Rocker Arm Technical Help

jtfairlane

New Member
Mar 5, 2006
468
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Somebody stick this in the useful technical thread index please.

There are a lot of people out there giving bad information about how to install rocker arms. After answering many of these questions, I am convinced that rocker arms and the valvetrain in general is one of the most commonly misunderstood things in all of Stangnet. This is not meant to be a be-all, end-all explanation of rocker arms, just something for beginners who need a starting point.

Rocker Arms 101:

There are three main styles of rocker arms used on small block ford heads. These include pedestal mount, stud mount, and shaft mount. I don't care what anyone tells you, none of them are just a bolt-on-and-go deal.

Pedestal Mount: Pedestal mount rocker arms are the type of rocker arm most commonly found factory installed on late model 5.0L engines. On most standard 5.0L engines, the rocker arms were plain old stamped steel. The 1993-1995 Cobra 5.0L engines received pedestal mount Crane 1.7 ratio roller rocker arms. All pedestal mount rocker arms are fastened to the cylinder head with a small 5/16" bolt. There are many performance pedestal mount rocker arms available, but of the three types of rocker arms, the pedestal mount is considered the weakest because it is held in place with the smallest fastener.

A couple examples of pedestal mount rocker arms:

Factory:
p67255_image_large.jpg

1993-1995 Cobra/Crane 1.7 Ratio:
cranerockerarms_md.jpg

Ford Racing:
rollerrocker.jpg


Pedestal Mount Installation Instructions: Only after you have ensured that you have the correct pushrod length, confirmed whether or not you need shims under the pedestals, that the rocker arm tip is centered on the valve stem tip, are you ready to install your pedestal mount rocker arms. One cylinder at a time, turn the motor over until that cylinder is at TDC on the compression stroke, and then slowly torque the rocker bolts for both rocker arms for that cylinder to 18-20/ft lbs. Pay attention to your torque wrench while you do this. You should be able to turn your torque wrench 1/4-1 full turn before it clicks at 18-20/ft lbs. If it clicks before 1/4 turn, or after 1 full turn, than you either have the wrong length pushrod or need to shim the pedestals and you need to figure out which before you start over.

For more comprehensive pedestal mount rocker arm instructions, please READ: http://cranecams.com/pdf/453e.pdf

Stud Mount: Stud mount rocker arms were factory installed on 1963-1968 Ford 289s, and early 302s any many other early engines. Most (not all) factory ford heads that came with studs were press in studs, which are not desirable for performance since those types of studs tend to pull out at high rpm with agressive cams and stiff valve springs. Screw-In Studs are the only type of stud used in performance aftermarket stud-mount heads. All small block ford 289/302 engines originally equipped with stud rockers had 3/8 studs. 3/8 referring to the section of the stud the rocker goes on. Studs commonly used in performance small block ford heads are available in either 3/8" or 7/16", both of which have a 7/16" thread that goes into the cylinder head's stud boss. Whenever you hear someone referring to a 3/8" or 7/16" stud, they are referring to the "top part" of the stud that the rocker arm goes on. The thicker the stud, the less prone they are to valvetrain flex. At high rpm, even studs can flex almost like trees in a windstorm. You can convert a head with 3/8" screw-in studs to 7/16" screw in studs without machining, but you will need different rocker arms since rocker arms are stud size specific, meaning you couldn't use a rocker arm for 3/8" studs on a 7/16" stud and vice versa. Stud mount rocker arms can be attached with a nylon lock nut or a poly lock. Poly locks are preffered because they are less likely to back the stud out of the head than nylon lock nuts are. If you have a really high revving motor, you can also tie all your studs together for increased stability with a stud girdle.

A couple examples of stud mount rocker arms/parts:

Factory:
interchange17.gif

interchange18.gif

Screw In Rocker Studs:
rocker_studs.jpg

Comp Cams Magnum Roller Tip with Lock Nut:
comp_cams_1417-16.jpg

Crane Gold Race with Poly Lock:
Rocker%20Arm%20Stud%20Mount%20Gold%20Race%20Alum%20(All%20PNs).jpg

Stud Girdle:
csp-g4402_w.jpg


Stud Mount Installation Instructions: Stud mount rocker arms, just like any other rocker arm, require correctly measured pushrod length and correct valvetrain geometry. To install them, you need to turn the motor over by hand in the direction of engine rotation. With the intake off, you can watch the lifters. When the exhaust lifter for a particular cylinder just starts to come out of its bore, you can now adjust the intake rocker arm for that cylinder. Why? Because if the exhaust valve is just opening, the intake valve is closed and on the base circle of the cam, where we need it to be to adjust it. After you've adjusted the intake valve, keep turning the motor over by hand and watch the intake lifter, once the intake lifter has come as far out of its bore as it can (max lift) and then starts going back down, pay attention. When the intake lifter reaches 1/2 way to 2/3 of the way back down, you can stop and adjust the exhaust rocker. The typical adjustment procedure is to spin the pushrod in your fingers as you tighten the rocker, when you start to feel resistance on the pushrod, the slack has been taken out of the pushrod and you are at zero lash. Make a 1/2-3/4 further of a turn on the lock nut or poly lock once you have done this (if using a poly lock, don't forget to tighten the allen head screw).

For more comprehensive instruction, please READ: http://compcams.com/Technical/Instructions/Files/151.pdf

Shaft Mount: Shaft mount rocker arms are by far the most expensive type of rocker arms you can buy, and were never factory equipment on 289/302 based small block fords. There are a number of aftermarket manufacturers that make shaft mount rocker kits for popular small block ford heads, such as the Trick Flow Twisted Wedge, AFR 165/185/205/225, etc. They are the absolute best for valvetrain stability because they tie the rocker arm bodies together, and are even more stable than a stud girdle setup. The stands that the shaft mount rocker arms ride on are fastened to the cylinder head stud bosses where the rocker studs used to be, and the shaft mount rocker arms are then fastened to the stand. For extremely high revving race motor with only the best parts, there is no substitute for a shaft mount setup. Consider this: most factory muscle cars with big block engines, such as the Ford FE, Hemi, etc. came from the factory with shaft mount rocker arms. Shaft mount rocker arms for SBF's are available from Crane, Jesel, Comp, Harland Sharp, and others.

A couple examples of stud mount rocker arms:

Crane Shaft Mount:
craneSportsman.jpg


Jesel Shaft Mount:
new_products_ss_shaft_rocker.jpg


Shaft Mount Installation Instructions: Just like with any other rocker system, you need to check to see if the rocker stand that the shaft rockers are mounted to need to be shimmed, and you also need to measure for proper pushrod length. The installation procedure is essentially identical to stud mount rocker arms, in that you turn the motor over by hand and adjust each rocker arm when its cam lobe is on the base circle. You also have a lash adjuster on the top of the rocker arm body that works in a semi-similar fashion to a poly lock that you would normally find on a stud mount rocker arm.

An example of Shaft Mount Installation Instructions: http://www.jeselonline.com/docs/instructions/INS-SS0051.pdf
 

Foxfan88

My Grandpa has great wood.
Sep 13, 2004
2,487
4
0
good info! a question though. is there any drawback to adjusting the rockers when a cylinder is on its compression stroke and both valves are shut and the lifters are at the bottom, and are on the base circle. this is how i adjusted mine and it seemed to work fine.
 

Fast63

New Member
Sep 20, 2007
717
0
0
good info! a question though. is there any drawback to adjusting the rockers when a cylinder is on its compression stroke and both valves are shut and the lifters are at the bottom, and are on the base circle. this is how i adjusted mine and it seemed to work fine.

No, there is nothing wrong with what you did, that's exactly what I do. This thread has decent information, but IMO, the OP is ignorant to all methods of adjusting and thinks the way he does it is the only good way.
 

jbernard

New Member
Jul 22, 2014
1
0
1
I have a question that I hope can be answered here on stangnet. okay so I have a 90 5.0 that's been mildly built, e cam,24lb injectors, gt40 intake ,gt40 aluminum heads etc. so the problem is I have these heads that have been milled to 56cc, since they were milled I had to buy shorter pushrods and I am using the stock rocker arms. I have been told by local performance shop to adjust the rocker arms only to 1/4 turn, so to achieve this I had to shim all the rocker arms. but the problem is the car taps like crazy. when I take the shims out I get about 1 full turn so according to this thread that should be okay. I just wanted to know if you guys thought that would be okay with my set up and if it would stop the tapping, also what is the difference between the 1/4 turn and 1 full turn like am I going to lose horsepower or what is it actually doing to the engine.
 

mikestang63

SN Certified Technician
Aug 27, 2012
11,291
8,777
214
I assume these are pedestal style rockers. The reason for the shorter pushrods is to compensate for the milled heads- in order to achieve the same proper valve geometry and also so the rocker contacts the valve tip in the middle of the stem. The shims are to achieve proper preload of the lifters, not to achieve proper valve geometry.

You need to adjust the rockers when the cam lobe for that cylinder is on the heel or lowest level. On pedestal style rockers you often do need to use shims to achieve proper preload- sometimes none, sometimes different size shims and the intake and exhaust side will differ as well. Anywhere from 1/2 to 1 turn preload on a street car is fine. 1/4 turn is too loose IMO, that is for racers who want less preload as they hit hi rpm's and have much higher cam lobe profiles . You will lose no HP. Don' go back to that local performance shop.

http://www.cranecams.com/uploads/instructions/453e_.pdf