Patriot 320 Followup and rocker geometry 101
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Patriot 320 Followup and rocker geometry 101

  1. #1
    steelcomp was here
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    Arrow Patriot 320 Followup and rocker geometry 101

    Here's a quick run down on properly determining pushrod length that I hope is helpful. This is also a follow up on the Patriot 320's and some of their issues.
    IMO valve train geometry is way overlooked by even some of the most professional builders, and there's some real misinformation regarding determining proper pushrod length and it's relation to rocker geometry.
    The only way to determine proper pushrod length is to check your rocker and it's relationship to the valve at mid lift. Period. This can be done during mock up, but better done after complete assembly with the full valve train. Pushrods should be the last thing you order for an engine since there are so many variables that effect pushrod length. You want to be at a point in your build where you're not going to be changing anything like deck height, head surface, valve depth, or even your cam. Now I realize that some of this may be splitting hairs to some, and like everything else it needs to be kept in context, but this is what's involved.
    First, set up a dial indicator on the cyl head so you can measure actual lift at the valve. Be sure your indicator is on the same angles as (parallel to) the valve, or your readings will be off.



    Install whatever pushrod you're using or checking, or your adjustable pushrod set to as close as you can to whatever length you think you'll need, set your lash accordingly and then rotate the engine and measure total lift. Divide your actual total lift by 2, then rotate the engine again until you're at that half-lift number (called mid-lift). What you want, ideally is, for the rocker to be at 90* to the valve stem at mid lift. By the rocker, I mean the line that represents the center of the rocker, from the center of the trunion, through the center of the roller tip.
    If your pushrod is the right length, this is what you'll see.



    This is NOT what you want to see:
    This is the Patriot head using a 9.400 ex pushrod (.100 longer than they recommend) with a new Isky 1.7 BB Chev rocker. Using the retainer as a reference to 90* to the valve, you can see the line through the rocker's center lines is no where near 90* to the valve stem. The pushrod is way too short, and only netted a valve lift of .603". With a lobe of .390, and a rocker ratio of 1.7, less .025 lash, we should be somewhere near .638, less cam deflection.



    I determined that the patriot head needed an ex pushrod length of 9.77" - 9.78". Patriot recommends 9.35" for their exhaust. I also believe I'm using an ex valve .100 shorter than what they recommend. With their longer ex valve, the rocker would have to sit that much higher and the problem would be even worse. Here's the Patriot head with the longer (correct length) pushrod. Again using the bottom of the retainer as a reference to 90* to the valve, you can sse this is very close. There was so much added lift gained by the proper length pushrpod that these actually turned out to be slightly long (by about .020")
    This same rocker, same lash, with this pushrod netted a lift of .638".

    Last edited by scott foxwell; 08-08-2009 at 02:37 PM.
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    steelcomp was here
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    continued:
    Unfortunately, with the Patriot heads, this length pushrod pushes the rocker so far up the stud that this is the result: Notice the roller tip on the valve.



    The other side of this is the pushrod end of the rocker. It should ideally have the same relationship to the pushrod as the valve, and you can see here that the pushrod end of the rocker is no where near 90* to the pushrod at mid lift.
    So what do you do at this point? The correct pushrod length yields a rocker that can't be used. When I called and asked Patriot about this and asked how they determine pushrod length, their answer was that they make sure the roller tip of the rocker is centered in the valve, which is all too common of an answer. Let's see. With the short pushrod, this is what we get:




    Well, there you have it. Rocker tip perfectly centered on the valve. This is at mid lift. Unfortunately, this couldn't be more wrong. Right off the bat you're losing almost .035" of valve lift, not to mention how the cam timing has changed. Also note, the pushrod side still isn't close. If you imagine a line through the center of the pushrod end (picture teh center of a 5/16" ball on the end of the p/r) and the trunion, you see how much angularity there is there.

    So what's the solution? Obviously the rocker needed to be lower on the stud, but still have correct geometry, and that wasn't going to happen with the BB Chev rocker. Well, in this case, just dumb luck was my solution. I had another set of rockers off a Ford TFS A 460 head that have a completely different configuration than the Chevy rocker, mainly at the poushrod end. Notice in the pic how much lower in relation to the rocker c/l the pushrod cup is on the Ford rocker. This, right off the bat, is going to require a shorter pushrod for the same application. The shorter the better with pushrods. Hmmm. Let's look at this "Ford" rocker set-up at mid-lift:



    Well, so far, so good. Rocker tip nicely centered on the valve, rocker sitting nicey on the stud. This is with the 9.400 pushrod from before. Net lift... .639". Is the rocker 90* to the valve at mid lift?
    Looks good to me. Pushrod end looks right, too.



    The intake side had the same issues of course. The corrected p/r length for intakes was 8.93 vs. their recommended length of 8.600

    In conclusion, all I can say is if you're running BB Chev rockers on your Patriot BB Chev heads and using their recommended length pushrods, your roller tips will be nicely centered on your valves, but your geometry will be terrible. Get the geometry correct, and you won't be able to run a BB Chevy rocker. Just to add, I tried several different BB Chev rockers as well, including the old stand by Crane Gold, all with basically the same result.

    BTW...I just want to add, this isn't my "invention" or my idea, or anything lke that. Rocker arms are some of the oldest mechanical devices out there, and date back to the beginning of the industrial age. There are SAE papers written that talk about rocker arm geometry that you could probably read for hours, so FWIW, I'm not making this stuff up. Jim Miller, of Miller Technology (Miller Rocker Arms) has a website called www.midlift.com, and was the one to really promote the mid lift theory. If you want to get a real education on rocker geometry, go to his website when you have an hour or two. I spoke to Jim years ago for many hours on the phone and this made so much sense to me, and I saw how wrong so much of the main stream info is that's out there, that I've since become sort of an advocate of the mid lift idea and thinking and try to promote it when I can. This just turned into a good opportunity with the Patriot head deal.
    Last edited by scott foxwell; 08-10-2009 at 06:47 PM.
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    i'm back!! 1QuickCP's Avatar
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    Id back the pushrod off and get the tip/roller geometry perfect and go with the less lift...or goodby valve guide really quick.....of course best deal is jesel or t and D and backset the shaft so you can use correct pushrod length and get everything 100%....GREAT picutres and writeup BTW....



    yup they need to move the stud in relation to the valve in there casting

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    Senior Member Jim W's Avatar
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    Dude, don't leave us just hanging.......

    What did you do????

    Jim
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    yeah is the forey the final answer ??? lol

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    steelcomp was here
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    Quote Originally Posted by Jim W View Post
    Dude, don't leave us just hanging.......

    What did you do????

    Jim
    I used the rockers that worked. The engine couldn't care less what "brand" they are or what they might have originally been designed for. In this case, they work perfectly, and that's where they stayed. Besides, what Chevy wouldn't run better with a little Ford in it.
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    Quote Originally Posted by 1QuickCP View Post
    Id back the pushrod off and get the tip/roller geometry perfect and go with the less lift...or goodby valve guide really quick.....of course best deal is jesel or t and D and backset the shaft so you can use correct pushrod length and get everything 100%....GREAT picutres and writeup BTW....



    yup they need to move the stud in relation to the valve in there casting
    It's not just the lift...it's also the changing of the cam timing, in relation to crankshaft degrees of rotation. In essense, you might as well install a completely different cam. Moving the stud back will only get the roller tip centered on the valve, but still won't solve the problem of how damn long the pushrod is, or how high the rocker sits on the stud.
    IMO there just wasn't enough design follow through on these heads.
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    Senior Member earlbrown's Avatar
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    How square was the pushrod side of the Ford rocker at midlift?

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    Quote Originally Posted by earlbrown View Post
    How square was the pushrod side of the Ford rocker at midlift?
    Sorry...I went back and edited the post to make it more clear that these Sharps are the Ford rockers. They're pretty darn close...close enough for me.

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    I'm No Expert Shaun's Avatar
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    So what did patriot do to there head that caused the mis-alignment? Just putting the rocker stud in the wrong location?

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    Quote Originally Posted by Shaun View Post
    So what did patriot do to there head that caused the mis-alignment? Just putting the rocker stud in the wrong location?
    More than that. It's a combination of things. They'll have to figure it out. Or not.
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    Bostick Racing Engines six-oh-nine's Avatar
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    I've run into this problem before... Crower makes an offset trunion rocker... they have it on .050 offset and .090 offset. Really helps with getting to fit nice and still have the geometry work out. And the coolest thing of all... the rocker still has "CHEV" stamped in it!
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    Nice write up! It is nice to show people posts like this when you are trying to explain something and they don't get it because they can't see it. I ran into this same issue with a set of Dart Pro 1's a bunch of years back. The big issue was if the pushrod length was right, it pushed the rocker so high that the roller tip actually came off the valve. After spending an hour on the phone explaining the problem they told us that is what their prostock engines do, and hung up the phone. (Gota love minimum wage phone jockeys).

    So was that the recommended valve length? I wonder what it might have looked like if they did not sink the seats so bad.

    Paul

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    IMO there just wasn't enough design follow through on these heads.[/QUOTE]


    100 % correct....

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