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valve adjustment
I'm putting the newly reconditioned heads back on my '69 351 Windsor and I've gotten a variety of advice on how best to adjust the valve lash. I have the stock, cast rockers with a ball-type pivot and they mount on a stud with a beveled shoulder.
Some have said to simply tighten the nut down on the stud and forget it. But that seems to hold the valve open slightly, even with the lifters clearly on the cam's base circle. Others have said to take clearance down to 0, judged by spinning and jiggling the pushrod and then tighten 1/2-3/4 turn. Input, anyone? |
What kind of lifters do you have? Are they oem, or are they anti pump up, solid or hydraulic? Many choices.
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What you are describing is stock non-adjustable rockers. If the machining was correct or the heads have not been surfaced to many times these are just tightened down to torque specs. If tightening down keeps the valves open you may have to buy a comp cams adjustment conversion kit.
Comp Cams Rocker Arm Adjusting Nuts & Kits - JEGS |
BrandX, the lifters are stock-style hydraulic Edelbrock units.
Thanks for weighing in, Wbulk. I figured the shouldered stud meant to torque 'em down, but I couldn't have the valves hanging open. I just had new exhaust valves and seats installed. I know the heads have been milled twice just since I've had them-just enough to clean them up, mostly. Maybe I should expect this with 44 year old heads. I suppose I need to check the geometry and see if shorter pushrods are indicated. |
I'm far from an expert in this topic, so take what I say with a large grain of salt. But I had to learn about this to deal with a problem last year. What I think I know is this. If everything (e.g., lifters, push rods, valve stems, head thickness, etc.) is exactly the right dimension, the lifters will achieve the desired preload exactly when the nut that holds the rocker on the stud reaches the torque required to hold the nut in place. If that combination of events does not occur simultaneously, one method of adjusting the geometry is to get a different length pushrod. But the new pushrod has to be exactly the right length. .. However, I heard of another solution that seems far more certain to me. Someone sells an aftermarket stud with a lockable nut. This allows the nut to be tightened until the lifter preload is correct, and then the nut is locked in place to secure the rocker. I don't recall the name of this aftermarket product.
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How many turns of the nut to achieve the desired preload vs. torquing til the assembly is seated? If the lifters are full of oil it is possible they will hold the valve open a small amount til the oil is bled off.
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The adjusting nuts do seem to be an easier and, probably, cheaper alternative than getting 16 pushrod lengths right on the money.
The number of turns needed to seat the nut on the stud varies somewhat, since the exhaust valves and seats are new and the intakes were re-faced. Thanks for your opinions, guys. |
Shorter push rods would solve the lifter adjustment, but I'm not sure the rocker would center over the valve stem correctly.
I am not certain that the locking adjusting nut would work well with the factory sled type rockers either. Wish I new for sure one way or the other. Give a look at roller rockers. I think there are some inexpensive stamped steel designs that are not full rollers, all the way to high dollar stuff that an all out race engine doesn't need. You need the guide plate with rollers and they require hardened push rods. You may need different length push rods to get the roller centered on the valve stems. If your setup already has the guide plates, it's possible your already set. Rollers are a better design. |
One thing to remember is ford at one point changed the style of heads. I do know the 68 302 was an adjustable type like the early chev rockers. I also know the 1976 302 was as you are describing as non ajustable. I do not know when the change occurred or if there is a difference on the 351 heads.
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You can tell by looking at the rockers, the head, and the shoulder on the stud. The rockers for non-adjustable are rail rockers. The rails ride on the sides of the stems to keep them centered. The older heads had slots in the heads that kept the push rods in the right place and no rails on the rockers.
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