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Discussion Starter · #1 ·
I’m having issues with my 1.73 ratio Pro Magnum Comp Cam rocker arms clearing the adjuster screw. I’m running trick flow 325 power port heads with 698 exhaust 726 intake lift cam along with running 100 thousandths longer valves than stock and lash caps. When the valves are closed, the adjustment screw hits the front side (valve side) of the slot in the rocker arm. We have adjusted the geometry and came up with 8.550 length push rods. I bought these rockers arms when I refreshed my motor. My old Ford SVO 1.73 worked and had plenty of clearance. I damaged one of them (reason for the refresh) so I bought all new rockers arms. Wondering if anyone has run into this issue when running these spacific rocker arms?
I’m good with getting different rockers, I just need to know which ones clear. TFS, Howard’s, Comp cam gold…. I can’t seem to find any where that lists the measurements of the slot in any of these rocker arms. Any help would be greatly appreciated. I will try and post pictures as well.
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In all my years, I have never put together a standard valve layout engine with a 0.700"+ roller cam with +0.100" valves (and a lash cap to boot) that required a shortish 8.55" pushrod. Are you sure you guys understand rocker arm geometry? Because from the looks of the rocker arm position in the above picture I'd say your pushrods are absurdly short.
 

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Discussion Starter · #4 ·


In all my years, I have never put together a standard valve layout engine with a 0.700"+ roller cam with +0.100" valves (and a lash cap to boot) that required a shortish 8.55" pushrod. Are you sure you guys understand rocker arm geometry? Because from the looks of the rocker arm position in the above picture I'd say your pushrods are absurdly short.
 

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Discussion Starter · #5 ·
I’m certainly no expert. The gentleman building my engine has a pretty good understanding I think. Rocker arm geometry determines push rod length. We developed our geometry by establishing 90 degree rocker angle to the valve/retainer. We nice this was established, we dividing max valve lift by 2. .726/2=.363. We have 7/16 / 20 TPI studs and common knowledge says .050” per turn. Divide that into .363 and you get 7.26 turns on the adjuster screw to develop proper rocker arm angle at mid lift. Having done all that first, we noticed the adjuster was hitting the front of the rocker arm slot when the valves were fully closed. We played around with push rod length but all that did was screw up our geometry. Essentially if we positioned the rocker arm so we could get the adjuster screw in, which would be the same as putting a longer push rod in, the roller tip was to far forward on the valve stem. We too originally thought it had to do with push rod length. But we ruled that out by trying several different lengths and even taking the lash cap off to see if that would make a difference. It did not. Knowing that I was using this exact set up with my old rocker arms, I thought maybe someone on this thread experienced the same issues with this type of rocker arm.
I certainly dont want to come across as knowing everything. I am just learning myself but I feel like I’ve gone through the correct steps to determine rocker arm geometry but can’t see to get past the adjuster screw contacting the rocker arm slot. Please tell me if I’m missing a step by n establishing good geometry. Thanks.
 

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...We developed our geometry by establishing 90 degree rocker angle to the valve/retainer. Once this was established, we dividing max valve lift by 2. .726/2=.363. We have 7/16 / 20 TPI studs and common knowledge says .050” per turn. Divide that into .363 and you get 7.26 turns on the adjuster screw to develop proper rocker arm angle at mid lift. Having done all that first, we noticed the adjuster was hitting the front of the rocker arm slot when the valves were fully closed. We played around with push rod length but all that did was screw up our geometry. Essentially if we positioned the rocker arm so we could get the adjuster screw in, which would be the same as putting a longer push rod in, the roller tip was to far forward on the valve stem. We too originally thought it had to do with push rod length. But we ruled that out by trying several different lengths and even taking the lash cap off to see if that would make a difference. It did not. Knowing that I was using this exact set up with my old rocker arms, I thought maybe someone on this thread experienced the same issues with this type of rocker arm.
...Thanks.
Not too sure I follow your description of how you set your up rocker arm geometry.

In regards to having the rocker perpendicular to the valve stem during 50% valve lift, that imaginary line should be drawn from the center of the trunnion to the center of the roller axle. (Not from the center of the trunnion to the bottom of the roller wheel.)

In regards to your concerns about where the roller wheel rests atop the valve stem while figuring rocker arm geometry : Forget about that. Wipe it from your mind. Where the roller wheel rests atop the valve stem has nothing (N-O-T-H-I-N-G) to do with valve train geometry. Correctly figure your geometry without any regard for roller wheel location. Once the rocker arm geometry is optimized then you may consider the wheel location afterwards. As long as it’s atop the valve stem throughout the rocker arm’s radial sweep then you’ll be fine.

There are a myriad of reasons why your roller wheel might be positioned outboard on the valve stem tip, not the least of which is that you have a +0.100” long valve leaning toward the rocker stud plus the lash cap too, thereby effectively moving the valve tip closer to the rocker stud than would be a standard length valve with no lash cap.

In regards to using the same setup as with your previous brand/type rocker arms: that does not apply here since there is no standard being used by the aftermarket rocker arm industry and so each manufacturer makes their rocker arm with differing design geometry than the next. So if you change brands, you usually have to change setup as well.

I suggest going to MILLER MID-LIFT and downloading the Valvetrain Tech downloads. I feel they are the most accurate and most logical and most wise application for optimizing valve train geometry. They are also the aforementioned Geometry Standard that the rocker arm insdustry should be following but were too proud (or maybe too embarrassed) to apply this Standard when it came to light and was registered with the U.S Patent Office. The asking price for the entire download is worth every penny and a lot more.
 

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Discussion Starter · #9 ·
Thank you, Sir. I have watched that video (great video) along with several others. We feel like the geometry itself is correct but can’t seem to figure out why the rocker arm slot is hitting the adjuster. I have gotten a few ideas from this thread that I will try and go from there. Thank you for your time!
 

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HI as Paul says in the picture he posted of yours Looks like your push rod is way to short.. at 0 lift if you put a straight edge on top of the valve spring cap it should be a straight line from the roller center to the center of the stud roller Yours is diffidently not your stud roller is way low.. which would mean very short push rod..
In your picture if you put a straight edge on top of the valve spring cap it lines up above the top of where the stud roller is and it should line up with the center of the stud roller at 0 lift..
If you follow what is said in the video you should get it right.. draw a straight line between the center of the valve tip to the center of the stud roller . .. lay a straight edge flat across the valve spring cap and the two rollers should line up at 0 lift.

good luck take care be safe
tim
 

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HI,, I was just looking at your pictures and in your first post the second picture that shows what looks like good geometry when I enlarged the picture the push rod isn't even touching the rocker .. you need at least another 1/4 inch or more longer push rod..

good luck take care be safe
tim
 

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….. at 0 lift if you put a straight edge on top of the valve spring cap it should be a straight line from the roller center to the center of the stud roller…..
tim
^^^This is not correct.^^^
This particular process is executed with the cam lobe set at 50% lobe lift then installing the rocker arm to 50% valve lift, where valve lift is 50% lobe lift x (rocker arm ratio).
 

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We feel like the geometry itself is correct but can’t seem to figure out why the rocker arm slot is hitting the adjuster. I have gotten a few ideas from this thread that I will try and go from there. Thank you for your time!
I don’t think the individual helping you with your build has a good grasp of rocker arm geometry. From the picture, it appears as though he is trying to position the roller wheel as close to center of the stem as possible while ignoring the geometric principals of valve train geometry, ie, not taking into consideration the angles, arcs, sweeps, and motions of the valve train. 98% of the videos on YouTube are wildly incorrect and one ought not study all of those searching for an answer. “Geometry” has become a buzzword in engine building to where many builders have come to believe it means “open and close the valves without failures,” when in fact it still has the exact same definition that Merriam-Webster has always given it.

If you want, you can install juuuuust enough pushrod length to get the poly lock on and dyno your engine, then let me change only the pushrods, at which point the engine will register more torque, register more peak horsepower, and rpm higher before valve float than the current setup….and this assumes the current setup doesn’t buckle pushrods before achieving float in the first place.

Educating anyone about valve train geometry can take 25,000 words or more. Rather than all that typing, feel free to give me a call at HFD when you’re in front to the engine and I’ll be happy to walk you through the basics.
 

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I had the same issue. Had to switch to Crowers.
 

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Discussion Starter · #16 ·
I had the same issue. Had to switch to Crowers.
Thank you. Looks like my old ones (ford SVO) clear just fine. The slot on the comp cams measures 1.26 and the slot on the SVO measures 1.60 and everything looks great as far as geometry and push rod length. Having to switch as well. I’ll look into the crower.
 

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Discussion Starter · #17 ·
I don’t think the individual helping you with your build has a good grasp of rocker arm geometry. From the picture, it appears as though he is trying to position the roller wheel as close to center of the stem as possible while ignoring the geometric principals of valve train geometry, ie, not taking into consideration the angles, arcs, sweeps, and motions of the valve train. 98% of the videos on YouTube are wildly incorrect and one ought not study all of those searching for an answer. “Geometry” has become a buzzword in engine building to where many builders have come to believe it means “open and close the valves without failures,” when in fact it still has the exact same definition that Merriam-Webster has always given it.

If you want, you can install juuuuust enough pushrod length to get the poly lock on and dyno your engine, then let me change only the pushrods, at which point the engine will register more torque, register more peak horsepower, and rpm higher before valve float than the current setup….and this assumes the current setup doesn’t buckle pushrods before achieving float in the first place.

Educating anyone about valve train geometry can take 25,000 words or more. Rather than all that typing, feel free to give me a call at HFD when you’re in front to the engine and I’ll be happy to walk you through the basics.
I appreciate that. I’m camping for the next few days but I may try and touch base with you when I get back. Looks like my old set of rockers fit great with the same push rod. The slot on the comp can is significantly smaller (1.27) than my old set of SVO (1.60). Everything as far as geometry looks great. My engine builder has been doing this for 30 years so I trust that he k owe what’s up. But I’m always looking for more advice and knowledge. Thank you for your response.
 
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