Engine - HT4100 Revised Distributor Drive Gear

Bulletin No. T 87-74
File in Group 6A
Number 88
Corp. Ref. No. 716109
Date Feb. '87

SUBJECT: REVISED HT4100 DISTRIBUTOR DRIVE GEAR

MODELS AFFECTED: ALL WITH HT4100 ENGINES

Figure 1 - Revised Distributor Gear:

Serviceman Bulletin T-86-79 outlines service procedures for vehicles equipped with HT4100 engines which experience abnormal distributor drive gear wear. Those procedures remain valid except that a revised distributor drive gear has recently been released. All 1987 Allantes and other 1987 vehicles beginning with the following vehicle identification numbers: (C-292647, E- 609515, K-811004) incorporate the revised gear.

For service use, the revised gear is available by ordering P/N 10499813. This new part replaces P/N 10499163 for all applications. The new gear which is constructed from an improved material can be identified by two grooves above and below the roll pin as shown in Figure 1.
Warranty Considerations

Previous bulletins on this subject, such as T-86-79, have described detailed procedures for diagnosis and repair. Most important among these procedures is the requirement that when distributor driven gear wear is discovered, the distributor drive gear (camshaft) must also be replaced. The reason for this is that the two gears wear together in a pattern and when only one of the pair is replaced the likelihood of a repeat failure is very high.

In spite of this requirement, Cadillac continues to receive warranty claims indicating that only the distributor driven gear was replaced. In the interest of customer satisfaction, Labor Operation J4520-B (Distributor Driven Gear Replacement) has been cancelled. Operation T6135 described in Bulletin T-86-79 must be used for this repair.