Rocker arms for 408 build

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12many said:
Been covered in the past:Chevy Roller Rockers the stock 5/16” stud mounting is IMO fine as is for most street pressures and rpms. I’d research as much as possible on any reports on stud breakage with the 5/16”....likely not going to find any but you never know. And then if you did, what spring pressure, rpm, the geometry correct? You could go to 3/8” but I’d be checking how much cast pedestal material will remain on each pedestal before enlarging. 7/16“ would be too big for the pedestal.
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I've read that thread and several others here that apply. Good thought on breakage. I've seen no reports of that.
Factory rockers have been known to wear through at the push rod. Likely from high spring pressure.


mbaird said:
I think the 5/16 is fine for our builds.
Solid roller , high rpms and big spring pressures would be a different story.
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We have several here plus Szilagyi who agree.
I think the risk of very bad things is small.
I'm planning on a rev limiter, also to reduce the risk.
 
If your worried about the 5/16 stud run a girdle but to add I was running the tall rocker covers and with the girdle I still had to remove the breather plate under cover for clearance but it worked out as I needed get any oil splash through either pcv or breather cap as girdle acts as a plate.
 
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67 gt said:
Had good sweep across the face tip and they were adjustable as I was running a solid flat tappet.La bottom end comp cams 803 lifters with the oil hole . Ball to ball Oil through push rods. Purchased rockers, guide plates and studs as a kit from Summit.
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Very cool and good to know as I believe they are quite similar to RHS heads.
All the info makes the thread of some use.

I may consider a girdle if it fits under factory valve covers.

Scratch that I guess, after your edit LOL
 
mbaird said:
I think the 5/16 is fine for our builds.
Solid roller , high rpms and big spring pressures would be a different story.
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As an example: I’m using the Comp 5/16” (4542-16) studs with 1.6 rocker arms on a mild hyd cam .323” lobe lift (.517” valve lift) with Hughes 1110 springs (120#closed, 310#open) Spin it to 6000 often no issues. I could have run the stock stamped setup in my case. The op’s initial post he mentioned .525” lift and 5800 rpm as a target. No need for girdles or enlarging mounting holes or extravagance in these mild cases.

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I just brought it up as people get cold feet running the 5/16 stud on cams running @ 550 or smaller lifts. Rocker Girdles are not expensive and are cheap insurance. Just ties em all in reducing flex.
 
Now that I think about it, not an option when using the bolt down factory rockers.
 
Hughes take on this issue.
Note that .580 is referring to the stud, not the stock rocker.

#2---Magnum & LA Heads

We believe the 5/16" stud is strong enough for all hydraulic roller cam with lifts up to 0.580". The heads can be removed, drilled and tapped for the larger studs. Here again you will need one with a thinner hex to clear the rocker as mentioned previously; we'll have them when you need them, part number 7601(call). If you are running a flat tappet or a solid roller cam with more than 0.600" lift we suggest a stud girdle P/N JPP 1194. We don't think the practice of installing 7/16" studs is a safe modification. Look at the boss for the exhaust studs, even the reinforced ones on the R/T heads. We are not comfortable with putting a stud that size in a boss that small. It won't strip out; it may just break off causing you to have to start over with a new head. The stud girdle can be used with the 5/16" bottom stud set-up too because it is 3/8" on top. The stud girdle will allow will you to run any spring pressure you want.
 
I figured a 3/8 stud top and bottom would be the way
 
From a Moparts thread.
It's from 2003 but there are several bits of info I did not find elsewhere.
He references a jig for rent to drill Magnum heads for LA intakes.

Dodge Magnum Head Poop Sheet & Drilling Jig Info

ROCKER GEAR:
Stock magnum rocker arms are actually the same rocker arms as the old AMC 290-401 engine series, and are 1.6 ratio instead of the LA 1.5 ratio. To determine the valve lift with 1.6 rockers, take your LA cam's valve lift and multiply by 1.067 (1.6/1.5).
Aftermarket roller rockers are usually the same pieces as SB Chevy pieces, and may require different rocker arm studs. Some kits may include them. Most aftermarket rockers are available in 1.6 or 1.7 ratio. Small Block Ford specific roller rockers (1.6 ratio) are reported to be a better fit because of minor differences in the rocker pivot to roller tip dimensions. CAT Chevy roller rocker have been successfully used as well.

Crane: offers a stud and guide kit: PN 36655-16, which is the same part number for a Ford 5.0L conversion. The rockers PN 11746-16 (1.6 ratio) are the same rockers for 5.0L Fords and SB Chevy's. These are the same parts as the roller rocker arm kit available through MP.

COMPCams: Now offers a “real” Magnum guide plate and it is preferred over the Crane Teflon thingys. In older Comp catalogs (and possibly their website) they list a PN4842 & PN4843. These are INCORRECT. This is an Oldsmobile guide plate and it WILL NOT work properly on a Magnum head.

Crower also has Magnum roller rockers available in rail (no guide plates necessary) or non-rail (guide plates required) as well as the other necessary hardware to install them.

If you're running a moderate hydraulic cam, stock rockers are fine. If you don't have junkyard ones new ones are available from MP:
MAGNUM V8 ROCKER ARM SET
Consists of 2 rocker arms,2 pivots,2attaching
boltsand 1 guide.for use with hydraulic cams
only,production 1.6 design ratio. NOT for
4.7L V8.
MP PN 4876050 (one cyl, need qty 8 )

NOTE: Roller rocker arms WILL NOT clear the baffles inside a stock valve cover. There are several ways to fix this:

1. Buy MP cast aluminum valve covers (spendy)
2. Cut the stock baffles out.
3. Bash the baffles in with a hammer.

4. Build a valve cover spacer out of wood or metal. I ended up bolting a valve cover to a piece of wood (maple or something) trimming around it with a flush cut router bit and made myself a 1/2" spacer. Painted it good and installed it with 2 valve cover gaskets and longer bolts. No leaks so far. Small Block Chevy valve covers will even fit if you enlongate the valve cover holes a bit. I had this setup for a while, but couldn’t keep it from weeping around the top of the bolts (didn’t really try too hard though) and went with a spacer. Some SBC valve covers can be purchased without the holes drilled. You could drill your own and possibly eliminate the weeping problem I had.
 
Idaho said:
I'm planning on a rev limiter, also to reduce the risk.
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IMHO: The rev limiter won't have any impact on stud breakage. The flexing force studs will be essentially the same each cycle at all RPM's and that will fatigue a weak stud regardless. Individual stud weakness is your issue.

FWIW Just a word of caution when mulling over all of this: You can't equate stud strength and durability with that of the stock Magnum pedestal setup. The way the forces work is different in regards to the strain within the parts, and the pedestal setup is superior for strength and fatigue issues. No wonder the stock Magnum rockers are what tend to break in that setup.
 
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nm9stheham said:
IMHO: The rev limiter won't have any impact on stud breakage. The flexing force studs will be essentially the same each cycle at all RPM's and that will fatigue a weak stud regardless. Individual stud weakness is your issue.

FWIW Just a word of caution when mulling over all of this: You can't equate stud strength and durability with that of the stock Magnum pedestal setup. The way to forces work is different in regards to the strain within the parts, and the pedestal setup is superior for strength and fatigue issues. No wonder the stock Magnum rockers are what tend to break in that setup.
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I appreciate your input. So you're saying the pedestal adds strength over studs and polylocks. Makes sense.
I suspect a 5/16 bolt through a pedestal never breaks, and has less flex thana 5/16 stud.
I'm considering keeping the pedestal setup. Are you suggesting that may be stronger than studs and rollers?
Maybe this is why the girdles make sense with studs.
Have you heard of Magnum rockers breaking? I only know of pushrod wearthrough. For that reason I may use the thicker stamped version.

It's very easy to advocate for upgraded valvetrain and I see the benefits.
I think its also easy to get into overkill, and even create setup hassle.
Everything I'm seeing suggests there is a threshold where the upgrade makes sense.

Lift over .525.
High spring load (over 350? not sure.)
High revs, especially continuous.
Desire/need for small horsepower gains.

Feel free to critique or add to the list.
 
Seems like this could allow one to dial in the factory rockers.
Or rollers. I have not heard of anyone using them.

adj pushrod.png
 
You are correct, factory bolt and fulcrum are stronger than a stud unless you put a girdle on it. Read my post from this summer, been running mag stuff for awhile,weak link on factory stuff Is the pushrods assuming 530ish lift-300lb open spring, mid 6,s rpm they are the first thing to go. Obviously lobe profile has a lot to do with this also. I think you'll be just fine with factory stuff. I have used those adj pushrods many times on sft motors, they work fine. If you want some reading on this stuff go to mopar chat circle track, guys there have been running this stuff for years because of class rules.
 
Thanks Junky. I looked there a bit. No search function without login. Found a bit just using google and circle track.

Regarding use of a rev limiter, this thread points to the value.
What are the practical limits to the stock Magnum Rocker package?

I ran stock rockers and pushrods in a 360 magnum circle track car. I had a hughes hyd roller .580ish lift, and 2.2 Litre retainers with the Mopar performance valve springs. I would have valve train issues if I spun it up past 6000 rpm. Likely pushrod flex would take the rocker and pushrod out. Keeping it inder 6000rpm everything was good

I have stock magnum rockers on my 360 with a .525 lift cam and 125# seat and 310# at .550 lift springs. I found that it bends valves at 7200rpm but since then I shift around 6000 and have not ever had a problem since. :)
 
Idaho said:
Seems like this could allow one to dial in the factory rockers.
Or rollers. I have not heard of anyone using them.

View attachment 1715462786
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16 of those x $12.95 each (ouch!) vs. cheaper lighter correct length pushrods? Doubtful one would need different length pushrods for 16 valves, or that they would be required in this or many cases? Might wanna buy a measuring pushrod, check as many as you care to, but the need for different lengths vs. one equal set? Quite a few brands that offer off the shelf length sets that may work, or order a set of custom, might be worth looking into.
 
Idaho said:
I appreciate your input. So you're saying the pedestal adds strength over studs and polylocks. Makes sense.
I suspect a 5/16 bolt through a pedestal never breaks, and has less flex thana 5/16 stud.
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Yes, you are on the right track. The strain (in the strict engineering sense of the word) peaks up just above the radius of the nut at the bottom of the stud, and the flexing and fatigue concentrates there. With the pedestal, the pedestal has to first stretch the bolt some in order to tip up off of the head and then flex the bolt. So the bolt is loaded mostly in straight tension with the pedestals, which is stronger.

The girdle helps spread the flexing load on each stud to the adjacent studs.

Ford had pedestals in the Cleveland engines in the early 70's and they could take a pretty good beating once you replaced the factory AL ones with steel ones.
 
So I went to the shop and pulled a rocker from a stock Magnum head. Amazing how having it in your hand gives clarity. Should have done it before... (duh)
It's obvious how much stronger the pedestal is than a stud. That square pedestal sits snug inside the guideplate channel (edited). My bet is its more stable than a 3/8 stud with girdle.

DE478C64-6566-4738-A143-05BAEB4DB3BC.jpeg
 
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I guess I have never bought them, always used used ones. As far as I know there are no thicker ones like the la stamped rockers. Elgin use to have a cryogenic treated ones but I have never used them, used stock ones are all I've ever had. At that price you would have some thinking to do, could go to bone yard if your up for that!
 
Found my login info for Moparts (hadn't been there for years) and came up with some interesting stuff. The circle track racers use this method to make the stock rockers adjustable by cutting off the square base, replacing it with a polylock. Of course it can't be as stable as a pedestal but apparently it works. They use a pedestal with a 3/8 hole, listed below and mount it on the 5/16 to 3/8 adapter studs.

magnum heads swap? - Moparchat - Home of MOPAR enthusiasts worldwide!

Here is the best way to do it and have adjustable rockers like a cheby.
get Comp cams guide plate # 4825-8 18bucks, Comp cams rocker studs # 4504-16 (5/16x3/8)65bucks. If you want to use stock magnum rockers get mopar #p4876514. This is the rocker folcrum with 3/8 hole. Cut the bottom of the folcrum off with die grinder. I will post a pic. Or you can use a chebby stock rocker but it will have to be a 1.6 ratio or you will have to grind pushrod tunnel. Get a set of 3/8 polly locks and you have adjustable system. Have been using this system for 2 seasons with zero problems

Mopar Performance P4876514 in our Camshafts Department | Autoplicity
 
A lot of ways to skin this cat, I would try to use all junk yard stuff, even the pushrods. You will have to check preload but they can be shimmed some. I've even got 1 motor with sft, aftermarket pushrods, shimmed the pedistals with arbor shims for valve clearance. Time consuming but turned it 7000 with 375 open springs, all with stock pedistals and rockers. If you have the cabbage buy hughes or one of the others set ups. A tightly bolted down pedistal is tough to beat.
 
Below are the beefed up stamped rockers. Not that spendy.
As for the adjustable push rods, I don't think factory rods will fit so I'll be buying a hardened set anyway, so its not adding that much.
I mentioned before my valve tip height varies around .020. I may figure out what most of them need, get that length, and a few adjustables.

Of the rollers, I think the Hughes stud mount package is a good deal. Likely would want a girdle. So then bigger valve covers...

mopar perf rockers.png


thicker rocker arms.png
 
If it was me, I'd evenly machine off part of the bottom of the pedestal, like maybe in the range of .050" to .100", and then come with a set of shims to put under the pedestal and lock them back down with the bolt like in the original setup. Adjustable, but retains the stability. Slow to adjust? Sure, but how often do most of us do that?

Optimizing geometry is another matter.....
 
Sounds like a very good solution for those staying under .525 or so. I think the valve contact angle would start to get ugly going higher.
It will be interesting to see the contact pattern of the stamped rockers. If it looks decent or just needs minor shims I will likely run them.
The pedestal is very hard. One guy broke 2 end mill bits and drilling 5/16 to 3/8 did not go well :(
 
Idaho said:
Kinda sad the Magnum lost the shaft rockers.
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I keep thinkin there has to be a way to convert.......a girdle if you will. Might be able to bring oiling up from within the valley via tubing
 
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