SERVICE MANUAL UPDATE-SEC.6A CYLINDER HEAD MEASUREMENT

Subject: ENGINE MECHANICAL - CYLINDER HEAD

Model and Year: 1990 GEO STORM

TO: ALL CHEVROLET DEALERS

Add this procedure to the other measuring procedure on page 6Al-l7 and 6A2-18 in the CYLINDER HEAD portion of the ENGINE MECHANICAL SECTIONS 6Al and 6A2 in the 1990 GEO Storm Service Manual (ST371-90).

MEASURE

Tool Required:

J 26900-9

Cylinder head mating surfaces for flatness. Using a precision straightedge and a J 26900-9 feeler gage, measure the cylinder head along diagonal lines where it contacts the exhaust and intake manifolds, and its engine block contact surface. If warpage along any axis exceeds 0.2 mm (0.0078 inch) the cylinder head must be reground; if warpage along any axis exceeds 0.4 mm (0.01 58 inch) the cylinder head must be replaced (Figures 1 and 2).

Figure 1 - Inspecting for Warpage DOHC Engine Shown, SOHC Similar.

Figure 2 - Cylinder Head Mating Surfaces DOHC Engine Shown, SOHC Similar.

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.