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Discussion Starter #1
Hi!

Engine started missfiring on one cylinder, after some quick research i found this.
Engine was running properly with good oil pressure, good oil etc.

I have emailed both RHDJapan and Tomei regarding this, interestingly this is the second Tomei Poncam that has snapped off for me.


 

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Discussion Starter #5
Yeah, here´s the one that snapped for me in 2007, at least it snapped off at the "right spot" and not through a lobe.
What was interesting with the one in this photo, was that there was only a 6mm circular dry spot in the middle of the snapped off halves (dry from oil), meaning that there was already a crack surrounding this dry spot. Luckily it snapped off when I was torque-tightening it, rather than when the engine was red-lining.

 

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That's shocking. I've had them in my previous gtr and was fine. I would be having words!
 

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That's bad, mine better not break.


Its very common with aftermarket cams though, from many different manufacturers. If they are not installed correctly, are torqued down in the wrong order or get dropped before fitting it can cause failure. I've heard about it from quite a few brands so it is worrying.
 

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Not just aftermarket cams, stock ones too.
I suggest a very close inspection of the break, I think you'll find it cracked on installation and has taken this long to finally let go.
You'd be aware that they'll snap like a carrot if the cam caps aren't pulled down evenly along the cam as well as across the caps.
As only a couple of valves springs are actually working as the cam is pulled down, it's easy to get ahead of yourself with the other easy caps.
Also were the pistons down the bores when the cams were installed?
Very easy to push valves into pistons if you follow the workshop manual and try to install cams at TDC.
I always have the crank passed TDC so there's no chance of valves into pistons.
 

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Not just aftermarket cams, stock ones too.
I suggest a very close inspection of the break, I think you'll find it cracked on installation and has taken this long to finally let go.
You'd be aware that they'll snap like a carrot if the cam caps aren't pulled down evenly along the cam as well as across the caps.
As only a couple of valves springs are actually working as the cam is pulled down, it's easy to get ahead of yourself with the other easy caps.
Also were the pistons down the bores when the cams were installed?
Very easy to push valves into pistons if you follow the workshop manual and try to install cams at TDC.
I always have the crank passed TDC so there's no chance of valves into pistons.
This comment is the most likely cause. The torque required to push the valves down is very small compared to the torque the camshaft can take if its not cracked.
 
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