Why do I keep breaking rocker arms?

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Slugfarm

Slugfarm

Mostly Harmless
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So I finally took my rebuilt 225 (1700 miles on rebuild) with its 3-speed manual transmission and big cam in to my mechanic to have it set up with one of @halifaxhops' hotrod distributors and during the tuneup something sounded off and when they checked the valves they found a broken rocker arm, the second since the rebuild (the first happened during the break-in). Mechanic says I must be revving too hard. I've got a tach so I know I tend to cruise all three gears in the high 2000s and usually shift up in 3000-4000 zone depending on conditions and level of friskiness. I thought slants could take a pounding. Am I doing something wrong? I s my mechanic full of ****?
 
Slugfarm said:
So I finally took my rebuilt 225 (1700 miles on rebuild) with its 3-speed manual transmission and big cam in to my mechanic to have it set up with one of @halifaxhops' hotrod distributors and during the tuneup something sounded off and when they checked the valves they found a broken rocker arm, the second since the rebuild (the first happened during the break-in). Mechanic says I must be revving too hard. I've got a tach so I know I tend to cruise all three gears in the high 2000s and usually shift up in 3000-4000 zone depending on conditions and level of friskiness. I thought slants could take a pounding. Am I doing something wrong? I s my mechanic full of ****?
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Can you maybe provide a picture of the break? They are actually pretty strong, considering all they're made from is folded over sheet metal. What kind of springs are you running? Mine has .465 gross lift, 250 @ .050 duration on a 108 LSA with Comp 942 springs. I've had ZERO issues for about two years and we drive her sometimes almost everyday. My next cam will have .539 lift and use the Comp 911 big block spring and I have ZERO doubt the rockers will be fine. Sounds like you have a problem somewhere.
 
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Are your Valve springs in Coil bind?
They should have at the very least
.050 clearance.
If they are going solid that would break
rockers.
 
I'll be picking up the car tomorrow (I hope) and I'll get photos and specs.
 
GTX JOHN said:
Are your Valve springs in Coil bind?
They should have at the very least
.050 clearance.
If they are going solid that would break
rockers.
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Exactly! And on a slant 6, the rocker would likely break BEFORE the pushrod would bend, because there is no exaggerated pushrod angle as on a small block. I think you may have nailed it.
 
Since the rebuild I've been struck by how loud the action under the valve cover is. I mean, it's really loud. Easily the most noticeable engine sound. Like an old typewriter or something.
 
RustyRatRod said:
Exactly! And on a slant 6, the rocker would likely break BEFORE the pushrod would bend, because there is no exaggerated pushrod angle as on a small block. I think you may have nailed it.
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Thanks: Well even a Blind Chicken gets a Lump of Corn
every now and then!
 
I agree with Above. There is not much in the way of easy failure with a slant engine. Unless of course you change the geometry with exotic stuff. I’m not sure of the cam you’re running but I’ve seen some seriously large cams in a slant with minimal modifications. Maybe the mechanic is not telling you something or they did and you did not retain it.
 
Can you list the cam specs? including what the valves are lashed at? Has any head work been done (milling, valve job, oversized valves, porting. etc)? Are you running stock type pistons and/or rods? Also, what valve springs?
 
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Rpm will not break a slant rocker. I had a 170 with 340 valve springs that would easily rev to 6,000 rpm. Never had any problem.
 
66fs said:
Rpm will not break a slant rocker. I had a 170 with 340 valve springs that would easily rev to 6,000 rpm. Never had any problem.
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Mine's touched 6200 a time or three. Still pullin like a ***** in church. No complaints.
 
About 8 years ago, I bought from a closing dealership what was advertised as a NOS set of Slant 6 rockers and shaft (all assembled) for my '72 Valiant. I questioned the "NOS" claim because of the box (I don't remember the aftermarket name that was printed on it ) but I was blinded at this "Great Find". Anyway, I took the whole shebang apart, cleaned and reassembled for installation. I installed it and within a minute of startup one of the rockers broke just ahead if the circle that rides on the shaft. Thankfully the broken piece didn't fall deep into the engine and no other damage was done other than the broken rocker. This was on a stock solid lifter cam engine with proper lash. Could there have been a bad batch of rockers? or was mine weakened/rusty from within? I took the whole assembly off and set it aside. I never really inspected deeply but still have the setup. This was my experience.
Hope you get yours sorted out, Good Luck!
 
Big cam, hmmm.

Wrong length pushrods can break rockers also. It can have the rocker angle wrong and rocker hitting things
 
Something binding or they did something stupid in assembly to hurt a rocker... i would check coil bind and guide clearance before anything else (as i'm sure has been stated)
 
Just picture the scenario that would have to happen to break the Slant six rocker arm. Coil bind that would flatten the cam first after bending the push rod unless it's a hell of a push rod so then the next weakest thing would be the rocker or stock adjuster. Now it's a question of what kind of breakage though did it split at the tip is there an alignment issue and or is the adjuster side bending sideways. Etc is this one of these milled .100 heads with stock push rods and the adjusters backed off until they're barely threaded in the rocker arm?
 
MOPAROFFICIAL said:
Just picture the scenario that would have to happen to break the Slant six rocker arm. Coil bind that would flatten the cam first after bending the push rod unless it's a hell of a push rod so then the next weakest thing would be the rocker or stock adjuster. Now it's a question of what kind of breakage though did it split at the tip is there an alignment issue and or is the adjuster side bending sideways. Etc is this one of these milled .100 heads with stock push rods and the adjusters backed off until they're barely threaded in the rocker arm?
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Mine was milled around .175 and trust me, there's a LOT more adjuster threaded into the arms than you would think. I wouldn't have run it otherwise.
 
RustyRatRod said:
Mine was milled around .175 and trust me, there's a LOT more adjuster threaded into the arms than you would think. I wouldn't have run it otherwise.
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A lot of adjuster means a lot of geometry to correct. Angle the top of that push rod further and further out accelerate/increase the lift... an uncle dookie garage trick right ? Jk
 
Easy way to fix rocker arm breakage in a slant six- swap out /6 for a V8.
Drop slant in Ocean for boat anchor.
LMAO! I’m surprised nobody has said this yet! Lol!
 
Syleng1 said:
Easy way to fix rocker arm breakage in a slant six- swap out /6 for a V8.
Drop slant in Ocean for boat anchor.
LMAO! I’m surprised nobody has said this yet! Lol!
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A "HEMI" makes a better boat anchor. It is heavier, and under water is the only place it will last longer than a slant. :p
 
I used to argue all the time with V8 guys when I was a slanter. It's not that the slant 6 can beat every engine out there when modified because it can't it's just that it's so neat it can go down the road as fast as it can when you do the right things. Obviously a lot of that reliability starts to trade off but it's that reliability that puts a slant owner on the high horse to begin with being so sturdy and like a wounded soldier carrying others off the battlefield it can carry on much easier/longer wounded than a wounded v8.

Even for the v8...theres a bigger more powerful contender called tthe v10..v12...etc. No reason to argue. Do what you like and don't be insecure about it.
 
I don't get why people seem to have to be the fastest.. it's always cooler to see something interesting.. where i live we have 2000hp **** driving around all the time and stuff... there is always someone faster :) I just wanna be fast enough to have fun :)
 
Icetech said:
I don't get why people seem to have to be the fastest.. it's always cooler to see something interesting.. where i live we have 2000hp **** driving around all the time and stuff... there is always someone faster :) I just wanna be fast enough to have fun :)
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As my post above was ...I don't care. Lol What I mean by that ...is I no longer take the time to try and think like other people as to why they do what they do in order to understand. I'm either inclined to help or inclined to turn away. The car is an escape in more ways than one and for some people in this day and age fast soothes the Restless running Souls
 
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