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RB26 Cylinder Head Exhaust Threads

BourneToLive
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BourneToLive Enthusiast

BourneToLive

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Hey everyone,

I’m having a bit of a crisis and would like some advice. 
I am in the process of assembling a head I had gotten back after NAPREC did their work. I had the exhaust studs removed prior to sending it to the machine shop, but afterwards when I tried threading in new studs, they wouldn’t go in straight. They would thread in smoothly by hand with almost no effort, but it doesn’t go in straight (noticeably circular motion) and eventually stops about halfway in. I had a couple go in perfectly straight with no effort, but when I removed them to try it again, they no longer when in straight and had the same issue as the others. The studs I’m using are M8x1.25, which I read was the standard. I did some research and decided to buy a chaser kit and new studs IEE NZ just in case. Has anyone experienced this? How screwed am I? Do I just need to run a chaser or tap and try again? Prefer a chaser because I heard taps can destroy existing threads. 
 

Note: I also have a new set of intake studs that went straight in just fine that I bought from IEE NZ. I bought the exhaust studs from the U.S.

Edited by BourneToLive
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GTSBoy Grand Master

GTSBoy

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Well, try the new studs first, in case the US sourced studs are actually the problem. But given that the head is off the engine, at least it won't be too hard for someone to install helicoils if it turns out the holes are stuffed.

You don't want to just run a tap or chaser through there if by doing so you leave behind 3/10ths of f**k all thread and the studs just pull straight out when you torque up the manifold nuts.

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BourneToLive Enthusiast

BourneToLive

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I visually inspected the threads and they look intact and not so dirty, so I don’t understand why they wouldn’t thread in straight. 
 

How would a chaser cause any damage? It’s intended to clean up the threads right? Even if it was cross threaded. That shouldn’t be the case though because the studs that were removed were OEM. The intake side had no issue. 

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GTSBoy Grand Master

GTSBoy

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46 minutes ago, BourneToLive said:

How would a chaser cause any damage? It’s intended to clean up the threads right?

A chaser is really just a tap. Just a less aggressive tap. It still has to be able to move metal to do its job. It may not cut the way a tap does, but it still has to push deformed threads around, and deformed threads are often a hair's breadth away from snapping off. Especially in cast aluminium alloys.

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