My "work" truck is a 51 Ford F-1, with a pretty hot 327 in it. Big hydraulic cam, stock type rockers, screw in studs, pushrod guides. The engine was rebuilt (reliable source) a LONG time ago, and never run. We got it running quite a few years back for my friend when we put together the truck, but he didn't drive it much. When he did take it out, he broke a couple rocker arm studs. Fast forward, I've got the truck now, and am updating it suspension/brake wise, finishing bodywork, etc. I've driven it to a local cruise night about a mile form home, but that's it. I took it out last Sunday for a 10 mile run, and broke another rocker stud! Why is this happening? I've adjusted the valves correctly....yeah, I know how, I built engines at my last job. What is confusing me is...why the studs? Typically they are the last thing to break. Valvetrain problems usually come up as broken rockers, worn through rockers, bent pushrods, collapsed lifters. I haven't seen many sheared studs, pulled ones, yeah, if they were press in, but not broken screw in studs. Is there a common cause for this? No, I haven't been really abusing the motor, either.
Sounds like the geometry is off. I made the mistake a while back that I didn't machine the bosses where the guide plates mount. You hafta remove the same amount from the boss as what the thickness of the new guide plates are. Dunno if that would cause what you are saying though. I'm sure someone on here should know.
Something's binding. Either the rocker SLOT lenght is too short for your high lift cam - or maybe you've got coil bind but even that would probably bend the pushrods first. Check the rocker arms slots if they're binding you ought to see telltale marks on the arms/studs - probably easier to see that on the ones that arn't broke yet.
If you pull the covers and roll the motor over real slow with a dial indicator on a stud - you should see it move. Prob is - if you've run it and already broke two, there's a good chance the rest of them are stressed to failure. Not only are ya gonna hafta swap the rockers, but the studs are gonna hafta be changed out, too. Good time to upgrade to a screw-in stud - if you haven't already.
Had a same problem on a ford, with a hi lift cam. long slot rockers are sold for that purpose. the weakest ones are breaking first. take a rocker off and i'll bet you will see shiney spots in the slot.
Since you are running stock type rocker arms I suppose the question is how much lift?Anything over .488ish usually requires a long slot rocker arm. I would pull all the rockers and inspect the studs for signs that the rockers are banging on the outboard side at max lift. I would also check the pushrods for true,since the most likey scenario is the rockers don't have long enough slots,and although they are not breaking is a good indicator they hardened push rods(required with guide plates)it is quite probable that at least one or more are bent.Maybe not immediately obvious to the naked eye but when roled on a flat surface gl*** or marble or someting perfectly flat will become readily apparent and any untrue,even slight will cause the lifters to tick intermitently and the push rod to eventually fail. Also check for signs of the pushrod rubbing in the hole through the head, (they always show signs of rubbing on the guide plates,shiny but not worn),but if the cam has enough lift to bang the rocker slot on the stud you should check the above.Most good machine shops enlarge the pushrod hole when setting up for screw in studs and guide plates,but you never know. The short slot rockers with a high lift cam is usually a novice ***embler mistake and everything else is probably okay,buuutttt.... it never hurts to look at all possibilities when parts are breaking. Good luck.
I'll just jump in to state the obvious. I'm sure you'll find the problem in the rocker slot as has already been stated. If you remove the rockers you'll find evidence of interference on the outboard side ot the stud. If this is the case you can still use your stock rockers by modifying them. I usuallly scribe a line on the lift side of the slot about 1/8" out toward the end of the rocker from the existing slot. Use a high speed grinder with a 3/8" dia stone and elongate the slot out to the line. Debur the new slot end both inside where the ball rides and the outside to prevent stress risers and overhanging metal from the grinding that might break off and get in the oil. This will usually end the problem. A quick check for adequate clearance can be made by taking a paper clip, stretching out one end and forming a 90 degree hook on the end. After the valvetrain has been re***embled and adjusted roll over an intake and an exhaust to full lift and try inserting the hook on the paperclip up into the slot from the bottom. If, at full lift ,your paperclip wire still will p*** through the gap between the rocker and the stud you've got enough clearance. Frank
Put long slot rockers in it. Don't recall the part number but they were a Corvette part or you can buy long slot rockers from any number of after market companies.
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