For 1990-2009 cars

# HT4100 ENGINE SERVICE PROCEDURE UPDATE AND P/N'S

#### Models Affected: 1982-1985 Eldorados, Sevilles, Fleetwoods, Devilles and Broughams

1. OIL DRAINBACK HOLES

When performing any service that requires removal of valve covers on an HT4100 engine, it is recommended that any sludge build-up in or around the oU drainback holes in the cylinder head (see Figure 1 for locations) be cleaned out as necessary.

2. REVISED CYLINDER HEAD GUIDE PIN

A new cylinder head guide pin has been implemented into production for an HT4100 engines.

The new cylinder head guide pin is a tubular pin that replaces the slotted pin, (see Figure 2) and requires a reduced diameter hole in the block. The tubular guide pin is smaller in diameter and cannot be used in blocks which are equipped with slotted pin The cylinder head assemblies are not affected and may be used on block assemblies with either guide pin.

GMWDD will stock both guide pins. The part numbers are as follows:

TYPE OF GUIDE PIN P/N ----------------- --- Slotted Pin 1618697 New Tubular Pin 1633910

3. PARTIAL ENGINE ASSEMBLY INSTALLATION

HT4100 partial engine assemblies, as suppled by GMWDD, include the block, pistons, piston rings, bore liners, and crankshaft. It is recommended that a new camshaft and lifter kit, P/N 1628822, be installed in all GMWDD HT4100 partial engine assemblies. The transfer of camshafts and/or lifters from one engine to another is not recommended.

4. CAMSHAFT REPLACEMENTS

If an HT4100 engine assembly experiences a repeat case of worn camshaft lobes, it is recommended that it be replaced with a new partial engine assembly (P/N 1626149 for transverse, P/N 1623537 for longitudinal).

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.