Chasing vs Tapping Block Threads (1 Viewer)

Joined
Dec 27, 2012
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Sonora, CA
 
Hi all. I'm in the middle of re-installing my cylinder head after a blown head gasket and a head refresh and have a question. After clearing the threads in two bolt holes, I've decided that the tap is too agressive and will revert to less violent ways to clear the rest of the threads . Have any of you actually used a M13 x 1.75 tap to clear these threads without problems? My machinest provided the tap so he thinks this is no problem but I'm skeptical . I don't do enough of these to know if I'm being overly nervous or am I going to pull these two bolts through the head when I get closer to 90 ft lbs. Anyone with some experience here? Thanks in advance, Paul
 

Dave 2000

Not all Land Rovers are useless!
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Jan 24, 2009
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Running a tap through should be no problem assuming it is the correct one. Put some grease on the tap and work gently in, remove and clean/regrease often.

Also, if the holes are blind you need a bottoming tap.


TBH, I just run a new greased bolt up and down ensuring the threads are clean, just check the thread perch is good.

Regards

Dave
 
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Taps have different diameter tolerances. If the holes were cut with a "tight tolerance tap" (class 3) and you are running a "standard tolerance tap" (class 2) into them you will remove some metal, as opposed to just chasing them, which should only clean up nicks and burrs.

Tight tolerance threads resist vibration loosening better than standard tolerance cut threads.
 
Joined
Dec 27, 2012
Messages
122
Location
Sonora, CA
 
Taps have different diameter tolerances. If the holes were cut with a "tight tolerance tap" (class 3) and you are running a "standard tolerance tap" (class 2) into them you will remove some metal, as opposed to just chasing them, which should only clean up nicks and burrs.

Tight tolerance threads resist vibration loosening better than standard tolerance cut threads.
This is almost certainly what's happening here. Do I need to worry that these bolts will not sustain the compressive load due to this? Would threadlock be appropriate for the two threads I used the class 2 tap on or should I just lube and torque and stop worrying? Thanks greatly, Paul
 
Joined
Sep 5, 2007
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I would just clean them out. I replaced all my head bolts when I did mine, so I had a stack of extra bolts, I cut 2 grooves on the bolt, one on each side of the bolt perpindicular to the treads.

Ran this "cleaner" in and out of each thread and cleaned it with carb cleaner between each pass. Cleaned them nicely and did not cut the threads at all.


something like this.

 

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