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Headed out on an errand the other day and within a few miles heard something I didn't like so turned around and headed back home to park it until later. A few days later I opened the hood and started it up and didn't like what I was hearing. It was definitely valve train but couldn't pinpoint it to left or right bank so pulled both valve covers and started looking for anything amiss. And this is what I found...
Trick Flow twisted wedge heads with Crane Gold roller rockers, stock TF springs and studs. Break is clean and no reason to believe that stud was ever damaged in any way. Probably less than 10,000 miles on motor and very little time over 4-4.5 grand. I'll probably do a compression check just to satisfy myself that there wasn't any piston to valve contact but beyond that not sure of why it failed.
The only odd thing is if I put the two pieces together, there seems to be a small piece missing. I've used a magnet in the head and didn't come up with anything but doubt it was like that before the break.
I ordered a pair of ARP replacements and reassemble if the compression test doesn't reveal anything.
That missing piece almost looks like it was nicked by an abrasive wheel. I think your question should be what came first a nick that weakened the stud or some kind of bizarre side load that broke it in half. I’m betting on the former. If it’s helpful to you, a broken rocker arm or stud rarely causes any damage other than beating up the inside of the valve cover, particularly if you run hydraulic lifters. The valve spring keeps the valve out of harms way. Best of luck to you in getting her running again!
The replacement stud arrived and I installed it today. Did a quick lash adjustment then pulled the plugs to run a compression check before starting it. All cylinders have good, strong readings which was a relief as I didn't want to do another tear down. Put valve covers back on and hit the key - fired up quickly and settled down to a nice idle minus some clatter!
That missing piece almost looks like it was nicked by an abrasive wheel. I think your question should be what came first a nick that weakened the stud or some kind of bizarre side load that broke it in half. I’m betting on the former. If it’s helpful to you, a broken rocker arm or stud rarely causes any damage other than beating up the inside of the valve cover, particularly if you run hydraulic lifters. The valve spring keeps the valve out of harms way. Best of luck to you in getting her running again!
The nick is so clean that I think it's just a piece that broke out when the stud snapped but it's still bizarre. No damage to inside of valve cover, in fact I didn't see the loose rocker until I started pulling all of them. It was just sitting there like there was no problem.
The replacement stud arrived and I installed it today. Did a quick lash adjustment then pulled the plugs to run a compression check before starting it. All cylinders have good, strong readings which was a relief as I didn't want to do another tear down. Put valve covers back on and hit the key - fired up quickly and settled down to a nice idle minus some clatter!
Sigh of relief, I gotta think. Well done sorting this out smartly.
Originally Posted by 65air_coupe
The nick is so clean that I think it's just a piece that broke out when the stud snapped but it's still bizarre. No damage to inside of valve cover, in fact I didn't see the loose rocker until I started pulling all of them. It was just sitting there like there was no problem.
High strength (think brittle = low material toughness) includes subject to sharp, rapid brittle fractures. These would almost always be clean breaks with little to no fatigue zones prior to failure. Lucky where it broke helped keep the pieces roughly in place. If it broke instead at the hex to stud corner it might have been less benign.
Originally Posted by DansYellow66
The little piece is probably down in your pan now. Do you have a magnetic oil pan bolt? Interesting break there - definitely a bad part.
Agree most likely location, given the oil return path. I would consider using a magnetic oil pan drain plug to see if it can be recovered, and if it matches the broken stud.
Originally Posted by Vette5311
I would replace all of them. Just sayin.
I would at least ponder this. If ARP QC let this one get by, there is a possibility that you might have a bad batch. Low possibility, but some.
Sigh of relief, I gotta think. Well done sorting this out smartly.
High strength (think brittle = low material toughness) includes subject to sharp, rapid brittle fractures. These would almost always be clean breaks with little to no fatigue zones prior to failure. Lucky where it broke helped keep the pieces roughly in place. If it broke instead at the hex to stud corner it might have been less benign.
I agree, when I've done failure analysis on these type of breaks in hardened materials, they looked pretty much like this one, that is no elongation and a clean break across the diameter. That being said, it makes little sense that this one broke as it did considering the missing piece appears to be no larger than the section of thread itself and as such did not reduce the cross-sectional area. And while that suggests a previous side loading stress, it's hard to imagine doing that to a single stud in the midst of all the others but I have no other explanation.
And while writing this, I was thinking back to those days of testing parts to failure and a test to break a 3/8" diameter hardened stud would be a violent event. Ductile parts let go with much less force so it surprises me to think of not noticing anything when this one failed while driving at low speed.
Agree most likely location, given the oil return path. I would consider using a magnetic oil pan drain plug to see if it can be recovered, and if it matches the broken stud.
I can't remember if I have a magnetic plug or not. I'll know at my next oil change but if not and the piece is in the pan, then it will probably flow out during the oil change and I'm not sure how important finding it is at that point.
I would at least ponder this. If ARP QC let this one get by, there is a possibility that you might have a bad batch. Low possibility, but some.
I did ponder it but these heads have at least 5,000 miles if not more. They belonged to Tom Parsons initially so don't know how many miles/hours they had with him but judging from their appearance, not much. Since the odds of another one breaking is low (my opinion) as is the risk of damage, I've elected to replace just the one. And I don't know that they're ARP, I think not since the replacement is slightly different.
Last edited by 65air_coupe; 10-20-2018 at 05:16 PM.
10-15-2018, 01:57 PM
What is that clattering?
