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Cummins N14 – Cylinder Head – Vacuum Testing Valve Seating for Reuse

Use valve vacuum tester, Part No. ST-1257, to inspect the seal between the valve and the valve seat.

Install the seal ring, Part No. 3823848, and the vacuum cup, Part No. 3823847, to the vacuum hose.

NOTE: The valves and the valve seats must be clean and dry when vacuum testing.
Cover the valve with the cup and the seal.
NOTE: The seal must make a tight contact on the cylinder head around the valve. The seal must completely fill the two milled areas between the valves.

Move the toggle switch (1) to the ‘‘ON’’ position.
Turn the vacuum control valve (2) to the ‘‘OPEN’’ position.
NOTE: The vacuum control valve is in the ‘‘OPEN’’ position if the vacuum gauge needle moves clockwise.

Operate the vacuum pump until the gauge indicates the specified vacuum.

Turn the toggle switch (1) to the ‘‘OFF’’ position.

Use a stopwatch. Start timing when the needle on the gauge indicates 457 mm-Hg [18 in.Hg].
Stop timing when the needle on the gauge indicates 203 mm Hg [8 in.Hg].
The elapsed time for the needle to move between the specified gauge readings must be 10 seconds or more.

If the elapsed time is less than 10 seconds, perform the following checks:
• Repeat the test to make sure the equipment is operating correctly.
• Use a mallet to lightly hit the valve stem to make sure the valve is seated. Repeat the test.
• Apply a thin layer of grease on the outside diameters of the insert and the valve head. Repeat the test.
The grease pattern will show the point of leakage.

NOTE: A break in the grease seal pattern will indicate leakage between the valves and the valve seat or the valve seat
insert and the cylinder head. Refer to Cylinder Head – Rebuild (02-02).