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Old 12-25-2003, 10:20 PM
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Rocker arm wearing into stud and bending pushrods?

This is kind of lengthy but stick with me here. Well the title pretty much sums it up. I have just rebuilt my 350. Engine internals include

brand new crank with journals .020 over
Comp 270 magnum cam
All new bearings
Block bored .040 over
Stock connecting rods
Domed pistons giving me about 9.5:1 compression
Comp lifters
Federal Mogul pushrods

Stock 76cc heads
used rocker arms
stock valve springs

This is all in a 71 chevelle with the stock springs and used rockers as mentioned.

After the rebuild it drove great. We broke the cam in just as recomended by comp, used plenty of lube and all upon installation. Broke the rings in too. Was still breaking the motor in. Well i changed the oil and filter and drove it a little further than usual. On the way to my destination i heard a pinging noise and threw it in nuetral and pulled over. The noise had stopped but it was missing badly. Pulled the valve cover and the #7 rocker armS had walked off the spring perches and bent both pushrods and wore a grove into the studs about half way into them at the bottom. Number 3 exhaust rocker was loose too and starting to do the same. Well i replaced the pushrods and rockers on all three mentioned and tried to drive her home VERY SLOWLY and it messed up again and bent #3 so i called a wrecker and got her towed home on a flat bed( how embarasing).

My question is what could cause this? I could think of a bunch of things but none seemed to really make sense, maybe you guys have had similar experiences or ideas?

And what do you guys suggest me do? I have about 500 bucks to fix this problem. Either get new heads or rework mine?

Thanks, MG

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Old 12-25-2003, 10:31 PM
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Replace the damaged stud(s).
Install new rockers and balls and push rods. Be sure and use new nuts. The studs can be replaced without pulling the engine.

My guess is the locking nuts was worn out, and backed off.

Troy

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Old 12-25-2003, 11:23 PM
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Studs wear also if nuts have been run off them a few times over the years. If this is your problem a double nut can help solve it or you could buy a nice set of setscrew locking adjustables for only a $100. New studs might be a good idea, especially on the studs that are damaged. As Troy said, sounds like your nuts backed off and the rockers slid off the valve. Might not be a bad idea to pull the pan and flush her out too, all that debris went straight to the bottom. Should have pulled both valve covers and checked the other valves...or towed it first. Don't ya just love hindsight!

Crappy luck, sorry man.
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Old 12-25-2003, 11:37 PM
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If you look at a stock rocker arm nut they are crimped a little. I can't remember off hand what they call it but you will notice the nut is more triangular shaped than round. Those nuts aren't recommended for reuse. As 4 Jaw said, I would recommend the setscrew type nuts used with roller rockers, (poly-locks).
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Old 12-26-2003, 06:09 AM
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Meangreen, a lot of stock rocker arms dont have a long enough rocker slot to deal with that size cam. The marks on the studs are coming from the rockers binding on the stud when they run out of slot. This will also give a lot of stud deflection which will break off rocker studs. At the minumum you need to get some long slot rocker arms. Roller rockers are the best choice because they dont drag sideways across the valve. Also poly locks to keep the arms locked down.
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Old 12-26-2003, 07:14 AM
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I ran across a problem like this a couple of times. I agree as stated before replace the worn studs and nuts. Plus I also used sloted rockers for extra insurance. It cured the problem.
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Old 12-26-2003, 07:39 AM
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At .470" lift, that cam is too big for both stock rocker arms and stock springs. You are experiencing both rocker arm binding and probably spring binding if you have rotators on the exhaust valves. You will need to use long slot rockers and replace the valve springs that are proper for your cam and eliminate the rotators, depending on what year the heads are. Also, the pushrod guide slots in the heads may be worn, causing the pushrods to have too much side-to-side movement.

What year heads are they?
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Old 12-26-2003, 08:11 AM
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Thanks everyone for your responses.
Its the stock heads, i can't remember the casting number but it was a stock 2 barrel motor. The weird thing was it ran great at first? And then just messed up. But to fix it i need to get new springs, new rocker arms and pivot balls and nuts, and new studs? How much would the new studs cost? And one more question, When i put the pivot ball on the flat side goes up right?

*Edit* Its not just marks on the studs, a couple are almost worn in half!?!
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Old 12-26-2003, 09:26 AM
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I agree with the theory that you are experiencing binding due to excessive lift that the stock rockers cannot handle. Chevy rockers that have an "O" stamped in the end have longer slots to deal with higher lift camshafts.

I would look at all your studs and check them for damage.

Vince
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Old 12-26-2003, 09:41 AM
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You will need to replace the studs that are grooved. Also, you should also check to see if the studs are pulling out. If the guide slots in the heads are worn, you'll have to put in screw-in studs and guide plates or get self-aligning rockers.
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Old 12-26-2003, 09:51 AM
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Meangreen, I had this problem with a old .454 lift crane fireball cam. I also tried to lengthen the slot with a file and then a die grinder with a carbide bit. Forget that, its some hard metal. Theres no set cam lift that you will get bind. All rocker arm sets are different so you have to look and verify they are not hitting.
PS, the flat sides are on the top.
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Old 12-26-2003, 10:01 AM
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The flat side of the nut goes down, the tapered side is the lock and goes up.If you installed them upside down that could be your problem. The rocker and balls are matched once the eng. has run keep them together.Like posted check for spring binding. You should only have to replace the damaged studs. HTH

Good Luck
Troy

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Old 12-26-2003, 10:33 AM
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69 ss rs full custom camaro 98 ISCA grandchampion
69 ss rs bb camaro wifes driver
66 Elcamino 350/all dz parts,ac,windows,loaded,my driver
69 ss chevelle bb conv.fresh frame off
26 T sedan street rod [/B][/QUOTE]


bfd
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Old 12-26-2003, 11:55 AM
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Well i think i am gonna get some new heads, either that or get mine reworked. I have a guy who has some camel hump heads with the 462 casting number , 2.02 valves 1.60 exhaust 64cc combustion chamber with heavy duty springs and just reworked all for 300 dollars and for another hundred he will throw in some roller rockers. So my question is now can the domed pistons work with the 64 cc combustion chamber?
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Old 12-26-2003, 02:33 PM
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Quote:


Originally posted by machine shop tom

69 ss rs full custom camaro 98 ISCA grandchampion
69 ss rs bb camaro wifes driver
66 Elcamino 350/all dz parts,ac,windows,loaded,my driver
69 ss chevelle bb conv.fresh frame off
26 T sedan street rod


bfd

machine shop tom;
The BFD is, this is called a signature, some have them and some don't,

Troy__________________

If you don't make mistakes. your not doing anything.

69 ss rs full custom camaro 98 ISCA grandchampion
69 ss rs bb camaro wifes driver
66 Elcamino 350/all dz parts,ac,windows,loaded,my driver
69 ss chevelle bb conv.fresh frame off
26 T sedan street rod

Last edited by troy-curt; 12-26-2003 at 02:45 PM.
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