Rail Type Rockers - need expert assistance

[oz]

Greetings,
I am rebuilding my 1969 302 now and am having some problem underatanding what I can and can't do with rail type rockers.

I bought an Edelbrock #7122 cam from a friend (224/234 dur; .496/.520 lift) and the Edelbrock catalog says in the notes that i have to use guideplates. The funny thing is that there are only 2 cams in the whole Ford section of the Edelbrock catalog that say this. They even sell basically the same cam under another number (#5082) for a 351W in the 'Torker-Plus' category and it does not say anything about guideplates (and it uses the same springs, etc).
To make it even stranger, Comp Cams sells tons of Ford cams and not a single one calls for guideplates... In fact, they call for their rail type roller tip rocker for all early Ford applications.

I asked Edelbrock for an explanation and all I got was the 'ya better do it or you'll void the warranty' crap. I wrote a 'stonger' followup email but if I can't get any usefull info I will have to call Comp or Crane, etc...

I have a good set of rail type valves (taller stem above lock) and screw in rocker studs (already installed). I plan to add roller tipped rail rockers (Comp or Coast High), locking nuts (adjustable), and go without guideplates with stock replacement (hardened) pushrods.... Will this work in my '69 or am I missing something???

Can anybody shed some light on this???

THANKS!!!!!

 

[rbohm]

the problem with rail rockers is that they dont tolerate cam with lifts much higher than the stock hipo 289 cams, which is .459 valve lift. much higher than that and you need to use a non rail rocker arm with guide plates. best to buy a set of roller rockers with the cam you want to use also.

 

[TOM B]

Rail type rockers are a cheap way of trying to stop the rocker from twisting off the valve. This type of rocker will put a heavy twist, side to side load on the valve stem, valve guides and on the rocker stud, (Not wanted) At higher RMP's and spring tension the more twist you must stop or you Will bent your valve stem or at least ruin your valve guides. Guide plates stop the twist at the pushrod so there is no twist in the rocker, stud or valve stem, but you must use hardend pushrods (Much Better). Company's like Edelbroke cant list everything else you need when swaping a cam or another part as they are not a school, but will sometimes tell you something about a part that they tested or had lots of returns for to protect themselfs. some company's have no comments or notes at all.
I would go with the guide plates, no questions asked, to protect your investment.

Hope this helps.

 

[D.Hearne]

If you've already popped for screw in studs, then you may as well go ahead and install guide plates under them, and get non-rail type roller rockers. The rail type rockers tend to chew up the valve tips. and with high lift cams , sometimes the "rails" can hit the retainers, this situation can ruin your day when you drop a valve.

 

[oz]

So if I were to convert to guideplates and regular rockers, could I save the valves since I have a good set of them with the longer stems (to account for the rail rockers)? Can the extra stem length be ground down by the machinist and reused?

What about adding the guideplates, will I need to get the heads cut down under the screw in studs to make up for the extra thickness of the guideplates?

Finally, if I were to add the guideplates, and could NOT grind down the long stem (rail type) valves, is there any way I can keep the valves? Once I add guideplates and assuming I have adjustable rockers, does it make a difference what valves I use? The alternative is to get new valves, guideplates, rockers, and hardened pushrods I guess.

THANKS!!!!!!!!!!!!

 

[D.Hearne]

You can keep the valves you have now. Ditto for the pushrods ( most likely) all that you need do is remove the studs, install the guide plates under them and screw them back down.( use a torque wrench and loctite on the studs) With shorter valve stems, you might run into problems with the guide plates raising the studs high enough to interfer with valve adjustment and the rockers bottoming out on the studs, but your valve stems are longer so this shouldn't be a problem. It would be wise to check for binding after installing the plates and rockers and adjusting a couple to spec, then rotating the motor to cycle the valves and see if anythings out of whack, before starting the motor though. And also check the geometry of the pushrods,rockers, and valve stems to be sure it's correct.

 

[TOM B]

You will have a lot stronger and properly set up system with non rail rockers and guide plates. Racers often use .100 longer valves when they build engines, this gives you a better geometry setup. In other words it helps to set up the rocker in the proper degrees so its roller tip hits exactly in the center of the valve stem and also to push the valve down straight and not at an angle to prevent guide and seat wear. The push rods do the same thing. if there to short or to long you will have a rocker roller that will pull back or push forward on the valve tip. Put it together with heads torqued and adjust 1 or more valves, then look to see where the rocker Tip is on the valve stem and look to see how far down you are to bottoming out on your stud. also check the rocker stud hole to see if it binds or gets to close to the end of the rocker slot when the valve is up and down position. This is where you measure for push rod lenth that you need to get it right. The only tool you might need is a pushrod measurement tool or make one yourself. Hope this helps and I didnt confuse you more. This is pretty easy way of doing it and YOU CAN do it OZ!.
Maybe someone else can explain it better.

 

[D.Hearne]

I think you just about covered it

 

[oz]

Thanks everyone, it does make sense. A friend of mine told me that if I wanted to add guideplates that I would have to have the screw in stud bosses machined down by the thickness of the plate to keep the geometry proper but if I understand correctly, the extra height (both valve and stud) will be an advantage... the only issue will be with pushrod length (and valve cover clearance) necessary to ensure proper rocker tip to valve interface.

As a side note - what is your opinion of the roller tipped rail type rockers sold by Comp? They spec them for all their Ford cams.... if this is an inferior way of doing it - why do they recommend them?

I went through this on my 5.0 but it has pedistal rockers so adjusting was done with shims (which wasn't necessary in my case).

Thanks again and Happy New Year!

oz

 

[D.Hearne]

Thanks everyone, it does make sense. A friend of mine told me that if I wanted to add guideplates that I would have to have the screw in stud bosses machined down by the thickness of the plate to keep the geometry proper but if I understand correctly, the extra height (both valve and stud) will be an advantage... the only issue will be with pushrod length (and valve cover clearance) necessary to ensure proper rocker tip to valve interface.

As a side note - what is your opinion of the roller tipped rail type rockers sold by Comp? They spec them for all their Ford cams.... if this is an inferior way of doing it - why do they recommend them?

I went through this on my 5.0 but it has pedistal rockers so adjusting was done with shims (which wasn't necessary in my case).

Thanks again and Happy New Year!

oz

Your friend may still be correct in saying that the stud bosses may need machining down. This depends on if the machinist that installed the studs, did this operation or not, and whether or not you will have interference from the guide plates being there. What you can do is take one guide plate and install it, then check for interference. In my opinion , Comp Cams roller tipped rail rockers are just a stop-gap measure to please a certain customer base that wants roller tipped rockers, but has the stock valve train and doesn't want to remove the heads and pay to have screw in studs & guide plates installed. It will work in some situations, but for someone who wants serious power and rpm capability,it ain't the way to do it. Comp Cams recommends it, because they have made a product and have to sell them to make money, they are a business afterall.

 

[oz]

I understand. Thanks!