Hot Rods Push rod guide plate--SBC

I've searched all I can regarding guide plates on a SBC. The situation is that the heads that came with my project originally had the pressed in rocker studs. Somewhere, those were removed and the heads were tapped for studs. So far, so good.

All the information states that the heads must be machined to allow the use of guide plates but it never says just how much.

May I assume that the stud spot faces must be machined the thickness of the guide plates in order to keep the geometry the same?

 

From what I have observed, guide plates are only needed when the cylinder heads you are using have large holes for the push rods or no hole since entire area is removed. In stock heads the small elongated hole was the guide plate. In 1963 I removed the press in studs and had the holes taped for screw in studs with no refacing of the head. Before that I left in the pressed studs and drilled into the cast iron at the side of the stud, taped the hole with the stud in place 10-24, and put in a short set screw. Both worked well.
Today the racing heads we buy have the flat area and I'm including photos of EQ 350CH heads. It's very precise and a different angle and plane of the bolting, spring seats, or valve cover machined surface.
The machining would need to be a 90* angle to the stud to keep original fulcrum point. Depth would be as you say at least the thickness of the plate. If you are using taller springs and push rods it would not matter as much. If you do this; remember to drill out the original guide holes in the heads. Good luck.

 

the height of the pad won't affect rocker geometry...it will only affect how far the nut threads on to the stud. right?

 

The guide plates that I have seen installed use a specific type of stud. This stud has a hex in the middle of it's length used for installation. The base of the hex clamps the guide plate in place.

Some screw in studs are basically the same diameter as the press in studs and don't have a hex for installation.

The hex type studs require the stud boss to be machined down to allow the base of the stud, once installed, to be the correct height and have the proper thread length for valve lash adjustments.

To answer your question, yes the boss would be cut down, but if a hex style stud is used, that increases the depth of cut.

 

Thanks for the responses. When I tried to adjust the valves with the guides in place the roller part of the rocker ended up on the edge of the valve stem. Upon hand cranking I determined that it only got worse with the roller nearly off the valve stem before recovering some.

I then tried the same thing without the guide plates (thickness of .125") in place. This time the roller landed where it was supposed to be.

That would mean that the boss should be cut down .125"?

 

Or longer push rods if that will help with the contact pattern on the valve stem.

 

I tried that with a Comp Cams length checking tool and that made it worse but on the other side of the valve stem.

 

Yes if you are using guide plates you machine the pedestal the thickness of the plate. Also a good time to open up the pushrod holes in the head.

 

All that should do is place the rocker .125 further down on the stud and less lock inside the poly locks. Adding guide plates should not effect rocker placement. The rocker would still be the exact same distance from the head, just have a plate between them now. That is dictated by push rods. Have you also changed rockers? Different heads than you were running? Different cam and/or lifters?

The only reason to machine the thickness of the plate is if you cannot get the rocker low enough to get the geometry right. On some heads you need to machine them because the thickness of the plate and hex shoulder of the stud don't let the rocker sit down where it should.

SPark

 

That is exactly what is happening. Thanks for the explaining it so it made sense.

 

Usually, .400" is the target thickness to remove from the top of the stud bosses for using guide plates.

 

I don't think it was mentioned but not only on a dimensional/rocker pivot/stem contact aspect, due to inconsistant casting a very important reason to machine the stud pedestal is to establish a true flat pad for the stud to torque against and stay torqued.

 

The other problem is that I think that these heads have had machine work on the rocker side. Is there a measurement for the boss as cast? Or a measurement from the face to the stock boss? I would be ok with the .400 number but I need to know how much, if any, has already been removed.

 

Messure the thickness of the hex on the screw in stud and the thickness of the guide plate... Add the 2 together...
That's how much to buzz off the stud bosses....

 

They make screw in studs without the hex.

 

I should add that if the push rod holes have been drilled out you will need guide plates or self aligning rocker arms.

 

If the PR holes have been opened up, how would SA rocker arms work?

Also, what would hold the guide plate in if the stud didn't have a hex?

 

If you do use guide plates, your also gonna need hardened pushrods..,. Those are a must!!!!

 

The rocker centers itself on the stem of the valve.
So you don't need guide plates.

 

A good set of pushrods and sufficient pushrod to head clearance and I don't really see the need. Are you going to buzz this thing 12 grand? Lippy

 

If you are turning 12 grand you will need guide plates with wider slots for those big Smith bros pushrods. LOl. THEN, pushrods are your least problem.