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valve lift and rocker arm ratio

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    Posted: 28-November-2020 at 6:06PM
I'm rebuilding my 351M (it's going to become a 410) and Comp recommends an after market rocker arm to accommodate the cam lift. They recommend something like their Magnum roller tip rockers (which require converting my pedestal mount heads to stud mount, Crane has a screw in kit to do this fairly easily.)

The thing is the stock rockers on my heads are 1.73 ratio, and the Magnums are 1.72 ratio, so the stock rocker arms should still allow for plenty of lift--even a little more than the aftermarket. Is there something I'm still missing?

Here are the cam specs. Intake lobe lift for instance, is 0.298. Multiply that by 1.73 = .52, which gets me right where I want to be with the cam's rated lift at 0.513.

Grind Number:XE262H
Engine Family:Ford 351C, 351M-400M 8 Cylinder (1970-1983)
RPM Operating Range:1,400-5,600
Cam Type:Hydraulic Flat Tappet
Lifter Style:Hydraulic Flat Tappet
Camshaft Series:Xtreme Energy
Camshaft Gear Attachment:1-Bolt
Usage:Street/Performance
Valve Springs Required:Yes
Camshaft Material:Cast Iron
California Proposition 65:WARNING: Cancer and Reproductive Harm P65Warnings.ca.gov
Advertised Intake Duration:262
Advertised Exhaust Duration:270
Intake Duration at .050 Inch Lift:218
Exhaust Duration at .050 Inch Lift:224
Intake Valve Lift:0.513
Exhaust Valve Lift:0.52
Lobe Separation:110
Assembly Lubricant Included:Yes
Intake Centerline:106
Lobe Lift Intake:0.298
Lobe Lift Exhaust:0.301
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72FordGTS Quote  Post ReplyReply Direct Link To This Post Posted: 29-November-2020 at 1:28AM
The cam on my 408 has .321" of lobe lift.  My engine uses the Scorpion pedestal mounted roller rockers and they work fine.  They are the correct 1.73:1 ratio which gives me .555" of total valve lift.  I know lots of others have used these rockers as well.



Edited by 72FordGTS - 29-November-2020 at 2:01AM
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Originally posted by 72FordGTS 72FordGTS wrote:

The cam on my 408 has .321" of lobe lift.  My engine uses the Scorpion pedestal mounted roller rockers and they work fine.  They are the correct 1.73:1 ratio which gives me .555" of total valve lift.  I know lots of others have used these rockers as well.


Did those work with stock valve covers or do they require taller ones?

And do you know what the difference between those and the Endurance 3024 are? Or the Race 1024?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72 RS 351 Quote  Post ReplyReply Direct Link To This Post Posted: 29-November-2020 at 3:42AM
Those are decent moderate cam lift figures. The studs of stud mount rockers are a weak link, and pedestal mount studs are smaller(5/16") and worse case scenario, weaker link still.

I'm just cautioning, the pedestal mount studs are not very strong, those should never be used with high rpm or long term use. It's a big subject that doesn't get discussed hardly ever.

So I'm sorry to be pointing out something that engine builders should think about, but virtually nobody does. Any stud mount roller rocker is less reliable than a stock OEM pedestal mount, no roller, cheap slide, rocker system. The OEM type can last for decades easily. The studs of the other type are experiencing high side load forces.

It typically isn't a problem for an engine raced at a track occasionally, or sees very low miles per year. The issue is often from long term, many miles of street use. At some point wear and stress on the studs will break one, and that is bad and you don't want that.

Keep an eye on your rocker studs, R&R the VC's yearly to inspect the studs where the trunion rides. The ideal rockers are shaft rockers, but those are crazy high($1000-$1700).

That lift level of the low .500" range is best for stud mount rockers, and anything ratio in the 1.7-1.73 range is fine for a Cleveland head(they can all attain a good valve geometry).
Don
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Post Options Post Options   Thanks (1) Thanks(1)   Quote 72FordGTS Quote  Post ReplyReply Direct Link To This Post Posted: 29-November-2020 at 3:44AM
They clear the stock valve covers without issue (I am running stock valve covers).  I pulled up my parts list, and it looks like my engine has the 1056 arms, which are the race series.  From what the decription says, the race series are decribed as:

" They're precision-crafted by high-tech manufacturing methods, then fully CNC-machined. These rockers offer more clearance for retainers and springs, and can easily handle .950 in. lift and 950 lbs. of open spring pressure."


Tim Meyer of TMeyer Inc was the one who suggest those rockers. He's built a ton of engines 335 series engines, so I trust his experience. I was looking at converting to stud mounted rockers but he talked me out of it.  He said for stock heads the machine work cost makes it better of to go to aftermarket heads (which I didn't want).  

Here are some pics of my engine:



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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72 RS 351 Quote  Post ReplyReply Direct Link To This Post Posted: 29-November-2020 at 4:26AM
You guys are keeping your rpm's down I'm sure, that helps a bunch. I had that kind of pedestal rocker on my first 351C in 1981. I was young in College and knew very little about engine concepts. I had just built that as my first engine. I did have one valve spring break, they were a used set from a friend's son, I forgot about that, when one header pipe was cherry red, scary.
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Yup,
Remember having no money in the early days.  I learned the hard way about torque settings and stretch the hard way.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rockatansky Quote  Post ReplyReply Direct Link To This Post Posted: 29-November-2020 at 6:39AM
1.72 vs 1.73 won't make a ratsasshair's worth of difference in the real world.

the Crane stud kit will hold up to the spring pressure the XE262 requires if it's installed properly,

but don't forget bolt down pedestal rockers are adjustable by shimming the pedestal and altering pushrod length to achieve correct geometry and lifter preload. you still have to check for correct pushrod length when changing to an aftermarket roller rocker, there's no guarantee the critical points are in exactly the same locations as the stock rockers
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lizer Quote  Post ReplyReply Direct Link To This Post Posted: 29-November-2020 at 8:32AM
Originally posted by 72 RS 351 72 RS 351 wrote:

Those are decent moderate cam lift figures. The studs of stud mount rockers are a weak link, and pedestal mount studs are smaller(5/16") and worse case scenario, weaker link still.

I'm just cautioning, the pedestal mount studs are not very strong, those should never be used with high rpm or long term use. It's a big subject that doesn't get discussed hardly ever.

So I'm sorry to be pointing out something that engine builders should think about, but virtually nobody does. Any stud mount roller rocker is less reliable than a stock OEM pedestal mount, no roller, cheap slide, rocker system. The OEM type can last for decades easily. The studs of the other type are experiencing high side load forces.

It typically isn't a problem for an engine raced at a track occasionally, or sees very low miles per year. The issue is often from long term, many miles of street use. At some point wear and stress on the studs will break one, and that is bad and you don't want that.

Keep an eye on your rocker studs, R&R the VC's yearly to inspect the studs where the trunion rides. The ideal rockers are shaft rockers, but those are crazy high($1000-$1700).

That lift level of the low .500" range is best for stud mount rockers, and anything ratio in the 1.7-1.73 range is fine for a Cleveland head(they can all attain a good valve geometry).

The crux of my question is really if it's safe to stick with my stock rockers (what I'd prefer) or if I need to use something with a roller fulcrum. The stock rockers have the ratio necessary to achieve the lift, but somebody else pointed out to me the fulcrum slot in the stock rocker is the limiting factor.  So the part about that which is confusing to me is the slot would still have to allow the rocker to attain a 1.73 ratio, otherwise it wouldn't be able to achieve the lift that ratio should be able to achieve.

I don't do high RPM driving. On my Mustang, which I felt like I drove a lot this year, I only ended up getting 300 miles on it for the year (didn't even get my new rear end fully  broke in :( ) and rarely do I exceed 4000-4500 rpm. I don't know that I ever have actually.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72 RS 351 Quote  Post ReplyReply Direct Link To This Post Posted: 29-November-2020 at 9:00AM
I don't know the limit of the stock rockers, but I think that very low .500" range is okay. If it was above .550" I'd worry about that.

I too don't push rpm's high much, everything I own is an automatic and nothing special. I see 5000rpm in two of my three 98 SUV's, that's the stock point for the 302 and 4R70 trans as programmed. I'd call over 6k getting high rpm's.

You might research more and see if someone knows what the lift limit of the stock rockers is. Rock may know or know where the answer is, he's a great source of information. I appreciate that too, that's invaluable for solving many issues, odd or common problems.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote 72FordGTS Quote  Post ReplyReply Direct Link To This Post Posted: 29-November-2020 at 9:50AM
I am not going to pretend to be any sort of expert.  I am just sharing my experience with my build, which doesn't sound too far off Lizer's engine. I can see high RPM use being an issue for the pedestal mounted rockers, but my engine sees maybe 5500 RPM max (WOT upshift).  It's not a 351C spinning to 7K.  I had many of these same conversations with Tim Meyer about the pedestal mounted roller rocker arms, and he reassured they were more than fine for my build. I am sure Rock will have more to say, he's our resident forum expert on these engines.

Rather than retype things out, I went to the ultimate source on the matter - George Pence.  This is what he has to say on the subject.  He also mentions the Scorpion arms, but says to limited them to 400 lb over the nose springs.

Originally posted by George Pence George Pence wrote:

ROCKER ARMS

The factory rocker arms are suitable for the hydraulic tappet applications being discussed. There are two common warnings in using the factory rocker arms: (1) Use only steel 4V fulcrums (the 2V fulcrums are made of aluminum). (2) Beware of factory rocker arms that have “lugs” along the edges immediately above either side of the fulcrum area. There is a problem with push-rod clearance when using those rocker arms with camshafts lifting the valves 0.550” or higher, therefore they should be replaced. Sealed Power #R-855 is a recommended replacement for the factory rocker arms.

Beyond those warnings the factory rocker arm has three potential weaknesses: (1) fulcrum bolt stretch, (2) push rod cup wear and (3) the quality of the valve stem contact patch (a rocker arm geometry issue).

Fastening the rocker arms to the pedestals with ARP #641-1500 bolts (4 packs) and #200-8587 washers (2 packs) is recommended to improve the strength of the fulcrum bolts and reduce the possibility of them stretching. The 1/8” thick washers are necessary because the ARP bolts are 1/8” longer than the factory bolts. With the fasteners thus improved the factory rocker arm is good for up to approximately 400 pounds over the nose and it can accommodate applications lifting the valves up to 0.615” off the seat. 0.615” valve lift was Ford’s recommended limit for the production rocker arms based on push rod clearance.

If you wish to upgrade to adjustable valve train and your motor’s factory iron cylinder heads are equipped with unmodified slotted rocker arm pedestals the Scorpion #3224 rocker arm can be bolted directly to the unmodified pedestal and provide push rod cup type valve lash adjustment. This is a high quality billet rocker arm that operates like an individual shaft mount rocker arm. Keep in mind the 5/16” fasteners limit this rocker arm to spring force of about 400 pounds over the nose.

If your motor’s cylinder heads are milled and tapped for 7/16” stud & guide plate type rocker arms the Yella Terra YT-6321 rocker arm is the hot tip. This very rugged rocker arm also performs like a shaft mounted rocker arm therefore it requires no studs, guide plates or hardened push rods. Internet pricing for the Yella Terra YT-6321 rocker arm is in the range of $785 US dollars for a set of 16.





The next step up in price is the T&D Machine individual shaft mount rocker arm, which is available in steel, this is its main benefit. Whereas billet aluminum rocker arms are good for about 10,000 miles, a steel rocker arm is a better choice for an engine planned for high mileage.

ROCKER ARM GEOMETRY

There are six variables which impact the geometry of a rocker arm; (1) the amount of camshaft lobe lift, (2) the design of the rocker arm, (3) the height of the rocker arm's fulcrum, (4) the rocker arm's lateral distance from the valve stem, (5) the height of the valve stem and (6) the length of the push rod. Optimum rocker arm geometry minimizes side thrust on the valve stem and guide which has two substantial benefits; (1) it minimizes the wear of parts AND (2) it minimizes the rocker arm’s contribution to oscillation induced valve train problems.

Geometrically ideal rocker arm geometry will set the rotational axis of the rocker arm at the same height (perpendicular) as the valve tip when the valve is 50% open. That’s just on the rocker tip side, there is also geometry on the push rod side, but getting close to the correct geometry on that side depends upon the rocker arm being designed with that as a consideration, and designed for the amount of lobe lift employed by your motor’s camshaft. When the geometry is correct on both ends the rocker arm will impart the most possible lift to the valve, this will not occur unless the geometry is correct at the rocker arm tip AND the push rod. This indicates the valve train is following the motion of the camshaft lobe most precisely, which is one of the primary goals of a high performance valve train.



Correct geometry at the rocker tip will place the sweep of the rocker tip nearest the rocker arm at fully closed and fully open, the sweep will be furthest from the rocker arm at 50% open, and the rocker tip shall be in the middle of its sweep at approximately 25% and 75% open. This geometry will always result in the narrowest sweep pattern, although there is nothing beneficial about a narrow sweep pattern, it is just a method of evaluating the rocker arm geometry. This description of sweep pattern will be in direct opposition to many of the rocker geometry instructions you shall run across. A few of the camshaft companies are notorious for promoting bogus rocker geometry instructions. The hot rod industry teaches home mechanics (and professional mechanics too) to focus on setting the rocker arm's contact patch on the valve tip, by manipulating the rocker arm's height and the push rod's length, at the expense of other concerns. This may achieve the most rudimentary aspects of rocker adjustment, and it may be convenient, but it cannot possibly result in an ideal adjustment. The most rudimentary aspects of rocker arm adjustment simply keep the operation of the rocker arm within four parameters; (1) the rocker arm should not contact the valve spring retainer when the valve is fully closed, (2) the rocker arm should not contact the push rod when the valve is fully open, (3) the rocker arm slot should never "bottom-out" against the fulcrum, saddle or stud at either extremity of its motion, and (4) the rocker arm tip should never bear down upon an edge of the valve tip; its sweep pattern does not have to be perfectly centered on the valve tip but it should contact the valve tip in the middle half of the valve tip's surface.

As you assemble a cylinder head you can detect rocker geometry and push rod length problems early on by paying attention to the valve stem heights; the valve stem heights should be equal across the cylinder head. If the valve stem heights are unequal, or if one particular valve stem is higher or lower than all the others, you SHALL run into problems.

There are two types of rocker arm designs to consider, the first is the stud mounted, push rod guided type of rocker arm. The height of stud mounted rocker arms is set by the lash adjusting nut (aka the poly lock). Adjusting lash with this type of rocker arm alters the rocker arm's height, and impacts the rocker arm's geometry. In order to maintain consistency in push rod length stud mounted rocker arms are best adjusted mounted on the engine in conjunction with a fixed length push rod.

The other type of rocker arm is the fixed-pedestal mounted type of rocker arm that fastens securely to the cylinder head's rocker arm pedestal. A fixed-pedestal mounted type rocker arm can provide lash adjustment just as easily as the stud mounted variety, by employing a push rod cup style adjuster. The factory rocker arm and the two Yella Terra rocker arms are all of this second type of rocker arm. The high-end T&D and Jesel shaft mount rocker arms are also fixed-pedestal mounted rocker arms. All fixed-pedestal mounted rocker arms are in fact a type of individual shaft mounted rocker arm; they are more stable and contribute fewer rocker arm induced problems to the valve train as long as the saddle/fulcrum is rigid enough. The height of most fixed-pedestal mounted rocker arm is raised by shimming the rocker arm fulcrum/saddle; it is lowered by removing material from the fulcrum/saddle or by removing material from the pedestal cast into the cylinder head. However Yella Terra offers saddles of varying height for their premium YT-6321 rocker arm. This is a very attractive feature of those rocker arms. Increasing valve length also has the same effect as lowering the rocker arm. This type of rocker arm makes it possible to adjust the relationship between the rocker arm tip and the valve tip independent of the push rod, with the cylinder heads sitting on your work bench.

If you are using the factory rocker arms and determine their geometry requires adjustment, a good starting point is to set the height of rocker arm to position the fulcrum’s pedestal approximately in the middle of the rocker arm slot at 50% valve lift. Do not Tufftride the factory rocker arm parts until after the rocker arm geometry has been sorted out.

It is popular to test rocker arm adjustment with the heads assembled on the short block by coloring the valve tips with a felt tip marker, assembling the valve train with the push rods set to zero lash, hand rotating the crankshaft through two revolutions and inspecting the contact patch pattern on the valve tips. As far as I am concerned, the contact patch does not need to be centered on the valve tip, it just needs to stay away from the edges.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72 RS 351 Quote  Post ReplyReply Direct Link To This Post Posted: 29-November-2020 at 1:14PM
Thanks Vince, that is excellent information about detailed guidance for the rocker arms and valvetrain. I was being conservative in my estimates of what would be reliable for the stock rockers.

I like that one paragraph the most, about the Yella Terra rockers. I hadn't read about that part which bolts onto the stud pad as a base for a "shaft" for twin roller bearing rockers. That sounds very promising for long term use.

For the 400 Lizer is building, I think the stock rockers or the Scorpion type of pedestal mount roller rockers would work well. His cam is not a radical lift or duration part, the springs will be under 400lbs I'll bet. The ARP bolts available to replace the stock rocker bolts are another great item to have available, for stock rocker uses.


"If your motor’s cylinder heads are milled and tapped for 7/16” stud & guide plate type rocker arms the Yella Terra YT-6321 rocker arm is the hot tip. This very rugged rocker arm also performs like a shaft mounted rocker arm therefore it requires no studs, guide plates or hardened push rods. Internet pricing for the Yella Terra YT-6321 rocker arm is in the range of $785 US dollars for a set of 16."
Don
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Rockatansky Quote  Post ReplyReply Direct Link To This Post Posted: 29-November-2020 at 2:36PM
the 1st issue with using stock rockers is if they're used or new, if they're used they'll have a wear ridge set in at the travel limits. the wear ridge on the lift side is the one that causes trouble with a cam that has more lift than the cam that wore in the ridges. when the new cam causes the rockers to travel over & past that wear ridge the rocker will balk and jump over the bump like a parking curb. this shock occurring every cycle of the rocker will definitely piss off the cam & lifters

new stock stamped rockers may be up to the task if they're set up at mid-lift, to have equal available travel both ways from center. and depending upon the rocker bodies themselves whether they're able to travel the needed amount at all? in the Ford OHO Newsletter there's an article describing how some rockers are formed a little different than others, you need to check them to make sure the 'bulge' doesn't inhibit travel in the fulcrum or interfere with the pushrod on the outside.




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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rockatansky Quote  Post ReplyReply Direct Link To This Post Posted: 29-November-2020 at 2:42PM
and beware discount offshore rockers, Billy Ray does a lift comparison of 2 rockers out of a set and the results are, not good

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