Making female thread hole with JB Weld?

Speakrdude

Ensign
Joined
Feb 25, 2004
Messages
942
Hello all. I had a bolt brake off down inside a cast iron mounting hole on an Onan Gen Set. I was able to drill it out but was ugly. I sealed the back side of the hole with tape and filled with JB Weld. The depth of hole is approx 1".
My question is, Is JB strong enough for me to tap threads into and move on or do I need to drill and insert a heli-coil. This is a 3/8-16 motor mount bolt, so lots of vibrations, etc.
 

Bob_VT

Moderator & Unofficial iBoats Historian
Staff member
Joined
May 19, 2001
Messages
26,019
Re: Making female thread hole with JB Weld?

If you can get to both sides of the hole ........why not use a nut and some long bolt.
 

Speakrdude

Ensign
Joined
Feb 25, 2004
Messages
942
Re: Making female thread hole with JB Weld?

yeah, I could do that. Would have to unsnap the windings cover to get to it, but should be no big deal.
 

Yacht Dr.

Vice Admiral
Joined
Feb 26, 2005
Messages
5,581
Re: Making female thread hole with JB Weld?

I would not trust JB weld for thread tapping .. you should use the through bolts like Bob suggested .. or Heli-coil it.

YD.
 

Fireman431

Rear Admiral
Joined
Sep 17, 2007
Messages
4,292
Re: Making female thread hole with JB Weld?

The JB Weld won't hold. It will at first and then will start to crumble once it gets hot.

I second either tapping to the next size bolt (1/2") or thru-bolt with nyloc nut.
 

Fishing Dude too

Lieutenant Junior Grade
Joined
May 13, 2011
Messages
1,035
Re: Making female thread hole with JB Weld?

The JB Weld won't hold. It will at first and then will start to crumble once it gets hot.

I second either tapping to the next size bolt (1/2") or thru-bolt with nyloc nut.

Next size would be a 7/16" but would be best option.
 

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: Making female thread hole with JB Weld?

My question is, Is JB strong enough for me to tap threads into and move on or do I need to drill and insert a heli-coil. This is a 3/8-16 motor mount bolt, so lots of vibrations, etc.

No, I am not that strong. :p

I think your best bet is to drill it out and tap it for 7/16" or even 1/2". I have done this approach a few times and had good results and it works a lot better than a helicoil or timeSert.

If there is room behind, Bob's idea of drilling it clean and using a longer bolt with a nut sounds doable.
 

Yacht Dr.

Vice Admiral
Joined
Feb 26, 2005
Messages
5,581
Re: Making female thread hole with JB Weld?

My question is, Is JB strong enough for me to tap threads into and move on or do I need to drill and insert a heli-coil. This is a 3/8-16 motor mount bolt, so lots of vibrations, etc.

No, I am not that strong. :p

I .. I .. um .. Guys .. thats just classic Iboats right there .. I dont care who you are ! :) :) :)

YD.
 

Tim Frank

Vice Admiral
Joined
Jul 29, 2008
Messages
5,333
Re: Making female thread hole with JB Weld?

I'd try 10 mm. first.
That gives you a free shot....and you can fall back on 7/16" if the hole is already too big.
Tap drill for 10 x 1.5 is a letter "Q"...might get away with 21/64".
 

boltonranger

Petty Officer 1st Class
Joined
May 2, 2004
Messages
204
Re: Making female thread hole with JB Weld?

One other thing to consider is to use a long bolt and put the epoxy at the back of the hole on the outside. This would keep the nut in place if you need to unscrew the bolt and yet provide the strength of the metal threads.

Like how carmakers weld nuts in place on the bottom of a floor board.
But you'd be using jbweld or the like as your weld. Then you wouldn't need access to the nut in order to remove/re-install the bolt.
-br
 

Mark42

Fleet Admiral
Joined
Oct 8, 2003
Messages
9,334
Re: Making female thread hole with JB Weld?

Heli coil over jbweld any day. If you can drill it out, and tap it, do it.

If you can't and want to use epoxy, go the the local industrial supply store (look in yellow pages) and buy some serious epoxy that has very low fillers. If you have epoxy left from a boat project, you are good to go. Boat epoxy generally has no fillers, and is pure epoxy. Thats why it can be a complete disaster if you leave brushes, cups, etc wet with pure epoxy on your work bench. LOL!!!!
 

Fishing Dude too

Lieutenant Junior Grade
Joined
May 13, 2011
Messages
1,035
Re: Making female thread hole with JB Weld?

For a cleaner install use threaded rod and a double nut, that way can be removed as a stud.
 

glastron09

Cadet
Joined
Jul 11, 2011
Messages
19
Re: Making female thread hole with JB Weld?

heli coil is the best bet , auto parts stor should have a kit to do this
 
Top