Rocker arm nut preload (breakaway torque)

[Duke W.]

Has anyone ever seen an OE rocker arm nut preload minimum spec - the minimum breakaway torque to be acceptable for reuse?

Has anyone ever taken a series of breakaway torque measurements on one or more engines to determine the typical range?

Duke

[Joe C.]

Re: Rocker arm nut preload (breakaway torque)

Duke,

I recently found them to be "all over the place" even with brand new GM nuts. I could "feel" them with a 3/8" drive rachet/socket, and did not actually measure them. Probably south of 24 inch-pounds.

Joe

[Duke W.]

Re: Rocker arm nut preload (breakaway torque)

Yes, I recall that there is wide variation, but don't you mean 24 lb-ft rather than 24 lb-in?

I find it easiest to use a 1/2" breaker bar to turn the nuts for valve adjustment. Too short a lever doesn't provide good control when you want to turn the nut just a few degrees.

Duke

[Mike McKown]

Re: Rocker arm nut preload (breakaway torque)

I measured some awhile back. Used. About 15-24 inch pounds. I measured a set of new ones and I think they measured about 10 ft. lbs. I would have bet they would have been more. The used ones wouldn't hold solid lifter adjustment by the way. The new ones would.

[Michael H.]

Re: Rocker arm nut preload (breakaway torque)

When we were required to use stock stamped steel rocker arms in SCCA in the 60's, I would always add a bit more prevailing torque with a "special Kent Moore" tool. (hammer) New nuts were, as you mention, all over the map when it comes to even torque. Once the critical adjustment was made, there were no problems.

Posi-Locks were legal in this division but I wouldn't even use those things on a lawn mower. Many DNF's and engine failures because of Posi-Locks.

[Joe C.]

Re: Rocker arm nut preload (breakaway torque)

Duke,

Again, just going by "feel". It "feels" like about 2-3 ft-lbs, (24-36 in-lbs). Requires very little torque to rotate the stud nuts. So little, that it's surprising how they hold fast. I removed Posilocks that Michael refers to, because they were very problematic. The "loose fitting" standard GM nuts miraculously, are very reliable.

Joe

[John M.]

Re: Rocker arm nut preload (breakaway torque)

Duke, Having just put new studs and nuts on a big block and then removing some from the small block I would say that the old small block ones required more torque all the way out. They are different in shape and were uniformly more resistant to turning than the new BB units IMO.
John

[Clem Z.]

i always locked them using a "pal nut"

and they stayed tight

[Clem Z.]

to use "posilocks you must first machine the

tops of the studs flat so the set screw has a good place to grip. set the lash .003/.004 loose,thighten the set screw, then just turn the posilock to get the proper lash setting. never had one come loose even in the daytona 500

[Verne Frantz]

Always used that method with No Problems *NM*

[Joe L.]

Re: to use "posilocks you must first machine the

clem-----

The step you describe is ABSOLUTELY necessary if "posi-lock" type nuts are used with STOCK GM rocker studs. Otherwise, you absolutely CANNOT use "posi-locks" with these studs without risking virtual certainty of the nuts loosening in operation.

The alternative, though, is to use ARP rocker studs. These studs are pre-machined to provide a perfect bearing surface for the posi-locks. Using the ARP studs is a convenient way to obtain the proper bearing surface. Plus, you get stronger and higher quality studs in the process. The ONLY way to go (as long as the rules for a racing application allow it).

Conversely, and a lesser-known fact, ARP studs should NOT be used with OEM-style, self-locking nuts. ARP specifically recommends against this and I totally agree with them.

[Mark S. Lovejoy]

So ARP Studs....

Require Posilocks? Or am I reading this wrong? ARP makes a self-locking nut?

[Joe L.]

Re: So ARP Studs....

Mark------

ARP studs do require the use of posi-locks. They don't have to be ARP posi-locks, though. ARP does not manufacture OEM-type, self-locking type nuts for rocker arm applications.

[Mark S. Lovejoy]

Re: So ARP Studs....

Joe,

Do you know if posi-locks will fit under stock BB valve covers? I have two sets and they both have drippers. I'm worried about interference.

I posed this question to ARP's tech line and they didn't know.

Thanks,

Mark

[Joe L.]

Re: So ARP Studs....

Mark-----

It depends on the posi-lock. The ones that are supplied with Comp Cams Pro Magnum Roller rockers fit with no interference, at all, with big block valve covers WITHOUT drippers. I tried them with big block valve covers with drippers, too. They seem to fit ok, but it might be necessary to use 5/16" thick valve cver gaskets.

Some of the other posi-lock nuts (like ARP) are taller than the Comp Cams versions. I don't know if they will fit, or not.