Big blocks dropping valves

[Todd Wilson]

I wanted to throw this out amongst the engine guys to see what they think. I have personally seen 3   440's drop valves and 1  413 drop a valve. None had excessive miles on them . Some were less then 100000miles.  All the engines were in stock form and were being used in truck applications where they were worked.   The 413 was in a dump truck and the 440's ranged from pickup trucks to a motorhome.



One 440 in particular  dropped a valve 2 different times?!


Any ideas or theorys?


Todd

[Chryco Psycho]

there can be a lot of reasons , valve springs can be become soft [try bending a coat Hanger between your thumbs for a while ] when being worked hard for a long period .causing the valve to float & drop the locks out
if a lifter bleeds down & smashes into the tip of the valve enough times it can drive the valve through the locks
heat can swell the valve stem & cause the valve to stick which can cause the valve train to become unstable , inadquate oiling can help too
were they intake or exhaust valves ?

[BigBlockSam]

i worked in a trucking place in the early 80's and the 360's were dropping valves. something about sodium filled valves . never got the complete story