Note On Shimming Pedestal Rockers

John Dirks Jr

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Some of you know after milling my heads .030 I shimmed the pedestal roller rockers to gain proper lifter preload. The process went well and all is fine but I wanted to point out a conflict in the installation instructions that came with the Ford Racing rocker kit (which are actually made by Crane Cams).

Just to preface, the Ford kit came with shims but I did not realize it. Because of this, I bought a shim kit boxed in Crane Cams packaging as well and I'm glad I did.

The instructions in the Ford kit basically said to shim the rockers individually as needed. The instructions in the Crane shim kit were different. They said that because the 302W engine uses steel bridges between the intake and exhaust valves for each cylinder, you "must" put the same amount of shims under both valves of any given cylinder. They said that unequal shimming across a single bridge would cock the bridge deck and cause problems. When I read this I totally understood. Again, I'm glad I didn't realize the Ford kit had shims and bought the Crane kit which warned me of this potential problem. I think Ford needs to correct or clarify their instructions in this kit to include "bridge pivot" style applications.

Incidentally, as I did my installation I was discovering that .060 shims were the ones on each cylinder that brought me in the middle of the spec range for preload. After about half way through the process, for a second or two, I was tempted to slap the rest together without even checking but I ditched that silly idea quickly. I'm glad I did because the very last valve I checked (intake for #1 cyl) would not achieve adequate preload with the .060 shim. So, cylinder #1 got .030, all the rest got .060. All valves (with exception of cyl #1) are now at 1/2 turn down from zero lash to bolt tq specs. On cyl #1, the intake is 1/2 turn and the exhaust is 3/4 turn. So, obviously there's a machining difference in the intake position for #1 cyl. In asking around, I've been told it's not uncommon.

If any of you are wondering why I did cyl #1 last, it has to do with my preference in adjusting valves. I don't choose to do any cylinder first or last. It just depends on what position the rotating assembly is in when I begin the process. Of the various ways to do this, here is the process I like to use, especially if the intake manifold is not on the engine.

I simply look at which lifters for a given cylinder are all the way up (on lobe). When I see this on a given cylinder, it means that the other lifter for that same cylinder must be somewhere on its base circle and in position for adjustment. Its the quickest, easiest and most fail safe method in my opinion.

Here are the instructions for the Ford boxed kit and the Crane Cams boxed kit. Read them over and tell me if you don't see the same conflict I do. The Ford instructions fail to mention "bridge pivot" style such as common on the HO 5.0 in stock form.

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Gearbanger 101

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I think you're a little confused regarding the instructions. They state the shims must be equal in thickness with "bridge pivot" style rockers arms....which our heads do not use (it's more of an Oldsmobile thing). You're confusing this with the "fulcrum guide plate". Two totally different set ups.

This is a "bridge pivot" style plate...

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...and this is a standard pedestal fulcrum guide plate.

RockerArmGuide__54662.1306473176.1280.1280.JPG


The bridge pivot design requires the shim to be placed under the mount, between the pedestal and the bridge plate, because they aren't designed to allocate the shims in place above the plate the way the pedestal guide plates are. Thus the reason the two shims would have to be the same thickness.

The pedestal style guide plate (which is utilized in the 302/351W set up) is designed to locate the shim above the plate, allocating it between the plate and the pedestal stand (or fulcrum) and not between the pedestal and the guide plate like with the bridge pivot design.

Because the pedestal guide plate is designed in this manor, there is no way to "cock" the rocker geometry to one side and damage the pedestal as it's noted in the above instructions. The plate itself always remains flat and fixed to the pedestal at 180-degree's, no matter how many shims are stacked under the fulcrum and therefore is not creating any alignment issues and thereby not placing any additional stress on the pedestal.

In short....using two different thickness shims is just fine with the standard Crane Pedestal mount set up. Many do so to compensate for differences in valve install height, or seat wear. This is one of the main benefits of the design. My guess is that Crane just included this as more of a "footnote" intended as a general instruction for a broad range of rocker designs. Though it's not specific to this application.

So if I were you, I'd check the pre-load on the lifters of that cylinder again. Because unless you've got any abnormal wear on one or the other, you might find one of the two push-rods to be a little tight side (not allowing the valve to completely close), or a little too loose side (causing a rattle and additional wear on the end of the push-rod) as a result.
 

John Dirks Jr

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Brian, thanks for clarifying that. I now have a better understanding. By bad. In the end, all of my set preloads are well within specs. Any change I made now would only be to one of the valves. The change would reduce the preload only 1/4 turn. On that valve, it's currently 3/4 turn which is well within specs considering the max load would be 1 full turn.

The valve train is quiet and the car runs great.
 

Gearbanger 101

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I'm pretty sure the pre-load on the lifter is supposed to be in the .040-.060 range...so you've probably got a little room for error in any case. You'll know if it's out. Idle will be rough and compression will be low on the cylinder if the pre-load is too much and the rocker will rattle (especially at cold start up) and clatter under acceleration if it's too little.

Since it seems to be running smoothly and quietly, you're probably within range.
 

John Dirks Jr

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You made me think about doing #1 over again. As it is now, all valves, with exception of exhaust #1, are torqed to specs about 1/2 turn down from 0 lash. The exception is exh #1 is 3/4 from 0 lash. If I put a different shim in that position it would put it at about 1/4 down from 0 lash. That would be close to minimum preload. With parts wearing over time, that valve could get noisey. I would rather have some extra preload in the bank than be at minimum from a starting point. I'm gonna leave it as is.

Thanks again for pointing out how I misunderstood the concern related to the installation instructions. I now understand that the kit boxed under the Ford icon would not need the bridge pivot language in the instructions since that style does not apply to Ford engines. And the Crane shim kit instructions are not specific to any particular make of engine, so they include the concern regarding bridge pivots.