Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

Go Back   Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum > General > Tech Talk

Tech Talk Technical Discussion About The Nissan 240SX and Nissan Z Cars


Reply
 
Thread Tools Display Modes
Old 11-16-2015, 07:53 PM   #1
TwoForDeh
Zilvia Junkie
 
TwoForDeh's Avatar
 
Join Date: Feb 2013
Location: NH
Posts: 426
Trader Rating: (0)
TwoForDeh is an unknown quantity at this point
Feedback Score: 0 reviews
RB25 Snapped Intake Camshaft

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?











__________________
IG: @thatrhd240
TwoForDeh is offline   Reply With Quote
Sponsored Links
Old 11-16-2015, 08:36 PM   #2
jedi03
Nissanaholic!
 
Join Date: Jul 2008
Location: albuquerque
Posts: 1,784
Trader Rating: (8)
jedi03 is on a distinguished road
Feedback Score: 8 reviews
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...
jedi03 is offline   Reply With Quote
Old 11-16-2015, 08:47 PM   #3
TwoForDeh
Zilvia Junkie
 
TwoForDeh's Avatar
 
Join Date: Feb 2013
Location: NH
Posts: 426
Trader Rating: (0)
TwoForDeh is an unknown quantity at this point
Feedback Score: 0 reviews
Quote:
Originally Posted by jedi03 View Post
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.


Sent from my XT1254 using Tapatalk
__________________
IG: @thatrhd240
TwoForDeh is offline   Reply With Quote
Old 11-16-2015, 09:34 PM   #4
jedi03
Nissanaholic!
 
Join Date: Jul 2008
Location: albuquerque
Posts: 1,784
Trader Rating: (8)
jedi03 is on a distinguished road
Feedback Score: 8 reviews
lol well my grandpa said some cars have gremlins...the only way to get rid of them is throw more money at them...
jedi03 is offline   Reply With Quote
Old 11-16-2015, 09:49 PM   #5
TwoForDeh
Zilvia Junkie
 
TwoForDeh's Avatar
 
Join Date: Feb 2013
Location: NH
Posts: 426
Trader Rating: (0)
TwoForDeh is an unknown quantity at this point
Feedback Score: 0 reviews
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?

Sent from my XT1254 using Tapatalk
__________________
IG: @thatrhd240
TwoForDeh is offline   Reply With Quote
Old 11-17-2015, 12:11 AM   #6
TwoForDeh
Zilvia Junkie
 
TwoForDeh's Avatar
 
Join Date: Feb 2013
Location: NH
Posts: 426
Trader Rating: (0)
TwoForDeh is an unknown quantity at this point
Feedback Score: 0 reviews
Quote:
Originally Posted by jedi03 View Post
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.
__________________
IG: @thatrhd240
TwoForDeh is offline   Reply With Quote
Old 11-17-2015, 08:13 PM   #7
dbeiler
Premium Member
 
dbeiler's Avatar
 
Join Date: Jun 2012
Location: Lancaster county, PA
Age: 30
Posts: 465
Trader Rating: (4)
dbeiler dbeiler dbeiler dbeiler dbeiler dbeiler dbeiler dbeiler dbeiler dbeiler dbeiler
Feedback Score: 4 reviews
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
dbeiler is offline   Reply With Quote
Old 11-17-2015, 08:20 PM   #8
TwoForDeh
Zilvia Junkie
 
TwoForDeh's Avatar
 
Join Date: Feb 2013
Location: NH
Posts: 426
Trader Rating: (0)
TwoForDeh is an unknown quantity at this point
Feedback Score: 0 reviews
Quote:
Originally Posted by dbeiler View Post
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.
__________________
IG: @thatrhd240
TwoForDeh is offline   Reply With Quote
Old 11-18-2015, 06:39 AM   #9
Jorgs_7
Zilvia Junkie
 
Jorgs_7's Avatar
 
Join Date: Sep 2015
Location: Plymouth MN
Posts: 406
Trader Rating: (1)
Jorgs_7 is just really niceJorgs_7 is just really niceJorgs_7 is just really niceJorgs_7 is just really niceJorgs_7 is just really niceJorgs_7 is just really niceJorgs_7 is just really niceJorgs_7 is just really niceJorgs_7 is just really nice
Feedback Score: 1 reviews
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.)
Jorgs_7 is offline   Reply With Quote
Old 11-18-2015, 07:29 AM   #10
OBEEWON
Post Whore!
 
OBEEWON's Avatar
 
Join Date: Feb 2006
Location: Hightened State of Emergency
Posts: 6,051
Trader Rating: (9)
OBEEWON has a reputation beyond reputeOBEEWON has a reputation beyond reputeOBEEWON has a reputation beyond reputeOBEEWON has a reputation beyond reputeOBEEWON has a reputation beyond reputeOBEEWON has a reputation beyond reputeOBEEWON has a reputation beyond reputeOBEEWON has a reputation beyond reputeOBEEWON has a reputation beyond reputeOBEEWON has a reputation beyond reputeOBEEWON has a reputation beyond repute
Feedback Score: 9 reviews
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?
__________________
OBEEWON is offline   Reply With Quote
Old 11-18-2015, 08:07 AM   #11
Sileighty_85
Post Whore!
 
Sileighty_85's Avatar
 
Join Date: Dec 2006
Location: Misawa, Japan
Posts: 6,815
Trader Rating: (8)
Sileighty_85 is close to perfectionSileighty_85 is close to perfectionSileighty_85 is close to perfectionSileighty_85 is close to perfectionSileighty_85 is close to perfectionSileighty_85 is close to perfectionSileighty_85 is close to perfectionSileighty_85 is close to perfectionSileighty_85 is close to perfectionSileighty_85 is close to perfectionSileighty_85 is close to perfection
Feedback Score: 8 reviews
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.
__________________
後輪駆動車1番
1989 Built SR GT2871R -363whp
1998 S14 W/RB25- 250ish (For Now)
1986 SR86 - 200ish
1990 R32 GTR - 320hp
Don't Buy Engines from JDM-Online http://zilvia.net/f/businesses/207457-jdm-online.html
Don't Buy XS-Power or SSAC Shit
Sileighty_85 is offline   Reply With Quote
Reply

Bookmarks


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -6. The time now is 04:29 AM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, vBulletin Solutions Inc.
vB.Sponsors
Copyright © 1998 - 2019, Zilvia.net™