Valve Seat Repair - MerCruiser 305 CID (5.0L) Service Manual

5.0l / 305 cid / 5.7l / 350 cid ENGINES

Valve Seat Repair

Valve seat reconditioning is very important, since seating of valves must be perfect for
engine to deliver maximum power and performance.
Another important factor is valve head cooling. Good contact between each valve and its
seat in valve head is important to ensure that heat will be properly dispersed.
Several different types of equipment are available for reconditioning valve seats. Equipment
manufacturer's recommendations should be followed carefully to attain proper results.
Typical "3 Angle" Valve Seat
Regardless of type of equipment, it is essential that valve guide bores be free from carbon
or dirt to achieve proper centering of pilot in valve guide, ensuring concentricity.
Measuring Valve Seat Concentricity
Index
Page 3A-38
°
a - Top Angle (30 )
°
b - Seat Angle (46 )
°
c - Bottom Angle (60 )
d - Seat Width
Intake 1/32-1/16 [.031-.063] In. (0.8-1.5 mm)
Exhaust 1/16-3/32 [.063-.094] In. (1.6-2.3 mm)
a
b
d
c
SERVICE MANUAL NUMBER 24
50668
72338
90-861327--1 OCTOBER 1999