Re: Trouble - broken manifold bolt.

Posted by Jim Kavanagh On 2018/6/18 1:59:23

This has gone from bad to worse.

I did get the stud out, but in doing so damaged with threads in the block either with the drill or, more likely, with the short depth extractors I first used.

Here is what I have:

The hole in the block is 3/8 x 16 pitch. The depth of the hole is .54" (including a small lip molded around the end of the hole in the water jacket) and is opened into the water jacket at the end, as are all the other holes in the block for the manifold studs. The first (top) .30" of threads are stripped out, they can still be seen, but they do not grab. The remaining .24" of threads are intact and will hold the stub, but it is not very tight, the stub can be easily threaded in by hand. It might hold torque, since the manifold is only torqued to about 30 Ft Lbs, but it will likely leak water.

I am considering several options:

1. I can drill out the hole to 10mm and tap the block. This will still allow the manifolds to slip over the stub. If I do this, I will probably go with a 1.5 pitch, which is almost the same as 16. Open to suggestions.

2. I have read on the internet (so you know it's true) that you can use an epoxy like JB Weld or Concor Quick Steel to make new threads that are supposed to be hard enough to withstand significant torque. You coat the stud with Vaseline and then with the epoxy, add some epoxy to the hole and thread the stud in. In a few minutes after the epoxy begins to set, you slowly back the stub out and let the epoxy cure for 24 hours. You then can chase the threads if need be. I have read that this is effective even for head bolts, which carry a lot of torque. These studs don't carry a lot of torque, but do get quite hot. They back to the water jacket though, so they can't get extremely hot. I like this solution because I still have a good amount of thread in the hole.

3. I have considered using something like a heli-coil, but I understand they are not meant for through holes because they might thread out through the bottom of the hole as the stud is being threaded in. I know there are other inserts out there, but I have no experience with any of these inserts.

4. I also have considered permanently exopying a very short allen stub to the bottom (back) of the hole (where there are still threads) to close it off from the water jacket. Then either drilling and tapping the top of the hole to 10MM, or using a heli-coil or other insert to accept the manifold bolt. My concern is that the tapped/repaired area would only have about .3" depth and I am not sure that is enough to safely torque everything down. I also am not sure that the epoxy would hold around the allen stub enough to insure that there would be no leaks.

I think that option 1 is probably the best in terms of insuring a good bite for the new manifold stud, do you see any problems with water leakage? If anyone has had experience using epoxy, I would love the hear about that.

In any case, I will use a sealer like Permatex on the stud to help insure I do not have leaks when all is completed

I am sure this is not the first time this has happened, so would love to hear any potential solutions.