Broken rocker arm mount
12-02-2012, 05:14 PM
#1
Broken rocker arm mount Just posting this up to share my pain lol. Happened last night on the way home. Got up on it on the way home and as I was coming off the highway on an off ramp, it died. Started right up but wouldn't idle. Was able to limp it home which fortunately was only about 5-10 mins away. Sounded like an exhaust leak/weird fluttering noise. After researching this morning, figured maybe it was a broken valve spring. Pulled the valve covers this afternoon and found that. I only have about 5-700 miles on the motor, not the same parts that are in my sig. Basically forged 347, Fast 102 with a Pat G cam. The heads are about 6 years old, with about 8-10,000 miles on them. PRC LS6 stage 1 heads, milled down to 60cc. The valve springs are Patriot Extremes .660 lift and had about 2k miles. Not blaming anyone or anything like that.
When I pulled it off, the rocker arm bolt on the non-broken side had backed most of the way out. The broken side is tight as you can see. Thinking a couple of things. The rocker arm bolt started backing out, and the high rpms took out the other side. Or maybe there was fluid in the bolt hole that expanded and cracked it out. Or it just decided to break. Not really sure, and I can't find anyone else that's broken one on the search. Here's the pics, and what do you all think:
When I pulled it off, the rocker arm bolt on the non-broken side had backed most of the way out. The broken side is tight as you can see. Thinking a couple of things. The rocker arm bolt started backing out, and the high rpms took out the other side. Or maybe there was fluid in the bolt hole that expanded and cracked it out. Or it just decided to break. Not really sure, and I can't find anyone else that's broken one on the search. Here's the pics, and what do you all think:
Last edited by Sube; 12-02-2012 at 06:09 PM.
12-02-2012, 07:11 PM
#6
No
Bolt loosened and the rockers 2 were being held to the head with 1 bolt. since they are a shaft it just poped the casting.
Not unheard of for a bolt to come loose if the valve train is a little out of control. Those rockers are very heavy over the valve and just make it harder to control the valve. Things start moving around and the bolts come loose.
Tim
Bolt loosened and the rockers 2 were being held to the head with 1 bolt. since they are a shaft it just poped the casting.
Not unheard of for a bolt to come loose if the valve train is a little out of control. Those rockers are very heavy over the valve and just make it harder to control the valve. Things start moving around and the bolts come loose.
Tim
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12-02-2012, 07:16 PM
#8
This has happened before if im not mistaken. I did a quick search and nothing turned up here so maybe it got deleted. I distinctly remember these heads having problems like this in the past. The material removed during porting weakens this area.
12-02-2012, 07:29 PM
#9
Just found a thread on it: https://ls1tech.com/forums/generatio...e-ms3-cam.html
It's from about 4 years ago, I bought my heads about 6 years ago.
It's from about 4 years ago, I bought my heads about 6 years ago.
12-02-2012, 10:07 PM
#11
After looking at this thread: https://ls1tech.com/forums/generatio...uld-wrong.html It looks like I just got a bad casting. Mine is broken on the same cylinder, same rocker mount. After looking at the broken piece, it's razor thin on one side. Dunno.
12-02-2012, 10:28 PM
#12
Simply looks like these heads do have a weakness. I suspect the ported runner was a contributing factor, but that rocker bolt backing out caused too much stress on the other one.
I did notice that stock rockers can only pivot so far back and forth. So this may also be another probable cause of the issue in your posted link. Too much lift...not enough rocker movement, there goes the casting.
I bet the failure occured over time (not instantaneous)...Stress, cracks, and finally let go.
I did notice that stock rockers can only pivot so far back and forth. So this may also be another probable cause of the issue in your posted link. Too much lift...not enough rocker movement, there goes the casting.
I bet the failure occured over time (not instantaneous)...Stress, cracks, and finally let go.
