ENGINE KNOCK - HT4100 REVISED BEARING INFORMATION

VEHICLES AFFECTED: 1982-1985 Eldorado, Seville, Fleetwood, Deville and Brougham

This bulletin is an addition to the 1983 Product Service Bulletin 6-224, dated December 15, 1983.

Some Cadillacs equipped with an HT4100 engine may experience an engine knock.

To correct this condition, a new deflashed crankshaft and a new No. 1 main bearing went into production beginning with 1984 model engine unit numbers T10L080120 and T10L254809 respectively.

Engines which are currently experiencing this condition should be serviced using the listed procedure:

1. Visually inspect for proper piston installation, off centered wrist pins, and piston to crankshaft interference as outlined in 1983 Product Service Bulletin, 6-127, and repair as required.

2. Inspect for crankshaft to block interference, and repair as required (refer to Figure 1 for possible crankshaft to block interference). 1982 and 1983 engines, and 1984 engines produced before EUN T10L080120 may require the installation of a deflashed crankshaft (P/N 1628920) when excessive interfezence is evident.

3. On all HT4100 engines, using a plastic gauging material according to the procedures described in the appropriate Service Information Manual, measure the No. 1 and No. 5 main bearing to crankshaft clearances and proceed as follows:

No. 1 Main Bearing ------------------ If the clearance is .1016mm (.004 inch) or less, install the new service No. 1 main bearing (P/N 18012316) which can be easily identified by its purple edge colour.

If the clearance is greater than .1016mm (.004 inch) install the new service No. 1 main bearing (P/N 18012317) which can be easily identified by its blue edge colour.

NOTICE: These two new service bearings must only be installed in the No. 1 main bearing bore due to their horizontal dimension change. If these bearings are installed in the No. 2 or No. 4 main bearing bores, crankshaft to bearing interference may result under certain temperature conditions which may cause severe engine damage.

No. 2 and No. 4 Bearing ----------------------- P/N 18009086 has been superseded in production by a slightly thicker bearing.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 No. 2 and/or No. 4 main bearings is required.

No. 5 Main Bearing ------------------- If the clearance is .1016mm (004 inch) or greater, install the new service No. 5 main bearings (P/N 18012878). These bearings can be identified by their blue edge colour.

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.