After a less than spirited drive, the Pantera came home with a noticeable tapping sound near the passenger valve cover. After removing the valve cover I quickly found the loose rocker. The source of the looseness was a mashed push rod end at the rocker arm. I have seen bent pushrods in the past but this is the first time for a mashed pushrod. The engine is a bone stock 1971 351C with low miles. Napa actually had the replacement in stock for less than $5. It is good that I caught it before the end completely broke off and dropped down to who knows where. Has anyone seen this before and/or know the root cause?
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Steve, I want to say its probably the incorrect length (too long). I believe the stock heads don't have any adjustment so the geometry is adjusted by the length. Might also be poor quality.
I had a 428 cj do that with what i think were stock pushrods. A stronger set of comp pushrods fixed it.
OEM and cheap replacement pushrods often have ends made by spinning tubing against a hardened cup until friction makes it go soft enough to bend and form a half-sphere that is about the same thickness as the pushrod wall. An oil hole may be left as formed or drilled. Aftermarket pushrods are usualllly made by welding a solid ball bearing onto a tube end, then drilling a hole for oil. A spin-formed end will not be as robust as a ball bearing in taking millions of small impacts.
As mentioned, you may have gotten a defective pushrod 50 years ago- Ford made them in trainload batches and statistical QC is not perfect. Just replacing the stock pushrod(s) may not permanently 'fix' things either: I've had stronger aftermarket pushrods punch clear thru the cup formed in stock stamped rocker arms. This is Smokey Yunick's 'weak-link engineering'. Nothing lasts forever.