Head bolt/stud TAP question

69427

69427

The Artist formerly known as Turbo84
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I was putting the head studs in today, and I have one that doesn't want to go in. The block threads don't look messed up (the stud threads are okay), but the other studs went in by hand/finger twisting. I need to just clean up the threads (7/16-14) in this hole. What kind of tap do I need to make sure it starts straight and doesn't cut any additional material? None of the holes go into the water jacket, so the depth is limited to about an inch and a quarter or so.

Thanks,
Mike
 
use a thread chaser first, it won't remove material. If the stud still doesn't go in, just use a ratchet or allen key. The studs should have an allen hex in them. Just don't crank the stud down tight. Did you lube the threads?
 
There are cleanup taps but if you have burred threads, I would use a regular tap. With care, a regular plug tap can be started by hand and will not cut the threads any bigger than they need to be.

I used to work for a machine tool company and they never used cleanup taps on rebuild work. If the threaded hole has residue from sealant or thread locker, the cleanup taps just push it into the threads and that will screw up torque readings.
 
In that aluminum block, I'd use a thread chaser with loads of lube- not WD-40, but some good oil like Tap-Majic
 
Twin_Turbo said:
use a thread chaser first, it won't remove material. If the stud still doesn't go in, just use a ratchet or allen key. The studs should have an allen hex in them. Just don't crank the stud down tight. Did you lube the threads?
Click to expand...

Yup. The studs are ARP units with the internal hex. I lubed all the of them prior to installation.

I had the block honed with a deck plate on it. I'm guessing perhaps this "head" bolt might have been sideloaded just prior to reaching the last threads as it was removed.
 
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SOLUTION TO ALL PROBLEMS !!!!!!!!!!!!
 
Well, struck out finding a thread chaser at a couple hardware stores. I'll probably just rig up something to clean up these threads.
I'll admit my ignorance here (as I've said many times, I'm an electrical engineer and have no business working on these things), but what does a thread chaser look like? Essentially, what's its physical construction that differs from a tap (which I prefer not to use)?

Thanks again,
Mike

Update: Well, I made a shadetree mechanic thread chaser by filing a few slits in a 7/16" bolt. Threaded it into the block hole, and it went in with minimal fuss. Excellent! I cleaned out the hole and then tried the stud. Won't go. Shit! I then measured the OD of the threads, and the bolt was .428", and the stud was .429". Okay, I looked through a few more 7/16" bolts in the bolt bin, and found one that was .432". Tried that, and it screwed right in. Tried the (.429") stud again, and no go. I tried the stud on a 7/16 nut, and no problem (confirming that I didn't have a brain fart and not realize these were metric studs LOL). So, I'm curious if the issue is the block hole thread ID being too small. This might explain why a .429" OD stud won't go in a hole that a .432" OD bolt will easily thread into.

Any opinions? (I'm heading back out to the garage. This engine better run damn decent when it gets in the car because it's been a complete PITA to get all the parts to play well together during assembly.)
 
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An over simplified description of a chaser is just a dulled tap. It will also slightly reform deformed threads.

The difference in using a bolt and a tap is the od. A tap cuts a deeper thread than the bolt uses. Typically, a bolt has only 75% intereference in a threaded hole, thus the reason why your bolt fits. Then the other thing is the thread pitch, since a larger od bolt fits, then I would assume the pitch is off.
There are different classes of thread fits, depending on purpose.

I assume you have tried different studs in that same hole you are having problems with. Will none of them fit? Or that stud in other holes?
I think ARP studs are rolled, (which are stronger than cut) so if it is just the one stud, it may be off spec.

If you have a piece of aluminum and the right sized tap, try tapping a hole and seeing if the stud fits in that.

If you find your stud is good then you can clean up the thread in your hole by using a tapered starter tap first with lots of cutting oil turning gently, being carefull to be straight. Finish by using a bottom tap.
Have done lots of rethreading without using chasers, without any problems, just be carefull. If it were mine, and the hole was found to be the culprit, I would recut it. I wouldnt cut the thread on the stud, though it probably would work too.

Find a copy of Machinist Handbook, everything you'll ever need to know about and work with metal. All the different classes of threading and fits is detailed.
BTW, Rigid, of plumbing fame, has one of the best cutting oils I have found, should have it at Homey Depot.
 
Well, after spending more hours of my life than I ever imagined on one stinking threaded hole, I finally got it put together. I ended up using one of my taps, and cleaned up the top 1/4 inch of the hole. Once I got the stud started after doing this, it screwed in the rest of the way with comparable friction/effort as the other studs. Given how far the studs thread into the hole, there's probably only about an 1/8 inch of tweaked threads that are engaged with the stud threads. The rest of the block threads (about an inch) are virgin threads.

Thanks for all the help and encouragement, guys!

Next stop, piston to valve clearance measurements.
 
Do this: Compare trhe threads of a KNOWN GOOD STUD THAT WILL SCREW IN with the threads of the one you're having trouble with. Just mesh the two threaded ends together and see how well they, ah, mesh.

You could have an odd-ball stud.

Jake
 
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