'67 Mustang 289 V8 Rocker Arm Poly Lock Nuts Keep Coming Loose. Wtf?

cjstang6791

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Jul 18, 2016
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Long time reader, first-time poster and I'm seeking some advice on a rocker arm nut issue. I've been working on my '67 Mustang 289 +.030 V8 with a fairly aggressive "street/strip" cam (290/228, .504 lift), Comp Cams Roller Tip "Rail Type" rockers using poly lock 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.

My problem: I've been trying to tune and roadtest this beastie, but for some reason, the POLY LOCKS KEEP COMING LOSE, 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!). 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 poly locks 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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Davedacarpainter

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Long time reader, first-time poster and I'm seeking some advice on a rocker arm nut issue. I've been working on my '67 Mustang 289 +.030 V8 with a fairly aggressive "street/strip" cam (290/228, .504 lift), Comp Cams Roller Tip "Rail Type" rockers using poly lock 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.

My problem: I've been trying to tune and roadtest this beastie, but for some reason, the POLY LOCKS KEEP COMING LOSE, 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!). 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 poly locks 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.
While this is an interesting question, I have no freaking idea.:shrug:

Go to the tech section of the classic mustangs subforum. You'll be up to your eyeballs with people that know what they are talking about there.:nice:

This is more of an intro the site forum.

Good luck brother, hope you get this answered for you.
 

cjstang6791

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Jul 18, 2016
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Thanks for the response Davedacarpainter. I actually posted this same question under 1965-70 Mustangs sub-forum and hope to hear something on the topic.
 
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Davedacarpainter

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Thanks for the response Davedacarpainter. I actually posted this same question under 1965-70 Mustangs sub-forum and hope to hear something on the topic.
The tech section will probably be the best there.

If you want to get someone's attention, put an @ sign before their username, like @cjstang6791 . This will send them a notification your interested in them reading what you posted.

Good luck brother