Topic: What to do when helicoils fail?

[n9viw]

Hey all,
   Searched all thru this forum and Greenspun as well, and beyond suggestions for JB Weld and Helicoils, I can't find anything else regarding repairing stripped holes. And nothing regarding stripped holes that a HELICOIL pulled out of!!
   Long story short, I was installing the exhaust on my '76 CB550k, and one of the studs on the #1 exhaust stripped out. I drilled, tapped, and helicoiled it, making sure to loctite the coil when it went in. I threaded the stud back in by hand, and left it overnight. The next day I went to reinstall the exhaust, and it pulled out AGAIN, taking the helicoil and a bunch of aluminum with it!
   Do I helicoil it up to the next size (7mm x 1), then back to the original size (6mm x 1)? Do I have it welded shut and redrilled/retapped? Can I make a slug out of T6 aluminum and drill and tap that once it's in? I just hate that I have to have the head off AGAIN, I'm worried that all this torquing/retorquing is bound to blow the threads of one of the head studs! Oy.
Thanks,
Nick

[Robert]

I keep reading and hearing about people having only limited success with helicoil in aluminium.
One thread insert product I was recommended is Ensat thread inserts. These work really great.

Here's some info.
http://www.kerbkonus.de/proddb/assistent.php?a=presel_ds&ds=20&lang=en

There are other similar products that I can't recall the name right now (recoil maybe). But I'm sure someone must know here.

[Tim.]

You might consider an aluminum welder.  For very little $, Chundy, another member here had a broken mount for his CB750's exhaust welded up, drilled and retapped.  Similar situation, but no studs on the 750.  The hole for the bolt was broken - they built it up with new aluminum, and I think ended up with a heli-coil in it too.  He then put the bolt in and no trouble.

Of course, that required pulling the head off the engine, which in the 750's case, meant pulling the engine out of the bike    Thankfully Honda engineers learned a thing or two and made the 500/550 frame big enough to allow the top end of the engine to come off without removing it altogether.

[cb650]

You might consider an aluminum welder.  For very little $, Chundy, another member here had a broken mount for his CB750's exhaust welded up, drilled and retapped.  Similar situation, but no studs on the 750.  The hole for the bolt was broken - they built it up with new aluminum, and I think ended up with a heli-coil in it too.  He then put the bolt in and no trouble.

We do this for a couple tranny shops on alum automatics.  Works good havent had a complant.


                         Terry

[Bodi]

The solid threaded things I've used are "keenserts".
They work very well if you have the room to install them, the outer threads are fairly large. I've never seen one fail like a helicoil will, although in severe use they wear out; these are commonly used as original parts on camera equipment etc. made of aluminum whaere mounting bolts are going to be used often. Aluminum threads wear quickly and are very easy to crossthread a steel bolt into.

[oldbiker]

A possible repair without removing the head (if you can get at it) is to drill and helicoil (or keensert or recoil etc.) the next size up and then turn up a stepped stud having a short length of the larger size to go into the insert and a length of the smaller diameter to mount the exhaust. Then the next time you have to remove the head for some reason you can then consider  getting the hole welded up and restored to the original size. I know of one repair done like this and the owner never bothered to go back to original.

[MRieck]

The solid threaded things I've used are "keenserts".
They work very well if you have the room to install them, the outer threads are fairly large. I've never seen one fail like a helicoil will, although in severe use they wear out; these are commonly used as original parts on camera equipment etc. made of aluminum whaere mounting bolts are going to be used often. Aluminum threads wear quickly and are very easy to crossthread a steel bolt into.

Yep...the Keenserts work OK and can be used if the Helicoil fails. I've had pretty good luck with Helicoils.

[Badboy]

I ,over the years,have used heli-coils a lot in aluminum. I have had good luck with them. I use a smaller drill than what is called for.If you use the one called for ,there is not enough meat left in the hole to get a good grip. In cast iron the drill called for is okay. The bushing types work good to if you have room. Another thing,when you drill into aluminum ,if you don't drill straight you will have a problem or if you wobble. Rule,make the hole as small as you can get by with and still tap it out.

[n9viw]

Thanks to all who replied, great info. I ended up taking it into a shop, where they recommended something called a ThreadSert from the same company that makes Keenserts, TimeSert I think it is. They used a model called BigSert, because the hole was so badly widened. The stud was MUCH more stable, and I got the exhaust on yesterday with no mishaps.
I think the reason it failed was because I must have poorly tapped the hole, but when I suggested filling, redrilling, and retapping to the shop owner, he noted that it would only be as strong as the original hole, whereas the steel BigSert would be MUCH stronger. It looks to be, too- if I had the money, I'd have had the entire head redone with these inserts!
Now, got the bike together, and am rewarded with starting issues.. but that's another thread! 
Nick

[Bob Wessner]

Glad to hear you're back on track. Good luck.