The surface quality (finish) of the cylinder head gasket surface is
machined to close tolerances that enable an effective sealing joint for
the MLS (multi-layered steel) gasket. To ensure all head gaskets seal
properly, be sure surfaces are clear of any gasket debris, RTV, oil,
and coolant using Motorcraft Silicone Gasket Remover (ZC-30) and
Motorcraft Metal Surface Prep (ZC-31). Use a lint free rag to mop up
the deck surfaces. Shop vacuums are unacceptable for mop up as the
cleaner is volatile. The block or head surface must be clean and dry
before running a flatness check.
Use a straightedge that is calibrated by the manufacturer to. be flat
with 0.0002? (0.005 mm) per running foot length. For example, the
straightedge may be 24? (61 cm) long. That means the machined edge must
be fiat within 0.0004? (0.010 mm) from end to end.
Special care is requlred to ensure the tool Is not damaged in handling
or storage. Be sure that the machined surface is free of nicks and
dents. If these properties are found, the cost of tool re-calibration
most likely will exceed the cost of a new straightedge. Machine shops
may not be able to hold the specified tolerance within the original
cost of the straightedge.
When checking for flatness, avoid running the feeler gauge butt end
against the straightedge. This action will curl or warpthe leaf and
prevent entry under the straightedge. Erroneous readings will result.
Instead, lay the leaf on the suspect area, placing the straightedge on
top of the leaf. A very easy pull orlbooseness of the leaf under the
edge will indicate a depression in the surface. Turn the edge 90
degrees to the area just checked. Confirm any suspicion by checking the
area more than one time.
Figure 1 and 2 demonstrates a 12 point check-system using a
grid format on a 4 cylinder bank. Important to note is that a localized
area of less than approximately 1.5 to 2.0 sq.in. will influence the
effectiveness of the MLS gasket sealing capability. Depressions or
marks measured to be over 0.001? deep will not seal properly. The
overall flatness check (head end to other end) is not as critical.
As shown with Planes 1 through 3 (Figure 1 and 2)check
these areas locally with the gauge looking for suspect depression areas
of 0.001 inch or more. Then, check these same areas again,
perpendicular, using Planes 4-12. The second pass will confirm a
suspect area because you are using a shorter span of the straightedge.
The first pass (Planes 1-3) is necessary because the overall end to end
flatness must be accounted for before doing the secondary passes (Planes 4-12).
Ford Motor Company approved straightedges are commercially available
through the Rotunda Tool Catalog at special pricing, or can be
purchased from Ihe local tool distributor or truck at regular
pricing.This edge meets or exceeds the requirements of testing Ford
engine components.
Some or all of this information was provided by the Automotive
Parts Remanufacturers Association (APRA). For more information on
technical bulletins available through APRA call 703-968-2772 or visit www.AutoBulletins.com. 
