You gotta see this ......

-
Yes really. Edelbrock is full of crap on the requirement. If you ran a stock 340 cam with ede heads/spring would an aftermarket/adjustable rocker be required, I think not... actually I know it's not.

I've run a 508/509 hyd cam with stock rockers and a slightly heavier than stock spring. Once you get to about 300# over the nose, the stock rockers will start failing. That's why I'd be interested which cam the OP installed. Anything under about 500-520 lift is typically OK.

Valve to piston does not differ between the garbage 340 open chamber head and the closed chamber piece Ede produces. Valves are in the same spot, only the chamber is opened up.

Nothing I posted in this thread is or was directed at any individual poster. If you took it that way, relax a bit. Those instructions are ridiculous IMO.
 
I should have been more clear regarding the heads, I confused the issue a bit by bringing up the 340 heads. I agree that's a piston to head issue with the chamber, the valve height doesn't change.

But even with the valves in the same spot regardless of the head, the valve to piston clearance is more of a consideration on the early 340's because of the piston height.

Of course, we don't know what pistons or cam was used yet, or if the clearance was checked. I just thought it was worth mentioning, it's a pretty spectacular failure for just stiff springs. Not impossible, but I'd check a few more things before just replacing the rockers.
 
Wish I had time to read all these threads. Also wish I had the knowledge to answer all these questions. Unfortunately I do bodywork, not engine work. I can only throw parts at an engine, not rebuild one. Edelbrock had questions too that I did not know too. So what I'm going to do is replace the rockers with stronger ones. The guy that built the motor did everything prior to me owning it. Wish I had more knowledge. I just wanted to see if anyone had this happen and to share he pics.
 
Man if you can't do the work yourself you should take it to a shop that can.

Changing the rockers out won't do a thing if the valves kissed the pistons to create that damage, you'll just break something else. Maybe that's not what happened, but it has to be checked at least. Same with the pushrod length, needs to be checked and the damaged pushrods replaced. What about the lifters? The lifters on those arms need to be checked too.

And if you don't know what cam is in there, you don't know if the spring pressure caused that issue either. Could be something else, could be the wrong springs, etc.

If you just throw parts at it, you could end up throwing a lot of expensive parts away.
 
70-duster said:
.........I just wanted to see if anyone had this happen and to share he pics.
Click to expand...
Don't have pictures but seen this happen on a 440 with stock rockers/push rods and 906 heads.

Is it possible the rocker shafts aren't on correctly and the rockers aren't getting oiled properly?
 
IMO if the piston/valve clearance was insufficient and came in contact with each other, the push rod WOULD be bent, way before the hole in the rockers.
 
So from what I hear you all saying, adjustable rocker arms are a good upgrade on even a stock 340. My 340 with stock rockers is at about 375HP, so you think I'd benefit? And it sounds like you believe it is pretty much mandatory for Edelbrock heads. It is interesting I have never heard this.
 
Mopar Tim said:
IMO if the piston/valve clearance was insufficient and came in contact with each other, the push rod WOULD be bent, way before the hole in the rockers.
Click to expand...

Happens at the same time. Do you think the pushrods that were rammed through those rockers are still straight? I mean, they're aftermarket push rods so I suppose it's possible they held up and the stock rockers didn't, but if I had to guess I'd say they're probably bent.

Like I said earlier, I've seen it. Pistons hit the valves on the bone stock 318 in my GT before I got it. Eyebrow marks on the pistons from the valves, a couple of bent valves, a couple of bent pushrods, and a couple of failed rockers (not quite as spectacular as the OP's). And, that was on a bone stock 318 with the pistons down in the bores, hydraulic lifters, stock skinny little push rods, stock cam, stock valve springs, etc. The stock stamped rocker pockets are not super durable, but the stock springs, cam, pushrods etc didn't cause the damage on mine, some kind of timing chain issue leading to hard parts coming together did.

Here's one of the failed rockers. Like I said, not quite as spectacular, but it would't have taken much more to pop this out
IMG_3731.JPG


The culprit
IMG_3758.JPG


And maybe that's not what happened with the OPs engine, but I sure as heck think it's possible, and definitely worth ruling out. There's a few different things that could have been at work in the OP's engine. The fact that it's an intake and an exhaust valve on the same cylinder is worth thinking about. If it were springs, why both valves on only one cylinder? Unless maybe we only have pictures of one cylinder but they all failed?

harrisonm said:
So from what I hear you all saying, adjustable rocker arms are a good upgrade on even a stock 340. My 340 with stock rockers is at about 375HP, so you think I'd benefit? And it sounds like you believe it is pretty much mandatory for Edelbrock heads. It is interesting I have never heard this.
Click to expand...

It's a spring pressure and valve lift thing, it's not unique to eddy heads. The stock rockers aren't that robust. Bigger cam, stiffer springs, more load on the rockers. The ductile adjustable rockers are stronger than the stamped rockers. The adjustment is nice to dial in the preload better, but the strength is more the concern here. If everything is stock the stamped rockers are ok, but start increasing the pressure on them and it's another thing to upgrade.
 
I was also under the impression that the stock Valvetrain could be used with the Edelbrock RPM heads. I just bought a set and I will be running the xe268H cam.
 
Mopar Tim said:
IMO if the piston/valve clearance was insufficient and came in contact with each other, the push rod WOULD be bent, way before the hole in the rockers.
Click to expand...
I had a valve nail a piston in my 440 before. It bent the valve and I found that by doing a compression test on it. I had 150 in a cylinders but one. I'll check he spark plugs and see if the one that went is not dirty as I changed all them righ after this happened cause I thought it was a bad plug. My wife did tell me it was backfiring and she pulled over and then it went away.
 
Well, it will likely backfire when you push one through.
Leak test that cylinder for bent valve before you pull the head.
 
Mopar Tim said:
IMO if the piston/valve clearance was insufficient and came in contact with each other, the push rod WOULD be bent, way before the hole in the rockers.
Click to expand...
FWIW, I have had a valve jam in the guide on a Jeep 4 banger and it punched the rocker arm; it tweaked the pushrod but only where it punched through the rocker. The weakest point is gonna go first.
 
Last edited:
harrisonm said:
So from what I hear you all saying, adjustable rocker arms are a good upgrade on even a stock 340. My 340 with stock rockers is at about 375HP, so you think I'd benefit? And it sounds like you believe it is pretty much mandatory for Edelbrock heads. It is interesting I have never heard this.
Click to expand...
It's all about valve lift and the resulting full open spring load, the cam ramp speed and the resulting valve lift speed, and the peak RPM's.
- Lower lift and slow ramps, like a stock 340 cam, would likely be just fine.
- Fast ramp cams like XE's and Voodoo's, are going to put more force on the valvetrain parts due to the fast ramps.
- Higher lift increases the full open valve spring force.

So what do you have for cam? And do you have the springs that came with the Edelbrock heads?
 
Back to the adjustable rocker comments. Other than stock cam and valve train, how do you know where the lifter preload is without a adjustable rocker? Tighten the shafts down and run it? Heck with longer pushrods (if you didn't measure to get the proper length) the preload could be at the end of the lifter piston travel. They could be bottoming out inside the lifter causing exactly what is going on here. Those pushrod pockets in the stock rockers don't just break for no reason.
 
trebor75 said:
I was also under the impression that the stock Valvetrain could be used with the Edelbrock RPM heads. I just bought a set and I will be running the xe268H cam.
Click to expand...
The stock valvetrain will bolt on and work but it is just a question of the rocker push-pocket strength.

The XE cams have fast ramps so that is going to put more force on the rocker arms and other valve train parts, when you increase the RPM's. But the maximum lift of that cam is only .47-.48" so that keeps the full open valve spring force lower; it will be around 275 lbs full open, which is moderately strong, but not super high.

You might be OK. You just have to try it.

For those running the stock valvetrain parts on these heads, I would like to hear:
- What cam is being used and the lift?
- If the Edelbrock supplied valve springs are being used?
- What peak RPM's do you run?
- Are the stock rockers just off 'some engine' or did you get the heavier ones like from Mancini?
 
70-duster said:
I had a valve nail a piston in my 440 before. It bent the valve and I found that by doing a compression test on it. I had 150 in a cylinders but one. I'll check he spark plugs and see if the one that went is not dirty as I changed all them righ after this happened cause I thought it was a bad plug. My wife did tell me it was backfiring and she pulled over and then it went away.
Click to expand...
Aaaaah.. the wife drove it LOL. BTW, can you tell us your cam's valve lift, or the cam PN?
 
toolmanmike said:
Back to the adjustable rocker comments. Other than stock cam and valve train, how do you know where the lifter preload is without a adjustable rocker? Tighten the shafts down and run it? Heck with longer pushrods (if you didn't measure to get the proper length) the preload could be at the end of the lifter piston travel. They could be bottoming out inside the lifter causing exactly what is going on here. Those pushrod pockets in the stock rockers don't just break for no reason.
Click to expand...
Why would it punch through the rocker? It would just hang some valves open, like a solid lifter adjusted too tightly. Yes? No? That is why I asked the OP if it ran OK at first; since it did, then there was some lifter travel left.... but maybe not much, and probably not like it ought to be.
 
nm9stheham said:
Why would it punch through the rocker? It would just hang some valves open, like a solid lifter adjusted too tightly. Yes? No?
Click to expand...
Agree but we haven't seen the valves or pistons. And we don't know the cam specs either. Hey, I'm guessing just like you.
 
nm9stheham said:
The stock valvetrain will bolt on and work but it is just a question of the rocker push-pocket strength.

The XE cams have fast ramps so that is going to put more force on the rocker arms and other valve train parts, when you increase the RPM's. But the maximum lift of that cam is only .47-.48" so that keeps the full open valve spring force lower; it will be around 275 lbs full open, which is moderately strong, but not super high.

You might be OK. You just have to try it.

For those running the stock valvetrain parts on these heads, I would like to hear:
- What cam is being used and the lift?
- If the Edelbrock supplied valve springs are being used?
- What peak RPM's do you run?
- Are the stock rockers just off 'some engine' or did you get the heavier ones like from Mancini?
Click to expand...

Thanks. Hmm, I'm not sure I want to take the chance. What would and affordable upgrade be? I'm shooting for around 400 hp in this build.
 
trebor75 said:
Thanks. Hmm, I'm not sure I want to take the chance. What would and affordable upgrade be? I'm shooting for around 400 hp in this build.
Click to expand...
I think I would go for a used set of the 273 adjustable rockers myself before using ones from China. Too many chances for things to not be right. And your valve lift is not too high so the 273 rockers would work.

There are threads on modifying the the 273 rockers for better oiling so that would be worthwhile to read. My conclusion is that these modifications are needed more and and more as you push towards continuous higher RPM use. If you are just cruising around at low and medium RPM's, you may be OK without them. But I personally would do the banana groove modifications regardless of use.

And, the general concensus is that you will have better success with a smooth bore rocker rather than a needle bearing type for general street use.

Don't know of any of these adjustable ones where you won't have to also change pushrods. If that added expense is a problem, then you could always try the heavy duty stock type rockers like from Mancini.
Mancini Racing Steel Rocker Arm Set, 1.5 Ratio

Mancini also shows these that look like 273 rocker reproductions with Crane adjusters. I don't know where the rockers are made.
Mancini Racing - A Engine Adjustable Rocker Arm Set

And you can never go wrong with these:
https://www.summitracing.com/parts/crn-69770-16/overview/

And a good used set of Crane Gold rockers would be excellent, but hard to find.
 
Last edited:
You must log in or register to reply here.
-

Back
Top