(4) Grind valve seats as follows: (a) Use
ST-685 Valve Grinding Machine or machine of equal
(b) Check condition of grinding
1. Mandrels must be straight and
of proper size to fit in guides.
2. Bushings in grinder must be
clean and must fit improperly in guide mandrel.
(c) Dress stone to 30 degrees from
(d) Grind valve seats, holding seating
severe angle will cause seat to be out-of-true depending
upon amount of wear in grinder bearings, mandrel,
bushings, etc., even though grinder has a universal joint.
iCheck valve seat width which should be 1/16 to 1/8 inch.
Figure 3-256. Coutnterbore for valve seat insert.
1. If seating area is wider than
1/8 inch maximum, stock can be removed with specially
dressed valve seat grinder stones.
2. Narrowing should not extend
beyond chamfer on seat insert. Chamfer provides for
(f) Dress wheel for final finish.
(g) Finish grind with light touches of
stone against face.
(h) Check valve seat concentricity
1. Use valve guide as a center.
Total run out should not
exceed 0.002 in.
3. The gage must be a perfect fit
on pilot mandrel.
Figure 3-257. Refacing valve seat.
(i) Check seat with mating valve as
e. Installation. Install valve seat and peen
around insert in at least 4 or 5 places with the peening
tool available as extra equipment in ST-257. A A/ inch
diameter round end punch may also be used.
3-47. alve Crossheads and Guides Replacement
Caution: Over-swagging around insert may
crack cylinder head.
a. General Valve crossheads are used on
engines with dual intake and exhaust valves to insure
that both valves under the crosshead are opened and
closed at the same time.
(1) Lift valve crossheads from crosshead
in cylinder head and the complete unit sent to the head
(2) Remove crosshead guides to be
Figure 3-258. Indicating valve seat insert.