Operation CHARM: Car repair manuals for everyone.
Manuals through 2025 now available!

Our trusted friends have launched a new website named LEMON, which has newer manuals. It also contains all the CHARM manuals.

LEMON is the spiritual successor to CHARM, I recommend you try it!

Link: lemon-manuals.la or lemon-manuals.org.ua

(Some people have issue connecting. LEMON is investigating. For now, use Firefox or change your DNS server)

Or, hide this message: temporarily or permanently

Valve Seat







Valve Seats
Upper Reduction Angle (A):
Inlet 20°
Exhaust 15°
Matching Surface Angle (B):
Inlet and Exhaust 45°
Lower Reduction Angle (C):
Inlet and Exhaust 60°
Valve Seat Width (a)
Inlet 1.4 - 1.8 mm
Exhaust 1.8 - 2.2 mm