Help me with this head dilema. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

eric27 · 05-19-2002, 10:11 AM

My 72' swb doesnt get to go much because it keeps breaking a screw in rocker arm stud. The heads are the vortech heads on a 350. It has broken the 2nd one and I have yet to ride it hard. It breaks off even with the head and it is a smooth break. It breaks the same one every time. Whats up with this???

*Zkast* · 05-19-2002, 10:25 AM

What are some of your specs? Lift, Rocker arm design/Ratio, valve spring pressure.

Couple of things come to mind first...
Rocker arm travel. If you have a high lift cam and arent using long slot rockers(if stock) you will bent or break the stud or bend the pushrod.

Also a cheap/easy way to get around not going with screw in studs was to pin them, if the person that pinned the studs drilled to high it will cause a weak spot in a very bad area.

Does it keep happening on the same valve? or all intakes or all exhausts..

------------------
<A HREF="http://www.zkast.com/display.php?file=piston/index.htm&t=1&m=homepage&b=Piston's%20Truck%20page" TARGET=_blank>Pictures
and more...</A>
piston@zkast.com
'71 LWB
350/350T, PS/PB
Special options? Yes, RUST... Need some?
------------------------------------------
Webmaster/Team owner
www.zkast.com
Garrett - Olathe, Kansas

eric27 · 05-19-2002, 10:28 AM

Same valve. Cam lift is 468 and machine shop put a stronger z-28 spring on them. I am still using the factory rocker arms.

PanelDeland · 05-19-2002, 05:31 PM

I think on the Vortecs you have to have the tops of the valve guides turned down if you run much cam lift.You might check how much clearance you have on that particular rocker arm to guide by turning the engine over by hand with the valve cover off.If the end of the rocker is hitting the top of the valve guide you have found the problem.Don't forget that the lifter may not be at it's full height if it's a hydralic.When it pumps up it may be enough to cause interference.
Also remember that if you are on the edge of clearance there may be a slight difference in the height of the guide casting.

------------------
Deland does Chevys 68Chevy panel(LIZ)
"A man and his truck,it's a beautiful thing"
"I have the body of a god,unfortunately it's Budda"

mikep · 05-19-2002, 05:58 PM

2 things.

1. Iv'e used the factory Z28 springs and theyr'e good for up to .500 lift keeping the valves on their seats and would be good beyond that but they are awefully tight on coil bind and will snap studs and break rockers if you arent careful. They are on the verge of being too stiff for the street. There are better modern design valve springs out there with smaller coil diameters.

2. Vortec heads need self aligning rockers made for vortec heads !!!! If you are using guide plates instead you'll need the bosses machined down to have the stud at the same depth or you wont have enough thread engagement and too much pressure will yank the threads. If you arent using anything to align the pushrods then that is definitely the culprit as your rocker geometry is all over the place.

Nice heads. I almost bought some for my current engine but I didnt want to have to buy rockers, a new manifold etc to match since I already had those items so I went with the WP sportsman II's instead

[This message has been edited by mikep (edited May 19, 2002).]

69 longhorn · 05-19-2002, 07:38 PM

I ran several sets of Z-28 springs,with cams in the 460-480 range on valve lift(on the older 'fuelie" heads).....no trouble. It definately sounds like something is binding,whether it be coil bind due to improper installed height,retainer to guide interferance,Or possibly rocker to stud interferance........its hard to say. You do need a long slot rocker when into & past the .450 lift range,& as posted the rockers are self aligning for the Vortecs. Good luck.......69

Longhorn Man · 05-19-2002, 07:44 PM

The vortecs are supposed to take special springs too, not run of the mill S.B. springs.

------------------
'69 G.M.C. 350/350. Trying to clean up the left over damage from the Dope-Smokin-Old-Man
I've been dubbed the Longhorn Freak/Fanatic/Expert, I just hope I can live up to it.
FINALLY got the HORNIAC...a '70 one ton Longhorn with a Pontiac 350/350 and lots of 'personality'. Check out The Longhorn Webite.
E-mail longhornmail@yahoo.com
My name is Andy...not Randy...I'm in Ohio...Not Illinois...close enough?
Columbus Ohio

Mike C · 05-20-2002, 06:49 AM

You need to check your rocker arm geometry as well as checking for coil bind and clearance to the guide. Should be fine with the lift you have, but obviously something is wrong. Do you have 1.6 rockers? That could be your problem. While a lot of people run them, I believe they are a crutch for the wrong cam.

------------------
70 GMC 3/4 ton Sierra Grande 402/TH400
72 Jimmy 4WD 4spd 4" & 35's
64 Corvette Coupe
68 Camaro 'vert TPI & TH700
69 Z/28 355 12.6's @110
72 Datsun 240Z-ol' reliable

Longhorn Man · 05-20-2002, 11:47 AM

Did you have the block milled exsesivly? How bout shaving the heads? This could mess up the valvetrain geomitry.

------------------
'69 G.M.C. 350/350. Trying to clean up the left over damage from the Dope-Smokin-Old-Man
I've been dubbed the Longhorn Freak/Fanatic/Expert, I just hope I can live up to it.
FINALLY got the HORNIAC...a '70 one ton Longhorn with a Pontiac 350/350 and lots of 'personality'. Check out The Longhorn Webite.
E-mail longhornmail@yahoo.com
My name is Andy...not Randy...I'm in Ohio...Not Illinois...close enough?
Columbus Ohio

05-19-2002, 10:11 AM	#1
eric27 Registered User Join Date: Sep 2001 Location: cooper,tx america Posts: 127	Help me with this head dilema. My 72' swb doesnt get to go much because it keeps breaking a screw in rocker arm stud. The heads are the vortech heads on a 350. It has broken the 2nd one and I have yet to ride it hard. It breaks off even with the head and it is a smooth break. It breaks the same one every time. Whats up with this??? __________________ 1972 SWB, VIPER BLUE, TILT, POWER DISC BRAKES,350-AUTO, FACTORY AM/FM. 1971 Camaro SS factory 4 speed project car. " I LOVE IT WHEN A PLAN WORKS"

05-19-2002, 10:28 AM	#3
eric27 Registered User Join Date: Sep 2001 Location: cooper,tx america Posts: 127	Same valve. Cam lift is 468 and machine shop put a stronger z-28 spring on them. I am still using the factory rocker arms. __________________ 1972 SWB, VIPER BLUE, TILT, POWER DISC BRAKES,350-AUTO, FACTORY AM/FM. 1971 Camaro SS factory 4 speed project car. " I LOVE IT WHEN A PLAN WORKS"

05-19-2002, 05:31 PM	#4
PanelDeland I am a Referee of life. Join Date: Jun 2000 Location: Greensboro N.C. Posts: 13,992	I think on the Vortecs you have to have the tops of the valve guides turned down if you run much cam lift.You might check how much clearance you have on that particular rocker arm to guide by turning the engine over by hand with the valve cover off.If the end of the rocker is hitting the top of the valve guide you have found the problem.Don't forget that the lifter may not be at it's full height if it's a hydralic.When it pumps up it may be enough to cause interference. Also remember that if you are on the edge of clearance there may be a slight difference in the height of the guide casting. ------------------ Deland does Chevys 68Chevy panel(LIZ) "A man and his truck,it's a beautiful thing" "I have the body of a god,unfortunately it's Budda" __________________ The 47-present Chevrolet and GMC Truck Message Board Network,it's owners,moderators,members,and associates of any type should not be held responsible for my opinion. You can't fix stupid,not even with duct tape. "My appearance is due to the fact that "GOD" does punish you for having too much fun!" Barrett-Jackson has perfected alchemy,they make rust into gold! "You can lead a horse to water but you can't saddle a duck" "Cleverly disguised as a 'Responsible Adult' "Sometimes your Knight in shining armor is just a retard in tinfoil"

05-19-2002, 05:58 PM	#5
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	2 things. 1. Iv'e used the factory Z28 springs and theyr'e good for up to .500 lift keeping the valves on their seats and would be good beyond that but they are awefully tight on coil bind and will snap studs and break rockers if you arent careful. They are on the verge of being too stiff for the street. There are better modern design valve springs out there with smaller coil diameters. 2. Vortec heads need self aligning rockers made for vortec heads !!!! If you are using guide plates instead you'll need the bosses machined down to have the stud at the same depth or you wont have enough thread engagement and too much pressure will yank the threads. If you arent using anything to align the pushrods then that is definitely the culprit as your rocker geometry is all over the place. Nice heads. I almost bought some for my current engine but I didnt want to have to buy rockers, a new manifold etc to match since I already had those items so I went with the WP sportsman II's instead [This message has been edited by mikep (edited May 19, 2002).] __________________ No truck :-(

05-19-2002, 07:38 PM	#6
69 longhorn Registered User Join Date: Aug 2001 Location: rock island,il,usa Posts: 5,382	I ran several sets of Z-28 springs,with cams in the 460-480 range on valve lift(on the older 'fuelie" heads).....no trouble. It definately sounds like something is binding,whether it be coil bind due to improper installed height,retainer to guide interferance,Or possibly rocker to stud interferance........its hard to say. You do need a long slot rocker when into & past the .450 lift range,& as posted the rockers are self aligning for the Vortecs. Good luck.......69 __________________ http://community.webshots.com/user/hotrodhorn

05-19-2002, 10:25 AM	#2
Zkast Account Suspended Join Date: May 2002 Location: Olathe, Kansas Posts: 929	What are some of your specs? Lift, Rocker arm design/Ratio, valve spring pressure. Couple of things come to mind first... Rocker arm travel. If you have a high lift cam and arent using long slot rockers(if stock) you will bent or break the stud or bend the pushrod. Also a cheap/easy way to get around not going with screw in studs was to pin them, if the person that pinned the studs drilled to high it will cause a weak spot in a very bad area. Does it keep happening on the same valve? or all intakes or all exhausts.. ------------------ <A HREF="http://www.zkast.com/display.php?file=piston/index.htm&t=1&m=homepage&b=Piston's%20Truck%20page" TARGET=_blank>Pictures and more...</A> piston@zkast.com '71 LWB 350/350T, PS/PB Special options? Yes, RUST... Need some? ------------------------------------------ Webmaster/Team owner www.zkast.com Garrett - Olathe, Kansas

05-19-2002, 07:44 PM	#7
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	The vortecs are supposed to take special springs too, not run of the mill S.B. springs. ------------------ '69 G.M.C. 350/350. Trying to clean up the left over damage from the Dope-Smokin-Old-Man I've been dubbed the Longhorn Freak/Fanatic/Expert, I just hope I can live up to it. FINALLY got the HORNIAC...a '70 one ton Longhorn with a Pontiac 350/350 and lots of 'personality'. Check out The Longhorn Webite. E-mail longhornmail@yahoo.com My name is Andy...not Randy...I'm in Ohio...Not Illinois...close enough? Columbus Ohio

05-20-2002, 06:49 AM	#8
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,738	You need to check your rocker arm geometry as well as checking for coil bind and clearance to the guide. Should be fine with the lift you have, but obviously something is wrong. Do you have 1.6 rockers? That could be your problem. While a lot of people run them, I believe they are a crutch for the wrong cam. ------------------ 70 GMC 3/4 ton Sierra Grande 402/TH400 72 Jimmy 4WD 4spd 4" & 35's 64 Corvette Coupe 68 Camaro 'vert TPI & TH700 69 Z/28 355 12.6's @110 72 Datsun 240Z-ol' reliable __________________ 44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax

05-20-2002, 11:47 AM	#9
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Did you have the block milled exsesivly? How bout shaving the heads? This could mess up the valvetrain geomitry. ------------------ '69 G.M.C. 350/350. Trying to clean up the left over damage from the Dope-Smokin-Old-Man I've been dubbed the Longhorn Freak/Fanatic/Expert, I just hope I can live up to it. FINALLY got the HORNIAC...a '70 one ton Longhorn with a Pontiac 350/350 and lots of 'personality'. Check out The Longhorn Webite. E-mail longhornmail@yahoo.com My name is Andy...not Randy...I'm in Ohio...Not Illinois...close enough? Columbus Ohio



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.