460 Ford Forum banner
1 - 6 of 6 Posts

·
Registered
Joined
·
7 Posts
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.
Automotive tire Motor vehicle Automotive design Rim Automotive wheel system

Tire Wheel Automotive tire Motor vehicle Automotive design

Automotive tire Cameras & optics Gas Engineering Scientific instrument

Automotive tire Motor vehicle Automotive design Engineering Gas
 

·
Registered
Joined
·
7 Posts
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.
 

·
Registered
Joined
·
7 Posts
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.
 

·
Registered
Joined
·
7 Posts
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!
 

·
Registered
Joined
·
7 Posts
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.
 

·
Registered
Joined
·
7 Posts
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.
 
1 - 6 of 6 Posts
Top