I Keep Breaking Rocker Arm Studs

[MidnightMantra]

Last 3 times out I have broke the rocker arm studs on the #2 cylinder. I am running a 468 BBC with a large roller cam. 310 Dur with .714 lift. After the second time I checked to see if the springs were bottoming out but there was .74 thousands gap between each spring coil. That should be sufficient. I noticed that this particular bank steams more out the headers than the other. This has always happend at 3500 rpm cruising speed on a long run. Is it possible that water is getting sucked into the cylinder somehow at this speed and compressing the water and not allowing the valve's to open and breaking the studs? I am running the banderlog valve so no water is coming out till 2000 rpm's. I am going to put new studs in again this weekend and run the headers dry. Process of elimination I guess. What is your unputs?

[Kachina26]

I would think the pushrods would bend before the rocker arm studs broke :confused: if it were water in the cyl. both studs?

[MidnightMantra]

Yes both studs are breaking, I have hardened 7/16 push rods. I am amazed myself that the rods have not bent. They are as straight as can be.

[Ken F]

How much spring pressure do you have? If your springs are spec for a car, chances are that they are way over what you need to turn 5-5500 rpm. Are you running stud girdles?
I've had the same problem running about the same lift only on a BBF.
I made special studs out of the strongest steel made, and still broke them.
Stud girdles solved the problem.
Ken F

[steelcomp]

few questions...
what heads
what rockers are you running
what rocker studs are you running
what spring pressures
what rpm
where are the studs breaking
You're not sucking water in at that rpm...not enough to hurt anything. You've got something else going on. Most likely a geometry prob. If you had that much water in a cyl while it's running, you'd bend a rod...or more.
Have you checked the clearance between the bottom of the retainer and the top of the guide? How 'bout the inner spring(s)?
How's the alignment between the tip of the rocker and the tip of the valve?
start there.

[MidnightMantra]

yes ken, This engine came out of my old drag car. Motor used to just run 1/4 mile only. No girdles, studs could be getting hot on long runs causing flex then snapping. That is a possibility.

[MidnightMantra]

dart heads, arp rocker arm studs, comp cams race push rods, comp springs with comp rockers, geomety looks good, valve fully open i have .74 thousands of clearance between spring coils, stud always snaps at base of the lock nuts. All this only on cyl #2 . I cruise at 3500 rpms and WOT at 5400 rpms. Never happned at WOT, always after a 10 mile run or so at 3500 cruise speed.

[steelcomp]

for some reason(s) there must be a harmonic vibration being set up in that cyl...cam lobes, cyl pressure, springs,...who knows. Stud bosses could be machined slightly off (stranger things have happened)
It's not the material...ARP is the best. If they were getting hot enough to work, then snap, you'd have other problems, and it wouldn't be isolated to one cyl. They ARE getting hot and snapping, but heat isn't the culprit. It's the result of them bending, like when you bend a piece of coat hanger, due to the harmonic vibration. Stud girdles are pretty much mandatory on alum heads w/ big rollers. Surprised you haven't broken a stud boss. I'd definately run a girdle...this will definately stop the breakage. You never ran it long enough for this to happen if you just 1/4 mile'd the motor. Probably tached right through the problem. The girdle will help stop some of the movement, and also absorb and distribute the frequency. You'd be surprised at how much smoother your motor will run. Cut your valve lash down to .016/.018, or .018/.020 hot. This will also help reduce unwanted valve train vibration, and help reduce valve bounce. This can be worth good hp, depending on how much you're already making.
steel

[MidnightMantra]

thanks for the input steelcomp. I am going to order me a girdle kit from Summit tommorrow. I gotta fix this problem, tired of getting towed in.

[MidnightMantra]

The cam is a solid roller, The heads have only been shaved to make them true. I have checked all anlge if contact with the rocker and everything is clear and has pleanty clearance. I think that I agree with steelcomp. The rocker studs are flexing casuing them to snap. Expecially with the amount of lift I am running. I am going to install a girdle kit and go from there. The last time out I ran the boat for about 3 hrs before the stud broke this time. what gets me it always happens at cruising speed 3500 rpms on a long run and not at WOT.

[kojac]

Midnight Mantra,
If you are only turning 5500rpm's at wot then I would suspect that your cam is way more lift and duration than you need for a jetboat. I would suggest a smaller cam with less duration. It would take some of the pressure off of the studs at high lift and you would probably see an increase in rpm's. A wider lobe center and shorter duration would help with the overlap and cut down on the chance of water coming into the motor from exhaust.
A jetboat drains horsepower at the top end and unless you have high compression you can't take advantage of a high lift long duration cam.
Kojac

[MidnightMantra]

I agree with you Kojac, it is a large cam for a jetboat. I pulled this engine directly from my dragcar. Left everything as it was except for the carb set up. I am running approx 12.5:1 compression now. It was higher but I changed to a thicker head gasket to reduce compression so I could run on 93.5 octane. I reduced from a 1150 to a 770cfm to cut down on fuel costs. I am planning this winter to install a tunnel ram with twin 770's and change to a "C" cut impeller. That should get me in my RPM range with my engine set up I hope. Motor is built to accomidate 7500 rpm's but I know I will never achieve that in the jet boat.

[steelcomp]

MM,
Valve train is a funny thing especially when you start running big lift rollers and high spring pressures. Every motor has it's "happy" spot, and it's "un happy" spot, especially a hard running performance motor. I've seen circle track motors that will eat themselves alive at 7500, but run them up to 7900 or 8000 or more, and they just love it. The harmonic vibrations for that cylinder (each are different) are for some reason out of control at that rpm. The vibrations are cyclic, and change with RPM. As your rpm increases, the vibrations smooth out. That's why as a drag motor, you never had the problem. Motor saw 3500 for what, maybe less than a second?
I'm not going to get into re-designing your motor...sounds like you're on the right track. That is a lot of cam, but jet boats seem to like a lot of cam. I'm building a 496 with a Lunati roller that sounds similar. .722" lift, 272, 280 @.05". (308/316 advertised.) The best running cam I have seen for a motor like yours was a 280/280 racer brown grind. Just get a girdle on it and you'll be OK.

[MidnightMantra]

Steel good luck on the engine. Here are my specs, engine combo sounds very close.
My Engine Breakdown.
427 Tall Deck Block/o-ringed
454 Lunati Crank
454 Childs and Albert aluminum connecting rods
454 12.5:1 dome top pistons custom cut for the tall deck stroke
Crane Roller Cam / Solid / 310 duration @ .714 lift
Gear Drive
Dart Heads 2.3 intake/1.88 exhaust
internally balance
msd 6al ignition system
Holley 770cfm carb.
Total: 468 ci stroker

[kojac]

Midnight mantra,
12&1/2 compression seems a tad high for 93 octane gas but with the timing cut back and only turning 5400 rpm's you are apparently getting by. Also running slightly rich might cool things off some. When you get into the 6200 to 6400 rpm range the extra heat might cause detonation on pump gas.
That motor needs the dominator to help it breath for top rpm"s.
The duration sounds about right for the compression your using but I would go for a lift range not to exceed .670 for durability.
A jet boat cruising about 10 miles at 3500 rpm's has the same strain on the valvetrain as a dragcar that has 100 quarter mile runs.
The top horsepower difference and rpm's on a jetboat would be minimal with the lower lift and unless you had a digital rpm tach you couldn't tell the difference. Durability would be greatly enhanced.
Anybody out there with the laptop dyno's could run a dyno comparitive test and verify what I'm saying.
I would Maybe use some octane booster or avaition gas to help keep detonation under control.
kojac

[Infomaniac]

Any guides changed in that head?
Retainers might be smacking the guides.

[DOHARA]

Are they the comp rockers that are stamped steel w/roller tip? If so get rid of them. I had the same problem until I went with a full roller rocker. Those stamped steel style have a tendancy to not get enough oil at the fulcrum ball and get hot and brake studs. the oiling hole is drilled to shoot oil up and over the rocker.