Originally Posted by shane.,herold
I am buildin a 74-ish 4 bolt main 350 for a racecar. it has:
double hump heads 64 cc i believe
screw in studs/guideplates set up to stock height according to machinist
1.65 harland sharp roller tip aluminium rockers
summit circle track solid lifter cam ( CT-103 )
standard deck height
fel pro head gaskets
arp head and rod bolts
double roller timing set
.060 over bore
i have it all put together, but i went to put rockers on and they bottom out on screw in studs before they come into contact with pushrod (standard length comp). So i put my Manley pushrod length checker on it and a standard length is perfect. Yet i put an adjustable pushrod in it and set it up to where the rocker will not interfere with the screw in stud and the tip of the rocker is way far on the outside of the valve stem..
I do not know where to go from here. I could order longer pushrods, but im expecting the guides to chew out or the valves to break at the 7000 rpms im expecting to run this engine. Could my valve spring height be wrong? It has double springs set up to match the cam recommendations.
When building a 7000 RPM engine you've got to abandon the usual practices. This is a place where you either need a .1 inch longer valve stem (above the lock groove) or use lash caps; maybe both to get the rocker up off the bottom of the stud, then dial in the push rod length for the new height based of roller sweep on the stem. It is likely that you will have to modify the depth of the slot in the push rod guide plate (not uncommon), it is sometimes helpful to use stepped guide plates that provide support closer to the end of the push rod.
One, also, cannot overlook the possibility that the rocker stud bosses were not machined as low as required causing the stud to sit too high. Fixing this if it is a problem will lead into longer studs.
You may need offset locks as well to push the spring around where the rocker body clears it. this of course leads into spring tension checking to be sure it is at spec. when installed.
What about stud girdles? I have a hard time envisioning that studs alone will provide enough support at 7000 RPM. They wiggle a lot under these RPMs and spring loads, last thing you want is a stud to break, or breakout of the head. By themselves 1.65 rockers add a lot of stress to the studs.
I wouldn't count on OEM rocker covers to fit over all this, some some tall covers might be needed.
Setting up a race engine can be a real PIA.