[markb0729]

I just put the heads back on a 66 289. The engine is pre-rail rockers. I had the guide holes in the heads drilled out, milled the rocker bosses and installed screw in rocker studs with guide plates. The push rods are standard length (6.800") Comp Cams hardened push rods (Part # 7632-16). I replaced the stock stamped rockers with comp cams roller tip rockers (Part # 1442-16).

I marked the valve tips with a dry erase marker on the intake and exhaust valves on cylinder 1 and set the lash. I rotated the engine and removed the rockers to check the rocker contact area on the valve tip and have a few questions.

1) The marks on the valve tips are a bit towards the exhaust side of the heads. The rocker travel on the valve tip is .075". After a ton of reading, it seems less rocker travel on valve tip is more important than the contact point being centered on the valve. Does my setup look okay or should I try to dial it in better?

2) The rockers seem to sit very close to the base of the screw in studs. I'm use to how the stock rockers sit on the previous press in studs which has a lot more space between the base of the rocker and rocker stud boss. I can turn the rocker adjustment screw about another half turn before it bottoms out on my current setup. Does this seem okay?

Below are some pictures:

1) Rockers Top
2) Rockers Front
3) Rockers Back
4) Valve Tips with marks
5) Intake Valve Tip
6) Intake Rocker Clearance
7) Exhaust Valve Tip
8) Exhaust Rocker Clearance

 

[maladezo]

I am no expert as I have always ran rocker shafts. But, it seems longer pushrods would put the contact area farther off center. The width of the contact area appears reasonable to me. And it is not very far off center. Did you try a pushrod length checker? I would think that would be a must. You are wise to take your time on this.

 

[zray]

Were the heads milled the thickness of the guide plates ?

I've used guide plates on two sets of HiPo heads without having to mill anything, and still had more room than what you have under the rocker arm. I was using Crane Gold Race rocker arms. But my Ferrea valves (1.94 / 1.60 ) were slightly longer than stock valves, so I used push rods that were slightly longer too. That moved everything away from the ARP studs.

Z

PS. For those people adding screw in studs, but not using guide plates: Do your studs have flat bases, or do they have a raised circumference ? If they're not completely flat , like the stock HiPo studs, you are at risk of cracking the stud bosses unless they are relieved. The ARP studs are not completely flat, unless they've changed them recently.

 

[markb0729]

I am no expert as I have always ran rocker shafts. But, it seems longer pushrods would put the contact area farther off center. The width of the contact area appears reasonable to me. And it is not very far off center. Did you try a pushrod length checker? I would think that would be a must. You are wise to take your time on this.

I have a push rod length checker but it has the lock nuts on it and won't work with the guide plates. Rather than buy a new checker, I'll get some washers the thickness of the guide plates and do some lengthening and shortening of the adjustable push rod and see what happens. The reason I asked about my current setup is that I currently have 6.800" push rods (stock length) and was wondering if the setup looked good as is. I'll adjust the length on the adjustable push rod and take some additional measurements. Nows the time to do it.

Were the heads milled the thickness of the guide plates ?

Yes, the rocker bosses were milled. I have some before and after pictures of the heads and I can tell they were milled. I'm assuming they were milled the thickness of the guide plates but I wasn't there when it was done so I can only hope that was what was done.

 

[pollock]

One sentence in your post jumped out at me: "I can turn the rocker adjustment screw about another half turn before it bottoms out..."

Maybe I am missing something, but the nut that holds the rocker down is really used to adjust your lifters. You are familiar with that procedure, right? Make sure the valves are fully closed (piston at TDC of compression stroke). Run the nut down finger-tight until the roller contacts the valve tip. Then turn it another 1/4 to 1/2 a turn and tighten the lock nut.

But that makes me notice another thing. It seems like your rockers should have lock nuts, maybe like the ones in this photo?

 

[pollock]

But, it seems longer pushrods would put the contact area farther off center.

This is correct. The photo indicates a shorter pushrod would tend to move the contact area to center.

 

[pollock]

I have a push rod length checker but it has the lock nuts on it and won't work with the guide plates.

I ran into this too. I was able to flip the checker over so that the nuts were in the lifter valley. I may have had to drop in there prior to bolting the guide plates down - can't remember.

 

[funnelcake]

I think you need longer studs. Ideal sweep is .060 or less and reasonably centered.

A Pushrod Length & Rocker Arm Geometry "Must Read"

 

[markb0729]

One sentence in your post jumped out at me: "I can turn the rocker adjustment screw about another half turn before it bottoms out..."

Maybe I am missing something, but the nut that holds the rocker down is really used to adjust your lifters. You are familiar with that procedure, right? Make sure the valves are fully closed (piston at TDC of compression stroke). Run the nut down finger-tight until the roller contacts the valve tip. Then turn it another 1/4 to 1/2 a turn and tighten the lock nut.

But that makes me notice another thing. It seems like your rockers should have lock nuts, maybe like the ones in this photo?

I’m familiar with the procedure for adjusting the valve lash. I did exactly what you said with one difference. I tightened the rocker but 3/4 turn at zero lash which is what most here say to do. You have a good eye. The nuts on the rockers I’m checking are just regular non locking nuts. I have locking nuts but using regular nuts for this procedure is easier to do and is easier on the rocker stud threads.

The bottoming out I mentioned happens after I adjust the preload on the lifter 3/4 of a turn at zero lash and then go another 1/2 turn after that. I’m not with the car at the moment (gotta pay the bills) but I’m not sure if the lifter is bottoming out or I’m running out of threads on the rocker shaft that’s why I was asking about the space between the rocker and the bottom of the rocker shaft.

 

[pollock]

Cool.

Yeah, the bottom of your rockers looks a little too close to the fillet at the bottom of the studs. 1/2 a turn on a 3/8-24 thread is only about .020, so that seems a bit too close for comfort. A longer pushrod would help but it would make your roller/valve tip situation worse. Longer studs, as suggested, would not help. The easiest fix I can think of is to have the stud bosses milled down a bit more.

Another thing to watch out for - make sure your rockers don't get misaligned by the guide plates. In other words, the slots aren't lined up properly between the lifter and the valve, and the rocker ends up a little crooked. That happened to me and over time the roller tips cut into the aluminum rocker bodies. I see that yours are steel so it would be slightly less of a concern. Comp Cams sells a split/adjustable guide plate now, just for this reason.

 

[macstang]

Probably not the answer you want but I would not leave that. It will wear the guides faster. If it was just a hair off center it is ok as long as the pattern is tight but I think yours is a bit over an acceptable offset of the pattern.

 

[markb0729]

Cool.

Yeah, the bottom of your rockers looks a little too close to the fillet at the bottom of the studs. 1/2 a turn on a 3/8-24 thread is only about .020, so that seems a bit too close for comfort.

My thoughts exactly.

A longer pushrod would help but it would make your roller/valve tip situation worse.

And a shorter push rod would require turning down the adjustment screw on the rocker more. Correct?

Longer studs, as suggested, would not help.

I'm not sure how a longer stud would help. But I welcome being enlightened. Threads going further down the stud would help but it would that would require a different stud design. Something like this: https://www.summitracing.com/parts/mrg-1076/applications

The easiest fix I can think of is to have the stud bosses milled down a bit more.

Crap! I was afraid of that. $44 in head gaskets down the drain. I wonder how much got milled off in the first place? I'll see if the shop remembers but I have my doubts.

Another thing to watch out for - make sure your rockers don't get misaligned by the guide plates. In other words, the slots aren't lined up properly between the lifter and the valve, and the rocker ends up a little crooked. That happened to me and over time the roller tips cut into the aluminum rocker bodies. I see that yours are steel so it would be slightly less of a concern. Comp Cams sells a split/adjustable guide plate now, just for this reason.

I haven't payed close attention to the rocker alignment yet and nothing has jumped out with respect to cylinder 1 but will check to make sure everything looks good. Hope I don't need adjustable guide plates.

Mark

 

[markb0729]

Probably not the answer you want but I would not leave that. It will wear the guides faster. If it was just a hair off center it is ok as long as the pattern is tight but I think yours is a bit over an acceptable offset of the pattern.

This is in reference to the rocker contact pattern on the valve tip. Correct? Are you are saying the pattern is off center too much and the pattern should be tighter?

 

[macstang]

The width looks ok to me but it is off center just a bit more than I would want.

Photo below courtesy of Lunati is the ideal but give take a hair either way off that would pass if it is not any wider.

 

[todd m]

Hello,
New to the forum. My Stage II 302 has a burned valve and I'm looking to go with new heads rather than going through these again.
The Edelbrock E Street PN 5025 is my choice, so far.
Any thoughts on aftermarket heads? Experience? Advise?
Thanks!

 

[markb0729]

The width looks ok to me but it is off center just a bit more than I would want.

Photo below courtesy of Lunati is the ideal but give take a hair either way off that would pass if it is not any wider.

Okay, got it. Thanks.

 

[markb0729]

Hello,
New to the forum. My Stage II 302 has a burned valve and I'm looking to go with new heads rather than going through these again.
The Edelbrock E Street PN 5025 is my choice, so far.
Any thoughts on aftermarket heads? Experience? Advise?
Thanks!

You'd be better off starting a new thread rather than posting this here. You'd probably get more responses directly addressing your question.

 

[kenash]

Hello,
New to the forum. My Stage II 302 has a burned valve and I'm looking to go with new heads rather than going through these again.
The Edelbrock E Street PN 5025 is my choice, so far.
Any thoughts on aftermarket heads? Experience? Advise?
Thanks!

Welcome to the forum. In fairness to you and to get you the best exposure to the talent here, you should re-state this question in a new thread. It's inserted into an existing thread regarding a much different issue. Thank you for offering.

 

[markb0729]

Okay. Consensus is that the center line on the valve tip is off, to far towards the exhaust side of the head. I kind of thought that too but you folks confirmed what I suspected. Thank you.

I pulled off the guide plate on cylinder 1 and put in some washers to match the thickness of the guide plate so I could use my push rod checker with the lock nuts. I adjusted the push rod length from the original 6.800" length to 6.750". The pattern on the valve tip moved closer to center BUT with the 6.750" push rod set at zero lash, I had only about a half turn on the rocker nut before it ran out of threads and bottomed out. As suspected, the rocker stud bosses need to be milled a bit further. I suspect my best push rod length is going to be in the 6.700 to 6.650 range. Regardless, the heads have to come off and the rocker bosses need additional milling. How much? I'm not sure but based on where I started and where I need to be, I'm estimating around 3/16". Do you folks think 3/16" is reasonable? I'd hate to weaken the bosses.

 

[macstang]

Just guessing that they didn't knock off the tops of the bosses to compensate for the thickness of the guide plates and the hex nutted end of the screw in studs. I have seen .220 quoted but the machine shop should have the exact number. Now comes the question, did they thread the bosses deep enough for your screw in studs after .220 is knocked off the bosses? This starts to sound like a complete do over sort of a thing for the machine shop.