462 Double Hump Heads & studs - Chevelle Tech
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  #1  
Old Feb 8th, 13, 5:27 PM
tlray tlray is offline
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Default 462 Double Hump Heads & studs

I have a set of 462 double hump chevy heads, just put screw in studs in and am using 1.5 roller rockers. Problem is:stock pushrods are too short, I have a set of trick flow 8" pushrods and they are also too short, the rockers bottom out against the bottom of the studs. Looks like I either need a 8.5 pushrod or get the boss's that the studs screw into milled down. Also the rocker roller wants to lay on the outside of the valve tip. I guess the question is: should I just go with longer pushrods or get the heads milled?
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  #2  
Old Feb 8th, 13, 6:34 PM
Tom Mobley Tom Mobley is offline
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Default Re: 462 Double Hump Heads & studs

the bosses need to faced down the thickness of the hex on the stud plus the guideplates. The hex on the stud needs to have a machined flat spot to seat on, otherwise the studs will break off under the head.

Are you using the studs that are screw-in but have no hex section, have to be double-nutted in?
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  #3  
Old Feb 8th, 13, 6:42 PM
tlray tlray is offline
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Default Re: 462 Double Hump Heads & studs

No Tom I am using the studs with the hex on them, but now that you mention that. Would studs with no hex work without milling the heads? I figure that the heads need about .400 milled off for the rocker roller to be centered in the valve head. Is there enough thread left after that to hold the stud?
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  #4  
Old Feb 8th, 13, 6:53 PM
RB69SS396Conv RB69SS396Conv is offline
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Default Re: 462 Double Hump Heads & studs

Sounds like the top of the stud bosses didn't get milled off as far as they should have.

Usual figure is somewhere around .375"; although that's not the "smart" way to measure it, since that's an "as-cast" feature and therefore not particularly precise. Works better to cut them to the same height above the deck, but I don't know that dimension off the top of my head.

Yes there is enough thread left; however there may not be enough water jacket. In some heads of that series of casting, the stud will bottom out on the outside of the intake ports, unless you cut a bit off the studs.
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Old Feb 8th, 13, 10:44 PM
Tom Mobley Tom Mobley is offline
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Default Re: 462 Double Hump Heads & studs

you can use the type with no formed hex without facing the bosses down. no guideplates. inspect the factory pushrod guide slots in the heads, make sure there's none getting "wallered out."
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  #6  
Old Feb 9th, 13, 9:24 AM
tlray tlray is offline
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Default Re: 462 Double Hump Heads & studs

I wasn't going to use the guide plates, not sure if I should or not. Since I am going to have to have the boss milled anyway, I guess I might as well. I am putting the heads on a 383 stroker with a 225/470 cam. Not planning on real highs revs. The guide plates keep your push rods centered and less chance of bending? Is that right?
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  #7  
Old Feb 9th, 13, 9:26 AM
RB69SS396Conv RB69SS396Conv is offline
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Default Re: 462 Double Hump Heads & studs

Somehow, the rockers have to be held straight and lined-up on the valves.

There are 3 common methods available: the slots in the heads, where the push rods go through, fit tightly to the PRs; guide plates, which do the same thing, but the holes in the heads have to be much larger so as not to interfere; and "self-aligning" rockers, which have little "rails" on the tip that enclose the valve, also requiring the larger holes through the heads.

One AND ONLY ONE of the 3 methods must be in effect at any one time. If 2 of them exist, they will "fight" each other, and almost certainly, something will bind SEVERELY somewhere, and parts will ALMOST CERTAINLY be destroyed brutally.

The slot method was used on virtually all stock SBCs (except for a very few high-perf ones, which used guide plates). The SA method is used on all SBCs from around 87 up. The guide plate method has been the favorite for racing for many years.

IMO the SA mehtod is "best" for a street motor, because it unambiguously forces the actual thing you want to control (rocker tip location on the valve stem) to be right. However it doesn't allow for ideal geometry in all cases when very high lifts are used.

Guide plates is the old standby. Been working well for A LONG TIME.

Slots in the heads has several issues (not least of which is, forcing the casting material to bear directly against a moving part) and is the least preferable IMO.

I would strongly suggest that you take the heads off, have the bosses milled down correctly and the holes for the PRs drilled out, and install guide plates and the studs with the hex. The studs on stock heads go into the water jacket and will leak coolant into the crankcase around the thread if not sealed. It's near impossible to guarantee that the ones without the hex shoulder will stay sealed over the long term, because they don't tighten "against" anything.
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  #8  
Old Feb 9th, 13, 9:52 AM
tlray tlray is offline
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Default Re: 462 Double Hump Heads & studs

Yes I think that is the best to do, heads milled, hex studs and guide plates. The heads are already off and I only have one set of springs on. The heads do have the slots for the pushrods, So I need to drill them out bigger so not to interfere with guide plates?
I assume by your username you have a '69 convertible? That is what this engine is going in, but mine is a Malibu. Any Pics?
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  #9  
Old Feb 9th, 13, 11:05 AM
Strokd66 Strokd66 is offline
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Default Re: 462 Double Hump Heads & studs

"It's near impossible to guarantee that the ones without the hex shoulder will stay sealed over the long term, because they don't tighten "against" anything."

The Pioneer replacement studs have a small ring at the top of the thread to tighten up against
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  #10  
Old Feb 9th, 13, 11:22 AM
RB69SS396Conv RB69SS396Conv is offline
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Default Re: 462 Double Hump Heads & studs

No, no pics unfortunately...

It's a gold SS with black top, stripes, & interior. It's a work in progress. (or, usually, mostly NOT in progress...)

Yes, the holes need to be drilled out; they can be made QUITE large before they run nito anything. The first thing they'll hit is the intake port, and you can see, that's quite a bit of material you can safely take out. Most people drill them to around " to 5/8", with the top tilted a bit toward the stud, and the whole hole (try saying THAT as fast as you can a bunch of times!!) nearer to the stud than stock, because that's the way the push rod moves more as lift increases, and to accommodate higher-ratio rockers.

And on those hex-less studs, if you tighten them enough to actually lock them in place enough that they won't accidentally back out when you loosen the rockers, you run the risk of splitting the boss. (yes I've seen heads ruined that way) I don't think they're A Good Idea at all. A "desperation" repair for a pull-out that pulled out, sure; a deliberate "build" option, not so much.
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  #11  
Old Feb 9th, 13, 12:26 PM
tlray tlray is offline
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Default Re: 462 Double Hump Heads & studs

Ok, I have the heads back into the bags, ( I just got them back from the machine shop to hot tank them and checked) Since I have the hex head studs anyway I am going with them and mill, and drill. Still waiting on a block anyway. Three 350 blocks cracked so far. One I thought was, the other I did all the relieving for the 400 crank and then took it to the shop to bore and clean,Duh, Cracked! The guy I got it off of took the next one to be checked. Cracked. He has more and is making it good.
I know the work in progress thing. I've been on my Chevelle for over 10 years, on the rotisseri for 5 years. Off and back on the frame, new rear quarters done, new door skins done, wanting to put the engine in before final install of fenders. I bought it when I was 19 I'm 57 now.
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  #12  
Old Feb 9th, 13, 4:57 PM
Tom Mobley Tom Mobley is offline
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Default Re: 462 Double Hump Heads & studs

>>> "I bought it when I was 19 I'm 57 now."

Why rush into anything?
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  #13  
Old Feb 9th, 13, 7:41 PM
RB69SS396Conv RB69SS396Conv is offline
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Default Re: 462 Double Hump Heads & studs

THat's like me... I was going to procrastinate, but I never really got around to it. Some day maybe I'll think about formally putting that off until ... later.
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  #14  
Old Feb 9th, 13, 8:53 PM
tlray tlray is offline
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Default Re: 462 Double Hump Heads & studs

Quote:
Originally Posted by Tom Mobley View Post
>>> "I bought it when I was 19 I'm 57 now."

Why rush into anything?
Well....I drove it until 1990 and kept hearing this noise when I hit a bump. Floor pans rubbing the driveshaft. Parked it Got married, had kids, played guitar in a Long Haired Rock n Roll band, Got around to working on it...10 years ago. It will be worth the wait.
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  #15  
Old Feb 9th, 13, 8:55 PM
tlray tlray is offline
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Default Re: 462 Double Hump Heads & studs

Quote:
Originally Posted by tlray View Post
Well....I drove it until 1990 and kept hearing this noise when I hit a bump. Floor pans rubbing the driveshaft. Parked it Got married, had kids, played guitar in a Long Haired Rock n Roll band, Got around to working on it...10 years ago. It will be worth the wait.
I forgot to say...I paid $600.00 for it..350, 4 speed convertible..in Texas
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