This will probably be a novel, but please bear with me. I do not want to ruin this new engine.
I am rebuilding my 400 for my '78 Bronco. Bored .040", crank .010"/.010", stock pistons, heads ported and surfaced, all new valves and springs, block decked to make compression (~9.2:1), custom ground Comp roller cam (208°/216° @ .050", .577"/.589" at the valves), stock replacement Ford roller lifters, Scorpion roller rockers, Performer manifold and carb (600 cfm), and 1 5/8" headers. I have learned everything I know about the 335 series engines out of this forum and really appreciate the guys that share thier knowledge to help others.
Here's my dilema. I think that I am going to have to make a comprimise between proper rocker geometry and lifter preload. I bought a couple of shim kits from Crane to be able to space the rockers up properly so that at mid-lift, the roller tip of the rocker was exactly in the center of the valve stem. It takes a lot of shim to get them up there. 4 thick ones to be exact. That much shim brings my pedestal-mount rockers up to where the "step" that is built into the pedestal no longer aligns the rocker with the valve stem. If I align it and then tighten the bolt down, it looks great, but I am pretty sure it won't stay aligned since the positioning of the rocker is determined solely by the bolt through the rocker, without the aid of the "step" in the pedestal to keep it aligned.
So, I knew to run these rockers that I have purchased, I would have to run less shim under them in order to get them down in the "step" to keep them aligned with the valve stem properly. I determined that 2 thicks and a 1 thin gave an acceptable compromise between rocker geometry and depth in the "step" in the pedestal. That shim combo located the rocker good left to right and at 0 lift, the roller tip on the rocker was probably 1/3 of the way across the valve stem. At less than 1/4 lift, the rocker was over the middle of the stem and stayed that way through full lift. No problem I thought.
I made an adjustable pushrod, and through trial and error, determined which length to order to give me an average of .035"-.050" of lifter preload (9.050").
Well, I got my pushrods today, and went out there and threw one in. Here is the problem. With the 2 thick and 1 thin shim as I had determined that I need to use, I got about .060" of preload in the lifter. Crap. No choice but to add more shim to get the preload back up to where I think it should be. I pulled the thin shim and added a thick (3 thick shims now). The preload was at .035" and the roller tip looked good on the stem

Here are my questions I guess: Since they are roller tip rockers, should I concentrate more on getting the tip just right on the stem, or go with a little less perfect alignment up there to use less shim in order to keep the rocker better located in the pedestal? I don't want to wear out the guides prematurely, but I also don't want a rocker to become misaligned and get off of the stem. Also, I am not sure how much preload I need in the lifters and what the advantages/disadvantages are to being closer to either end of the tolerance? What range should I stay in as I shim the rockers to set the preload?

Any help on this would be greatly appreciated. Again, sorry for soaking up the bandwidth with my long-winded explanations.

 

Are you sure the springs are the right height? You should be able to get the rockers to traverse the valve stem properly without much of a shim at all. Check the head dimensions to make sure that all of the dimensions are correct. The valve spring seats may have been machined also.

 

I assume that everything is correct. The guy that did my machine work is a dyed in the wool Ford man about 70 years old and he has been doing this all of his life. I know that we used stock replacement valves and he set them all to the same installed height when he did the seats. They looked correct when looking at them from the chamber side and all of the stems are the same height when you lay a straight edge across the top of them.

 

I guess if I use the rockers and pushrods that I have, the only adjustment in the rocker alignment is going to be more or less shim, and that is going to change the preload in the lifter. What "range" of preload should I be shooting for?

 

Take out all the shims and check your valve tip alignment. Then re-measure for pushrods. Something is way wrong for it to be that far off. Your pushrods should be shorter than OEM units. On second thought with the roller lifters you can't compare at all.

 

Yeah, the roller lifters stand quite a bit higher out of the lifter bores, which makes for a shorter pushrod. The stock rods are supposedly 9.500" long. The adjustable pushrod I made ended up being .415" shorter than the stock ones, so I assumed it was 9.085". I don't have any calipers that long to verify.

If I install the rockers with no shims, the roller tip is close to the back edge of the stem at 0 lift. At maybe 1/2 lift (~.300" at the valve), the roller tip is a little more than 1/4 of the way across the stem, and at full lift, the tip is about in the middle of the stem.

As I add shims under the rocker, that geometry gets better and better. 4 thick shims makes it beautiful throughout its full travel, but brings the rocker up completely out of the notch in the pedestal so that there is nothing to keep the rocker from turning sideways off of the stem (other than the bolt that holds it on). 2 thicks and a thin seems to be the best compromise between geometry and still being down in the notch a little to hold the rocker in position.

Since I now have my pushrods in hand, when I put one in with 2 thicks and a thin, I ended up with about .060" of lifter preload. If .060" is acceptable, then I am probably o.k. If I need less preload, I am going to have to shim, which gets me back into that gray area of "sort of" being deep enough in the pedestal notch to keep the rocker located.

 

Are you using checking springs when your trying to figure pushrod length ?

 

I agree with Eric (Torque1st) that your problem is most likely the pushrods. If your caliper isn't big enough to measure the pushrod length, get a bigger caliper or ask your machinist to measure it for you. With a non-adjustable valve train, pushrod length is critical.

The only reason to use shims is to adjust the lifter preload (i.e., compensate for minor inconsistencies in valve train lash), and even then, you should use only the minimum necessary. Do not use shims to adjust the rocker/valve tip geometry!

Is the problem actually in the pedestal-to-valve stem measurement? (That is, can you verify the geometry problem with no pushrods?)

Assuming the rocker/valve tip geometry is incorrect when checked without pushrods (thereby eliminating the pushrod length variable from the equation), then you have two alternatives:

1. Get lash caps for your existing valves, and have your machinist custom fit each one to get the correct geometry.

2. Get new custom valves with over-length stems, and have your machinist cut each stem individually to get the correct geometry.

So why would you need to do this? Because even though everything appears to line up by eyeball and by straight edge, the manufacturing tolerance in the pedestal machining is sufficiently large that you need to custom fit each valve with the rocker to correct the inaccuracy. Obviously, this approach requires each pushrod to be measured and fitted individually to maintain the correct geometry.

Is this really necessary? Maybe, but only if your particular heads happen to be victims of the "maximum" tolerance. Otherwise, you might be overly concerned about the precision of the valve train geometry in a non-racing engine. That's your call.

 

Mark: I did use very light checking springs when determining pushrod length and cycling the rocker through it's travel.

Bubba: Your response is very interesting. The problem is there without the pushrod ever being in the equation. If you set the heads up on the workbench, install a rocker onto any pedestal and snug down the fulcrum bolt that holds it in place, then get down and look at it from the side, the tip of the rocker is close to the rear edge of the valve stem. If you start loosening the fulcrum bolt while pulling up on the rear (pushrod end) of the rocker, the alignment looks a lot better when you get maybe 1 to 2 turns out on the retaining bolt. Therefore, it was taking too much shim to get the rocker up high enough to make the geometry look good.

That can only mean 2 things: Either my valve stems are up too high or my rockers are too short. Since the rockers are marked 1.73, I have to believe that my valve stems are up too high. I remember the guy that I ordered the Comp cam through told me to let him know the installed height of the valves so that he could send me the proper springs. The installed height that the machinist told me to tell him was 1.9".

It is pretty obvious now that I look at it in those terms that if my valve stems were shorter, then the alignment would be better. That sounds like it could get to be a nightmare. Different valves, different springs, etc.

I guess I have to work out the geometry issue, then re-measure for pushrods once I have that corrected, huh? One thing that no one ever addressed: How much lifter preload should I be shooting for when I get to that point?

 

Lifter preload should be specified by the lifter manufacturer. Use the manufacturer's recommended preload.

After everything else is set up correctly, measure the pushrod length with the lifters at the correct preload. That's how you determine the necessary pushrod length.

In a non-adjustable valve train, pushrod length (and shims only if necessary) controls lifter preload.

If you haven't already, try this technique for checking the rocker/valve geometry:

http://www.barkerengines.com/tip050102.htm

This is a more precise way to check where the rocker is contacting the valve stem tip, and you can compare one valve (or rocker) to another for variations.

 

So in order to get this right, I need to install shorter valves, which in turn means I may need to install different springs to have the right spring pressure since I will have less installed height. Then when all of that is accomplished, I need to get the correct length pushrod so that I get proper preload with very little or no shim.

Looks like I will not be dropping her in the Bronco this evening!

 

What not just buy the crane adjustable set up ? You will be a lot better off.

 

I appreciate all the help from you guys. I was almost ready to start throwing a bunch of shims under the rockers to get it right. I can just envision a rocker getting off to one side, mashing down the retainer, the locks flying out, and the valve dropping into the cylinder.

That would be known as "The cuss heard around the world"!!!!!

 

The "installed height" refers to the height of the valve spring, as measured between the bottom of the retainer and the top of the spring seat. It is determined by the location of the retainer lock groove(s) on the valve stem, the type of retainer and locks, and the position of the valve spring seat on the top of the head.

Of course, with stock-size valves, the location of the retainer lock grooves is also relative to the position of the valve seat. If the seat is recessed in the head, the lock grooves will be located farther above the spring seat, increasing the spring's installed height.

You can get custom valves with different stem lengths, and with or without retainer grooves. If you get them without grooves, you can cut the grooves wherever you want (and thus specify the spring installed height that you want).

If you shorten your existing valves by turning down the tip of the stem, it will not change the position of the retainer grooves, and therefore, it will not change the spring installed height.

If you have to cut grooves lower on the stem of custom valves (to get things to fit), you can machine the valve spring seats on the heads to lower them a corresponding amount, and maintain a standard installed height.

 

I think I may have found the problem. I believe that I have the wrong rockers. I have part# SCP1024, which according to the Scorpion catalog that came with the rockers, are for the 429/460 (pedestal mount). It lists a part# SCP1092 for the 351C/351M/400 (pedestal mount). I guess that I will have to wait until Monday and call them up to see what the difference is. They are both 3/8" pedestal mount 1.73 ratio rockers. There must be some differences in the trunion and rollere tip height?