1966 - 1968 Corvette: Service Bulletin: Valve Hitting Top of Piston
Subject: Valve Hitting Top of Piston
Model and Year: 1966 - 1968 Corvette with 427 CU. IN. 430 H.P. Engine
Source: Chevrolet Dealer Service Technical Bulletin
Bulletin No: 68-T-17
Date: Jan. 11, 1968
TO: ALL CHEVROLET DEALERS
Reports have been received of valve "float" at extreme high engine speeds, causing the exhaust valve to hit the top of the piston on 1966-68 Corvettes equipped with the special 427 cu. in. 430 h.p. engine (RPO L-88). This condition was corrected in production, effective August 23, 1967, by reducing the installed valve spring height with a new valve spring assembly and two additional spring shims.
In service, the installed valve spring height can be reduced sufficiently to eliminate valve float by adding two (2) shims #3875916 under the existing production valve spring shim on all intake and exhaust valves.