Ok here is my set up. 305 (416) heads, stock 1987 rocker arms from a 305 TPI roller cam motor, stock push rods from the same motor, camshaft is 270 HR (218 degrees duration at .050 and .498 in lift), and springs have a installed height of 1.800 with 120 to 125 lbs closed pressure and 320 lbs open pressure, and stock roller lifters. Guide plates have been installed. In case it matters this is all in a roller 350 block.

One of my studs snaped off. I did not check the geometry because to be honest I am not sure if I would be able to accurately tell if it was off. But with the higher spring height and higher lift cam I am starting to think that is the culpret. Also I a not 100% sure but I was under the impression these rocker arms are non-self guided since they were on an 87 motor and I do not see any rails or anything on them. But the tip for the valve stem does seam to have quite an indention in it.

Any way does anyone see anything right off the bat that might have caused this? Is anyone else running somthing similiar to this that can tell me if they had to change the pushrod lenght? Or perhaps did I just get a bad stud?

 

Here is the rocker arm and other end of stud.

 

Just a guess but id have to say thats just too much lift for those heads. I know press in studs will easily come out with a lot of lift. Thats the only thing that I can think of right off the bat.

 

you need to check valve train geometry as the cam lobe lifts and closes the valve. can't really tell much from a pic. why do you have guide plates? you have SA rockers don't you? if that's the case there's your answer.

 

I do not think these are self guiding. From what I understand self guiding where installed from 88 on up. These are factory 87 and also they do not have any nothces or rails on the tips to guide the valve stems.

When looking at the rocker arms for geometry what should I be looking for. The springs are not binding and everything seems to work fine. Is there an angle I should be looking at. should the rocker arm be at 90 degrees to the stud at any point in the cycle?

 

check comp or lunati site. not long ago i saw a good diagram of what you want, it's hard for me to explain, basically you want the tip of the rocker to stay i nthe center of the valve tip as the cam rotates 360*. the sites ought to give you *** instruction on checking push rod length too, as a rule for every .050 increase i nlift you want a .050 increase in push rod length

 

If your rocker arms are stock, they may not have enough of a slot to clear the studs at the high lift of your cam.

Check your other studs and see if they are getting marked or scored.

I've seen high lift cams snap rocker studs when using regular slot rockers.

jms

 

That rocker arm is incredibly wasted, at every single wear point. look at the tip, look at how deep the valve stem ate into it; look at the fulcrum, look how wallowed out that "slot" is. Your springs are inadequate. You need all new rockers I'm sure, and probably all new studs, because lots of the rest of them are probably sawed in half like that one. The one valve tip I can see looks pretty stressed too; looks rounded around the edge. The push rod tip in the pic is all pitted. You're lucky a stud was what gave out first, not a spring.

 

RB83L69, thanks for noticing the wear. I thought that looked quite excesive especially where the rocker arm meets the valve tip. I am suprised you were able to see anything with those crappy blurry pics I took. What I don't understand is why the springs would be a problem. I know you are probably right but I don't understand why. The springs are not the comp cams springs for the comp cam, but they supposedly (spelling) have the same specs according to the shop that put them together that comp cams suggests. And any way I don't understand why having inadequate springs would do this. I thought I would just get valve float at upper rpms. Why is it causing the valve tip to try and come through my stock rocker arms?

By the way I do feel lucky that this is all that happened. It could have been much worse.

 

Real-world valve springs are far from your ideal physics-class versions. An "ideal" spring would be perfectly linear throughout its cycle; i.e., you want to compress, you press on it; you want to compress it twice as far, you press on it with twicw as much force. The reality is quite different. They are linear only over a small range of compression, then the force required starts to increase dramatically. So in the case of a valve spring, it might take 50 lbs of pressure to compress it .100"; but it might take 120 lbs instead of 100 to compress .200", and 200 lbs instead of 150 to compress it .300", and 320 lbs to compress it .400" (near the limit of the strength of a stock valve train with stamped sheet metal garbage rockers with those), and so on. As you compress them to near the point at which the coils bind, the force rises even faster. Then, you have even bigger problems: have you ever hit a spring with a hammer? Go buy a Slinky and watch and see what happens when you suddenly move one end; you'll see a wave of compression travel down the spring where the coils get closer together than the "static" case of merely pressing on it. And of course, that's what's going on in a valve train: each valve literally gets "hammered" open thousands of times a minute.

But that's not all... they create heat too. Springs can be made of few turns of thicker wire, or more turns of thinner wire. If you take 2 springs that are made of 2 different size materials like that and make them so they have the same rate (lbs per inch), then each little section of the one made of few coils of thicker wire has to bend a little bit more than the one made of more coils of thinner wire. Have you ever taken a coat hanger and bent it back and forth until it breaks? Go do that right now, and as soon as it breaks, touch the ends. Come back and tell me what you felt. Well that's what happens to your valve springs too; all that bending heats them up. If you heat that kind of material up enough, eventually it does 2 things: it tries to conform to the shape it's held in (which reduces its tension), but since the metal is harder, it's hjarder to compress. You end up with a spring that checks weak, but is even more non-linear than a new one. Ands since it's weak, it doesn't control valve motion any more, especially at the seat; at high RPMs, the valve bounces off the seat when it closes, which robs power, and hammers the whole valve train even more.

What has happened in your motor is that your valve springs are totally inadequate for the amount of lift you're subjecting them to. They are reaching a severely non-linear portion of their operating range, and creating so much force on all the valve train parts that they can't stand it. I'd bet if you looked at the tip of your cam lobes, you'd see damage there too, they're probably pitted from the excessive force. And, if you checked their seat pressure, I'd bet there's less than 60 lbs holding them closed, where there should be at least 100 lbs for a cam that aggressive to work right.

This is why cam mfrs will not warranty a cam unless you change the springs per their recommendation. If your cam is wiped, and you had put the right springs in there, I guarantee you Comp would send you a new cam, no questions asked, except that they would want the old one back. (You might wonder how I know that ...) I also guarantee that if you didn't follow their recommendations, they will not replace the cam. They're not just trying to make a few more coins off of you when they try to get you to replace your valve springs, there's a good reason for it.

I have learned the hard way over the years to never, ever trust what somebody who built a motor tells me the springs are good for. If I don't have the part number, I don't believe them. Yours is just one of several posts on this BBS right now by people with similar failures, where they ran the springs that came on their heads or whatever, that were supposedly "good" to some lift greater than whatever cam they were running, and still had stuff fail. Lots of people use cheap springs with these great ratings; the 2 brands I see the most trouble with are K-Motion, and GMPP. Funny thing about that... neither of those companies will warranty your cam. But Comp, Crane, Lunati, Utradyne, etc. - all the real cam companies - have a policy exactly as I just described.

Put the right valve springs in the motor, don't believe what anybody tells you about their ratings unless they come from a cam mfr with that cam mfr's part number you can verify (no "jthse are just like Comp" or "they're as sgood as Lunati" or I've been running them on my motor"), and get those stupid stock rockers off of there if you want some performance that lasts. Use the springs Comp recommends, and I'd suggest at least their cast steel ball-fulcrum roller tip rockers. Since your heads have guide plates, you MUST NOT run self-aligning rockers. Roller fulcrum rockers would of course be better, but are also more $$$.

 

ok, looks like I am ordering springs and rockers. Sorry to have taken up so much of your time for that explanation. The more I think about it the more that sounds like exactly what was happening. The few times I reved the motor above 4000 rpms it did not behave like I expected. I heard a sort of rattling, smacking sound that sounded more like valvetrain than pinging. And the power was dropping off considerably.

I hate to ask another question, but do you think I should go with a pushrod that is about .100 inch longer to go with the cam that is about .100 inch more lift than factory?