Upfront, I want to state that I am not a "pro" engine builder, but I have been building and racing my own FEs since the mid 70s, and have never been very concerned about pushrod length, since the rocker arm geometry is pretty much fixed by design of the FEs rocker arm stands height, so as long as the pushrod was long enough to span the distance between the lifter and the rocker adjusting screws, I figured that was "good enough". I have used nothing but factory cast iron heads, and flat tappet cams, and even with pretty agressive flat tappet solid cams, well over .650" lift, 7000 RPM shifts, and the valve springs needed to work with them, I never had any issues with rocker or pushrod life, although I did have periodic shaft breakage, before I started using end supports , actually mostly the Oregon Cam rocker support system , since the early 80s. Over the past several years, many here, and on other FE groups, said that the rocker screws should have no more than 2 or 3 threads showing below the bottom of the rocker arm body. So, when I put the mild 428 CJ together for my 59, I was somewhat concerned that with the standard length ball & cup pushrods that I have been using for decades on various FEs , would require the adjusting screws on my factory iron adjustable rockers to be cranked down so far that only a couple of threads would be above the rocker body. So for the initial cam break in and dyno pulls, I installed my Erson roller rockers, as they fit with the rocker screws about 1/2 way, and I had been driving the first 500 miles with the Ersons, although since the cam in this 428 is a mild solid flat tappet (.518" lift, 228 @ .050 dur), I wanted to put the iron rockers on. I ordered a set of custom pushrods from Smith Brothers, that are 9.450", which is .100" longer than what I had with the Ersons, and installed the iron rockers on new shafts and another Oregon Cam support assembly. Put it all together, the adjusting screws had the supposed ideal 2 threads showing below the rocker bodies, and took it for a drive. Ran great, and seemed noticeably quieter that the aluminum Ersons, so I decided to head out for a local cruise night. About 10 miles from home, all of a sudden, there was a louding ticking noise, and it started running a bit rough, so I turned around, and headed for home. As I drove , it started getting louder, and started backfiring thru the carb, & running very jerky, about 2 miles from home, it got so bad I couldn`t make it up a moderate hill, so pulled over, and had my wife tow me home with my truck and a tow strap. I pulled the valve covers, and found 4 broken rocker arms, 3 exhaust. 1 intake, all were split at the threaded section, and all still had the adjusting screws threaded into the broken pieces. Also I found 2 bent pushrods on the adjacent rocker for cylinder # 3 & 7. I replaced all the rockers , with another set of iron rockers, retaining the same Oregon Cam supports, and reinstalled the 9.350" Comp pushrods. I had to crank the adjusting screws almost all the way down, and since, I have driven the car another 300 miles, including a few 5500 RPM blasts thru the gears. (When the other rockers broke, I had yet to go over 3000 RPM). So did having the longer pushrods cause this, or did I possibly have 1 fluke rocker break, and the resulting cylinder pressure from the exhaust unable to escape, cross thru the intake manifold, and somehow cause the other rockers to fail? All I know at this point is, the shorter "wrong" pushrods seem to be working fine, with the rocker screws cranked way down, and the more ideal length pushrods gave me grief. Any thoughts? The only time I ever had a iron rocker break before, was when a connecting rod broke, and the piston whacked the head hard enough to bend a valve.
