Valve Spring Pressure - BBC stocker

Jim Hanig · 06-27-2018, 08:45 PM

[QUOTE=Chipper Chapman;566240]My new motor 396/325hp stocker broke a valve first weekend out (had dyno time too), upon disassembly it was found that all 8 intake valves had been making light contact, of course it was one of them that broke.

My tightest ptv clearance upon assembly ( and checking again during autopsy) was .070" which should be plenty, which leads me to believe it must have been lofting the valves open due to lack of adequate spring pressure. Springs were setup to be 250# on the seat and 500# over the nose which all recommendations said should be enough. Obviously not however. Just wondering if any of you have suggestions of what we should set it up to this time. Cam is steel core, dlc coated trend lifters, pac 1325 springs and steel retainers. Fire away with any suggestions, and thank you
who told you needed 250 on the seat? I have ran several 396/454 oval port engines with no way near that much seat or open pressure. I wou call pac and get the correct spring.

06-27-2018, 08:45 PM	#7
Jim Hanig Senior Member Join Date: Aug 2006 Location: Pukwana SD Posts: 860 Likes: 554 Liked 99 Times in 49 Posts	Re: Valve Spring Pressure - BBC stocker [QUOTE=Chipper Chapman;566240]My new motor 396/325hp stocker broke a valve first weekend out (had dyno time too), upon disassembly it was found that all 8 intake valves had been making light contact, of course it was one of them that broke. My tightest ptv clearance upon assembly ( and checking again during autopsy) was .070" which should be plenty, which leads me to believe it must have been lofting the valves open due to lack of adequate spring pressure. Springs were setup to be 250# on the seat and 500# over the nose which all recommendations said should be enough. Obviously not however. Just wondering if any of you have suggestions of what we should set it up to this time. Cam is steel core, dlc coated trend lifters, pac 1325 springs and steel retainers. Fire away with any suggestions, and thank you who told you needed 250 on the seat? I have ran several 396/454 oval port engines with no way near that much seat or open pressure. I wou call pac and get the correct spring.