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Old 12-11-2008, 05:39 PM
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355 is breaking rocker arms

Hey guys I am just now gettin my car goin right.... I've got the gears for it now, finally. I added it to the insurance and got plates then the first trip around the block, I got on it pretty good, I don't think it ever got past 6000 though, and it went to rattling and popping back through the carb. I new immediatly that it was something in the valve train, but I thought i broke a spring at first, so I shut it down immediately to avoid any further damage, let it cool for a few and I have T handle valvecovers and I knew I heard it coming from the passenger side, so I pulled the V/C and seen 1 rocker with the cup broken 1/2 way out the bottom, and I guess it ot loose and got under the one right beside it and lifted the press in stud up 1/4"...

I called my dad and told hime to bring me a couple rocker arms (stock ones) of the other heads I got layin around, and grab a ratchet, 5/8 plug socket, and a hammer. He arrived I fixed it. tapped the stud back down, installed spare rockers... started up adjusted them, put v/c back on and away I went. Did good for 3 days then it did the same thing in a different spot. First it was over #2 the second time it was over #5, on the opposite side of the motor, and again the bottom cup was 1/2 blown out and the one beside it lifted the stud......

Is this just bad rockers, coincidense, or do I have deeper issues?? I fixed it the same way again and now its fine again, but who knows for how long....
Cam is lunati bracket master II 300/300 515/515 lift, voodoo lifters, comp springs, hardened pushrods, but the rockers are stockers....

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Old 12-11-2008, 06:18 PM
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Why

so can anyone think of why this might be happening other then that they are stock rockers, cuz this isn't a "new" motor.... It's far from old, has prolly 20-30 hours on it. with several mud drag passes.
BTW, It is oiling fine, I cut the top off an old v/c and watch her run... Not a lot at idle, but if you gas it she'll shoot ya in the eye!!!
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Old 12-11-2008, 06:38 PM
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Pulling the stud out of the head!!! Oh man...

Stock heads? (Cast iron?) with the pressed in style

With hardend pushrods and guide plates it'll help keep them streight which is good... Your weak link is going to be the rocker arm at this point.

I would suggest checking for coil bind on your spings. When they get into a bind it'll break the weakest parts.. being your studs or stock rockers.

Hope you can mend it fast before it really casues some problems,
Scott~
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Old 12-11-2008, 06:55 PM
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At .515 lift you should have pinned the rocker studs. You need to check to be sure your push rods are not binding in the pushrod holes in the heads as well.

My first though when I read this was coil bind. Did you check for this when you installed the larger cam? I suggest you not drive it anymore until you figure out what's wrong, you are getting real lucky right now that you haven't done more damage. If you hang a valve open you will not be happy. Did you check your valve train geometry?
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Old 12-11-2008, 08:09 PM
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you should definitely check you valve train geometry. are the right locks and retainers on the valves, mixing 10* locks and 7* retainers or visa verse can cause the valve tip to be receded almost even with the retainer causing the rocker to be in a bind. Just check everything while rotating the engine by hand you should see what is going on. look between the rocker and spring make sure there is room from o lift to full lift.
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Old 12-11-2008, 10:05 PM
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Do the rockers have a lot of miles on them? Had this exact thing happen reusing stock rockers on a budget 350 re-build years ago. New cam= more lift. The used rockers with the wear in the cup could not take it. After about 6 of them bit the dust, I swapped in new ones. Lesson learned
Not sure if you were using new rockers or not.
Are they long slot rockers? That cam has a lot more lift than a stock rocker was made to run.....
chas
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Old 12-11-2008, 10:49 PM
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broken rocker arms

Too much cam, too much spring pressure, slots in rocker arms not "long" enough, valve to piston clearence problem, hydraulic lifters adjusted too tight, loose nut behind the wheel. The last one's just a joke.
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Old 12-12-2008, 03:07 PM
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355 breakingrocker arms

HI, just reading the above posts, i hope you find an inexpensive solution .Also im curious how the guide plates are secured with a push in type rocker bolt?
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Old 12-12-2008, 04:50 PM
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all been done

This motor has had all of the above mentioned done... I didn't build it, but it was built by a guy I know from hopkinsville, KY who owns his own Hi perf shop. Builds motors all the time... The springs are comp 981 or 918 can't remember for sure and they are at the proper installed height, 1.75" i think..

The rockers are old yes and reused. like I said if the geometry was off or there was coilbind issues, it should have shown itself by now... As i said this motor has seen been ran alot and its been ran HARD, several mud drag passes shifting at 7000. I really feel its the rockers myself, I just wanted to see if anyone else had expierienced this same problem.

With the 981 springs and already having 515 lift would there be much power gain by going to a 1.6 ratio rocker?? I plan on buying some roller tip rockers but I'm not sure what ratio would be best. 1.6 would put me close to 545 lift??
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Old 12-12-2008, 06:05 PM
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You need long slot rocker arms.

Available at Summit for a very reasonable price.

Do not buy 1.6 ratio rockers. You didn't build the motor, you don't know piston to valve clearance. You have a fairly large cam, 'adding' more lift with 1.6 rockers is not a good idea.
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Old 12-12-2008, 07:53 PM
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With that large a lift cam at high rpm you are pulling out the studs, pin them or remove the heads and have threaded studs installed.

Btw hammering them back in again just means it will pull out easier the next time, I am willing to bet they are now bent and wrecked as a result.

Pull the heads and do it right, pressed in studs are even marginal for under 1/2" lift cams.
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Old 12-13-2008, 09:37 AM
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It seems to me that most here have listed your possible problems. Myself, I am leaning towards the springs solid-stacking. Especially if you have rotators on the exhaust springs.

Something else to think about. I have seen several instances where a 3-keyway timing set has been mis-aligned to where there was exhaust valve-to-piston interference, but the engine ran well enough to not give a clue as to why the screw-in studs were breaking.

tom
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Old 12-13-2008, 08:46 PM
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not pulled out

The studs have never pulled all the way out they just raised up about 1/8-1/4 of an inch.

This may be a dumb question but I don't have a spare set of 882 heads to look at, but do they have a solid runner or are they like thethe 416 casting with the crater is the runner where the stud goes through??? the reason I ask is that I was just wunderin if there was a "bottom out point when I knocked the studs back down or if they'll go straight through into the runner??
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Old 12-14-2008, 03:06 PM
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Re: 882 heads

I have been reading your thread here and had to go out to the bench and check a set of 882 heads I have sitting around. The studs do go through into the runner. They are easily felt with the finger.

With respect to your rocker breakage and the pulling of the stud, I get this gut feeling that due to the lift you are utilizing with this cam, you may not necessarily be getting spring binding but you may very well be close. Have you taken a double check on the length of the push rods you are using? It sounds like you have matched the components with the exception of the rocker arms and push rods. Also, I do agree that with so many unknowns as to the engine component clearances, the 1:6:1 rocker ratio is a dangerous chance to take. With that lift, stick with the 1:5:1 ratio for now.

Again, check and make sure you are using the right length push rod and that they are not mismatched accidentally.
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