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Old 06-23-2004, 05:43 PM
western star's Avatar
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Rockers cutting studs on 350 sbc

Changed the rockers from stock to roller tip and ran them for a few days but the engine started to smoke badly when I started it up. Pulled the rockers off and noticed that the umbrella valve seals had come off the heads and were riding up the valves. At least 3 I could see. Also noticed that one stud had been cut half way through on the side. I checked the others and there were signs of cutting that was starting. I am also using the other O-ring seal on the valve. These rockers were 1.5 ratio made by Comp. If the valve guides are worn could this be the reason the new rockers are cutting in. The engine has always been a healthy runner burning clean. The cam is a 268 Comp hydrolic. Would changing the rockers really do this to an older motor? Is it possible that the ratio could have been wrong and the valve travel could have bumped the two seals together and move them? I guess I'm going to have to pull the head to replace the pressed in stud right? Man oh man I should have left well enough alone. Also the plugs were really gummed up with oil. The plugs on this engine have always come out clean with good color. I also checked the compression and it was 155 on all cylinders give or take a few pounds. What happened?

Last edited by western star; 06-23-2004 at 06:01 PM.
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Old 06-23-2004, 05:53 PM
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I think you have answer a lot of your question in your post i would recheck the rocker ratio i believe the comps are 1.52 or 1.55 if they are the steel with the roller on the end.As far as cutting into the studs i really never sat down and looked at why they do that other then i know the guides are usely wiped out but i never truly looked at it as that being the problem.







mike
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Old 06-23-2004, 06:00 PM
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Mike they are the steel rockers with the roller tips.
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Old 06-23-2004, 06:05 PM
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Those type of rockers are not real accurate i would check your retainer to seal clearance and make sure you have at least .060 thousands clearance.




mike
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Old 06-23-2004, 06:17 PM
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Can a rocker stud be replaced in the car or maybe I should just pop both the heads off and have a machine shop check them out. I am replacing the engine next year so I don't want to get a complete head job if I can avoid it. I'll replace the seals and put the stock rockers back on and hopfully get some more miles out of her.
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Old 06-23-2004, 06:22 PM
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Yes it can be done in the car as long as you can borrow the correct tool or rent it.





mike
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Old 06-24-2004, 08:48 AM
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The slot in the new rocker isn't long enough for the cam lift. The slot in the rocker contact's the stud and chew's into it. Seal problems probably stemed(?) from lateral movement of the stud and valve stem.
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Old 06-24-2004, 09:08 AM
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Yeah i agree with johnsongrass.

The opening in the rocker body doesn't have enough clearance for the rocker studs when the camshaft lobe is towards the top of its travel. Sounds like you have high ratio rockers...

Always check your valvetrain geometry and clearaces before final assembly.

tbw
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Old 06-24-2004, 09:40 AM
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How many miles are on this engine? If it's quite a few say 100,000 , then I would have all the guides checked and replaced if necessary.

I would check those new stamped steel rocker arms for burs and use a riffler on them to get rid of any edges on the insides that could cause damage and follow up with some sand paper.

Also make sure you press those valve seals on real good! I use an old hollowed out thick body ink pen if ya can believe it. Works real well too, the plastic of the pen does'nt kill the surface of the seal.
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Old 06-24-2004, 11:05 AM
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im not sure how you would get a press in stud out in the car, but once it's out you could tap for a screw in type stud. check the tops of the valves where your rockers are chewing thru the stud too as that could cause it to chew thru the side of the stud if the top of the valve isnt flat
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Old 06-24-2004, 01:31 PM
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Ya that's where it is chewing through. The side of the stud not the top of the stud like the manifold side or the header side. Lets just say as you are looking at the stud it would be at the 9 o'clock postion. It almost looks like a hacksaw has cut into it and very straight. It has cut it half way through and a little on the other side. To risky to run like that. Thank you for all your info.
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Old 06-24-2004, 01:43 PM
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Check to see if the pushrod guide holes in the head are worn side-to-side. Check the valve springs for coil bind and make sure the retainers aren't binding on the seals. Umbrella seals are designed to ride on the valve stem, positive seals are designed to stay on the guide. Make sure of which you have.
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Old 06-24-2004, 05:09 PM
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Machine Shop Tom thanks. The heads were machined to take the umbrella seals and good point on checking the guide holes for the push rods and they do appear to have a little wear but not to bad. I have a line on a set of new 202's and will put them on. I can use the 202's later on another engine build.
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