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Acceptable roller rocker contact at valve tip and pushrod to rocker contact?

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Paul Kane
the tree man
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Acceptable roller rocker contact at valve tip and pushrod to rocker contact? Empty Acceptable roller rocker contact at valve tip and pushrod to rocker contact?

Post  the tree man March 20th 2020, 2:17 pm

Mocked up my top end to calculate pushrod length (SCJ heads,Scorpion Race Series rockers,SFT cam 125 on the seat/340 open). Had a couple hiccups but not bad. Just need a bit of input/reassurance on the results. As a start point I went with the 90* valve stem to rocker arm at mid lift method and tried a dozen different pushrod lengths from there.
  EXH             INT
9.40 .680    9.15 .680
9.35 .675    9.10. 675
9.30 .675*  9.05 .675*  (I thought this was the best compromise for maintaining lift/pull the intake roller in a bit/better pushrod angle at the rocker/
9.25 .672    9.00 .670           less pushrod contact at the rocker trunion area.)
9.20 .670    8.95 .662
9.15 .665

Two issues. Exhaust roller was fine,very close to the center of the valve tip,but the intake runs out to about .055 from the valve edge. Is that still acceptable considering the sissy spring rates? I could add a lash cap if necessary but would prefer not to. Also,the alignment with the SCJ guide plates leaves a bit to be desired and I may cut/weld them.

The other issue was pushrod contact at the rocker. I assume with the valves relocated closer to the intake the pushrod gets steeper and the relief in the rocker is shy a smidge to clear. They are way overkill for my setup and have a ton of meat in this area so a very light clearancing will do the job. Is this a common problem on a large body aluminium rocker? Again,appreciate the help.

the tree man

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Post  Paul Kane March 20th 2020, 5:27 pm

Two reasons that I can think of for the pushrod hitting the backside of the rocker arm body at the trunnion are:

1) the rocker arm over-arcing, and,
2) use of Scorpion rocker arms.
[Also, 3) It could be the rocker arm's design geometry relative to the engine application.]

Based on the results of some destructive testing (using specific ANSI testing specs for the rocker body aluminum grades) performed on a lot of stud rocker arm bodies from various manufacturers, my belief is that the Scorpion rocker bodies are intentionally designed and manufactured with an overall larger rocker body (ie, larger than most of their competition) because of Scorpion's choice of aluminum, which is far more malleable (softer) than the grades of aluminum used by just about every other rocker arm manufacture, and that makes for a weaker rocker arm generally speaking.  Scorpion's "fix" seems to be to just make their rockers out of more material (make them bigger and thicker for increased structural integrity).  As a result, the pushrod is more likely to interfere with the backside of the larger Scorpion rocker body at full-lift.  Not to mention the mass moment of inertia of that big-mass rocker weighing down over the valve and spring. Incidentally, even though the Scorpion rockers are "beefier" by way of their immense size I have still seen more of them break than any other brand, but you need not worry since the observed failures were always with big solid roller springed engine (not a flat tappet cam such as you have).
___________________________________

If you will be staying with those exact rocker arms on the SCJ heads, and you will be using the Minimal Sweep Theory (ie, trunnion-to-roller axle perpendicular to the valve stem at half-lift) as you noted above, then I suggest you stick with that approach in strict fashion regardless of where the roller wheel rests atop the valve. If the roller wheel is literally off the stem tip, the look for a different rocker arm with a roller-to-trunnion dimension that works with the SCJ's rocker stud-to-valve tip dimension. Not all rocker aftermarket arms are for a given engine have the same design geometry and other dimensions.
Paul Kane
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Post  the tree man March 20th 2020, 8:49 pm

That echoes what I see and I understand how it should look/work. It may not be optimised but I'm comfortable where I'm at. The rockers are rated at 950 lbs/.950 lift which I'm sure is very optimistic and,you're right,it's obvious they got there by adding size;however,way overrated for my application so I felt it was a reasonable choice. This is a bit of a budget build,currently an over-budget build,and middle of the road product is the call. I'll steam forward as is and everything should be fine. Good thing I ordered all my stuff when I did. Stroker kit took a bit longer than expected but showed up in time for me to get it before he border shut down. That would have sucked. Block is in for machining and I'll have a couple more questions once it's back. Thanks.Paul.

the tree man

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Post  rmcomprandy March 21st 2020, 3:22 pm

With a roller tip rocker arm ... anywhere on the valve tip, not close to the edge will work fine.
It is most important to get the pushrod side to be nearest to correct.

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Post  the tree man March 21st 2020, 4:17 pm

Since experimenting and swapping of components is cost prohibitive the current arrangement is the call. I split the the difference on both sides of the rocker and the result will be fine. Everything I've researched and purchased for this project has not been of max effort intent but has been of reasonable quality/fit,no bargain basement junk,to maintain the spirit of the project for reliability and power without winning the race.......to the poor house! More questions to follow.

the tree man

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Post  Dave De March 23rd 2020, 9:34 am

I found that the guide plates for SCJ heads had to cut, rotated, and welded to get good rocker tip alignment. I am rather picky to keep the roller tip on the center of the valve stem even if lash caps are used.
Dave De
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Post  Lem Evans March 23rd 2020, 10:43 am

Maybe it's the rocker arm you are using but, the lengths you stated are longer than what I've seem work.

8.800"-8.850" intake & 9.100"-9.150" is usual.

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Post  the tree man March 23rd 2020, 12:07 pm

Those lengths you posted I also read were the norm and I did try pushrods shorter than in my list but continued to lose a lot of lift until I was under what the cam is speced at. The pushrod side of the rocker sweep got better and the rod/rocker contact almost disappeared;however,as the rocker got steeper it also got close to the retainer and the witness mark on the valve tip was at least twice the width. To eliminate some variables I did check cam lobe lift to make sure I wasn't chasing my tail and it was bang on the cam card. Also,these heads were combined with a big roller cam in the previous motor and I thought taller valves may have been installed but they are stock height. Even though the Scorpion rocker is way thicker,when I compared pics with the FRPP blue rockers the pushrod pocket in the Scorpions appears significantly deeper so that may be the issue. The alignment of the guide plates is definitely wonky and I'll have to make a judgement call on that. At least,for a change,it doesn't cost anything to correct.

the tree man

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Post  Lem Evans March 23rd 2020, 4:55 pm

Got a buddy that's got a frpp blue/crane gold or crower s.s. rocker you can borrow?

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Post  the tree man March 23rd 2020, 6:16 pm

I do actually and they're the steel rockers,I think Crower Enduro's,that were on these heads before I got them. He had the pushrods from that setup also and,if I recall,they were in the range you posted earlier. He's a big Ford race guy and I'm sure has more than one type of rocker for 460's. I'll probably contact him this week. I have the Scorpion's so with the current state of the world and my tight completion time for this engine to get back in the car my options are exhausted. I know this set up will be fine but am very curious to see the difference in the architecture of some different rockers and how i affects lift,geometry etc. Knowledge is power and I need more.

the tree man

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Post  the tree man March 31st 2020, 12:57 am

Got my block back from machining and went through the rocker/pushrod thing one more time. Since the block hadn't been decked the .020 yet in my previous measuring I had just shimmed the head with some thin cardboard to approximate where it would eventually sit but it was a bit short. With the block now decked to zero and an old,compressed head gasket installed it ends up about .010 higher so the numbers are a bit different but still consistent. I did mooch an A460 and CC Ultra Pro Magnum XD rocker for comparison. There's different diameter trunions and wheels on the three so I only spent a bit of time fiddly measuring and calculating then just installed them all to see the difference. The A460 had the shortest trunion center to roller center (1.569) but lifted the valve within a couple thou of the Scorpion which is a bit longer (1.582). The Comp was longest (1.655) and obviously lifted the most,almost .010 more,but it ran the wheel right out to the very edge of the valve tip and would need a lash cap for sure. The pushrod side of the rockers was tricky to measure for comparison but the A460 and Scorpion are very similar. The Comp kinda had a different layout on both sides. I tried an 8.850 and 9.150 pushrod and same drill as before,lost about .010+ lift and the sweep across the valve tip got a fair bit wider. I'm going run with the 9.050 and 9.300 pushrods and could probably get away with another .050 but I got in a panic with the COVID retail closures so ordered the pushrods a while back. Hope they arrive. If I had a choice,I'd run the A460/Crane Gold rocker since it's ridiculously smaller than the Scorpion and the shorter lever lines up better on the valve tip;however,they're almost a couple hundred Canadian bucks more so for function and price the Scorpions will be fine.

the tree man

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Post  Lem Evans March 31st 2020, 9:49 am

The XD axle shaft is off set drilled. It's a long BBC body but with the off set it's lever length is functionally about the same as the A460.

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Post  Big inches April 1st 2020, 12:01 pm

good to know

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