So, here's what I've got. It's a new rebuilt shortblock 306 with my previous GT40P heads I had on my old engine. We're going to a new Flowtech cam, new beehive valve springs, and Scorpion pedestal mount roller rockers. So, we need to figure out how long of pushrods I need, how to get proper rocker arm geometry, and shim the rockers for the consistent/balanced lifter preload. I tried starting with rocker geometry using the Half Lift method, outlined in this video:
https://www.youtube.com/watch?v=o5is9BsH5OU
BUT, when I would go to try and get the rocker level with the valve retainer, I could barely even make that happen with the rocker mounting bolt just barely biting. It may not have even been level at that point, I'm not sure. But anyway, I moved on from there. Half lift on my cam is .275". Thread pitch on the 5/16-18 bolts is .055. So that comes out to 5 turns of the bolt. When I turn the bolt 5 turns (which really isn't enough thread biting), the rocker is a good .130" from the pedestal.
Every video I've seen of this method uses stud mount rockers. Is this even a thing you can do with pedestal mount rockers? Do stud mount rockers not even sit down on something? Do they just sort of float there on the stud? I wouldn't know, I've never even seen them in person, let alone worked with them. Two more handy videos on pushrod length, but with stud mount rockers:
https://www.youtube.com/watch?v=76wbtu9l09A
https://www.youtube.com/watch?v=5MjAxnGeGKw
Setting up where the middle of the rocker sits with pedestal mount rockers (with shims) seems to be more about getting proper lifter preload at mounting bolt torque than at what angle it does what, like in this video.
https://www.youtube.com/watch?v=pJSj-3XS8ts&t=1s
That guy seems to already have to correct pushrods to work with, lucky bastard. So, there's another nice technique that I don't feel like I can rely on because my situation is different.
Apparently if I had a small block chevy though, figuring out my pushrod length would be as easy as slapping on of these guys on there...
https://www.youtube.com/watch?v=UBO-Mgp0Og8
But again... the easy way is not for me. According to a customer question on Summit, these DO NOT fit Fords. Of course they don't.
I am still early in the process, but I have tried rolling a couple of patterns on the valve tip.
The first was too low on the tip, as well as too long (the roller rolled too far). I did this one with the .130" in shims (too much) the Half Lift method told me I needed. According to the pedestal rocker video above, Ford says you can only have up to .090" total in shims on a roller rocker. On a whim, I thought I would also try rolling one with a not so crazy .040" shim in there. For the pushrod length, I lengthened it until it was at zero lash with the rocker snugged down and then torqued down the rocker. For that test, I got a nice pattern right on the middle of the valve, but it was still too long. I should mention too, I was using a solid lifter for these. The pedestals have not been machined, they are stock height, and I believe the valves are stock height for the intake, and very close to the same for exhaust. The installed height of the springs is 1.825. I was using check springs for the tests though.
Then I thought with that setup I could try a piston to valve test. I got .230" for intake. Does that sound reasonable? I know my pistons have some pretty big valve reliefs...
Anyway, what would you do in my place? How would you figure out your pushrod length? I should mention the original pushrods will not work. They are too short (which is weird too). I just hate the fact that the Half Lift method got me results that are far from what they should be. Today I was at the point where I was just trying things at random....
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