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

cjstang6791

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Jul 18, 2016
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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.
 

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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.
 

cjstang6791

Member
Jul 18, 2016
6
1
13
39
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.

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".