft driven gear.
16. Clean all sealing surfaces, removing all old gasket material.
Installation of new matched set balance shaft gears:
1. Install driven gear (small diameter gear) and bolt finger tight.
2. Install and align drive gear dot to dot with timing mark of the driven gear.
3. Install drive gear stud to 16 Nm (12 lb.ft.) to ensure the shoulder of the stud is below the counter bore in the gear.
4. Install camshaft sprocket and chain. Ensure their timing is correct. If the camshaft and crankshaft have not been disturbed, the crankshaft and camshaft sprockets should be dot to dot.
5. Install the camshaft sprocket nut and bolts. Torque to 28 Nm (21 lb.ft.).
6. Torque driven balance shaft gear bolt to 20 Nm (15 lb.ft.) plus an additional 35° using a J 3660 degree meter, torque driver.
7. At this point, the gear change is complete. Follow the removal steps in reverse order to install the remaining components. Consult the service manual for torque specifications.
CORRECTION
II. The following steps should be followed to diagnose the detonation type rattle noise which occurs between 2000 - 2500 RPM under load (condition II):
1. Ensure the ESC (Electronic Spark Control) system is working properly. Refer to the ELECTRONIC SPARK CONTROL section of the LIGHT DUTY TRUCK FUEL AND EMISSIONS section of the service manual. This section includes an "ELECTRONIC SPARK CONTROL SYSTEM CHECK" with a fault tree for the 4.3L CPI engine.
2. Operate the vehicle with premium fuel. If the noise is eliminated, the noise is not coming from the balance shaft rear needle bearing. Refer to the DRIVEABILITY SYMPTOMS section of the LIGHT DUTY TRUCK FUEL AND EMISSIONS service manual. BRAVADA ONLY: Refer to Bravada service manual section 6E.
3. If the ESC system is functioning properly and the noise is still audible using premium fuel, the source of the noise is most probably the rear needle bearing of the balance shaft.
4. To eliminate the possibility of the rear needle bearing rattling, a production running change was made in early May 1992, to a different type bearing. The needle bearing was changed to a journal type sleeve bearing (much like a camshaft bearing). This type bearing requires pressure fed oil, therefore, an engine block casting change was made to allow an oil passage to be drilled from the vertical oil gallery coming from the oil filter to the rear balance shaft journal.
5. If the detonation type rattle noise is unacceptable to the customer, the engine must be replaced using an SPO Goodwrench engine assembly part number 12520408.
Important:
Dealers are to retain all parts replaced for inspection in accordance with GM Service Policy and Procedures section 1.7.4 - Disposition of Defective material.
Important:
Replaced engine blocks are NOT to be provided to engine rebuilders. They should be returned as per instructions shipped with the replacement engine.
6. MEM-CAL information: When replacing a 1992 needle bearing engine (only produced prior to the May 1992 VIN break-points) with a sleeve bearing engine, the MEM-CAL must be updated to the later 1992 version. See part number information below. These new MEM-CALs are required to change the ESC calibration for the sleeve bearing engine. Without the correct calibration MEM-CAL, the engine will detonate.
7. ESO (Electronic Spark Control) information: The sleeve bearing engine "sounds" different to the ESO system. To make the sleeve bearing engine operate properly the 1992 M and L van vehicles, the knock sensors and locations have been changed. The 1992 M/L motors require only one 3900 ohm knock sensor mounted in the transmission flange close to the distributor. Connect the knock sensor harness to the knock sensor in the transmission flange. The second knock sensor connector harness at the middle of the right cylinder head will not be used on the 1992 model year M and L vans with the sleeve bearing engines. To ensure the harness does not lie on the exhaust manifold and short out, tie the connector back onto the harness using a plastic tie strap. The S and T trucks will continue using both 8200 ohm knock sensors with the sleeve bearing engine. No modification to the existing harness is necessary.
Sleeve Bearing Balance Shaft Knock Sensor Information
VIN Breakpoints for Sleeve Bearing Engines Beginning with:
Engine Broadcast Code Information (last three digits of the engine I.D. number located In front of the right cylinder head at deck height):
WARRANTY INFORMATION
Condition I - For vehicles repaired by changing balance shaft drive gears:
Condition II - For vehicles repaired by installing a Goodwrench engine:
Important:
Applicable miscellaneous items, such as engine oil and engine coolant, should be added to the above part allowance amount and included in the Net Amount (DMN) column of the claim.
PARTS INFORMATION
Content:
Cylinder and case, cylinder head assembly, crankshaft, crankshaft main and rod bearings, piston and connecting rod assembly, T Truck/L Van oil pan and screen assembly, camshaft, valve lifters, push rods, camshaft chain and sprockets, balance shaft, balance shaft drive gears, valve lifter retainer, front cover and pointer, valve rocker cover, oil fill cap, harmonic balancer.
Additional Parts Required to Dress-Out the Goodwrench Engine:
(Quantity: 1 each, except as noted)
Parts are currently available from GMSPO.
Calibration Information for 1992 Model Year Vehicles with Sleeve Bearing Engines:
Torque Specifications