Rb25 Snapped Intake Camshaft

[thatrhd240]

Hey guys. I'm a long time lurker of the forum because of your vastly greater knowledge as opposed to over here in the US. I posted this on Zilvia and wanted to post it up here to see what you guys think. I figure since this is my first post, I'll introduce myself and my car first.

My names Joey. I've been building this s13 for the last 2.5 years. It's been a long couple years but well worth it. The build is documented on both my Instagram @thatrhd240 and also on a build thread on Zilvia.net if you want to check it out.

Specs with the RB:

Holset HY35

Tial 38mm wastegate

Tial 50mm BOV

JECS 740cc injectors

Apexi PowerFC

Z32 MAF

Put down 448rwhp at 21psi. Currently running 17psi for my ringland's safety sake until I do forged bottom end over this winter.

Feel free to ask any questions!

"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 f**ky.

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?

[Ben C34]

Man, that's crazy.

Belt tension is tricky to describe, as people use different amount of force to gauge it, but typically you want to be able to twist the belt 90 degrees without heaps of force. (with your fingers) see how it can vary!

How would you say that compares with the tension yu had on the belt?

[thatrhd240]

When you say 90*, are saying back and forth combined? If I'm not mistaken, you want to be able rotate it by hand 45* in between the cam gears. Correct me if I'm wrong. Which is right about where it was.

[MagicMikeZ32]

What cams and springs you running?

[thatrhd240]

I'm running stock cams/springs for the time being.

[GTSBoy]

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.

[MagicMikeZ32]

Something else to look at will be cam gear balance.

[thatrhd240]

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.

After doing a little research using issues with the VCT, I found this thread. Pretty similar to what happened to me.

http://zilvia.net/f/showthread.php?t=512715

Edited November 17, 2015 by thatrhd240

[PranK]

I can't stop looking at your engine bay. Gorgeous!

[thatrhd240]

I can't stop looking at your engine bay. Gorgeous!

Thanks! I appreciate it!

[GTRPSI]

Check your cam seats for straightness.

As much as people machine a head to flatten it, few run a straight edge across the seats to see if the head is bowed across the cam seats.

If a head warps, it does not just warp at the face, the camshaft end also warps too.

Another quick way to check is to remove the valves and seats, fit the cams and caps and see if the cam turns without any hard points in the rotation......(old school way)

[Jordy32]

jeez, you did a good job of it!

Car looks awesome too

[thatrhd240]

jeez, you did a good job of it!

Car looks awesome too

Check your cam seats for straightness.

As much as people machine a head to flatten it, few run a straight edge across the seats to see if the head is bowed across the cam seats.

If a head warps, it does not just warp at the face, the camshaft end also warps too.

Another quick way to check is to remove the valves and seats, fit the cams and caps and see if the cam turns without any hard points in the rotation......(old school way)

Thanks for the responses guys. So, I dropped the 2 bent valves and replaced them. Threw the head back on. Everything is good so far (going on a week and a half of driving). We couldn't find any sort of solid evidence as to why anything happened so I just put it back together with my other set of stock cams. I'll keep you posted if anything happens!

[MagicMikeZ32]

I fear we will be back here again soon unfortunately...

Get your cam gear ballanced

[thatrhd240]

I used my cams and gears from my other head. I didn't use the gear that was on it when it snapped. I actually hung that one up on my wall haha.

[MagicMikeZ32]

I only mention this because, there has been 3 snapped cams on vg engines recently, 2 of them on the same engine using the same gears. Gear was checked for balance and was out.

2nd time was on warmup driving @2500rpm

Edited December 1, 2015 by MagicMikeZ32