Air_Adam

Hey guys, I got a problem I need some help with.

I put a new set of heads on my 350 about a month ago, and a set of 1.52 ratio Comp Pro Magnum roller rockers. These are non-self aligning rockers for 3/8" studs.

Now, the problem I have is that I now have a broken rocker stud. I've heard that because of the larger trunion size of the Pro Magnum rockers, they need longer rocker studs as well. Silly me didn't listen.

The stud broke off because the poly-lock did not have enough thread to grab onto. It broke off flush with the bottom of the poly-lock.

Now... changing out the stud(s) is not a big deal, because they are screw-in studs with guide plates.

What I want to know, is what studs I should replace mine with, so that the poly-locks have enough thread to grab onto that I won't have this problem again.

Anyone who has used these rockers and replaced the studs with ones of the proper length, what did you use? I'm looking for a part number (or at least the size) that you used.

My heads are tapped for a 3/8" thread stud, and the rockers are for a 3/8" thread as well.

Please help, I need to get this fixed ASAP!!!

ede

far as i know all studs are the same length, were your heads modified for screw in studs of were they made for them? only thing i can think of is if they were modified too much was milled off the boss. my guess is you have a geometry problem and not a problem with thread engagement. did you check the geometry when you set it up?

Dialed_In

iTrader: (3)

You can buy longer studs but it doesn't sound like that's your problem. That would be a band aid over a bullet hole. The BS you heard about the Comp rocker arms is a load of bull, they will work fine with a stock style/length stud. Is it possible that the trunion was upside down when you installed that rocker? That would account for the lack of thread engagement and broken stud.

Air_Adam

Nope... the trunion wasn't upside down. I caught myself installing a few like that at first, and went over all of them after. None were upside down.

They were modified for screw-in studs and guide plates by the machine shop. They were milled down for them like they should have been.

I know the studs were too short, because on every single poly-lock, the setscrew went way farther down into the poly-lock to 'lock' it than it should have. I've heard of this problem many times because of the size of the trunion on these rockers.

The geometry is good, I used a method RB83L69 desribed in a post a long time ago that I found with a search.

Air_Adam

Also... I remember EvilCartman posting pics of an engine he built with some different heads (aluminum ones.. AFR i think) with the same rockers I am using, and it looked like he had the same problem, with the poly-locks not grabbing enough thread to hold safely. I don't think its a stud milling problem on my heads.

EvilCartman

iTrader: (1)

Yup, the set screws are recessed quite a bit and I still haven't gotten around to getting the ARP studs. The only problem I've had was one polylock didn't get tightened enough and backed off, that caused a pushrod to break.

mw66nova

iTrader: (13)

hmmm....bizarre...i'm running the 113 heads and they are made with screw in studs...my studs are stock though and i'm running the pro-mags (best roller rocker out there for stock style valvetrain imho) and i don't have any issues.

Air_Adam

Yes! thats what I was talking about... you can see exactly what I'm talking about in that pic. See how deep the set screws go into the poly-locks? Thats the problem I have with mine, and it caused a broken stud.

Cartman - What studs are you getting, do you know yet? I need to know which studs will work for these rockers. What size is the base thread on the stock rockers? Is it 3/8" or 7/16"? Everything ARP has with a 3/8" top has a 7/16" bottom thread. If they do indeed have a 7/16" thread on the bottom, then it looks like PN 134-7104 is what I want - longer stud above the hex (0.145" taller), with more threads on it as well.

EvilCartman

iTrader: (1)

Just looked at AFR's site, the ARP 134-7104 studs are an optional part for my heads. Guess I'll be getting them hehe. They list the ones that come with the heads as "standard length".

Air_Adam

So if what you (and probably me) have is 'std length' studs, then the 134-7104's are an optional longer stud then?

EvilCartman

iTrader: (1)

Looks to be the case, I'll order up a set this week and see.

Air_Adam

I just did the same... Hopefully these are what I (we?) need for these rockers.

I just got lucky it didn't snap off at high speed at the track... outcome of that could have been much worse.

sofakingdom

iTrader: (1)

Screw-in studs for SBC are virtually always 7/16", unless you have the "repair" studs.

The actual "installed height" of the stud is HIGHLY DEPENDENT on how the heads are machined. If whoever machined them cut a little more than usual off of the bosses, then the studs will be "too short". The intake ones MAY also run into the top of the intake runners.

Verify that you REALLY have 3/8" studs; and if so, get the right thing in there. Then, if the RIGHT studs (such as ARP, SPS, Comp, etc.) are either too short or they hit the top of the intake runner casting on the water jacket side, you can use washers as spacers to raise them up.

Too long of a push rod, or just simply having to use a real long push rod for whatever reason, will also cause the rocker to end up sitting way high on the stud.

The Comp rockers aren't the problem.

Irockz

iTrader: (1)

SBC studs are 7/16" at the base,where they screw into the cylinder head itself.However,the standard,stock replacement stud diameter is indeed 3/8".
There are a multitude of reasons why your rockers set so high on the stud,including all of the reasons Sofa mentioned,I've ran into the same thing before.
I can't remember the part #,but I know ARP makes a stud that is about 1/4" or so longer,sounds like you've found it.
Sofa is also correct that it's not the Pro Mags in particular that are causing this problem,I've had this same problem on a couple of different occasions,with different brands of rockers.

spartyon

I also am having a problem with rocker arms but its not the stud thats the problem. I am using Motown 220 heads with the arp head studs that they recomend. The problem is that my crane golds don't sit flush with the stud bottom. They sit higher. Is this going to be a problem. After measuring for a pushrod that is where the best alignment fell. I do, however, get "a lot" of the stud to screw onto.

SLEEPER 86

spartyon;
you don't want the bottom of the rocker arm contacting the base of the stud where the diameter gets wider.
you are fine where you are at. how much is a lot?

adam & cartman;
did you guys take a sharpie and mark the valve stem tip, then set valve lash and rotate the assembly a few times to check rocker arm geometry? the wear pattern should be centered on the valve stem tip, and the narrower the better, but not as important as a centered wear pattern. if the wear pattern is high on the tip, you need longer pushrods. if it's low (towards the exhaust), you need shorter pushrods. a checking pushrod is really helpful here. lots of people make them, but i really like the comp hi-tech one that has measurements marked on it. about 25 bucks though, that will tell you exactly which length pushrods you will need.
next you need to set the spring installed height. the best and easiest way to check this is to use a valve spring height micrometer (about $39 from various places). i hate to buy tools i will only use a few times, but these are worth it!).
once you get the pushrod length and spring height right, you can set the valve lash. you can do a search for that depending on the type lifters you have. also be sure you don't have any binding between the pushrods and heads.
that should get you set up, if you still have issues with stud length, then consider longer studs. until then, think about other issues.
DON'T forget to check clearance between the retainer and guide, the outer spring coils at full lift, and (if you have them, the inner spring coils. the damper (the flat wound spring) should be fine. one last thing, make sure your pushrods are straight by rolling them across a piece of glass.

Eric B

TTOP350

iTrader: (8)

use ARP studs with poly locks. the set screw wont set square on the cheaper brand studs because they arent ground flat across the top.. I have seen many AFR heads with broken studs because they use the cheap ones

Air_Adam

My rocker geometry is good... it was checked when the top end was reassembled. Turned out I didn't need pushrods any longer than stock. I just used stock length pushrods and they give the proper geometry, so I doubt its a 'pushrods are too long' problem. The other rockers all appear to be almost bottomed out on the studs... like, just barely above the hex. This is why I think its just that the trunion size is the problem? It is significantly bigger on these rockers than others I've seen.

Sofa - Indeed the studs do have a 7/16" base. Thanks for pointing that out. I knew that, it just slipped my mind when I wrote that post. Thanks for the correction

I'm not sure exactly what 'stock spec' for machining the stud bosses is, but I asked the shop that did my heads, and they were machined and checked to be factory specs for screw-in studs with guideplates.

EvilCartman

iTrader: (1)

Just to add in, my rocker geometry is also good.