I was today years old...
Thread Starter
Pro
Joined: Sep 2024
Posts: 526
Likes: 117
I was today years old...
When I learned that a slightly higher lift cam will cause factory rocker nuts to back off on their own. Good news is that roller rockers fix that noise permanently.
It's amazing what you find out when you try stuff, then fail, then use google. Who knew?
It's amazing what you find out when you try stuff, then fail, then use google. Who knew?
Burning Brakes
Joined: Dec 2017
Posts: 1,043
Likes: 414
2023 C3 of the Year Finalist - Modified
I have never heard of it, or experienced it.
How does cam lift change the fact that the rocker nuts are crimped at the end to prevent rotation?
How does cam lift change spring pressure?
whether the valve is open .4 or .5 the spring stiffness is unchanged, so the force on the rocker nut is unchanged.
but yeah, the factory ones are tapered at the end to prevent backing off, I can’t speak to aftermarket ones, or poly-lock type.
How does cam lift change the fact that the rocker nuts are crimped at the end to prevent rotation?
How does cam lift change spring pressure?
whether the valve is open .4 or .5 the spring stiffness is unchanged, so the force on the rocker nut is unchanged.
but yeah, the factory ones are tapered at the end to prevent backing off, I can’t speak to aftermarket ones, or poly-lock type.
Le Mans Master
Joined: Aug 2015
Posts: 6,122
Likes: 1,998
From: St. Charles MO
I agree with most of what you wrote. However, the very nature of a spring is to add force as it is compressed. Assuming a linear spring rate of lb/in, then compressing the spring adds "k" amount of force for every inch of compression, where "k" is the spring rate. So if a spring has a rate of 300lb/in and is installed with a 100lb preload when the valve is closed (just making up numbers here), then opening the valve 0.400" is going to give a total spring force of 220lb whereas opening it 0.500" will give a force of 250lb.
Instructor
Joined: Feb 2023
Posts: 157
Likes: 175
From: Louisville, Kentucky
Possible, but not likely if he didn't increase the spring rate. More likely that the nuts didn't lock properly when he reinstalled them after changing the cam. Tapered lock nuts have a finite cycle life. After a few removals/reinstalls they can wear the threads on the stud or the nut - whichever is softer - and they don't lock as well as they did when new. Another one can be the lifter not being on the base circle when the rockers were tightened, that can result in a bad torque value and some slop that'll make some noise.
Thread Starter
Pro
Joined: Sep 2024
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Here is more of the back story. I have a set of China Dart Pro1 200cc Heads, similar to the AFR Enforcers that are out there. 3/8" screw in studs. I upgraded to LS6 beehive springs and then slapped on the factory stamped steel rockers and commensurate hardware, including the factory tapered nuts. About 3-4 of the rockers would loosen up just idling around for 3 minutes or so. The cam is not super high lift XE270HR which is like .490 and .510, or something like that.
It is possible that the factory nuts lost their locking feature over time and the higher lift of the cam and other mods exacerbated the issue.
It is possible that the factory nuts lost their locking feature over time and the higher lift of the cam and other mods exacerbated the issue.
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