HT4100 ENGINE KNOCK MAIN BEARING USAGE UPDATE
VEHICLES AFFECTED: 1982-86 ELDORADO, SEVILLE, FLEETWOOD, DEVILLE, AND BROUGHAM
1. HT4100 Engine Knock
Some Cadillac equipped with an HT4100 may experience an engine knock. Engines experiencing this condition should be serviced as follows:
A. Visually inspect for proper piston installation, off centered wrist pins, and piston to crankshaft interference as outlined in Product Service Bulletin 83-6-127 and repair as required.
B. Inspect for crankshaft to block interference. Some engines may require the installation of a machined counterweight crankshaft when interference is evident. This crankshaft is P/N 1629092 for transverse engines or 1629093 for longitudinal engines.
C. Using the following plastic gauging procedure, measure the #1 main bearing to crankshaft clearance.
NOTICE: Main bearing clearance specifications are for an assembled engine (clyinder heads and intake manifold and torqued to specifications). Because bearing clearances differ significantly between a non-assembled and an assembled engine, bearing clearance measurements should be made on an assembled engine only. Measuring bearing clearances on a non-assembled engine may result in incorrect readings.
#1 Main Bearing Clearance Checking
Remove and discard existing #1 bearings and install new current production #1 main bearings (P/N 18014329) which can be identified by a red edge colour in the #1 main bearing bore. Using the procedures detailed below, measure the clearance with this bearing.
1. With main bearing cap removed, wipe oil from crankshaft journal and bearing insert.
2. Place a piece of plastic gauging material in center of cap (Figure 1). When using plastic gauging material, plastic material and part being measured must both be at room temperature. If parts are excessively warm, an incorrect reading may result. Fresh plastic gauging material is recommended for greatest accuracy.
3. Reinstall main bearing cap. Tighten main bearing cap screws to 115 N.m (85 ft. lbs.).
When bearings are being measured with engine in chassis, crankshaft must be supported in order to take up clearance between upper bearing shell and crankshaft. This can be done by removing bearing caps adjacent to bearing being checked and placing a strip of 0.13 mm (.005 inch) brass shim stock between lower bearing shell and crank shaft bearing journal.
When reinstalling bearing caps with shims, lightly tighten attaching screws to avoid damaging bearing caps.
NOTICE: It is extremely important to position tangs of bearings in notches in block and cap or both could be damaged.
4. Remove main bearing cap and determine clearance by comparing width of flattened plastic gauging material at its widest point, with graduations on plastic gauging material container. Number within matching graduation on envelope indicates clearance (Figure 1).
- If clearance is less than .05 mm (.002 inch) leave the red bearing (P/N 18014329) in the engine.
- If clearance is .05 mm (.002 inch) or greater,install the service #1 main bearing (P/N 18014307), which can be identified by its blue edge colour.
NOTICE: These two new bearings (P/N 18014329 and 18014307) may only be used in the #1 main bearing bore due to horizontal dimensional change. If these bearings are installed in the #2 or #4 main bearing bores, crankshaft to bearing interference may result under certain temperature conditions which may cause severe engine damage.
2. Main Bearing Update
Bearings #2 through #5 do not significantly contribute to HT4100 engine knock. They have, however, been updated as a result of research on the #1 bearing.
A. #2 and #4 Main Bearinq
P/N 18009086 has been superseded in production by a slightly thicker bearing. The new bearing (P/N 18013442) should be used whenever replacement of #2 and/or #4 main bearings is required.
B. #5 Main Bearing
P/N 18009087 has been superseded in production by a slightly thicker bearing. The new bearing (P/N 18013793) should be used whenever replacement of the #5 main bearings is required.
In addition, service technicians have been provided the ability to reduce operating clearance of the #5 main bearing if it is suspected as a source of bearing noise by the release of a new oversize #5 bearing. This bearing (P/N 18012878 - identified by its blue edge marking) should be installed if the clearance checking procedure described above for the #1 bearing is performed on #5 and the resulting clearance is .05 mm (.002 inch) or greater. Measurement with a new production bearing must always be performed to make this decision.
C. Bearing Identification
To eliminate potential confusion resulting from the various part numbers associated with the main bearing revisions, the following chart is provided for your information
Service Bearing Edge Part Part Application Position Colour Number* Number** Status
Original Production #1 None 18006622 18009086 Obsoleted by 18012316 2nd Design Production #1 Purple 18012275 18012316 Obsoleted by 18014329 3rd Design Production #1 Red 18014079 18014329 Service Only O.S. #1 Blue 18012276 18012317 Obsoleted by 18014307 Service Only O.S. #1 Blue 18014306 18014307 Original Production #2 & #4 None 18006622 18009086 Obsoleted by 18013442 2nd Design Production #2 & #4 None 18013016 18013442 Original Production #3 None None 18009088 Original Production #5 None None 18009087 Obsoleted by 18013793 2nd Design Production #5 Pink None 18013793 Service Only O.S. #5 Blue None 18012878
* Part number is number stamped on back of bearing shell. Use this number for identification.
** Service number is number GM Parts assigns to part and prints on box. Use this number for ordering parts.
General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.
