Engine Setting Up Your Valvetrain GT40P 302

ZephyrEFI

Member
Mar 9, 2019
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Shakopee, MN
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:

View: 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.

Dv5r5sj.jpg


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:

View: https://www.youtube.com/watch?v=76wbtu9l09A


View: 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.

View: 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...

View: 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.

I am still early in the process, but I have tried rolling a couple of patterns on the valve tip.
p9uXJTY.jpg


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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ZephyrEFI

Member
Mar 9, 2019
53
11
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Shakopee, MN
Yeah, it was helpful, thanks!

I especially like this portion from the pedestal mount rockers instructions page:

"Step 5: Turn the bolts by hand until there is no clearance between the roller and the valve stem (make sure the pushrod is seated in the rocker arm cup). Slowly torque the bolt to 18-20 FT-LBS. Since you are pushing down the plunger in the hydraulic lifter as you torque the bolt, it will probably take a minute or two to complete the procedure. The bolt should have turned between one-quarter to one full turn to reach the torque setting. This will give the correct lifter preload of .020" to .060". If the bolt turned more than one turn, you will have to shim the pedestal (use Ford Racing Performance Parts shim kit M-6529-A302). NOTE: M-6500-A301 anti-pump-up lifters only need .020" to .030" preload. If the bolt turned less than ¼", you will have little or no lifter preload. The solution for this is longer pushrods. These are available from a number of companies, such as Crane Cams Tech Line (904) 258-6174. There are many modifications that may have been made to the engine which will change the lifter preload, such as valve jobs, different cams, different thickness head gaskets, head milling, etc. It is a good idea to check the rocker arm pattern on the valve stem tip. Use a felt tip marker to “paint” the tip. Then, with the rocker arm in place, turn the engine through two revolutions. Remove the rocker arm and inspect the pattern. It should be nearly centered on the tip. If it appears to be too close to the edge of the tip, call the Ford Racing Tech “Hot Line” for assistance. Note: The lifter preload may be different between the intake and the exhaust or between one side of the engine and the other. Therefore, you must check lifter preload on each rocker arm. "

No mention at all of farting around with rocker angles. I also emailed Scorpion themselves. They had this to say:

"We only use the half lift method to verify proper geometry on solid lifter and shaft/stud mount applications. With regards to pedestal mount rocker arms, we recommend checking for proper lifter preload, as well as checking the witness mark on top of the valve (left by the roller). To do this, just blacken the valve tip with a sharpie/permanent marker, install the rocker (with a lifter pumped up) and roll the engine over several times, remove the rocker and check the witness mark. The witness mark should be no larger than 0.080", and should be close to centered on the valve. The best way to determine proper pushrod length (to achieve the required lifter preload and pattern on valve) is to use an adjustable checking pushrod. You can purchase these through any retailer (Jeg's, Summit, etc.), and they are relatively inexpensive. You will have to remove a valve spring and install a checking spring (included with some adjustable pushrod kits, also sold by themselves in pairs), full spring pressure can bend the adjustable pushrod tool, as they are made of aluminum. You can also start with a stock length pushrod and see where that puts you as far as preload and pattern on valve. Just let us know if you run into problems with this method, or if something checks out of spec."

Another major consideration here is that I ran these heads before with stock pushrods and rockers with no problems. The pedestals and valves have not changed since that time. This rocker geometry thing just has me overwhelmed at this point mostly because I'm getting results I shouldn't be. It just doesn't make sense, and it keeping me from figuring out anything else.
 
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