HT4100 CYLINDER HEAD GUIDE PIN RELEASED FOR SERVICE USE

VEHICLES AFFECTED: 1982-84 and Some 1985 Eldorado, Seville, Fleetwood, Deville and Brougham Models ----------------------------------------

A new 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 TlOL499404 use the tubular dowel pin (P/N 1633910) previously described in Product Service Bulletin 85-6-186. The new stepped pin may not be used in engines which currently use the tubular dowel pin.

GM Parts 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

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.