Engine - Service Procedures Update
Bulletin No. T 85-73File in Group 6A
Number 71
Corp. Ref. No. 8054266
Date April '85
SUBJECT: HT4100 ENGINE SERVICE PROCEDURE UPDATE
MODELS AFFECTED: 1982-1985 ELDORADOS, SEVILLES, FLEETWOODS, DEVILLES AND BROUGHAMS
1. OIL DRAINBACK HOLES
FIGURE 1 - OIL DRAIN 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 oil 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 all HT4100 engines.
FIGURE 2 - GUIDE PINS:
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 pins. 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 supplied 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).