CYLINDER HEAD EXHAUST VALVE GUIDE WEAR REVISED

MODELS AFFECTED: 1987 SKYLARKS/SOMERSETS WITH THE 2.5L ENGINE (VIN CODE U) 1987 CENTURYS WITH THE 2.5L ENGINE (VIN CODE R)

NOTICE: This bulletin is being reissued to change .005" oversize stem from 10044618 to 10104418. Please discard original bulletin 87-6-17.

Some 1987 vehicles with 2.5L L-4 engines may experience worn exhaust valve guides in the cylinder head. An engine with this condition may exhibit valve train noise, missing, and a rough idle. This condition could be caused by puddled chrome on the exhaust valve stems, which results in a rough surface, and accelerates wear.

If an engine exhibits these symptoms, measure valve stem-to-guide clearance of all exhaust valves. If one or more exhaust valve guides in the cylinder head are worn to the point where clearance is .004" to .006", ream all these valve guides to the appropriate oversize diameter, recondition all exhaust valve seats, and replace all four exhaust valves with the correct oversize valves as described in the service manual. Initially, some oversize valves may not be available from GMSPO. If this is the case, replace the cylinder head and all four exhaust valves with standard size valves.

EXHAUST VALVE PART NUMBERS

Part Number 10044612 - Standard Size Stem Part Number 10044613 - .003" Oversize Stem Part Number 10104418 - .005" Oversize Stem

CYLINDER HEAD PART NUMBERS

Part Number 10049099 - Skylark/Somerset Part Number 10049100 - Century

All engines have a build sequence number on a large bar code sticker located on the exhaust manifold side of the cylinder block above the oil pan rail. Engines having numbers higher than the following, which appear on the sticker, should not exhibit premature exhaust valve guide wear:

CAR LINE STICKER NUMBER WARRANTY INFORMATION -------- -------------- -------------------- Century 0378434 Use applicable labor time Skylark/Somerset 6188498 and operation.

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.