Breaking rockers - bad mistake

https://www.hotrod.com/articles/rescue-random-chrysler-rocker-failures-really-arent/

It is an interesting article but the bottom line is that the person who built the engine wasn't paying attention. Ended up costing a bunch of time and money over the years before they figured it out.

B3 racing Mike, makes custom shaft shims for your heads & cam combination. Instead of a bunch of stacked funky shims.

I read that in the last issue. I just shook my head when they machined the spring pockets bigger. They didn't correct the geometry and made the rocker arm weaker.

And this guy is a pro.

He didn't fix a thing, and contrary to what Dave Hughes told me, yes Dave, your rockers need to be correct too.

the person who built the engine wasn't paying attention
Never happened to me - my cat immediately detects any errors.

No one noticed that geo remark?
"Brandes’ method, at rest (valve closed, pushrod not lashed), the tip is centered over the valve-stem tip both longitudinally (edge-on) and laterally (side-on). Shim the shaft spacers and shaft pedestals as needed to get there. Using an adjustable checking pushrod and light checking springs, set the preliminary valve lash to zero, and adjust pushrod length to achieve minimum motion off-center through the cam cycle."

I've been doing this stuff for 40 years, and I have no idea what he said. I'll bet Marlan Davis didn't either.

The Brandes method sounds like something that would/could be used for a stud mounded rocker, correct? As said, B3 for the shaft stuff if you aren't (and I'm not) skilled enough to move your shaft pedestals around to correct the pattern and sweep width.

Am I off on this?

Also, after reading the article I am wondering why we need a 1.540" OD spring for a .600 lift cam? Is it not taboo to clearance rocker arms? Does it not matter as much with a smaller cam?

They did mix up pushrod length for a stud mounted rocker with an article on shaft mounted rockers which adds to the confusion. I'm not sure about cutting the Hughes rockers, I would not have done that. That cam didn't seem radical enough to require cutting the rocker arms. A stout beehive or the dual conical spring or a smaller spring of some type most likely would've fit. I'm also not a fan of adding the shims under the shafts. I've worked on a bunch of race engines over the years and I've never had to add shims under the shaft. So when I see that I wonder what is going on.

What I thought was interesting was the root problem. If someone came on here and said their engine was breaking rocker arms how many people would ask if the pistons were installed in the correct holes? That is what the root cause was but it isn't something I'd normally put on the top of the list of problems.

I would say that the root cause of this issue would be an outlier.

It reminds me of when my high school shop teacher gave me a good lesson by asking me to diagnose a car that was missing on one cylinder. He mentioned that it had new plugs. I checked the entire ignition system before going back a finding one of the new plugs had been dropped prior to installation and the gap was closed. The lesson is that if your hypotheses, or premise, assumes any false information you will be fighting the wrong battle to solve the problem at hand. In this case it was originally assumed that the engine was assembled correctly, yet eating parts at random? No, incorrect premise. Clearly something was not correct. Did they mention the original p-to-v clearance on the intakes?

Knowing that it was a mild cam and it wasn't spinning high rpm would these symptoms be indicative of a mechanical interference occurring? I guess the lesson is to keep that bore scope handy lol.

Thats got to be one of the most pathetic articles ive read in a long time, good fodder for the chevy guys.

My take on the lesson learned is have at least one guy in your crew thats not a dumbass. If a build is known to eat rockers, hey lets keep replacing them vs pulling it down and finding the issue NOT.

IMO thats a first time assembler (not builder) rookie mistake, if the valve cuts in the piston are not symmetrical there is always a pattern to follow. And its so easy to lay rolled clay on a full bank, set a head on and turn one cycle and inspect.

I f up alot of things but my builds dont eat parts, they maybe get mocked up 4-5 times and gets the pan and intake pulled for inspection after the dyno but they never eat parts.

Builds dont eat rockers, I could take one that breaks and chalk it up to a bad part, more then one and its time to come apart.

I use a 1.46 diameter spring on a .680 lift cam on my street racer, that build here was crap from the gate.

The beehive spring would give you some rocker clearance but it still doesn't fix the geometry issue.

As you say, that spring wasn't big enough to be a problem. The problem is the shaft is too low, and too close to the valve.

Move it up and away from the valve and any retainer would clear.

Marlan Davis is an excellent reason not to read Hot Rod.

A reputation for breaking rocker arms.

Initially, Brandes thought it was a random, old-age-related problem.

Huh? The two contradict themselves.


They should stick to 318 powered dusters.

Sounds more and more like a road kill episode of trying to get a junker to make it home. The blind leading the blind.

It was running 11.3 with the pistons mixed up and still only broke a rocker occasionally. Seems like in the end they straightened out the original builders mistakes. I work with a guy that does body and paint on the side, whether he’s drinking or not.
Sometimes it’s a crap shoot

Yeah the valve to piston clearance was probably just super tight. So it spun over by hand but had problems when the guy ran it out the back door. The original engine builder messed up the piston install and then he must not have bothered to check valve to piston. And evidently nobody else ever checked VP even after the problems they ran into.

I don't think the article said what heads are on the engine. I'm guessing they are either EZ or SR heads with an Indy dual plane intake? If it is screwed together correctly that combo should make 600+ hp.

"Don’t mix Miller time with engine assembly time. "


Sums it up

Always use flattops with no reliefs so you bend all the valves, much easier to troubleshoot
I had a 318 with 360 heads that use to bust rockers, too much spring pressure for the stockers, used the MP HD ones and that fixed it.

I seem to hear my Old Man talking..."Unbelievable".

Pete's Garage sent me a T-Shirt for pointing out the pistons were hung on the rods wrong. Look a #6 piston starting around 17:15

https://www.youtube.com/watch?v=4vDZjiKAAkQ&t=60s

Good eye. It wasn't easy to see that they had put the piston on wrong in that video. I would've missed that detail.

SMH.

Not impressed in the least by Petes vid there. In the first two minutes what he was saying is a head scratcher if a first timer needed to decide on a std or .040 piston and a rolling assembly. A rolling assembly makes me think of a armored division in display mode.

If hed use more then a $8 ring compressor made for farm tractors and beating the pistons in hed be able to put the upper rod baring half in the rod, it takes alot to knock out a new bearing shell on assembly.

Id have to use his T shirt to was my push mower.

I'm sure about cutting the Hughes rockers - it tells you EXACTLY where they'll break. There are places in the engine where a sharp edge is a bad idea (piston dome) but harmless. Where that cut was taken is the worst possible place to remove any metal (the center of a span stressed in tension), and more so leaving a sharp negative profile with a violent change in cross-section.
If you absolutely have to remove metal there, cut only to the minimum depth to assure clearance (don't be surprised if some rockers need more than others - an extrusion or casting isn't accurate from the mold down to .001"), then blend & radius the cut into the parent shape in all directions so that the original cut is invisible. I would polish it, but that's just my OCD.

in my opinion, a large diameter "ball nose" endmill would work good for clearancing rocker arms, instead of the sharp tip, normal, endmills usually used. less blending needed, and no sharp corners created, causing potential stress risers. has anyone done it this way ? if not, why ?

This^^^

I had a special end mill mad u just to clearance
rockers if they needed it.. was a 1 1/2" with
a 1/8" radius at the bottom.. I could do a small
plunge cut in one shot

I imagine lots of people do it that way. I always use a bullnose or ball end end mill when cutting an area that will have tensile stress. That is just a common design practice.

Fly cutter with a generous radius

Funny with really high lift you can't start in the center of the valve, unless you plan on using the retainer as part of the rocker path too. Lol

It's not only a function of lift, but the actual length (not the rocker ratio) of the valve-side lever is X-important. A really long rocker (Gen-1 hemi exhaust) is moving almost vertically with low lift with a very short scrub path.

If you think you have to grind or cut the rocker arms, discover the real problem and fix that.

STICKY THIS SENTENCE^^^^^^^^^^^^^^

/THREAD

The "real problem" is apparently bad rocker arms. Way too often, they try to make a small change in an existing product (Olds V8 to Windsor, BBC to Ford L6) to save R&D, but they don't have anyone on staff competent to say "wait a minute, there are other differences...". Rocker arm geometry (not application) was settled engineering 300 years ago, they're not paying attention.
Don't modify them? Throw them away? And replace them with what? Ask the manufacturer "do these fit?" What answer do you think you'll get? Is Barton, T&D, and Jesel the answer for everyone?

We have tolerated crap from even the most expensive sources far too long to expect NEVER to get a part that needs adjustment, etc.

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