I rebuilt the B18 in my 65' 1800 last year and after doing all the proper break in stuff, correct cam lube on cam lobes and lifters. Using RP break in oil. Running for thirty minutes between 2-3 thousand RPM. Changed the oil and filter right after, used more RP break in oil for the next 1300 miles, then at the beginning of this spring changing the oil to RP HPS oil which has higher levels of phosphorous and zinc for flat tappet/performance engines. After all that i have a severe failure on the number three valve, after adjusting the valves numerous times because the valve train seemed to get "noisy" i finally checked all the clearances before re adjusting, sure enough just one valve did not hold its adjustment, the clearance grew .010" in just under fifty miles! My magnetic drain plug also shows the telltale metallic paste of bad wear. I will be pulling the head to investigate but was wondering what happened? Also if i find the lifter bore is fine and the cam measures lift correctly can i just replace the one bad lifter? The lifters all spun fine in their bores when i installed them and everything is new. Stock "C" grind with stock type lifters and pushrods all new from VP autoparts. Any help or advice is highly appreciated.
Thanks!