Engine '67 Mustang 289 V8 Loose Rocker Arm Polylock Nuts Wtf?

Trying to tune and road test my '67 Mustang 289 V8, but for some reason, the POLYLOCKS KEEP COMING LOOSE, and not always on the same cylinder or bank -- sometimes left, other times, right. I'm confident the valve adjustment procedure and pre-load and zero lash have been done correctly (performed more than once so you tend to get good at these things. LOL!). Engine is a 289 +.030 has a fairly aggressive "street/strip" cam (290/228, .504 lift), Comp Cams Roller Tip "Rail Type" rockers AND using polylock nuts (some type from JEGS I bought years ago. YES, heads were machined for screw-in type studs, but no guideplates. Carb is EDB 1406, brand new out of box, and I've adjusted float level, etc.

I'm thinking of ordering a set of replacement STOCK TYPE rocker ball and nuts kits from Summit Racing. Am I just NOT cranking down the polylocks enough to keep damn rockers tight for more than a few starts? Just don't want to bend any pushrods or valves at this stage. Thanks for your input and shared experiences with this PITA issue.

DailyDriver_68 said:

Check the ends of your push rods and make sure they are not wearing down. I have the same rockers on my 289. The ends of my push rods were wearing down and it seemed like my rocker adjustment was backing off. It was occurring in a short amount of time. As my push rods wore down, the ends became mushroom shaped instead of spherical. I bought a better quality set of hardened push rods and haven't had any issues for three years. I am running the stock type rocker nuts.

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Thanks for the insight @DailyDriver_68. I recall checking the pushrods (for straightness and excessive wear) during the last time I relashed all the valves after a different polylock nut backed off (3rd cylinder I believe). I believe I'm using hardened pushrods as well (been 15 years so can't be 100% certain). Additionally, the screw-in studs are all still seated, so no apparent issues on this end of the valvetrain.

I just ordered a set of stock rocker arm nuts from Summit Racing. Hopefully these will help keep the valves in adjustment for alot longer than with these so-called "polylocks".