RB25 Snapped Intake Camshaft

[TwoForDeh]

Hey dudes. I just wanted to send some things all your way to get some more heads in on this. After talking with my machinist and quite a few hours with Ricky at Raw Brokerage, we still can't really come up with a logical answer.

A few weeks back, I was turning onto a street. I had just started moving and I heard this weird tapping noise and the motor shut off immediately. After pushing it to my buddies shop down the street, I pulled off the timing cover because it sounded like my timing belt had snapped. After pulling off the upper cover, I noticed the timing belt was still in place.

After I saw that, I decided to rotate the motor by hand. I noticed the intake cam gear wobbling a little bit and noticed it was a little cockeyed. I took the oil cap off and looked down while rotating by hand and noticed the cam itself wasn't rotating.

I grabbed the cam gear and moved it around and it fell right off. It snapped right in the middle of the first cam journal. Split the VCT oil galley right in the middle. The first thing I thought of was maybe an oil feed issue being that RB's do have oiling issues.

Fast forward to the next day...I took the valve cover off and the pulled the cam caps off to take the cam off. First thing I looked for was any sort of noticeable signs of oil starvation or anything else that would have caused it...nothing. There was so blueing or yellowing of the cam journal, the cam, nothing. The cam cap had a little bit of scoring, I'm assuming from when it actually snapped and rotated all fucky.

Prior to this happening, another random thing happened. While driving down the street, cruising, not doing anything stupid (although I wish I was so I had a cooler story to tell), and I hear this loud ass rapping noise. I pulled over and heard the noise under the exhaust side valve cover. I pulled the cover off on the side of the road and saw the rear most exhaust cam cap sitting in the middle of the 6th and 7th cam journals on top of the cam. The cam cap bolts had snapped clean off in the head, out of completely nowhere. So, instead of sourcing another cap, getting everything line honed, and all that jazz, I just got a loaded head from a buddy and got machined, cleaned up, etc.

People have told me install error, oil issues, etc. This isn't my first rodeo, especially with the RB. I know all the torque specs and sequences by heart but I still have the FSM right next to me and follow it for assurance. The ONLY thing that I knew needed addressing was the timing belt tension itself. When it warmed up, it would whir a little bit, but, it wasn't crazy loud or excessive. And a timing belt that's just a little too tight isn't going to snap a cast iron camshaft out of nowhere.

This head has about 500 miles on it. It wasn't something that happened right off start up. It actually made it 2.5 hours each way down to Staggered the day before this happening, without any issues. I have the head off at the machine shop getting the 2 bent valves replaced so I can put it back together. I just wanted to post this up to see if there was anything that maybe Ricky and I missed, and address whatever said issue could be before throwing it back together. Here's a couple photos. What do you guys think?

http://i1204.photobucket.com/albums/bb414/joeyjohnsick911/IMG_20151014_090902411.jpg (http://s1204.photobucket.com/user/joeyjohnsick911/media/IMG_20151014_090902411.jpg.html)

http://i1204.photobucket.com/albums/bb414/joeyjohnsick911/IMG_20151017_135626949.jpg (http://s1204.photobucket.com/user/joeyjohnsick911/media/IMG_20151017_135626949.jpg.html)

http://i1204.photobucket.com/albums/bb414/joeyjohnsick911/IMG_20151017_135638042.jpg (http://s1204.photobucket.com/user/joeyjohnsick911/media/IMG_20151017_135638042.jpg.html)

http://i1204.photobucket.com/albums/bb414/joeyjohnsick911/IMG_20151017_135645109.jpg (http://s1204.photobucket.com/user/joeyjohnsick911/media/IMG_20151017_135645109.jpg.html)

http://i1204.photobucket.com/albums/bb414/joeyjohnsick911/IMG_20151017_142315813_HDR.jpg (http://s1204.photobucket.com/user/joeyjohnsick911/media/IMG_20151017_142315813_HDR.jpg.html)

http://i1204.photobucket.com/albums/bb414/joeyjohnsick911/IMG_20151031_145904124.jpg (http://s1204.photobucket.com/user/joeyjohnsick911/media/IMG_20151031_145904124.jpg.html)

[jedi03]

There's alot that could have happened...not enough oil, cam was dropped at some time...bad luck...torque to much on cam caps or timing belt...etc...

[TwoForDeh]

cam was dropped at some time...bad luck...

This is actually something we talked about too. Before the head was in my possession, maybe the cam was dropped or stressed in it's journey over here and there was a crack on the cam itself. And then with the belt being a little tight, made it even weaker?

I think with there not being any sure signs of one thing going wrong, it was either a mixture of things, something we're missing, or the pure fact I have the WORST luck in the world.


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[jedi03]

lol well my grandpa said some cars have gremlins...the only way to get rid of them is throw more money at them...

[TwoForDeh]

Posted up the same thread on SAU because the Aussies are nutty with RB's. One guy answered this.

"If I had to guess I'd point the finger at the VCT actuator having a fit and that causing the cam to snap.* The break surface does not look like a torsional break through, so it's not like the actuator would have seized and the sudden speed change between front and rear caused it to twist off.* It looks more like it was snapped in beam loading (ie loaded across the break surface) which could have happened if the actuator had stuffed up enough to allow the cam gear to be pulled down by the timing belt tension."

Thoughts?

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[TwoForDeh]

lol well my grandpa said some cars have gremlins...the only way to get rid of them is throw more money at them...


After doing a little more research after reading that guys response, I found this thread from a few years ago. http://zilvia.net/f/showthread.php?t=512715

Maybe my VCT oil feed is clogged up or something from the machine shop? But, if that were the case, I think we'd be looking at a much more mangled head, similar to this guys.

New head gasket comes in tomorrow but I want to try and shed as much light on this stupid thing before I throw it back together and potentially run into the same issue.

Thanks for the ideas so far guys. Always good to get more input.

[dbeiler]

First, cam cap hardware doesn't just snap. It was overtorqued. I'm guessing the remaining cap bolts were fudged as well.

This is clearly not an oil starvation problem. Lack of oil would have left a gulled, gouged, discolored mess. Somebody dropped the camshaft or installed it incorrectly. The FSM does not mention the importance of tightening the bearing cap hardware in a very equal and progressive fashion.

I've seen "educated" people slap a camshaft onto a head and proceed to tighten down one cap (and only one cap) till it seats against the head. When asked, they reply, "You're supposed to torque it in stages." You sure are, but it's too late at that point. The camshaft is likely already cracked.

My diagnosis: Somebody installed the camshaft and proceeded to tighten down that first cam cap without progressively tightening the remaining caps. The (opening) valve springs put extreme pressure on the camshaft which caused it to crack at the weakest point.

Now you're stuck with the mess.
Sorry about your luck :-/

[TwoForDeh]

First, cam cap hardware doesn't just snap. It was overtorqued. I'm guessing the remaining cap bolts were fudged as well.

This is clearly not an oil starvation problem. Lack of oil would have left a gulled, gouged, discolored mess. Somebody dropped the camshaft or installed it incorrectly. The FSM does not mention the importance of tightening the bearing cap hardware in a very equal and progressive fashion.

I've seen "educated" people slap a camshaft onto a head and proceed to tighten down one cap (and only one cap) till it seats against the head. When asked, they reply, "You're supposed to torque it in stages." You sure are, but it's too late at that point. The camshaft is likely already cracked.

My diagnosis: Somebody installed the camshaft and proceeded to tighten down that first cam cap without progressively tightening the remaining caps. The (opening) valve springs put extreme pressure on the camshaft which caused it to crack at the weakest point.

Now you're stuck with the mess.
Sorry about your luck :-/

Thanks for the reply...but, in regards to the "someone" who installed it, I was that someone. I ALWAYS tighten in many stages between each cam cap and bolt, in accordance to the FSM sequence. I probably tighten in more stages than most people. We've been leaning more towards the cam was dropped at some point before I got it because this cam was new to me when I put it in.

The new head gasket came in today. I'll be putting everything back together over the next day or 2. I'll keep you posted to let you know if anything funky shows up. I do, however, have the worst luck out of anyone I know, which is even more apparent in this case haha.

[Jorgs_7]

Id guess:

Some sort of flaw in the grain structure,
Maybe the OEM heat treatment wasn't "perfect" (doubtful)
Loaded with abnormal forces (torque sequence, spec, etc.)

[OBEEWON]

Wow that is nuts. Very strange. The only thing that seems logical is over torque but you said you know the specs. Maybe your tq wrench is out of calibration?

[Sileighty_85]

its possible the Cam caps were installed 180* off. If so the cam will bind.

I did it to my exhaust cam when I was putting my RB25 back together but caught the mistake right after I did it.