Can I Re-tap to fix these smashed threads? Tapping Tips?

[TheUser]

To make a long story short, I broke part of my head off where the lower intake bolt threads in. I'm going to try to use a longer bolt in that hole to make use of the bottom threads..they appear to be flattened a bit...kinda smashed. Could I use a tap and fix them? I wanted to get this car back togetehr this weekend and shops are most likely all closed, but if a tap wouldn't work, I may be forced to wait. Would the tap of that size (5/16) fix make the threads good again? Any tips for tapping?

 

[TT91]

Thats alot of missing material. Welding may be an option if you still have the broken piece. How thick is deck below the hole? Drilling a deeper hole MAY cause you to run into problems.If it were me, I would get it welded. Good luck

 

[BlackFox5.0]

Welding it might make it weaker causing more problems....I don't know if the heads are treated or anything, but if they are it's a bad idea to weld them.

 

[TT91]

they look like stock cast heads. Welding them couldnt hurt unless you heated up the deck to an ENORMOUS tempturature.

 

[Ranchero5.0]

I would go to the local lowes or Home depot and get some 5/16 all thread rod and stud that hole. Run it in through the head after cleaning out the threads with a tap and put a lock nut on the bottom of the head. It's a lot easier and quicker vs pulling the head to weld and then having the concerns of warping the head from the excess local heat.

BTW, it's an old mechanics trick that actually works well. Just put a nut on the threaded rod before you cut it off. That way when you remove the nut it'll straighten out the threads where the rod was cut. Painless.

Jamie

 

[jrichker]

If you re-thread the hole with a tap, you'll meed a bottoming tap. A bottoming tap does not have a point on it.They are used to thread blind holes that need good threads down to the last 2-3 threads or so. If you take a regular tap and grind the end off flat until the threads start to look good, that's pretty much what a bottoming tap looks like.

See http://www.mscdirect.com/IWCatProdu..._Id=731&pcount=15&Product_Id=105171&Keyword=Y for a picture of a bottoming tap

Of all the ideas presented so far, I think Ranchero5.0's idea is the best. Use a bottoming tap to do the threads, a threaded rod with some locktite on it and you are good to go.

 

[TheUser]

I don't understand why a bottoming tap is necessary, but I really know nothing about this subject. Why do I not want all of the threads to be good? The smashed threads are in the top part of that hole. The head is off the car. I posted last Sunday when I created this mess and I was told the best idea would be to get a longer bolt for the intake bolt.

Ranchero: Are you saying put a stud in the head and leave it in there? So then I'd put the lower on, then the nut and then cut?

 

[BlackFox5.0]

Ranchero: Are you saying put a stud in the head and leave it in there? So then I'd put the lower on, then the nut and then cut?

Thats what he is saying I believe.

 

[jrichker]

II don't understand why a bottoming tap is necessary, but I really know nothing about this subject. Why do I not want all of the threads to be good? The smashed threads are in the top part of that hole. The head is off the car. I posted last Sunday when I created this mess and I was told the best idea would be to get a longer bolt for the intake bolt.

Ranchero: Are you saying put a stud in the head and leave it in there? So then I'd put the lower on, then the nut and then cut?

With a standard tap, the tap is tapered to make it easy to start. The first 5 or 6 rows of threads are shallow and do not cut fully. When you turn the tap, the threads after the taper do the rest of the cutting. As a result, the threads closest to the bottom of a blind hole (one that has a closed bottom) do not get a full cut of the threads. This is because the tapered part of the tap is what cut the threads. This prevents the stud or bolt from screwing in all the way to the bottom of the hole.

In order to get a full cut on the threads closest to the bottom, use a bottoming tap. It has a full cut on all but the first 2 rows of threads. When it cuts threads, it gives a full cut to all but the very bottom of the blind hole. More fully cut threads = stronger hold on the stud or bolt. This is because the rod will screw in almost all the way to the bottom of the hole and have more threads to hold it in place.

Reading what Ranchero5.0 wrote, he did say to use threaded rod and a nut to lock it in place. Cut the threaded rod off maybe 3/4" longer than the bolt that came out of the hole. You may have to do a dry test fit (no gaskets on the intake manifold) to get the right fit for the stud length.

The only thing I would do differently is to use Lock Tite on the threaded rod instead of a nut. This would eliminate any clearance problems between the nut and the lower surface of the intake manifold.

 

[Ranchero5.0]

J, the intake bolt hole isn't blind, it goes all the way through the head. I was suggesting just run the all thread all the way through and then put the nut on the bottom and lock it in place. I studded all the bolt threads on my AFR's.

I've seen this a ouple times on guys that put edelbrock heads on 302's. You only get about three threads in the edels before you start to torque it down. Gorillas rip the threads right out of the head and then wonder what to do.

Jamie

 

[jrichker]

J, the intake bolt hole isn't blind, it goes all the way through the head. I was suggesting just run the all thread all the way through and then put the nut on the bottom and lock it in place. I studded all the bolt threads on my AFR's.

I've seen this a ouple times on guys that put edelbrock heads on 302's. You only get about three threads in the edels before you start to torque it down. Gorillas rip the threads right out of the head and then wonder what to do.

Jamie

You're right. Looking closer at the bolt hole in question brings back memories of the few times I have had occasion to remove the lower manifold. There is room on the back side for a nut to hold the threaded rod in place. I probably would still use a bit of LockTite on the nut to avoid any possiblity of it working loose.

Joe R.