I understand that the stamped style rocker arms were invented by Pontiac and then used by Chevy in '55 on the then new small block v8. My question is if the rockers have the same ratio and use the same size stud are they interchangeable? If not can Chevy rockers be modified to fit in a Pontiac engine without extreme measures? I'm going to a swap meet next week, Chevy rockers seem to be on every table. I would prefer to avoid an expensive mistake.
They wont work, plenty of aftermarket available for Pontiac arms. I dont know what your working on, but usually getting rid of the bottleneck studs and going to 7/16 will allow more options. I have also used sbf aftermarket to go to a 1.6 ratio.
Use big block chevy studs if your Pontiac has screw in studs...makes them adjustable when normally Pontiacs arent. Don't remember what rockers we used though...
Thanks guys; I figured that the studs would have to be changed. I was mostly wondering if there were other issues.
You will need short BBC studs, the tall ones will not clear older valve covers. I buy the long ones and cut them down, since the long ones are what most places sell. You will also need the shortest Poly-locks to clear your valve covers. Some Ford rocker arms will fit the Pontiac, but not Chevrolet. Stock Pontiac, stamped rocker arms are quit strong and will run a long time. If you are looking for more lift, look to the cam, or at aftermarket roller rocker arms. Pontiac did use 1.65 ratio rockers on the Ram Air engines.
Thanks for that info. I knew that Chevy and Ford rockers didn't interchange; something about trying to put SBC rockers into a 300 Ford six. I didn't know that Ford & Pontiac would cross. Now the question becomes which Ford rockers since there are several styles out there. I guess that I need to do more research before grabbing a set off of the swap meet table. Thanks again. I suppose that a reasonable person would just pick up the catalogue and order a new set for the application; but where is the fun in that?
All Pontiac passenger car heads had stud-oiled rocker arms through 1963 with the exception of 389/421 Super Duty heads and 421 HO heads. The rocker studs were hollow so that the oil gallery in the head could feed the rocker balls. 1964 was a transition year, common low-performance heads still oiled through the studs. High-performance engines such as the GTO 389 and big Pontiac 389 Tri-Power and 421 HO engines featured pushrod oiling of the rockers. All 1965 and later Pontiac heads had pushrod oiled rockers from then on. Of interest is the hollow press-in studs were used for many, many years after the stud-oiled heads were obsolete. Up through about '73 which was when all Pontiac heads went to screw-in studs they still had the hollow studs in the press-in stud heads. I've personally removed the hollow studs from a set of '71 #66 455 heads while converting them to screw-in studs. I presume that they were either using up truckloads of old inventory or perhaps just never changed the tooling or design of them.
Thank you, I learned something today. I have a '63 421 HO and it didn't have the hollow studs. The only other Pontiac heads that I have taken apart are a couple of 455s from the mid '70s. Since I have several Pontiac heads laying around I suppose that it would be educational to look them over.
Take a closer look, those studs are hollow on your '63 9770716 421 HO heads. You'll see a very small hole drilled through the side of the stud near where the rocker balls would reside. The fact that they're hollow isn't readily apparent at a glance. The studs are drilled up from the bottom most of the way and then through the side to oil the rockers, they're not drilled all the way through to the top. Of course your pushrod-oiled '63 421 HO didn't utilize the oil passage drilled through the stud, but nevertheless the hollow studs were used. I have a '64 421 HO here that I recently had built that uses the same exact head that your '63 421 HO uses. We removed the hollow press-in studs, had the stud bosses milled down by .250" and installed 7/16-14 Heli-Coil inserts so we could use BBC screw-in studs.
It has been a number of years since taking the 421 heads apart. What I do remember is that I wasn't the first to be under the valve covers. The stud bosses had been drilled crosswise through the studs with pins inserted through both. I assume that was to prevent the press in studs from pulling out. There were also some home brew spacers between the rocker balls and the adjusting nuts. Since the engine had a fairly radical solid lifter cam I'm guessing that this was a way to have enough thread on the studs to adjust the valves. The set up worked well enough that I put 50K+ miles on it. The 421 is currently resting in a corner of my shop awaiting a worthy car to put it in. When that happens I expect to upgrade the valve train with something a little more professional. Milling the stud bosses and putting in the Heli-Coil inserts sounds like a good way to ensure the rocker studs stay put. When the day comes to do that I am hoping that the cross drilling doesn't interfere with milling down the stud bosses.
Anything larger like a 1.65 aftermarket rocker will run into issues of the pushrods rubbing the head and will require elongation of the pushrod hole. So carefull consideration is required on camshaft and rocker choices.
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