Intake Cam Failures - Materials, Design, or both?

[Remorseless]

One of these days I'd like to get a hold of one of the failed cams to do some testing on it. I'm curious as to how deep the heat treating penetrates, and how hard the lobes are. I think that there is a good possibility that it's a combination of ill effects that wipe them out with improper treatment of the cam itself, and poor lubrication. If cams are coming from more than one supplier, or if there is variation of the alloys, and heat treating process that would help explain the difference in why some fail faster than others.

Are the PUG cams failing with the rollers still intact? My thought has always been it's cheap roller bearings failing and collapsing and then wiping out the cams, and that the rollers that are going are just in a less-well-oiled spot in the valvetrain. Couple that with Jeep struggling to get all the casting sand out of the engines over the years and cheap bearings getting gummed up in a spot where oiling isn't amazing, and that's a pretty plausible way for the cam to get wiped out.

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[jeepingib]

Are the PUG cams failing with the rollers still intact? My thought has always been it's cheap roller bearings failing and collapsing and then wiping out the cams, and that the rollers that are going are just in a less-well-oiled spot in the valvetrain. Couple that with Jeep struggling to get all the casting sand out of the engines over the years and cheap bearings getting gummed up in a spot where oiling isn't amazing, and that's a pretty plausible way for the cam to get wiped out.

The followers use rollers and a slider like section. Most of the failures are on the slider portion. This leads to a rolling bending metal fatigue failure of the cam. Which points to either a metallurgical problem, lubrication problem, or both.

 

[bmpcamry09]

The followers use rollers and a slider like section. Most of the failures are on the slider portion. This leads to a rolling bending metal fatigue failure of the cam. Which points to either a metallurgical problem, lubrication problem, or both.

That slider is the exact reason I think VVL high lift is speeding up failures. There’s no pressure on that middle slider until VVL goes in to high lift mode. At least the way I understand it.

 

[Remorseless]

The followers use rollers and a slider like section. Most of the failures are on the slider portion. This leads to a rolling bending metal fatigue failure of the cam. Which points to either a metallurgical problem, lubrication problem, or both.

Right, this revised one for the JL

I just think it's more likely that this is collapsing when it shouldn't and the cam damage is a secondary effect rather than the primary failure. That coating on the slider section does seem to wear away on the teardowns I've seen, though how detrimental this is to the cam I dunno. So unless a supplier royally fucked up their heat treating of cams for the better part of a decade and the properly-hard slider section was eating a too-soft cam, or that rocker's not keeping contact away from parts that shouldn't be contacted. Either one's possible, but given Jeep's fuckups with the JK roller bearings, I'd surprised if the newer one didn't have similar issues.

 

[mwilk012]

Dumb movie but funny GIF.

One of these days I'd like to get a hold of one of the failed cams to do some testing on it. I'm curious as to how deep the heat treating penetrates, and how hard the lobes are. I think that there is a good possibility that it's a combination of ill effects that wipe them out with improper treatment of the cam itself, and poor lubrication. If cams are coming from more than one supplier, or if there is variation of the alloys, and heat treating process that would help explain the difference in why some fail faster than others.

You can probably go pick up one from your local dealer if they’re at all friendly.

 

[mwilk012]

Are the PUG cams failing with the rollers still intact? My thought has always been it's cheap roller bearings failing and collapsing and then wiping out the cams, and that the rollers that are going are just in a less-well-oiled spot in the valvetrain. Couple that with Jeep struggling to get all the casting sand out of the engines over the years and cheap bearings getting gummed up in a spot where oiling isn't amazing, and that's a pretty plausible way for the cam to get wiped out.

Yes. Because there is no roller.

 

[roaniecowpony]

Are the PUG cams failing with the rollers still intact? My thought has always been it's cheap roller bearings failing and collapsing and then wiping out the cams, and that the rollers that are going are just in a less-well-oiled spot in the valvetrain. Couple that with Jeep struggling to get all the casting sand out of the engines over the years and cheap bearings getting gummed up in a spot where oiling isn't amazing, and that's a pretty plausible way for the cam to get wiped out.

PUGs don't have rollers on the intake high lift (center) part of the rocker, which is the part interface that is failing. They have a funky design of a slipper shoe causes a really complex valve lift profile.

 

[jeepingib]

I used the wrong term, I had failure stuck in my head when I should have said fatigue.

When the surface of one part repeatedly slides against the surface of another part it produces a cyclic stretching action at the surfaces. If the surface stress that develops as a result of the stretching action exceeds the fatigue strength of the metal, tiny surface cracks will initiate and grow into the part. Surface pits form when the cracks join. Once pitting starts, more pits form until the surface is no longer usable. This action is sliding contact stress fatigue wear.

Contact stress fatigue (CSF) wear occurs when surfaces that roll or slide against each other are overloaded. Overloading may occur also because of misalignment or because that lubricant film has weakened due to lower viscosity or higher temperature. CSF also may occur because parts have been used beyond their expected service life.

 

[roaniecowpony]

Dumb movie but funny GIF.

One of these days I'd like to get a hold of one of the failed cams to do some testing on it. I'm curious as to how deep the heat treating penetrates, and how hard the lobes are. I think that there is a good possibility that it's a combination of ill effects that wipe them out with improper treatment of the cam itself, and poor lubrication. If cams are coming from more than one supplier, or if there is variation of the alloys, and heat treating process that would help explain the difference in why some fail faster than others.

They are surface hardened and from first hand observations, I'd estimate the hardness layer is .020-.040 inches. That's more than enough and has been for most of a century of engines. The chilled cast-iron camshaft has been around a long long time. The failures show a trend of which lobes fail. That points away from the heat treat as a suspect for me. (I spent many years as a QA engineer tracking down manufacturing problems)

 

[roaniecowpony]

I used the wrong term, I had failure stuck in my head when I should have said fatigue.

When the surface of one part repeatedly slides against the surface of another part it produces a cyclic stretching action at the surfaces. If the surface stress that develops as a result of the stretching action exceeds the fatigue strength of the metal, tiny surface cracks will initiate and grow into the part. Surface pits form when the cracks join. Once pitting starts, more pits form until the surface is no longer usable. This action is sliding contact stress fatigue wear.

Contact stress fatigue (CSF) wear occurs when surfaces that roll or slide against each other are overloaded. Overloading may occur also because of misalignment or because that lubricant film has weakened due to lower viscosity or higher temperature. CSF also may occur because parts have been used beyond their expected service life.

As a BBQ prophet, we likely have much more interesting and delicious things to talk about than flat cams.

 

[Remorseless]

Yes. Because there is no roller.

Bad terminology, I know the updated part, I'll still probably always call it a roller though.

PUGs don't have rollers on the intake high lift (center) part of the rocker, which is the part interface that is failing. They have a funky design of a slipper shoe causes a really complex valve lift profile.

Yep, I know the updated part, I'm just stuck in the past with what I call them. I guess the part I don't know is I assume there's a bearing somewhere in the assembly to facilitate smooth movement and I know from other's posts that the "wheels" on the assembly can end up with play in them. I've been fortunate in that none of my 3 Pentastars have needed any valvetrain work, so I haven't seen one of the new parts in person yet, just making assumptions.

 

[LSJKU]

Thanks for the discussion guys. This is wha the forum is really about. I would much rather read you guys shares on what makes my 3.6L tick (or better, not tick) than what "duck holder" fits best on the dash or if 35s will fit stock rims. Why? Because I don't have your expertise. education or knowledge on the subject, but I read, listen and learn.

That said, I am definitely having @bmpcamry09 disable the VVL when he tunes my JLR as this seems to be an ongoing issue.

Mr. Cowpony, you can change the subject to BBQ any time you want. I love BBQ too. A subject much more tantalizing than "duck holders," for sure!

 

[bmpcamry09]

Thanks for the discussion guys. This is wha the forum is really about. I would much rather read you guys shares on what makes my 3.6L tick (or better, not tick) than what "duck holder" fits best on the dash or if 35s will fit stock rims. Why? Because I don't have your expertise. education or knowledge on the subject, but I read, listen and learn.

That said, I am definitely having @bmpcamry09 disable the VVL when he tunes my JLR as this seems to be an ongoing issue.

should be any day now

 

[roaniecowpony]

Bad terminology, I know the updated part, I'll still probably always call it a roller though.



Yep, I know the updated part, I'm just stuck in the past with what I call them. I guess the part I don't know is I assume there's a bearing somewhere in the assembly to facilitate smooth movement and I know from other's posts that the "wheels" on the assembly can end up with play in them. I've been fortunate in that none of my 3 Pentastars have needed any valvetrain work, so I haven't seen one of the new parts in person yet, just making assumptions.

That "slipper shoe" just pivots up and down from the pin on the end. It's a "plain bearing" pin, if you will. There is nearly no surface speed/minute on the pin surface. It pivots the shoe up to contact the cam lobe, to get into the high lift mode. The high lift mode is the default position for start-up. Oil pressure, from a PCM controlled solenoid, is used to actuate it to the retracted low lift (outboard rollers) position.

 

[roaniecowpony]

Thanks for the discussion guys. This is wha the forum is really about. I would much rather read you guys shares on what makes my 3.6L tick (or better, not tick) than what "duck holder" fits best on the dash or if 35s will fit stock rims. Why? Because I don't have your expertise. education or knowledge on the subject, but I read, listen and learn.

That said, I am definitely having @bmpcamry09 disable the VVL when he tunes my JLR as this seems to be an ongoing issue.

Mr. Cowpony, you can change the subject to BBQ any time you want. I love BBQ too. A subject much more tantalizing than "duck holders," for sure!

Now, there's a thought. Modified rockers to keep them mechanically locked in the high lift mode.

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