TM 5-3895-346-14
EXHAUST VALVES
ENGINE OVERHAUL
For service replacement, change the new spring when a load of less than 25 pounds will compress it to 1.93
inches (installed length).
The new and former valve springs are interchangeable in an engine rated below 2800 rpm using a low-lift (V7L)
camshaft. However, on any given valve bridge, it is recommended that both springs be the same.
When a former spring is replaced in an engine rated at 2800 rpm with a low-lift (V7L) camshaft, all of the
springs must be replaced with the new spring.
Inspect the valve spring seats and caps for wear. If worn, replace with new parts.
Carbon on the face of a valve could indicate blowby due to a faulty seat. Black carbon deposits extending from
the valve seats to the valve guides may result from cold operation due to light loads or the use of too heavy a
grade of fuel. Rusty brown valve heads with carbon deposits forming narrow collars near the valve guides is
evidence of high operating temperatures. High operating temperatures are normally due to overloads,
inadequate cooling, or improper timing which results in carbonization of the lubricating oil.
If there is evidence of engine oil running down the exhaust valve stem into the exhaust chamber, creating a
high oil consumption condition because of excessive idling and resultant low engine exhaust back pressure,
replace the valve guide oil seals or, if not previously used, install valve guide oil seals.
Effective with four-valve cylinder head engines built the second quarter of 1980, a new exhaust valve guide oil
seal is being used. The new oil seal (Fig. 17) has a metal case and the slightly reduced inner diameter of the
seal provides a press fit on the valve guide. The former oil seal was retained by a spring at the small end and
a retainer at the large end. The former and current oil seals are interchangeable on a cylinder head.
Clean the carbon from the valve stems and wash the valves with fuel oil. The valve stems must be free from
scratches or scuff marks and the valve faces must be free from ridges, cracks, or pitting. If necessary, reface
the valves or install new valves. If the valve heads are warped, replace the valves.
Clean the inside diameter of the valve guides with brush J 7793 as shown in Fig. 4. This brush will remove all
gum or carbon deposits from the valve guides, including the spiral grooves.
Inspect the valve guides for fractures, chipping, scoring, or excessive wear. Measure the valve guide inside
diameter with a pin gage or inside micrometer and record the readings. After inspecting and cleaning the
exhaust valves, measure the outside diameter of the valve stems with a micrometer and record the readings.
Compare the readings to obtain the valve-to-guide
Figure 4. Cleaning Valve Guide
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