Cylinder Head Guide Pin - Revised

Bulletin No. T 86-41
File in Group 6A
Number 75
Corp. Ref. No. 805 5666
Date Mar. '86
SUBJECT: HT4100 CYLINDER HEAD GUIDE PIN FOR SERVICE USE

MODELS AFFECTED: 1982-1984 AND SELECTED 1985 ELDORADO, SEVILLE, FLEETWOOD, DE VILLE AND BROUGHAM

FIGURE 1 - CYLINDER HEAD GUIDE PIN:

A new design stepped cylinder head guide pin (P/N 1634935) has been released for service use on all 1982 through 1984 HT4100 engines as well as 1985 HT4100 engines built before Engine Unit Number T1OL499404, which is located on the right hand valve cover. The stepped cylinder head guide pins replace the original slotted pins (Figure 1) and must be installed whenever the cylinder heads are removed on these engines.
1985 Cadillacs equipped with an HT4100 engine built after engine unit number T1OL499404 use the tubular dowel pin (P/N 1633910) previously described in Serviceman Bulletin T-85-75, Group 6A, Number 71. The new design stepped pin may not be used in engines which currently use the tubular dowel pin.

GMWDD will stock both the stepped and tubular dowel pins. The part numbers are as follows.

Type Of Guide Pin

Tubular Pin 1633910
New Service Stepped Pin 1634935