INFO. ON APPEARANCE/MECHANICAL DIFFERENCES (4.3L LB4 ENGINE). GMC Truck GMC C Pickup

SUBJECT: INFORMATION ON APPEARANCE AND MECHANICAL DIFFERENCES OF THE 4.3L LB4 ENGINES PRODUCED BY TONAWANDA AND ROMULUS ENGINE PLANTS

MODELS: 1992 S/T, C/K, AND G

The purpose of this service bulletin is to inform field personnel of the appearance differences and the mechanical differences of the 1992 4.3L LB4 engine, manufactured at Tonawanda, NY vs. Romulus, MI.

TONAWANDA-(LB4)

Engine Identification Number beginning with "T" located on the front of the engine block at deck height in front of the right cylinder head.

1. Engine painted as components; therefore the aluminum intake manifold will be silver in color.

2. Net Valve lash rocker arm assembly (new stud, ball, and nut).

3. Camshaft bearing order revised to allow engine plant assembly of the bearings from the rear of the block.

1. Largest outside diameter 2. Mid Size O.D. 3. Smallest O.D.

ROMULUS--(LB4)

Engine Identification Number beginning With "W" located on the front of the engine block at deck height in front of the right cylinder head.

1. Engine painted as an assembly. This is the appearance of previous model years; black intake manifold and engine block.

2. Adjustable rocker arm studs.

3. Camshaft bearing order is the same as previous years.

1. Largest O.D. 2. Mid Size O.D. 3. Smallest O.D.

Note: Both engine plants will use a new camshaft with a smaller lobe base circle and a long travel roller lifter. These were engineered to be compati- ble with the net valve lash (Tonawanda) feature.

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.