I was pulling the hub off the crankshaft snout and didnt realize till after it was off that my 1/4 socket/extension had messed up the threads. The trial fit show that it was going inside the threaded area and pressing against the flat back of the hole. Unfortunately under load the socket I had on the end jammed itself on the face of the threads and pushed about 3-4 rows of it back before it held it in place. After a few long and loud sh**'s and Fu**'s I calmed down and realized I might be able to fix it by taping or chasing the threads. Why not, I thought, since there is still an inch of good threading there? So I am at work looking at the taps we carry for 7/16-20 and wondering what everyone thinks of my cleaning out the mashed threads and just getting another starting point cut? Whats everyone think? We only have spiral point plug taps in stock, but I think that should work. I thought about chasing them, but I'm not sure a chaser would cut a new starting thread spot. I can order any kind of tap made, but I dont want to mess up the remaining threads. How butt raped am I? When I was initally yelling I was thinkning "There goes doing justa cam.

-Dustin-

 

Can't hurt to try running a tap through it.

I would definitely avoid using the 1/4" extension method. Get a good long grade 8 bolt to pull against...

 

I know this sorta is a little late but they do make a special tool for removing the balancer.

That being said, I was told that you have to pull the crank to get it repaired. I have never done it but that is what I was told by two different people.

Good Luck,
Bobby

 

I assume by 'a new thread starting spot' you mean into the existing thread grooves, just at a different depth/ o'clock etc.. [at first read I thought you meant cut new over the old, [but not into the existing grooves], but that defies logic]
You want to try to cut the threads into the same 'starting spot' [existing thread grove].. it's not going to be easy to do, but then alll the remaining good threads should be OK and hold the hub on.. if you cut new threads in another 'starting spot', all the threads may [will?]end up ruined/crossthreaded etc..
I'd carefully 'ease' [Dremel?]the damaged threads, to be sure that the new threads will align with the old.. If new threads cut out of alignment with the old, you'll just end up with a mess.. other than that a Heli Coil is a possible solution also..
Plug tap might be harder to try to get into the existing threads, a standard tap would be better I think..
It should still hold OK, if successful..
If there are any good threads left where they are crushed, [I am thinking that maybe the crushed area is on one side,etc/] leave those there when easing the damaged threads so that will help start the tap into the existing threads more accurately... good luck with it... patience..

 

I don't know if they make them for all sizes of threads, but I know you can get spark plug hole repair kits that the tool fits inside the hole, then expands and cleans up the existing threads starting from the inside out. That way you don't destroy your existing theads by trying to start a tap at the end and not matching the existing thread spiral.

 

I was thinking along the lines that many of you are. Best case scenario is if I could get the starter thread open then the bolt would just go right in. A thread repair like shoebox mentioned would be nice, but I'm not sure where to find them. The spiral plug tap is handy here at work and I'll see how it works, although as mentioned I'd like to have a bottom tap. It's also easy to return. We have helicoils here too, but I'd rather use them as a last resort. Although I do feel lucky in a sense that the fastening assembly for the front hub doesnt have direct outward force applied upon it as does head or main bolts. So its not a high strain assembly. Wish me luck, I think I'm going to try and clean up the extra metal from the first few threads and then try to ease the tap into the existing threads. As said I wont be trying to make new ones. The threads were pressed down evenly into the whole, so its just like a thin washer of mushed metal is in front of the threads right now.

-Dustin-

 

The way I've fixed these in the past is to clean out the mashed threads (drimal tool or a thread pic) and chase the hole out.
when you're ready to install the hub or balancer,
use a long threaded rod (with a nut and large washer) screwed all the way into the crank hole to install the balancer or hub. be sure the hub or balancer is fully seated. next get a good quality fine thread stud with long threads on it (long enough to bottom out in the crank hole, with a washer, nut and at leat 5-10 threads extra). clean the crank hole and stud with loc tite cleaner ( i've also used alchol) trial assemble, then apply liberal amount of red loc tite to the crank threads and to the stud. run the stud all the way in (may have to double nut it and wrench it in tight) then install the big washer and fine thread nut. I use blue lock tight on the nut ( I've also used self locking nuts as well) then torque it all down and let it sit for a couple of days.
You will probably be grabbing more threads than the original bolt was as the stud reachs further into the crank. the fine threads of the stud and the red lock tight will keep the stud in for good. I've probably fixed 10-15 cranks this way..some had maybe half the original threads in them. many of these ran for days at a time as pump engines...

but you gotta have the stud all the way in, the threads clean and let everything sit and cure good.

On the ones that the threads were completely screwed, we tapped them out to the next size (std or metric) drilled the washer and got a correct size/length bolt.

may be over kill, but the last thing you want to happen is the balancer to come flying of at 5000rpms...will really screw things up....

Good luck
Greg

 

If the need to remove the hub arises, removal shouldn't be a problem but reinstalling almost needs the removal of the threaded rod\stud. I suppose you could break loose the rod with a vise grip or is the red threadlocker too strong?

 

I ran into the same problem the other day but used a larger socket which that, created a metal rim, so I was un able to even stick the old bolt back in. I had to file it down in order make the hole larger to stick the bolt back in and when I finally was able to a couple threads were f@#ked up so luckily I was able to break off the ones that were messed up and was able to get the bolt back in there. that was a big pain in the behind so I hope it works out for you as it did for me.

 

You might be able to find or borrow a tool similar to this, and it claims to restore threads from inside out.

http://www.nes.co.il/pro_info.html

 

I've had good luck with the snap on thread restoring taps; however,I don't know how badly you messed up the threads. They don't remove as much material as a thread cutting tap, and they are relatively inexpensive.



Mike

 

What I've done in the past in another SBC was to just go ahead and drill and tap to the next size, in this case, 1/2-20. The olutside diameter of the 7/16 bolt is .4375" and the nominal tap drill size for a 1/2-20 is .4531", so drill the crank with a .453" drill picked up from your local machine shop supplier (along with the tap), then re-tap the crank snout. With our stock cranks being cast it really isn't bad to do at all. There are only two things to be cautious of: 1. You do NOT want to break the tap off in the crank otherwise you will be pulling the motor. 2. You will have to take the balancer hub and drill the center bolt hole out to except the larger bolt. Then just put it back together. Hope this helps or gives you another option to think about.

Buddy

 

Thanks for all the great suggestions, this thread got much more feedback than I expected. I ended up just pulling the smashed/cracked threads out with a small screw driver first. Then I just slowly and patiently used the spiral plug tap to recondition the first few threads of what was left and kept checking my progress with the crank bolt. After a few checks I got the bolt to find its threads and put in all the way in a few times and now the treads are like new. Turns out only 2-3 theads got messed up, with the 7/16-20 thread pitch is only 1/10 of an inch lost. Thanks alot fella's, I probably would have had to resort to your other suggestions had it not gone so well.

-Dustin-

 

I think it would be a good idea to warm the hub up some before installing it, to expand it and keep the install forces as low as possible. I suspect the highest forces ever applied to those threads are during hub installation. They are now weaker than stock, so I would want to make the installation a little easier as a precaution.

 

When we have to work on one that has been studded, we use a extra long nut used to connect threaded rods and and thread on a short length of threaded rod then use a nut and spacer washer to pull it on.

Greg