john-e-boy

Do the heads need to be machined or anything?

From the looks of it, it looks like the guide plate will raise the rocker about 1/4 of an inch or so. Won't that effect the performance?

I am using manly valves, compcam rockers, crane springs, on LT4 heads do I need to do anything to make the guide plates work?

Thanks
John

Bud M

The guide plate will raise the rocker arm stud by the thickness of the guideplate material. Since the rocker arm adjuster screws down on the stud to the same height the rocker arm will not sit any higher because of the guideplate.
I have not worked on an LT4 head but it should all go together easily.

john-e-boy

If I am picturing it right, the guide plate raises the stud say 1/4 inch which inturn raises the rocker 1/4 inch so wouldn't that change the height of the rocker?

I am thinking that shouldn't where the stud mounts be milled down the thickness of the guide plate.

Just trying to understand

thanks
John

shoebox

The rocker will merely ride a little lower, relative to the height of the stud. IOW, the adjusting nut will be screwed down a little further so that the rocker will be in the same relative position as it was before. (at least that is the way I see it)

Mtrhds94Z

Your 1/4 inch 'estimate' is way off... [ it's more like a 1/16-3/32"] Therefore not really a problem.. it's about 2 more turns down on the adjusting nut..

john-e-boy

OK sorry, was just throwing an assumption out there for the sake of visualization. Just measured them they are approximately 1/8 inch.

Just to make sure, that 1/8 of an inch isn't going to effect anything?

Am I visualizing this wrong, I am percieving it as the nut pushing the rocker down on top of the stud where it flares out.

Is it really that the rocker is pushing up on the nut and doesn't really touch the flared part of the stud because the height of the valves and the height of the pushrod keep it suspended off the flared part of the stud and pushes against the nut and insert. ( I think I am starting to see it right)

I am not trying to doubt anyone, just want to get everything done right.

Thanks
John

Dave88LX

Wow. I think I'm even more confused now that I read this thread.

I guess I'm not understanding how tightening a nut will compensate, unless it pushes the rocker arm further down the stud? I'd need pics to understand I guess.

thewinner

lol who cares? they are proven to work. just leave them alone.

Dave88LX

I'd venture to guess the people that are about to drop $600+ on a valvetrain care.

shoebox

The rocker just floats on the stud. The stud keeps the rocker centered in the correct position relative to the pushrod and valve. The pushrod is holding it up on one side and the rocker is resting on the valve stem on the other side. The rocker does not sit down on the base of the stud. I really don't know the amount of space there is between the bottom of the rocker and the base of the stud, but adding guideplates will not make enough difference to matter.

Check out this cutaway drawing. I just noticed that it even shows guideplates under the rocker studs . You can see that the bottom of the rockers are up off the base of the studs.

thewinner

dave, tons of people run guideplates with no problems. You are being too cautious

Dave88LX

LOL thewinner, you sould like the guy on the phone when I called Scat asking them what the compression height was on the pistons that came with the LT1 383 rotating assembly. He told me that I was trying to "overengineer" things. I wanted to punch him right there and then Not saying I want to punch you, don't take it that way haha.

I'm just saying, with so many parts of the engine and so many clearances coming down to the .001 to .005, and the fact I'm about to drop $3000+ on this engine that I could be spending on this 5.8 Turbo that I'm trying to get goin (Yeah a FORD! ), I don't think trying to understand this to the best of my ability to make the best decision for my application is really a problem. I think it's rather smart "Too cautious" my ***

Shoebox, cool drawing man! That makes a lot more sense how you explained how the rocker arm sits. I'm just tryin to see which is the best way to go. I'll probably need new pushrods anyways

GA93FORMULA

The rule regarding guideplates is to machine the rocker stud boss the same thickness as the guideplate to be installed/introduced. Failure to do so will not likely cause a noticeable loss of power... at least not initially. However, it will certainly upset valvetrain geometry. As a result, more frictional related heat is created; valve springs will fatigue quicker, valve guide wear will increase and eventually the valves will land on their seats in different locations and disrupt the valve to valve seat seal. Then compression will fall off due to gases blowing by the unsealed valves. Power losses from the above mentioned can easily reach 40-50 horsepower, and even more with power adders. All those little geometry related errors add up quickly. Excessive valvetrain friction kills torque. The goal is a rigid & stable valvetrain with minimal frictional related power losses.

shoebox

Since the rocker arm floats on the stud, there is no geometry change unless you change the length of the pushrod or valve stem. Regardless of the length of the stud and when lashed identically, the rocker arm is going to sit in the exact same place relative to valve.

On engines that you merely torque down the rocker arms, the stud height at the base would matter.

GA93FORMULA

Alright Shoebox, I see your argument. But, I still disagree. Where did you get your info on guideplates in relation to valvetrain/rocker geometry. True, the rocker arm floats and will sit in the same place relative to the valve, but not relative to the rocker stud boss. The rocker arm would be a greater distance from the rocker stud boss (unless the bosses are machined accordingly). Hence, the travel of the rocker arm tip across the top of the valve stem is altered. Correct pushrod/valve stem length is (as you noted) crucial to rocker arm geometry. Check out page 93 of the book: John Lingenfelter on modifying SBC. Also check out page 55 of the book: Building and modifying SBC cylinder heads by David Vizard. Both men are engineers and highly reputable race engine builders. Both clearly state the importance of machining the rocker stud bosses when installing guideplates (on SBC heads previously unequipped with guideplates). Sure, I would like to bypass this particular machining process and save the time and money, but I like to be absolutely sure my valvetrain is dead on.