#1  
Old 05-20-2022, 01:23 PM
Dauntless1971 Dauntless1971 is offline
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Default Running roller rockers without guide plates

It sounded like a plus threaded rocker studs installed when I read the ad for this used 1964 326 engine I picked up. Best I can tell the studs do appear to be threaded just not with nut at the base. Though the seller kept the roller rockers, pushrods and polylocks for his new 455 engine. And as I look into getting replacement rockers it seems a whole new can of worms has been opened. I am sure there are more damaged guides on the other side. Is it possible now to just use stock stamped rockers? Or do I have to get the heads milled, new studs and use guide plates?
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  #2  
Old 05-20-2022, 02:17 PM
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To do it right the heads have to come off and get reworked.

Milling down the stud bosses to the correct height would be the first step in order to allow the use of either Comp Cams or Isky small block Chevy adjustable guide plates. Next some new screw in studs with the bottom hex that retain the guide plates are needed.

The old worn guide slots in the heads will need to be drilled out and eliminated so they don’t fight or interfere with the new guide plates in aligning the pushrods.

If you try to cut corners and just put stamped stock rockers or any others for that matter on it you’ll be dealing with issues caused by the worn guide slots which will eventually end up with a failure of some sort.

Since your heads are desirable 093 high compression GTO and big Pontiac performance heads they’re worth spending some money on in my opinion. Or you could sell them and buy some small chamber heads to maintain the compression on your 326 but I doubt you’d be saving any money in that pursuit.

On my own ‘64 421 HO heads I didn’t use guide plates with my screw in studs and roller rockers because the original guide slots machined in the heads were pristine, of course if the slots were worn I would have opted for the guide plates.
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Old 05-20-2022, 07:35 PM
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With all that said you might get off with less cash outlay if you’re able to source a pair of good ‘65 -‘67 326 heads or ‘65 -‘66 high compression 389 heads with guide slots in pristine condition. Then have a simple valve job done and use them as is with the original press in studs and a mild factory cam (066) that’s less stressful on the press in studs.

Good machine work along with new valves and guides is the best way to insure longevity and protect against break downs. However a pair of used 326 heads that were not abused or high mileage might be an option, as long as they’re local to you and cheap to free.

Several years back I gave away a nice clean pair of 1967 #140 heads that came off of a good running 326. They were nice enough to be used after a quick cleaning, the guy who gave them to me unnecessarily took apart a complete 326 that he yanked to install a new 455, I had no use for them and rather than store them I gave them away.

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Old 05-20-2022, 07:55 PM
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It’s not a can of worms really, because had the seller let you buy the motor with the roller rockers on it you might have just plopped it in, ran it and had a failure from the worn guides that you did not know where bad!

That would have been a real stinky can of worms!

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Old 05-21-2022, 09:26 AM
mgarblik mgarblik is offline
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It's really hard to evaluate what exactly you have there. It's possible those push rod holes were modified to allow clearance for 1.65 or 1.6 rocker arms? No way to tell since you don't have the arms. It's also possible the studs were tapped for threads by hand and not in a mill or seat and guide machine. This often results with studs in all sorts of weird porcupine positions when tapped by hand. That can be a real problem. My first step with these would be to place a straight edge down the set of 8 studs and try to determine as best you can if they are installed straight in both planes. If they are straight, then proceed as B-man has suggested and install proper hex studs after cutting the stud bosses down. Then clearance the heads and use factory or adjustable guide plates and you should be OK. This could be anything from pretty basic to fairly complex depending on how the currently installed studs were done to begin with. Hope it works out for you.

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Old 05-21-2022, 12:13 PM
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If you want to do as b-man suggested, I have a pair of complete #140 heads that you can have for free if you can pick them up in San Diego or Niwot Colorado. Date codes D047 and D117. I don't really know what kind of shape they are in but I have had them sitting around for 40 years or more, so maybe they have not been thrashed. I can take a closer look at them in the next few days if you think that you might be interested.

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Old 05-22-2022, 03:39 PM
Dauntless1971 Dauntless1971 is offline
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Quote:
Originally Posted by shermanator2 View Post
If you want to do as b-man suggested, I have a pair of complete #140 heads that you can have for free if you can pick them up in San Diego or Niwot Colorado. Date codes D047 and D117. I don't really know what kind of shape they are in but I have had them sitting around for 40 years or more, so maybe they have not been thrashed. I can take a closer look at them in the next few days if you think that you might be interested.
Thank you shermanator that is very considerate of you. I might be able to arrange something, but I think the valve angle changed for the 67 heads.

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Old 05-22-2022, 03:42 PM
Dauntless1971 Dauntless1971 is offline
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Quote:
Originally Posted by mgarblik View Post
It's really hard to evaluate what exactly you have there. It's possible those push rod holes were modified to allow clearance for 1.65 or 1.6 rocker arms? No way to tell since you don't have the arms. It's also possible the studs were tapped for threads by hand and not in a mill or seat and guide machine. This often results with studs in all sorts of weird porcupine positions when tapped by hand. That can be a real problem. My first step with these would be to place a straight edge down the set of 8 studs and try to determine as best you can if they are installed straight in both planes. If they are straight, then proceed as B-man has suggested and install proper hex studs after cutting the stud bosses down. Then clearance the heads and use factory or adjustable guide plates and you should be OK. This could be anything from pretty basic to fairly complex depending on how the currently installed studs were done to begin with. Hope it works out for you.
I will see if they are in a straight line first. I am looking into all options right now. Thank you magarblik

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Old 05-22-2022, 03:45 PM
Dauntless1971 Dauntless1971 is offline
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Quote:
Originally Posted by b-man View Post
With all that said you might get off with less cash outlay if you’re able to source a pair of good ‘65 -‘67 326 heads or ‘65 -‘66 high compression 389 heads with guide slots in pristine condition. Then have a simple valve job done and use them as is with the original press in studs and a mild factory cam (066) that’s less stressful on the press in studs.

Good machine work along with new valves and guides is the best way to insure longevity and protect against break downs. However a pair of used 326 heads that were not abused or high mileage might be an option, as long as they’re local to you and cheap to free.

Several years back I gave away a nice clean pair of 1967 #140 heads that came off of a good running 326. They were nice enough to be used after a quick cleaning, the guy who gave them to me unnecessarily took apart a complete 326 that he yanked to install a new 455, I had no use for them and rather than store them I gave them away.
Thank you b-man lots of good information for me.

  #10  
Old 05-22-2022, 03:49 PM
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Quote:
Originally Posted by Dauntless1971 View Post
Thank you shermanator that is very considerate of you. I might be able to arrange something, but I think the valve angle changed for the 67 heads.
The 326 heads in 1967 had the same valve angle as as the 1966 and earlier 326/389/421 heads.

1967 was a transition year, the low performance 326 and 400 heads were still early style small valve 20 degree valve angle without guide plates. The all new for 1967 big valve (2.11/1.77) high performance heads were 14 degree valve angle with guide plates, some with screw in studs (#670) and some with press in studs (#061).

The use of a factory 066 .407” low lift cam really doesn’t cause issues even if the pistons used don’t match the heads as far as valve angle is concerned.

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Old 05-22-2022, 04:44 PM
Dauntless1971 Dauntless1971 is offline
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Ok I did not know. But I do know of a set of 670 heads used but in good shape. They would work if I have a low lift camshaft. Might be a simple answer to move ahead quickly with my project.

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Old 05-22-2022, 04:52 PM
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Something like this?
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  #13  
Old 05-22-2022, 05:16 PM
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Just be sure to check to make sure the big valves won’t interfere with the small bore on the 326.

Might be okay but make sure.

Big valve #48 heads were used on the 1969 350 HO (3.875” bore), this the only instance where the factory used that combination.

Your 3.72” bore 326 may have interference so you’d best be sure before sealing it all up.

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  #14  
Old 05-23-2022, 12:48 PM
KEN CROCIE KEN CROCIE is offline
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The guide slots may have been lengthened for 1.65 rockers, but they are worn excessively on the sides as well.
The studs appear to be Pioneer or Isky.
The 326/389/first design 400 use a shorter rocker arm than the later 14 deg. engines, although people have used them.

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Old 05-23-2022, 04:11 PM
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You can not run a 670 head , or any 14 degree head on a 326 motor here are the pictures to prove that.

Also even as you can see in my other picture using a small valve 389 head no less your limited to about .440” lift depending on the head gasket used and the deck clearance the motor may have, that is unless you notch / chamfer the bore or go to a .040” over bore to get that intake valve to clear.
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Old 05-23-2022, 08:18 PM
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Why can’t he go with a 3/8” pushrod and machine the slots to specs, if the studs are installed correctly?

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  #17  
Old 05-23-2022, 10:39 PM
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Quote:
Originally Posted by J.C.you View Post
Why can’t he go with a 3/8” pushrod and machine the slots to specs, if the studs are installed correctly?
I think he's beyond that. if you look at the right hand slot in his second picture, it's pretty worn out.

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Old 05-23-2022, 11:08 PM
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I have a full set of factory 389 guide plates that slip over the straight studs and held in place buy the rockers.Very rare if they would help.I can post pics.Tom

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Old 05-23-2022, 11:46 PM
KEN CROCIE KEN CROCIE is offline
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I used to sell 326/389 guide plates as Tom S described as PR -21. They are so simple to use , so ingeniously designed, some of my customers wanted to know where the instruction sheet was! Just drop them over the studs and your done. Use with hardened pushrods.

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Old 05-24-2022, 06:03 AM
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Tom, can you post a picture of these plates, I would like to see how the rockers hold them in place?
Thanks in advance!

Also I can not see as posted in #16 here why he can't go up to a 3/8" custom hardened push rod with the correct ends to get things back to good again once the holes are drilled and ovaled out for the needed clearance.

There's over a .060" difference between the stock push Rods and 3/8" push Rods, and I don't see his heads being worn out that far!

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Last edited by 25stevem; 05-24-2022 at 06:17 AM.
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